namespace.c

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/*-------------------------------------------------------------------------
 *
 * namespace.c
 *    code to support accessing and searching namespaces
 *
 * This is separate from pg_namespace.c, which contains the routines that
 * directly manipulate the pg_namespace system catalog.  This module
 * provides routines associated with defining a "namespace search path"
 * and implementing search-path-controlled searches.
 *
 *
 * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/catalog/namespace.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/parallel.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "catalog/dependency.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_conversion.h"
#include "catalog/pg_conversion_fn.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_opfamily.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_ts_config.h"
#include "catalog/pg_ts_dict.h"
#include "catalog/pg_ts_parser.h"
#include "catalog/pg_ts_template.h"
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
#include "funcapi.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "parser/parse_func.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/sinval.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/catcache.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"


/*
 * The namespace search path is a possibly-empty list of namespace OIDs.
 * In addition to the explicit list, implicitly-searched namespaces
 * may be included:
 *
 * 1. If a TEMP table namespace has been initialized in this session, it
 * is implicitly searched first.  (The only time this doesn't happen is
 * when we are obeying an override search path spec that says not to use the
 * temp namespace, or the temp namespace is included in the explicit list.)
 *
 * 2. The system catalog namespace is always searched.  If the system
 * namespace is present in the explicit path then it will be searched in
 * the specified order; otherwise it will be searched after TEMP tables and
 * *before* the explicit list.  (It might seem that the system namespace
 * should be implicitly last, but this behavior appears to be required by
 * SQL99.  Also, this provides a way to search the system namespace first
 * without thereby making it the default creation target namespace.)
 *
 * For security reasons, searches using the search path will ignore the temp
 * namespace when searching for any object type other than relations and
 * types.  (We must allow types since temp tables have rowtypes.)
 *
 * The default creation target namespace is always the first element of the
 * explicit list.  If the explicit list is empty, there is no default target.
 *
 * The textual specification of search_path can include "$user" to refer to
 * the namespace named the same as the current user, if any.  (This is just
 * ignored if there is no such namespace.)  Also, it can include "pg_temp"
 * to refer to the current backend's temp namespace.  This is usually also
 * ignorable if the temp namespace hasn't been set up, but there's a special
 * case: if "pg_temp" appears first then it should be the default creation
 * target.  We kluge this case a little bit so that the temp namespace isn't
 * set up until the first attempt to create something in it.  (The reason for
 * klugery is that we can't create the temp namespace outside a transaction,
 * but initial GUC processing of search_path happens outside a transaction.)
 * activeTempCreationPending is TRUE if "pg_temp" appears first in the string
 * but is not reflected in activeCreationNamespace because the namespace isn't
 * set up yet.
 *
 * In bootstrap mode, the search path is set equal to "pg_catalog", so that
 * the system namespace is the only one searched or inserted into.
 * initdb is also careful to set search_path to "pg_catalog" for its
 * post-bootstrap standalone backend runs.  Otherwise the default search
 * path is determined by GUC.  The factory default path contains the PUBLIC
 * namespace (if it exists), preceded by the user's personal namespace
 * (if one exists).
 *
 * We support a stack of "override" search path settings for use within
 * specific sections of backend code.  namespace_search_path is ignored
 * whenever the override stack is nonempty.  activeSearchPath is always
 * the actually active path; it points either to the search list of the
 * topmost stack entry, or to baseSearchPath which is the list derived
 * from namespace_search_path.
 *
 * If baseSearchPathValid is false, then baseSearchPath (and other
 * derived variables) need to be recomputed from namespace_search_path.
 * We mark it invalid upon an assignment to namespace_search_path or receipt
 * of a syscache invalidation event for pg_namespace.  The recomputation
 * is done during the next non-overridden lookup attempt.  Note that an
 * override spec is never subject to recomputation.
 *
 * Any namespaces mentioned in namespace_search_path that are not readable
 * by the current user ID are simply left out of baseSearchPath; so
 * we have to be willing to recompute the path when current userid changes.
 * namespaceUser is the userid the path has been computed for.
 *
 * Note: all data pointed to by these List variables is in TopMemoryContext.
 */

/* These variables define the actually active state: */

static List *activeSearchPath = NIL;

/* default place to create stuff; if InvalidOid, no default */
static Oid  activeCreationNamespace = InvalidOid;

/* if TRUE, activeCreationNamespace is wrong, it should be temp namespace */
static bool activeTempCreationPending = false;

/* These variables are the values last derived from namespace_search_path: */

static List *baseSearchPath = NIL;

static Oid  baseCreationNamespace = InvalidOid;

static bool baseTempCreationPending = false;

static Oid  namespaceUser = InvalidOid;

/* The above four values are valid only if baseSearchPathValid */
static bool baseSearchPathValid = true;

/* Override requests are remembered in a stack of OverrideStackEntry structs */

typedef struct
{
    List       *searchPath;     /* the desired search path */
    Oid         creationNamespace;      /* the desired creation namespace */
    int         nestLevel;      /* subtransaction nesting level */
} OverrideStackEntry;

static List *overrideStack = NIL;

/*
 * myTempNamespace is InvalidOid until and unless a TEMP namespace is set up
 * in a particular backend session (this happens when a CREATE TEMP TABLE
 * command is first executed).  Thereafter it's the OID of the temp namespace.
 *
 * myTempToastNamespace is the OID of the namespace for my temp tables' toast
 * tables.  It is set when myTempNamespace is, and is InvalidOid before that.
 *
 * myTempNamespaceSubID shows whether we've created the TEMP namespace in the
 * current subtransaction.  The flag propagates up the subtransaction tree,
 * so the main transaction will correctly recognize the flag if all
 * intermediate subtransactions commit.  When it is InvalidSubTransactionId,
 * we either haven't made the TEMP namespace yet, or have successfully
 * committed its creation, depending on whether myTempNamespace is valid.
 */
static Oid  myTempNamespace = InvalidOid;

static Oid  myTempToastNamespace = InvalidOid;

static SubTransactionId myTempNamespaceSubID = InvalidSubTransactionId;

/*
 * This is the user's textual search path specification --- it's the value
 * of the GUC variable 'search_path'.
 */
char       *namespace_search_path = NULL;


/* Local functions */
static void recomputeNamespacePath(void);
static void InitTempTableNamespace(void);
static void RemoveTempRelations(Oid tempNamespaceId);
static void RemoveTempRelationsCallback(int code, Datum arg);
static void NamespaceCallback(Datum arg, int cacheid, uint32 hashvalue);
static bool MatchNamedCall(HeapTuple proctup, int nargs, List *argnames,
               int **argnumbers);

/* These don't really need to appear in any header file */
Datum       pg_table_is_visible(PG_FUNCTION_ARGS);
Datum       pg_type_is_visible(PG_FUNCTION_ARGS);
Datum       pg_function_is_visible(PG_FUNCTION_ARGS);
Datum       pg_operator_is_visible(PG_FUNCTION_ARGS);
Datum       pg_opclass_is_visible(PG_FUNCTION_ARGS);
Datum       pg_opfamily_is_visible(PG_FUNCTION_ARGS);
Datum       pg_collation_is_visible(PG_FUNCTION_ARGS);
Datum       pg_conversion_is_visible(PG_FUNCTION_ARGS);
Datum       pg_ts_parser_is_visible(PG_FUNCTION_ARGS);
Datum       pg_ts_dict_is_visible(PG_FUNCTION_ARGS);
Datum       pg_ts_template_is_visible(PG_FUNCTION_ARGS);
Datum       pg_ts_config_is_visible(PG_FUNCTION_ARGS);
Datum       pg_my_temp_schema(PG_FUNCTION_ARGS);
Datum       pg_is_other_temp_schema(PG_FUNCTION_ARGS);


/*
 * RangeVarGetRelid
 *      Given a RangeVar describing an existing relation,
 *      select the proper namespace and look up the relation OID.
 *
 * If the schema or relation is not found, return InvalidOid if missing_ok
 * = true, otherwise raise an error.
 *
 * If nowait = true, throw an error if we'd have to wait for a lock.
 *
 * Callback allows caller to check permissions or acquire additional locks
 * prior to grabbing the relation lock.
 */
Oid
RangeVarGetRelidExtended(const RangeVar *relation, LOCKMODE lockmode,
                         bool missing_ok, bool nowait,
                       RangeVarGetRelidCallback callback, void *callback_arg)
{
    uint64      inval_count;
    Oid         relId;
    Oid         oldRelId = InvalidOid;
    bool        retry = false;

    /*
     * We check the catalog name and then ignore it.
     */
    if (relation->catalogname)
    {
        if (strcmp(relation->catalogname, get_database_name(MyDatabaseId)) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cross-database references are not implemented: \"%s.%s.%s\"",
                            relation->catalogname, relation->schemaname,
                            relation->relname)));
    }

    /*
     * DDL operations can change the results of a name lookup.  Since all such
     * operations will generate invalidation messages, we keep track of
     * whether any such messages show up while we're performing the operation,
     * and retry until either (1) no more invalidation messages show up or (2)
     * the answer doesn't change.
     *
     * But if lockmode = NoLock, then we assume that either the caller is OK
     * with the answer changing under them, or that they already hold some
     * appropriate lock, and therefore return the first answer we get without
     * checking for invalidation messages.  Also, if the requested lock is
     * already held, LockRelationOid will not AcceptInvalidationMessages, so
     * we may fail to notice a change.  We could protect against that case by
     * calling AcceptInvalidationMessages() before beginning this loop, but
     * that would add a significant amount overhead, so for now we don't.
     */
    for (;;)
    {
        /*
         * Remember this value, so that, after looking up the relation name
         * and locking its OID, we can check whether any invalidation messages
         * have been processed that might require a do-over.
         */
        inval_count = SharedInvalidMessageCounter;

        /*
         * Some non-default relpersistence value may have been specified.  The
         * parser never generates such a RangeVar in simple DML, but it can
         * happen in contexts such as "CREATE TEMP TABLE foo (f1 int PRIMARY
         * KEY)".  Such a command will generate an added CREATE INDEX
         * operation, which must be careful to find the temp table, even when
         * pg_temp is not first in the search path.
         */
        if (relation->relpersistence == RELPERSISTENCE_TEMP)
        {
            if (!OidIsValid(myTempNamespace))
                relId = InvalidOid;     /* this probably can't happen? */
            else
            {
                if (relation->schemaname)
                {
                    Oid         namespaceId;

                    namespaceId = LookupExplicitNamespace(relation->schemaname, missing_ok);

                    /*
                     * For missing_ok, allow a non-existant schema name to
                     * return InvalidOid.
                     */
                    if (namespaceId != myTempNamespace)
                        ereport(ERROR,
                                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                                 errmsg("temporary tables cannot specify a schema name")));
                }

                relId = get_relname_relid(relation->relname, myTempNamespace);
            }
        }
        else if (relation->schemaname)
        {
            Oid         namespaceId;

            /* use exact schema given */
            namespaceId = LookupExplicitNamespace(relation->schemaname, missing_ok);
            if (missing_ok && !OidIsValid(namespaceId))
                relId = InvalidOid;
            else
                relId = get_relname_relid(relation->relname, namespaceId);
        }
        else
        {
            /* search the namespace path */
            relId = RelnameGetRelid(relation->relname);
        }

        /*
         * Invoke caller-supplied callback, if any.
         *
         * This callback is a good place to check permissions: we haven't
         * taken the table lock yet (and it's really best to check permissions
         * before locking anything!), but we've gotten far enough to know what
         * OID we think we should lock.  Of course, concurrent DDL might
         * change things while we're waiting for the lock, but in that case
         * the callback will be invoked again for the new OID.
         */
        if (callback)
            callback(relation, relId, oldRelId, callback_arg);

        /*
         * If no lock requested, we assume the caller knows what they're
         * doing.  They should have already acquired a heavyweight lock on
         * this relation earlier in the processing of this same statement, so
         * it wouldn't be appropriate to AcceptInvalidationMessages() here, as
         * that might pull the rug out from under them.
         */
        if (lockmode == NoLock)
            break;

        /*
         * If, upon retry, we get back the same OID we did last time, then the
         * invalidation messages we processed did not change the final answer.
         * So we're done.
         *
         * If we got a different OID, we've locked the relation that used to
         * have this name rather than the one that does now.  So release the
         * lock.
         */
        if (retry)
        {
            if (relId == oldRelId)
                break;
            if (OidIsValid(oldRelId))
                UnlockRelationOid(oldRelId, lockmode);
        }

        /*
         * Lock relation.  This will also accept any pending invalidation
         * messages.  If we got back InvalidOid, indicating not found, then
         * there's nothing to lock, but we accept invalidation messages
         * anyway, to flush any negative catcache entries that may be
         * lingering.
         */
        if (!OidIsValid(relId))
            AcceptInvalidationMessages();
        else if (!nowait)
            LockRelationOid(relId, lockmode);
        else if (!ConditionalLockRelationOid(relId, lockmode))
        {
            if (relation->schemaname)
                ereport(ERROR,
                        (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                         errmsg("could not obtain lock on relation \"%s.%s\"",
                                relation->schemaname, relation->relname)));
            else
                ereport(ERROR,
                        (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                         errmsg("could not obtain lock on relation \"%s\"",
                                relation->relname)));
        }

        /*
         * If no invalidation message were processed, we're done!
         */
        if (inval_count == SharedInvalidMessageCounter)
            break;

        /*
         * Something may have changed.  Let's repeat the name lookup, to make
         * sure this name still references the same relation it did
         * previously.
         */
        retry = true;
        oldRelId = relId;
    }

    if (!OidIsValid(relId) && !missing_ok)
    {
        if (relation->schemaname)
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_TABLE),
                     errmsg("relation \"%s.%s\" does not exist",
                            relation->schemaname, relation->relname)));
        else
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_TABLE),
                     errmsg("relation \"%s\" does not exist",
                            relation->relname)));
    }
    return relId;
}

/*
 * RangeVarGetCreationNamespace
 *      Given a RangeVar describing a to-be-created relation,
 *      choose which namespace to create it in.
 *
 * Note: calling this may result in a CommandCounterIncrement operation.
 * That will happen on the first request for a temp table in any particular
 * backend run; we will need to either create or clean out the temp schema.
 */
Oid
RangeVarGetCreationNamespace(const RangeVar *newRelation)
{
    Oid         namespaceId;

    /*
     * We check the catalog name and then ignore it.
     */
    if (newRelation->catalogname)
    {
        if (strcmp(newRelation->catalogname, get_database_name(MyDatabaseId)) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cross-database references are not implemented: \"%s.%s.%s\"",
                            newRelation->catalogname, newRelation->schemaname,
                            newRelation->relname)));
    }

    if (newRelation->schemaname)
    {
        /* check for pg_temp alias */
        if (strcmp(newRelation->schemaname, "pg_temp") == 0)
        {
            /* Initialize temp namespace if first time through */
            if (!OidIsValid(myTempNamespace))
                InitTempTableNamespace();
            return myTempNamespace;
        }
        /* use exact schema given */
        namespaceId = get_namespace_oid(newRelation->schemaname, false);
        /* we do not check for USAGE rights here! */
    }
    else if (newRelation->relpersistence == RELPERSISTENCE_TEMP)
    {
        /* Initialize temp namespace if first time through */
        if (!OidIsValid(myTempNamespace))
            InitTempTableNamespace();
        return myTempNamespace;
    }
    else
    {
        /* use the default creation namespace */
        recomputeNamespacePath();
        if (activeTempCreationPending)
        {
            /* Need to initialize temp namespace */
            InitTempTableNamespace();
            return myTempNamespace;
        }
        namespaceId = activeCreationNamespace;
        if (!OidIsValid(namespaceId))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_SCHEMA),
                     errmsg("no schema has been selected to create in")));
    }

    /* Note: callers will check for CREATE rights when appropriate */

    return namespaceId;
}

/*
 * RangeVarGetAndCheckCreationNamespace
 *
 * This function returns the OID of the namespace in which a new relation
 * with a given name should be created.  If the user does not have CREATE
 * permission on the target namespace, this function will instead signal
 * an ERROR.
 *
 * If non-NULL, *existing_oid is set to the OID of any existing relation with
 * the same name which already exists in that namespace, or to InvalidOid if
 * no such relation exists.
 *
 * If lockmode != NoLock, the specified lock mode is acquired on the existing
 * relation, if any, provided that the current user owns the target relation.
 * However, if lockmode != NoLock and the user does not own the target
 * relation, we throw an ERROR, as we must not try to lock relations the
 * user does not have permissions on.
 *
 * As a side effect, this function acquires AccessShareLock on the target
 * namespace.  Without this, the namespace could be dropped before our
 * transaction commits, leaving behind relations with relnamespace pointing
 * to a no-longer-existent namespace.
 *
 * As a further side-effect, if the selected namespace is a temporary namespace,
 * we mark the RangeVar as RELPERSISTENCE_TEMP.
 */
Oid
RangeVarGetAndCheckCreationNamespace(RangeVar *relation,
                                     LOCKMODE lockmode,
                                     Oid *existing_relation_id)
{
    uint64      inval_count;
    Oid         relid;
    Oid         oldrelid = InvalidOid;
    Oid         nspid;
    Oid         oldnspid = InvalidOid;
    bool        retry = false;

    /*
     * We check the catalog name and then ignore it.
     */
    if (relation->catalogname)
    {
        if (strcmp(relation->catalogname, get_database_name(MyDatabaseId)) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cross-database references are not implemented: \"%s.%s.%s\"",
                            relation->catalogname, relation->schemaname,
                            relation->relname)));
    }

    /*
     * As in RangeVarGetRelidExtended(), we guard against concurrent DDL
     * operations by tracking whether any invalidation messages are processed
     * while we're doing the name lookups and acquiring locks.  See comments
     * in that function for a more detailed explanation of this logic.
     */
    for (;;)
    {
        AclResult   aclresult;

        inval_count = SharedInvalidMessageCounter;

        /* Look up creation namespace and check for existing relation. */
        nspid = RangeVarGetCreationNamespace(relation);
        Assert(OidIsValid(nspid));
        if (existing_relation_id != NULL)
            relid = get_relname_relid(relation->relname, nspid);
        else
            relid = InvalidOid;

        /*
         * In bootstrap processing mode, we don't bother with permissions or
         * locking.  Permissions might not be working yet, and locking is
         * unnecessary.
         */
        if (IsBootstrapProcessingMode())
            break;

        /* Check namespace permissions. */
        aclresult = pg_namespace_aclcheck(nspid, GetUserId(), ACL_CREATE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, ACL_KIND_NAMESPACE,
                           get_namespace_name(nspid));

        if (retry)
        {
            /* If nothing changed, we're done. */
            if (relid == oldrelid && nspid == oldnspid)
                break;
            /* If creation namespace has changed, give up old lock. */
            if (nspid != oldnspid)
                UnlockDatabaseObject(NamespaceRelationId, oldnspid, 0,
                                     AccessShareLock);
            /* If name points to something different, give up old lock. */
            if (relid != oldrelid && OidIsValid(oldrelid) && lockmode != NoLock)
                UnlockRelationOid(oldrelid, lockmode);
        }

        /* Lock namespace. */
        if (nspid != oldnspid)
            LockDatabaseObject(NamespaceRelationId, nspid, 0, AccessShareLock);

        /* Lock relation, if required if and we have permission. */
        if (lockmode != NoLock && OidIsValid(relid))
        {
            if (!pg_class_ownercheck(relid, GetUserId()))
                aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                               relation->relname);
            if (relid != oldrelid)
                LockRelationOid(relid, lockmode);
        }

        /* If no invalidation message were processed, we're done! */
        if (inval_count == SharedInvalidMessageCounter)
            break;

        /* Something may have changed, so recheck our work. */
        retry = true;
        oldrelid = relid;
        oldnspid = nspid;
    }

    RangeVarAdjustRelationPersistence(relation, nspid);
    if (existing_relation_id != NULL)
        *existing_relation_id = relid;
    return nspid;
}

/*
 * Adjust the relpersistence for an about-to-be-created relation based on the
 * creation namespace, and throw an error for invalid combinations.
 */
void
RangeVarAdjustRelationPersistence(RangeVar *newRelation, Oid nspid)
{
    switch (newRelation->relpersistence)
    {
        case RELPERSISTENCE_TEMP:
            if (!isTempOrTempToastNamespace(nspid))
            {
                if (isAnyTempNamespace(nspid))
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                             errmsg("cannot create relations in temporary schemas of other sessions")));
                else
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                             errmsg("cannot create temporary relation in non-temporary schema")));
            }
            break;
        case RELPERSISTENCE_PERMANENT:
            if (isTempOrTempToastNamespace(nspid))
                newRelation->relpersistence = RELPERSISTENCE_TEMP;
            else if (isAnyTempNamespace(nspid))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                         errmsg("cannot create relations in temporary schemas of other sessions")));
            break;
        default:
            if (isAnyTempNamespace(nspid))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                         errmsg("only temporary relations may be created in temporary schemas")));
    }
}

/*
 * RelnameGetRelid
 *      Try to resolve an unqualified relation name.
 *      Returns OID if relation found in search path, else InvalidOid.
 */
Oid
RelnameGetRelid(const char *relname)
{
    Oid         relid;
    ListCell   *l;

    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);

        relid = get_relname_relid(relname, namespaceId);
        if (OidIsValid(relid))
            return relid;
    }

    /* Not found in path */
    return InvalidOid;
}


/*
 * RelationIsVisible
 *      Determine whether a relation (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified relation name".
 */
bool
RelationIsVisible(Oid relid)
{
    HeapTuple   reltup;
    Form_pg_class relform;
    Oid         relnamespace;
    bool        visible;

    reltup = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(reltup))
        elog(ERROR, "cache lookup failed for relation %u", relid);
    relform = (Form_pg_class) GETSTRUCT(reltup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    relnamespace = relform->relnamespace;
    if (relnamespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, relnamespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another relation of the same name earlier in the path. So
         * we must do a slow check for conflicting relations.
         */
        char       *relname = NameStr(relform->relname);
        ListCell   *l;

        visible = false;
        foreach(l, activeSearchPath)
        {
            Oid         namespaceId = lfirst_oid(l);

            if (namespaceId == relnamespace)
            {
                /* Found it first in path */
                visible = true;
                break;
            }
            if (OidIsValid(get_relname_relid(relname, namespaceId)))
            {
                /* Found something else first in path */
                break;
            }
        }
    }

    ReleaseSysCache(reltup);

    return visible;
}


/*
 * TypenameGetTypid
 *      Try to resolve an unqualified datatype name.
 *      Returns OID if type found in search path, else InvalidOid.
 *
 * This is essentially the same as RelnameGetRelid.
 */
Oid
TypenameGetTypid(const char *typname)
{
    Oid         typid;
    ListCell   *l;

    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);

        typid = GetSysCacheOid2(TYPENAMENSP,
                                PointerGetDatum(typname),
                                ObjectIdGetDatum(namespaceId));
        if (OidIsValid(typid))
            return typid;
    }

    /* Not found in path */
    return InvalidOid;
}

/*
 * TypeIsVisible
 *      Determine whether a type (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified type name".
 */
bool
TypeIsVisible(Oid typid)
{
    HeapTuple   typtup;
    Form_pg_type typform;
    Oid         typnamespace;
    bool        visible;

    typtup = SearchSysCache1(TYPEOID, ObjectIdGetDatum(typid));
    if (!HeapTupleIsValid(typtup))
        elog(ERROR, "cache lookup failed for type %u", typid);
    typform = (Form_pg_type) GETSTRUCT(typtup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    typnamespace = typform->typnamespace;
    if (typnamespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, typnamespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another type of the same name earlier in the path. So we
         * must do a slow check for conflicting types.
         */
        char       *typname = NameStr(typform->typname);
        ListCell   *l;

        visible = false;
        foreach(l, activeSearchPath)
        {
            Oid         namespaceId = lfirst_oid(l);

            if (namespaceId == typnamespace)
            {
                /* Found it first in path */
                visible = true;
                break;
            }
            if (SearchSysCacheExists2(TYPENAMENSP,
                                      PointerGetDatum(typname),
                                      ObjectIdGetDatum(namespaceId)))
            {
                /* Found something else first in path */
                break;
            }
        }
    }

    ReleaseSysCache(typtup);

    return visible;
}


/*
 * FuncnameGetCandidates
 *      Given a possibly-qualified function name and argument count,
 *      retrieve a list of the possible matches.
 *
 * If nargs is -1, we return all functions matching the given name,
 * regardless of argument count.  (argnames must be NIL, and expand_variadic
 * and expand_defaults must be false, in this case.)
 *
 * If argnames isn't NIL, we are considering a named- or mixed-notation call,
 * and only functions having all the listed argument names will be returned.
 * (We assume that length(argnames) <= nargs and all the passed-in names are
 * distinct.)  The returned structs will include an argnumbers array showing
 * the actual argument index for each logical argument position.
 *
 * If expand_variadic is true, then variadic functions having the same number
 * or fewer arguments will be retrieved, with the variadic argument and any
 * additional argument positions filled with the variadic element type.
 * nvargs in the returned struct is set to the number of such arguments.
 * If expand_variadic is false, variadic arguments are not treated specially,
 * and the returned nvargs will always be zero.
 *
 * If expand_defaults is true, functions that could match after insertion of
 * default argument values will also be retrieved.  In this case the returned
 * structs could have nargs > passed-in nargs, and ndargs is set to the number
 * of additional args (which can be retrieved from the function's
 * proargdefaults entry).
 *
 * It is not possible for nvargs and ndargs to both be nonzero in the same
 * list entry, since default insertion allows matches to functions with more
 * than nargs arguments while the variadic transformation requires the same
 * number or less.
 *
 * When argnames isn't NIL, the returned args[] type arrays are not ordered
 * according to the functions' declarations, but rather according to the call:
 * first any positional arguments, then the named arguments, then defaulted
 * arguments (if needed and allowed by expand_defaults).  The argnumbers[]
 * array can be used to map this back to the catalog information.
 * argnumbers[k] is set to the proargtypes index of the k'th call argument.
 *
 * We search a single namespace if the function name is qualified, else
 * all namespaces in the search path.  In the multiple-namespace case,
 * we arrange for entries in earlier namespaces to mask identical entries in
 * later namespaces.
 *
 * When expanding variadics, we arrange for non-variadic functions to mask
 * variadic ones if the expanded argument list is the same.  It is still
 * possible for there to be conflicts between different variadic functions,
 * however.
 *
 * It is guaranteed that the return list will never contain multiple entries
 * with identical argument lists.  When expand_defaults is true, the entries
 * could have more than nargs positions, but we still guarantee that they are
 * distinct in the first nargs positions.  However, if argnames isn't NIL or
 * either expand_variadic or expand_defaults is true, there might be multiple
 * candidate functions that expand to identical argument lists.  Rather than
 * throw error here, we report such situations by returning a single entry
 * with oid = 0 that represents a set of such conflicting candidates.
 * The caller might end up discarding such an entry anyway, but if it selects
 * such an entry it should react as though the call were ambiguous.
 *
 * If missing_ok is true, an empty list (NULL) is returned if the name was
 * schema- qualified with a schema that does not exist.  Likewise if no
 * candidate is found for other reasons.
 */
FuncCandidateList
FuncnameGetCandidates(List *names, int nargs, List *argnames,
                      bool expand_variadic, bool expand_defaults,
                      bool missing_ok)
{
    FuncCandidateList resultList = NULL;
    bool        any_special = false;
    char       *schemaname;
    char       *funcname;
    Oid         namespaceId;
    CatCList   *catlist;
    int         i;

    /* check for caller error */
    Assert(nargs >= 0 || !(expand_variadic | expand_defaults));

    /* deconstruct the name list */
    DeconstructQualifiedName(names, &schemaname, &funcname);

    if (schemaname)
    {
        /* use exact schema given */
        namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
        if (!OidIsValid(namespaceId))
            return NULL;
    }
    else
    {
        /* flag to indicate we need namespace search */
        namespaceId = InvalidOid;
        recomputeNamespacePath();
    }

    /* Search syscache by name only */
    catlist = SearchSysCacheList1(PROCNAMEARGSNSP, CStringGetDatum(funcname));

    for (i = 0; i < catlist->n_members; i++)
    {
        HeapTuple   proctup = &catlist->members[i]->tuple;
        Form_pg_proc procform = (Form_pg_proc) GETSTRUCT(proctup);
        int         pronargs = procform->pronargs;
        int         effective_nargs;
        int         pathpos = 0;
        bool        variadic;
        bool        use_defaults;
        Oid         va_elem_type;
        int        *argnumbers = NULL;
        FuncCandidateList newResult;

        if (OidIsValid(namespaceId))
        {
            /* Consider only procs in specified namespace */
            if (procform->pronamespace != namespaceId)
                continue;
        }
        else
        {
            /*
             * Consider only procs that are in the search path and are not in
             * the temp namespace.
             */
            ListCell   *nsp;

            foreach(nsp, activeSearchPath)
            {
                if (procform->pronamespace == lfirst_oid(nsp) &&
                    procform->pronamespace != myTempNamespace)
                    break;
                pathpos++;
            }
            if (nsp == NULL)
                continue;       /* proc is not in search path */
        }

        if (argnames != NIL)
        {
            /*
             * Call uses named or mixed notation
             *
             * Named or mixed notation can match a variadic function only if
             * expand_variadic is off; otherwise there is no way to match the
             * presumed-nameless parameters expanded from the variadic array.
             */
            if (OidIsValid(procform->provariadic) && expand_variadic)
                continue;
            va_elem_type = InvalidOid;
            variadic = false;

            /*
             * Check argument count.
             */
            Assert(nargs >= 0); /* -1 not supported with argnames */

            if (pronargs > nargs && expand_defaults)
            {
                /* Ignore if not enough default expressions */
                if (nargs + procform->pronargdefaults < pronargs)
                    continue;
                use_defaults = true;
            }
            else
                use_defaults = false;

            /* Ignore if it doesn't match requested argument count */
            if (pronargs != nargs && !use_defaults)
                continue;

            /* Check for argument name match, generate positional mapping */
            if (!MatchNamedCall(proctup, nargs, argnames,
                                &argnumbers))
                continue;

            /* Named argument matching is always "special" */
            any_special = true;
        }
        else
        {
            /*
             * Call uses positional notation
             *
             * Check if function is variadic, and get variadic element type if
             * so.  If expand_variadic is false, we should just ignore
             * variadic-ness.
             */
            if (pronargs <= nargs && expand_variadic)
            {
                va_elem_type = procform->provariadic;
                variadic = OidIsValid(va_elem_type);
                any_special |= variadic;
            }
            else
            {
                va_elem_type = InvalidOid;
                variadic = false;
            }

            /*
             * Check if function can match by using parameter defaults.
             */
            if (pronargs > nargs && expand_defaults)
            {
                /* Ignore if not enough default expressions */
                if (nargs + procform->pronargdefaults < pronargs)
                    continue;
                use_defaults = true;
                any_special = true;
            }
            else
                use_defaults = false;

            /* Ignore if it doesn't match requested argument count */
            if (nargs >= 0 && pronargs != nargs && !variadic && !use_defaults)
                continue;
        }

        /*
         * We must compute the effective argument list so that we can easily
         * compare it to earlier results.  We waste a palloc cycle if it gets
         * masked by an earlier result, but really that's a pretty infrequent
         * case so it's not worth worrying about.
         */
        effective_nargs = Max(pronargs, nargs);
        newResult = (FuncCandidateList)
            palloc(offsetof(struct _FuncCandidateList, args) +
                   effective_nargs * sizeof(Oid));
        newResult->pathpos = pathpos;
        newResult->oid = HeapTupleGetOid(proctup);
        newResult->nargs = effective_nargs;
        newResult->argnumbers = argnumbers;
        if (argnumbers)
        {
            /* Re-order the argument types into call's logical order */
            Oid        *proargtypes = procform->proargtypes.values;
            int         i;

            for (i = 0; i < pronargs; i++)
                newResult->args[i] = proargtypes[argnumbers[i]];
        }
        else
        {
            /* Simple positional case, just copy proargtypes as-is */
            memcpy(newResult->args, procform->proargtypes.values,
                   pronargs * sizeof(Oid));
        }
        if (variadic)
        {
            int         i;

            newResult->nvargs = effective_nargs - pronargs + 1;
            /* Expand variadic argument into N copies of element type */
            for (i = pronargs - 1; i < effective_nargs; i++)
                newResult->args[i] = va_elem_type;
        }
        else
            newResult->nvargs = 0;
        newResult->ndargs = use_defaults ? pronargs - nargs : 0;

        /*
         * Does it have the same arguments as something we already accepted?
         * If so, decide what to do to avoid returning duplicate argument
         * lists.  We can skip this check for the single-namespace case if no
         * special (named, variadic or defaults) match has been made, since
         * then the unique index on pg_proc guarantees all the matches have
         * different argument lists.
         */
        if (resultList != NULL &&
            (any_special || !OidIsValid(namespaceId)))
        {
            /*
             * If we have an ordered list from SearchSysCacheList (the normal
             * case), then any conflicting proc must immediately adjoin this
             * one in the list, so we only need to look at the newest result
             * item.  If we have an unordered list, we have to scan the whole
             * result list.  Also, if either the current candidate or any
             * previous candidate is a special match, we can't assume that
             * conflicts are adjacent.
             *
             * We ignore defaulted arguments in deciding what is a match.
             */
            FuncCandidateList prevResult;

            if (catlist->ordered && !any_special)
            {
                /* ndargs must be 0 if !any_special */
                if (effective_nargs == resultList->nargs &&
                    memcmp(newResult->args,
                           resultList->args,
                           effective_nargs * sizeof(Oid)) == 0)
                    prevResult = resultList;
                else
                    prevResult = NULL;
            }
            else
            {
                int         cmp_nargs = newResult->nargs - newResult->ndargs;

                for (prevResult = resultList;
                     prevResult;
                     prevResult = prevResult->next)
                {
                    if (cmp_nargs == prevResult->nargs - prevResult->ndargs &&
                        memcmp(newResult->args,
                               prevResult->args,
                               cmp_nargs * sizeof(Oid)) == 0)
                        break;
                }
            }

            if (prevResult)
            {
                /*
                 * We have a match with a previous result.  Decide which one
                 * to keep, or mark it ambiguous if we can't decide.  The
                 * logic here is preference > 0 means prefer the old result,
                 * preference < 0 means prefer the new, preference = 0 means
                 * ambiguous.
                 */
                int         preference;

                if (pathpos != prevResult->pathpos)
                {
                    /*
                     * Prefer the one that's earlier in the search path.
                     */
                    preference = pathpos - prevResult->pathpos;
                }
                else if (variadic && prevResult->nvargs == 0)
                {
                    /*
                     * With variadic functions we could have, for example,
                     * both foo(numeric) and foo(variadic numeric[]) in the
                     * same namespace; if so we prefer the non-variadic match
                     * on efficiency grounds.
                     */
                    preference = 1;
                }
                else if (!variadic && prevResult->nvargs > 0)
                {
                    preference = -1;
                }
                else
                {
                    /*----------
                     * We can't decide.  This can happen with, for example,
                     * both foo(numeric, variadic numeric[]) and
                     * foo(variadic numeric[]) in the same namespace, or
                     * both foo(int) and foo (int, int default something)
                     * in the same namespace, or both foo(a int, b text)
                     * and foo(b text, a int) in the same namespace.
                     *----------
                     */
                    preference = 0;
                }

                if (preference > 0)
                {
                    /* keep previous result */
                    pfree(newResult);
                    continue;
                }
                else if (preference < 0)
                {
                    /* remove previous result from the list */
                    if (prevResult == resultList)
                        resultList = prevResult->next;
                    else
                    {
                        FuncCandidateList prevPrevResult;

                        for (prevPrevResult = resultList;
                             prevPrevResult;
                             prevPrevResult = prevPrevResult->next)
                        {
                            if (prevResult == prevPrevResult->next)
                            {
                                prevPrevResult->next = prevResult->next;
                                break;
                            }
                        }
                        Assert(prevPrevResult); /* assert we found it */
                    }
                    pfree(prevResult);
                    /* fall through to add newResult to list */
                }
                else
                {
                    /* mark old result as ambiguous, discard new */
                    prevResult->oid = InvalidOid;
                    pfree(newResult);
                    continue;
                }
            }
        }

        /*
         * Okay to add it to result list
         */
        newResult->next = resultList;
        resultList = newResult;
    }

    ReleaseSysCacheList(catlist);

    return resultList;
}

/*
 * MatchNamedCall
 *      Given a pg_proc heap tuple and a call's list of argument names,
 *      check whether the function could match the call.
 *
 * The call could match if all supplied argument names are accepted by
 * the function, in positions after the last positional argument, and there
 * are defaults for all unsupplied arguments.
 *
 * The number of positional arguments is nargs - list_length(argnames).
 * Note caller has already done basic checks on argument count.
 *
 * On match, return true and fill *argnumbers with a palloc'd array showing
 * the mapping from call argument positions to actual function argument
 * numbers.  Defaulted arguments are included in this map, at positions
 * after the last supplied argument.
 */
static bool
MatchNamedCall(HeapTuple proctup, int nargs, List *argnames,
               int **argnumbers)
{
    Form_pg_proc procform = (Form_pg_proc) GETSTRUCT(proctup);
    int         pronargs = procform->pronargs;
    int         numposargs = nargs - list_length(argnames);
    int         pronallargs;
    Oid        *p_argtypes;
    char      **p_argnames;
    char       *p_argmodes;
    bool        arggiven[FUNC_MAX_ARGS];
    bool        isnull;
    int         ap;             /* call args position */
    int         pp;             /* proargs position */
    ListCell   *lc;

    Assert(argnames != NIL);
    Assert(numposargs >= 0);
    Assert(nargs <= pronargs);

    /* Ignore this function if its proargnames is null */
    (void) SysCacheGetAttr(PROCOID, proctup, Anum_pg_proc_proargnames,
                           &isnull);
    if (isnull)
        return false;

    /* OK, let's extract the argument names and types */
    pronallargs = get_func_arg_info(proctup,
                                    &p_argtypes, &p_argnames, &p_argmodes);
    Assert(p_argnames != NULL);

    /* initialize state for matching */
    *argnumbers = (int *) palloc(pronargs * sizeof(int));
    memset(arggiven, false, pronargs * sizeof(bool));

    /* there are numposargs positional args before the named args */
    for (ap = 0; ap < numposargs; ap++)
    {
        (*argnumbers)[ap] = ap;
        arggiven[ap] = true;
    }

    /* now examine the named args */
    foreach(lc, argnames)
    {
        char       *argname = (char *) lfirst(lc);
        bool        found;
        int         i;

        pp = 0;
        found = false;
        for (i = 0; i < pronallargs; i++)
        {
            /* consider only input parameters */
            if (p_argmodes &&
                (p_argmodes[i] != FUNC_PARAM_IN &&
                 p_argmodes[i] != FUNC_PARAM_INOUT &&
                 p_argmodes[i] != FUNC_PARAM_VARIADIC))
                continue;
            if (p_argnames[i] && strcmp(p_argnames[i], argname) == 0)
            {
                /* fail if argname matches a positional argument */
                if (arggiven[pp])
                    return false;
                arggiven[pp] = true;
                (*argnumbers)[ap] = pp;
                found = true;
                break;
            }
            /* increase pp only for input parameters */
            pp++;
        }
        /* if name isn't in proargnames, fail */
        if (!found)
            return false;
        ap++;
    }

    Assert(ap == nargs);        /* processed all actual parameters */

    /* Check for default arguments */
    if (nargs < pronargs)
    {
        int         first_arg_with_default = pronargs - procform->pronargdefaults;

        for (pp = numposargs; pp < pronargs; pp++)
        {
            if (arggiven[pp])
                continue;
            /* fail if arg not given and no default available */
            if (pp < first_arg_with_default)
                return false;
            (*argnumbers)[ap++] = pp;
        }
    }

    Assert(ap == pronargs);     /* processed all function parameters */

    return true;
}

/*
 * FunctionIsVisible
 *      Determine whether a function (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified function name with exact argument matches".
 */
bool
FunctionIsVisible(Oid funcid)
{
    HeapTuple   proctup;
    Form_pg_proc procform;
    Oid         pronamespace;
    bool        visible;

    proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
    if (!HeapTupleIsValid(proctup))
        elog(ERROR, "cache lookup failed for function %u", funcid);
    procform = (Form_pg_proc) GETSTRUCT(proctup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    pronamespace = procform->pronamespace;
    if (pronamespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, pronamespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another proc of the same name and arguments earlier in
         * the path.  So we must do a slow check to see if this is the same
         * proc that would be found by FuncnameGetCandidates.
         */
        char       *proname = NameStr(procform->proname);
        int         nargs = procform->pronargs;
        FuncCandidateList clist;

        visible = false;

        clist = FuncnameGetCandidates(list_make1(makeString(proname)),
                                      nargs, NIL, false, false, false);

        for (; clist; clist = clist->next)
        {
            if (memcmp(clist->args, procform->proargtypes.values,
                       nargs * sizeof(Oid)) == 0)
            {
                /* Found the expected entry; is it the right proc? */
                visible = (clist->oid == funcid);
                break;
            }
        }
    }

    ReleaseSysCache(proctup);

    return visible;
}


/*
 * OpernameGetOprid
 *      Given a possibly-qualified operator name and exact input datatypes,
 *      look up the operator.  Returns InvalidOid if not found.
 *
 * Pass oprleft = InvalidOid for a prefix op, oprright = InvalidOid for
 * a postfix op.
 *
 * If the operator name is not schema-qualified, it is sought in the current
 * namespace search path.  If the name is schema-qualified and the given
 * schema does not exist, InvalidOid is returned.
 */
Oid
OpernameGetOprid(List *names, Oid oprleft, Oid oprright)
{
    char       *schemaname;
    char       *opername;
    CatCList   *catlist;
    ListCell   *l;

    /* deconstruct the name list */
    DeconstructQualifiedName(names, &schemaname, &opername);

    if (schemaname)
    {
        /* search only in exact schema given */
        Oid         namespaceId;

        namespaceId = LookupExplicitNamespace(schemaname, true);
        if (OidIsValid(namespaceId))
        {
            HeapTuple   opertup;

            opertup = SearchSysCache4(OPERNAMENSP,
                                      CStringGetDatum(opername),
                                      ObjectIdGetDatum(oprleft),
                                      ObjectIdGetDatum(oprright),
                                      ObjectIdGetDatum(namespaceId));
            if (HeapTupleIsValid(opertup))
            {
                Oid         result = HeapTupleGetOid(opertup);

                ReleaseSysCache(opertup);
                return result;
            }
        }

        return InvalidOid;
    }

    /* Search syscache by name and argument types */
    catlist = SearchSysCacheList3(OPERNAMENSP,
                                  CStringGetDatum(opername),
                                  ObjectIdGetDatum(oprleft),
                                  ObjectIdGetDatum(oprright));

    if (catlist->n_members == 0)
    {
        /* no hope, fall out early */
        ReleaseSysCacheList(catlist);
        return InvalidOid;
    }

    /*
     * We have to find the list member that is first in the search path, if
     * there's more than one.  This doubly-nested loop looks ugly, but in
     * practice there should usually be few catlist members.
     */
    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);
        int         i;

        if (namespaceId == myTempNamespace)
            continue;           /* do not look in temp namespace */

        for (i = 0; i < catlist->n_members; i++)
        {
            HeapTuple   opertup = &catlist->members[i]->tuple;
            Form_pg_operator operform = (Form_pg_operator) GETSTRUCT(opertup);

            if (operform->oprnamespace == namespaceId)
            {
                Oid         result = HeapTupleGetOid(opertup);

                ReleaseSysCacheList(catlist);
                return result;
            }
        }
    }

    ReleaseSysCacheList(catlist);
    return InvalidOid;
}

/*
 * OpernameGetCandidates
 *      Given a possibly-qualified operator name and operator kind,
 *      retrieve a list of the possible matches.
 *
 * If oprkind is '\0', we return all operators matching the given name,
 * regardless of arguments.
 *
 * We search a single namespace if the operator name is qualified, else
 * all namespaces in the search path.  The return list will never contain
 * multiple entries with identical argument lists --- in the multiple-
 * namespace case, we arrange for entries in earlier namespaces to mask
 * identical entries in later namespaces.
 *
 * The returned items always have two args[] entries --- one or the other
 * will be InvalidOid for a prefix or postfix oprkind.  nargs is 2, too.
 */
FuncCandidateList
OpernameGetCandidates(List *names, char oprkind, bool missing_schema_ok)
{
    FuncCandidateList resultList = NULL;
    char       *resultSpace = NULL;
    int         nextResult = 0;
    char       *schemaname;
    char       *opername;
    Oid         namespaceId;
    CatCList   *catlist;
    int         i;

    /* deconstruct the name list */
    DeconstructQualifiedName(names, &schemaname, &opername);

    if (schemaname)
    {
        /* use exact schema given */
        namespaceId = LookupExplicitNamespace(schemaname, missing_schema_ok);
        if (missing_schema_ok && !OidIsValid(namespaceId))
            return NULL;
    }
    else
    {
        /* flag to indicate we need namespace search */
        namespaceId = InvalidOid;
        recomputeNamespacePath();
    }

    /* Search syscache by name only */
    catlist = SearchSysCacheList1(OPERNAMENSP, CStringGetDatum(opername));

    /*
     * In typical scenarios, most if not all of the operators found by the
     * catcache search will end up getting returned; and there can be quite a
     * few, for common operator names such as '=' or '+'.  To reduce the time
     * spent in palloc, we allocate the result space as an array large enough
     * to hold all the operators.  The original coding of this routine did a
     * separate palloc for each operator, but profiling revealed that the
     * pallocs used an unreasonably large fraction of parsing time.
     */
#define SPACE_PER_OP MAXALIGN(offsetof(struct _FuncCandidateList, args) + \
                              2 * sizeof(Oid))

    if (catlist->n_members > 0)
        resultSpace = palloc(catlist->n_members * SPACE_PER_OP);

    for (i = 0; i < catlist->n_members; i++)
    {
        HeapTuple   opertup = &catlist->members[i]->tuple;
        Form_pg_operator operform = (Form_pg_operator) GETSTRUCT(opertup);
        int         pathpos = 0;
        FuncCandidateList newResult;

        /* Ignore operators of wrong kind, if specific kind requested */
        if (oprkind && operform->oprkind != oprkind)
            continue;

        if (OidIsValid(namespaceId))
        {
            /* Consider only opers in specified namespace */
            if (operform->oprnamespace != namespaceId)
                continue;
            /* No need to check args, they must all be different */
        }
        else
        {
            /*
             * Consider only opers that are in the search path and are not in
             * the temp namespace.
             */
            ListCell   *nsp;

            foreach(nsp, activeSearchPath)
            {
                if (operform->oprnamespace == lfirst_oid(nsp) &&
                    operform->oprnamespace != myTempNamespace)
                    break;
                pathpos++;
            }
            if (nsp == NULL)
                continue;       /* oper is not in search path */

            /*
             * Okay, it's in the search path, but does it have the same
             * arguments as something we already accepted?  If so, keep only
             * the one that appears earlier in the search path.
             *
             * If we have an ordered list from SearchSysCacheList (the normal
             * case), then any conflicting oper must immediately adjoin this
             * one in the list, so we only need to look at the newest result
             * item.  If we have an unordered list, we have to scan the whole
             * result list.
             */
            if (resultList)
            {
                FuncCandidateList prevResult;

                if (catlist->ordered)
                {
                    if (operform->oprleft == resultList->args[0] &&
                        operform->oprright == resultList->args[1])
                        prevResult = resultList;
                    else
                        prevResult = NULL;
                }
                else
                {
                    for (prevResult = resultList;
                         prevResult;
                         prevResult = prevResult->next)
                    {
                        if (operform->oprleft == prevResult->args[0] &&
                            operform->oprright == prevResult->args[1])
                            break;
                    }
                }
                if (prevResult)
                {
                    /* We have a match with a previous result */
                    Assert(pathpos != prevResult->pathpos);
                    if (pathpos > prevResult->pathpos)
                        continue;       /* keep previous result */
                    /* replace previous result */
                    prevResult->pathpos = pathpos;
                    prevResult->oid = HeapTupleGetOid(opertup);
                    continue;   /* args are same, of course */
                }
            }
        }

        /*
         * Okay to add it to result list
         */
        newResult = (FuncCandidateList) (resultSpace + nextResult);
        nextResult += SPACE_PER_OP;

        newResult->pathpos = pathpos;
        newResult->oid = HeapTupleGetOid(opertup);
        newResult->nargs = 2;
        newResult->nvargs = 0;
        newResult->ndargs = 0;
        newResult->argnumbers = NULL;
        newResult->args[0] = operform->oprleft;
        newResult->args[1] = operform->oprright;
        newResult->next = resultList;
        resultList = newResult;
    }

    ReleaseSysCacheList(catlist);

    return resultList;
}

/*
 * OperatorIsVisible
 *      Determine whether an operator (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified operator name with exact argument matches".
 */
bool
OperatorIsVisible(Oid oprid)
{
    HeapTuple   oprtup;
    Form_pg_operator oprform;
    Oid         oprnamespace;
    bool        visible;

    oprtup = SearchSysCache1(OPEROID, ObjectIdGetDatum(oprid));
    if (!HeapTupleIsValid(oprtup))
        elog(ERROR, "cache lookup failed for operator %u", oprid);
    oprform = (Form_pg_operator) GETSTRUCT(oprtup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    oprnamespace = oprform->oprnamespace;
    if (oprnamespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, oprnamespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another operator of the same name and arguments earlier
         * in the path.  So we must do a slow check to see if this is the same
         * operator that would be found by OpernameGetOprid.
         */
        char       *oprname = NameStr(oprform->oprname);

        visible = (OpernameGetOprid(list_make1(makeString(oprname)),
                                    oprform->oprleft, oprform->oprright)
                   == oprid);
    }

    ReleaseSysCache(oprtup);

    return visible;
}


/*
 * OpclassnameGetOpcid
 *      Try to resolve an unqualified index opclass name.
 *      Returns OID if opclass found in search path, else InvalidOid.
 *
 * This is essentially the same as TypenameGetTypid, but we have to have
 * an extra argument for the index AM OID.
 */
Oid
OpclassnameGetOpcid(Oid amid, const char *opcname)
{
    Oid         opcid;
    ListCell   *l;

    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);

        if (namespaceId == myTempNamespace)
            continue;           /* do not look in temp namespace */

        opcid = GetSysCacheOid3(CLAAMNAMENSP,
                                ObjectIdGetDatum(amid),
                                PointerGetDatum(opcname),
                                ObjectIdGetDatum(namespaceId));
        if (OidIsValid(opcid))
            return opcid;
    }

    /* Not found in path */
    return InvalidOid;
}

/*
 * OpclassIsVisible
 *      Determine whether an opclass (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified opclass name".
 */
bool
OpclassIsVisible(Oid opcid)
{
    HeapTuple   opctup;
    Form_pg_opclass opcform;
    Oid         opcnamespace;
    bool        visible;

    opctup = SearchSysCache1(CLAOID, ObjectIdGetDatum(opcid));
    if (!HeapTupleIsValid(opctup))
        elog(ERROR, "cache lookup failed for opclass %u", opcid);
    opcform = (Form_pg_opclass) GETSTRUCT(opctup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    opcnamespace = opcform->opcnamespace;
    if (opcnamespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, opcnamespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another opclass of the same name earlier in the path. So
         * we must do a slow check to see if this opclass would be found by
         * OpclassnameGetOpcid.
         */
        char       *opcname = NameStr(opcform->opcname);

        visible = (OpclassnameGetOpcid(opcform->opcmethod, opcname) == opcid);
    }

    ReleaseSysCache(opctup);

    return visible;
}

/*
 * OpfamilynameGetOpfid
 *      Try to resolve an unqualified index opfamily name.
 *      Returns OID if opfamily found in search path, else InvalidOid.
 *
 * This is essentially the same as TypenameGetTypid, but we have to have
 * an extra argument for the index AM OID.
 */
Oid
OpfamilynameGetOpfid(Oid amid, const char *opfname)
{
    Oid         opfid;
    ListCell   *l;

    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);

        if (namespaceId == myTempNamespace)
            continue;           /* do not look in temp namespace */

        opfid = GetSysCacheOid3(OPFAMILYAMNAMENSP,
                                ObjectIdGetDatum(amid),
                                PointerGetDatum(opfname),
                                ObjectIdGetDatum(namespaceId));
        if (OidIsValid(opfid))
            return opfid;
    }

    /* Not found in path */
    return InvalidOid;
}

/*
 * OpfamilyIsVisible
 *      Determine whether an opfamily (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified opfamily name".
 */
bool
OpfamilyIsVisible(Oid opfid)
{
    HeapTuple   opftup;
    Form_pg_opfamily opfform;
    Oid         opfnamespace;
    bool        visible;

    opftup = SearchSysCache1(OPFAMILYOID, ObjectIdGetDatum(opfid));
    if (!HeapTupleIsValid(opftup))
        elog(ERROR, "cache lookup failed for opfamily %u", opfid);
    opfform = (Form_pg_opfamily) GETSTRUCT(opftup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    opfnamespace = opfform->opfnamespace;
    if (opfnamespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, opfnamespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another opfamily of the same name earlier in the path. So
         * we must do a slow check to see if this opfamily would be found by
         * OpfamilynameGetOpfid.
         */
        char       *opfname = NameStr(opfform->opfname);

        visible = (OpfamilynameGetOpfid(opfform->opfmethod, opfname) == opfid);
    }

    ReleaseSysCache(opftup);

    return visible;
}

/*
 * CollationGetCollid
 *      Try to resolve an unqualified collation name.
 *      Returns OID if collation found in search path, else InvalidOid.
 */
Oid
CollationGetCollid(const char *collname)
{
    int32       dbencoding = GetDatabaseEncoding();
    ListCell   *l;

    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);
        Oid         collid;

        if (namespaceId == myTempNamespace)
            continue;           /* do not look in temp namespace */

        /* Check for database-encoding-specific entry */
        collid = GetSysCacheOid3(COLLNAMEENCNSP,
                                 PointerGetDatum(collname),
                                 Int32GetDatum(dbencoding),
                                 ObjectIdGetDatum(namespaceId));
        if (OidIsValid(collid))
            return collid;

        /* Check for any-encoding entry */
        collid = GetSysCacheOid3(COLLNAMEENCNSP,
                                 PointerGetDatum(collname),
                                 Int32GetDatum(-1),
                                 ObjectIdGetDatum(namespaceId));
        if (OidIsValid(collid))
            return collid;
    }

    /* Not found in path */
    return InvalidOid;
}

/*
 * CollationIsVisible
 *      Determine whether a collation (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified collation name".
 */
bool
CollationIsVisible(Oid collid)
{
    HeapTuple   colltup;
    Form_pg_collation collform;
    Oid         collnamespace;
    bool        visible;

    colltup = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
    if (!HeapTupleIsValid(colltup))
        elog(ERROR, "cache lookup failed for collation %u", collid);
    collform = (Form_pg_collation) GETSTRUCT(colltup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    collnamespace = collform->collnamespace;
    if (collnamespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, collnamespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another conversion of the same name earlier in the path.
         * So we must do a slow check to see if this conversion would be found
         * by CollationGetCollid.
         */
        char       *collname = NameStr(collform->collname);

        visible = (CollationGetCollid(collname) == collid);
    }

    ReleaseSysCache(colltup);

    return visible;
}


/*
 * ConversionGetConid
 *      Try to resolve an unqualified conversion name.
 *      Returns OID if conversion found in search path, else InvalidOid.
 *
 * This is essentially the same as RelnameGetRelid.
 */
Oid
ConversionGetConid(const char *conname)
{
    Oid         conid;
    ListCell   *l;

    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);

        if (namespaceId == myTempNamespace)
            continue;           /* do not look in temp namespace */

        conid = GetSysCacheOid2(CONNAMENSP,
                                PointerGetDatum(conname),
                                ObjectIdGetDatum(namespaceId));
        if (OidIsValid(conid))
            return conid;
    }

    /* Not found in path */
    return InvalidOid;
}

/*
 * ConversionIsVisible
 *      Determine whether a conversion (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified conversion name".
 */
bool
ConversionIsVisible(Oid conid)
{
    HeapTuple   contup;
    Form_pg_conversion conform;
    Oid         connamespace;
    bool        visible;

    contup = SearchSysCache1(CONVOID, ObjectIdGetDatum(conid));
    if (!HeapTupleIsValid(contup))
        elog(ERROR, "cache lookup failed for conversion %u", conid);
    conform = (Form_pg_conversion) GETSTRUCT(contup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    connamespace = conform->connamespace;
    if (connamespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, connamespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another conversion of the same name earlier in the path.
         * So we must do a slow check to see if this conversion would be found
         * by ConversionGetConid.
         */
        char       *conname = NameStr(conform->conname);

        visible = (ConversionGetConid(conname) == conid);
    }

    ReleaseSysCache(contup);

    return visible;
}

/*
 * get_ts_parser_oid - find a TS parser by possibly qualified name
 *
 * If not found, returns InvalidOid if missing_ok, else throws error
 */
Oid
get_ts_parser_oid(List *names, bool missing_ok)
{
    char       *schemaname;
    char       *parser_name;
    Oid         namespaceId;
    Oid         prsoid = InvalidOid;
    ListCell   *l;

    /* deconstruct the name list */
    DeconstructQualifiedName(names, &schemaname, &parser_name);

    if (schemaname)
    {
        /* use exact schema given */
        namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
        if (missing_ok && !OidIsValid(namespaceId))
            prsoid = InvalidOid;
        else
            prsoid = GetSysCacheOid2(TSPARSERNAMENSP,
                                     PointerGetDatum(parser_name),
                                     ObjectIdGetDatum(namespaceId));
    }
    else
    {
        /* search for it in search path */
        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
            namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            prsoid = GetSysCacheOid2(TSPARSERNAMENSP,
                                     PointerGetDatum(parser_name),
                                     ObjectIdGetDatum(namespaceId));
            if (OidIsValid(prsoid))
                break;
        }
    }

    if (!OidIsValid(prsoid) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("text search parser \"%s\" does not exist",
                        NameListToString(names))));

    return prsoid;
}

/*
 * TSParserIsVisible
 *      Determine whether a parser (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified parser name".
 */
bool
TSParserIsVisible(Oid prsId)
{
    HeapTuple   tup;
    Form_pg_ts_parser form;
    Oid         namespace;
    bool        visible;

    tup = SearchSysCache1(TSPARSEROID, ObjectIdGetDatum(prsId));
    if (!HeapTupleIsValid(tup))
        elog(ERROR, "cache lookup failed for text search parser %u", prsId);
    form = (Form_pg_ts_parser) GETSTRUCT(tup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    namespace = form->prsnamespace;
    if (namespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, namespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another parser of the same name earlier in the path. So
         * we must do a slow check for conflicting parsers.
         */
        char       *name = NameStr(form->prsname);
        ListCell   *l;

        visible = false;
        foreach(l, activeSearchPath)
        {
            Oid         namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            if (namespaceId == namespace)
            {
                /* Found it first in path */
                visible = true;
                break;
            }
            if (SearchSysCacheExists2(TSPARSERNAMENSP,
                                      PointerGetDatum(name),
                                      ObjectIdGetDatum(namespaceId)))
            {
                /* Found something else first in path */
                break;
            }
        }
    }

    ReleaseSysCache(tup);

    return visible;
}

/*
 * get_ts_dict_oid - find a TS dictionary by possibly qualified name
 *
 * If not found, returns InvalidOid if failOK, else throws error
 */
Oid
get_ts_dict_oid(List *names, bool missing_ok)
{
    char       *schemaname;
    char       *dict_name;
    Oid         namespaceId;
    Oid         dictoid = InvalidOid;
    ListCell   *l;

    /* deconstruct the name list */
    DeconstructQualifiedName(names, &schemaname, &dict_name);

    if (schemaname)
    {
        /* use exact schema given */
        namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
        if (missing_ok && !OidIsValid(namespaceId))
            dictoid = InvalidOid;
        else
            dictoid = GetSysCacheOid2(TSDICTNAMENSP,
                                      PointerGetDatum(dict_name),
                                      ObjectIdGetDatum(namespaceId));
    }
    else
    {
        /* search for it in search path */
        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
            namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            dictoid = GetSysCacheOid2(TSDICTNAMENSP,
                                      PointerGetDatum(dict_name),
                                      ObjectIdGetDatum(namespaceId));
            if (OidIsValid(dictoid))
                break;
        }
    }

    if (!OidIsValid(dictoid) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("text search dictionary \"%s\" does not exist",
                        NameListToString(names))));

    return dictoid;
}

/*
 * TSDictionaryIsVisible
 *      Determine whether a dictionary (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified dictionary name".
 */
bool
TSDictionaryIsVisible(Oid dictId)
{
    HeapTuple   tup;
    Form_pg_ts_dict form;
    Oid         namespace;
    bool        visible;

    tup = SearchSysCache1(TSDICTOID, ObjectIdGetDatum(dictId));
    if (!HeapTupleIsValid(tup))
        elog(ERROR, "cache lookup failed for text search dictionary %u",
             dictId);
    form = (Form_pg_ts_dict) GETSTRUCT(tup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    namespace = form->dictnamespace;
    if (namespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, namespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another dictionary of the same name earlier in the path.
         * So we must do a slow check for conflicting dictionaries.
         */
        char       *name = NameStr(form->dictname);
        ListCell   *l;

        visible = false;
        foreach(l, activeSearchPath)
        {
            Oid         namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            if (namespaceId == namespace)
            {
                /* Found it first in path */
                visible = true;
                break;
            }
            if (SearchSysCacheExists2(TSDICTNAMENSP,
                                      PointerGetDatum(name),
                                      ObjectIdGetDatum(namespaceId)))
            {
                /* Found something else first in path */
                break;
            }
        }
    }

    ReleaseSysCache(tup);

    return visible;
}

/*
 * get_ts_template_oid - find a TS template by possibly qualified name
 *
 * If not found, returns InvalidOid if missing_ok, else throws error
 */
Oid
get_ts_template_oid(List *names, bool missing_ok)
{
    char       *schemaname;
    char       *template_name;
    Oid         namespaceId;
    Oid         tmploid = InvalidOid;
    ListCell   *l;

    /* deconstruct the name list */
    DeconstructQualifiedName(names, &schemaname, &template_name);

    if (schemaname)
    {
        /* use exact schema given */
        namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
        if (missing_ok && !OidIsValid(namespaceId))
            tmploid = InvalidOid;
        else
            tmploid = GetSysCacheOid2(TSTEMPLATENAMENSP,
                                      PointerGetDatum(template_name),
                                      ObjectIdGetDatum(namespaceId));
    }
    else
    {
        /* search for it in search path */
        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
            namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            tmploid = GetSysCacheOid2(TSTEMPLATENAMENSP,
                                      PointerGetDatum(template_name),
                                      ObjectIdGetDatum(namespaceId));
            if (OidIsValid(tmploid))
                break;
        }
    }

    if (!OidIsValid(tmploid) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("text search template \"%s\" does not exist",
                        NameListToString(names))));

    return tmploid;
}

/*
 * TSTemplateIsVisible
 *      Determine whether a template (identified by OID) is visible in the
 *      current search path.  Visible means "would be found by searching
 *      for the unqualified template name".
 */
bool
TSTemplateIsVisible(Oid tmplId)
{
    HeapTuple   tup;
    Form_pg_ts_template form;
    Oid         namespace;
    bool        visible;

    tup = SearchSysCache1(TSTEMPLATEOID, ObjectIdGetDatum(tmplId));
    if (!HeapTupleIsValid(tup))
        elog(ERROR, "cache lookup failed for text search template %u", tmplId);
    form = (Form_pg_ts_template) GETSTRUCT(tup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    namespace = form->tmplnamespace;
    if (namespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, namespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another template of the same name earlier in the path. So
         * we must do a slow check for conflicting templates.
         */
        char       *name = NameStr(form->tmplname);
        ListCell   *l;

        visible = false;
        foreach(l, activeSearchPath)
        {
            Oid         namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            if (namespaceId == namespace)
            {
                /* Found it first in path */
                visible = true;
                break;
            }
            if (SearchSysCacheExists2(TSTEMPLATENAMENSP,
                                      PointerGetDatum(name),
                                      ObjectIdGetDatum(namespaceId)))
            {
                /* Found something else first in path */
                break;
            }
        }
    }

    ReleaseSysCache(tup);

    return visible;
}

/*
 * get_ts_config_oid - find a TS config by possibly qualified name
 *
 * If not found, returns InvalidOid if missing_ok, else throws error
 */
Oid
get_ts_config_oid(List *names, bool missing_ok)
{
    char       *schemaname;
    char       *config_name;
    Oid         namespaceId;
    Oid         cfgoid = InvalidOid;
    ListCell   *l;

    /* deconstruct the name list */
    DeconstructQualifiedName(names, &schemaname, &config_name);

    if (schemaname)
    {
        /* use exact schema given */
        namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
        if (missing_ok && !OidIsValid(namespaceId))
            cfgoid = InvalidOid;
        else
            cfgoid = GetSysCacheOid2(TSCONFIGNAMENSP,
                                     PointerGetDatum(config_name),
                                     ObjectIdGetDatum(namespaceId));
    }
    else
    {
        /* search for it in search path */
        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
            namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            cfgoid = GetSysCacheOid2(TSCONFIGNAMENSP,
                                     PointerGetDatum(config_name),
                                     ObjectIdGetDatum(namespaceId));
            if (OidIsValid(cfgoid))
                break;
        }
    }

    if (!OidIsValid(cfgoid) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("text search configuration \"%s\" does not exist",
                        NameListToString(names))));

    return cfgoid;
}

/*
 * TSConfigIsVisible
 *      Determine whether a text search configuration (identified by OID)
 *      is visible in the current search path.  Visible means "would be found
 *      by searching for the unqualified text search configuration name".
 */
bool
TSConfigIsVisible(Oid cfgid)
{
    HeapTuple   tup;
    Form_pg_ts_config form;
    Oid         namespace;
    bool        visible;

    tup = SearchSysCache1(TSCONFIGOID, ObjectIdGetDatum(cfgid));
    if (!HeapTupleIsValid(tup))
        elog(ERROR, "cache lookup failed for text search configuration %u",
             cfgid);
    form = (Form_pg_ts_config) GETSTRUCT(tup);

    recomputeNamespacePath();

    /*
     * Quick check: if it ain't in the path at all, it ain't visible. Items in
     * the system namespace are surely in the path and so we needn't even do
     * list_member_oid() for them.
     */
    namespace = form->cfgnamespace;
    if (namespace != PG_CATALOG_NAMESPACE &&
        !list_member_oid(activeSearchPath, namespace))
        visible = false;
    else
    {
        /*
         * If it is in the path, it might still not be visible; it could be
         * hidden by another configuration of the same name earlier in the
         * path. So we must do a slow check for conflicting configurations.
         */
        char       *name = NameStr(form->cfgname);
        ListCell   *l;

        visible = false;
        foreach(l, activeSearchPath)
        {
            Oid         namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            if (namespaceId == namespace)
            {
                /* Found it first in path */
                visible = true;
                break;
            }
            if (SearchSysCacheExists2(TSCONFIGNAMENSP,
                                      PointerGetDatum(name),
                                      ObjectIdGetDatum(namespaceId)))
            {
                /* Found something else first in path */
                break;
            }
        }
    }

    ReleaseSysCache(tup);

    return visible;
}


/*
 * DeconstructQualifiedName
 *      Given a possibly-qualified name expressed as a list of String nodes,
 *      extract the schema name and object name.
 *
 * *nspname_p is set to NULL if there is no explicit schema name.
 */
void
DeconstructQualifiedName(List *names,
                         char **nspname_p,
                         char **objname_p)
{
    char       *catalogname;
    char       *schemaname = NULL;
    char       *objname = NULL;

    switch (list_length(names))
    {
        case 1:
            objname = strVal(linitial(names));
            break;
        case 2:
            schemaname = strVal(linitial(names));
            objname = strVal(lsecond(names));
            break;
        case 3:
            catalogname = strVal(linitial(names));
            schemaname = strVal(lsecond(names));
            objname = strVal(lthird(names));

            /*
             * We check the catalog name and then ignore it.
             */
            if (strcmp(catalogname, get_database_name(MyDatabaseId)) != 0)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                  errmsg("cross-database references are not implemented: %s",
                         NameListToString(names))));
            break;
        default:
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                errmsg("improper qualified name (too many dotted names): %s",
                       NameListToString(names))));
            break;
    }

    *nspname_p = schemaname;
    *objname_p = objname;
}

/*
 * LookupNamespaceNoError
 *      Look up a schema name.
 *
 * Returns the namespace OID, or InvalidOid if not found.
 *
 * Note this does NOT perform any permissions check --- callers are
 * responsible for being sure that an appropriate check is made.
 * In the majority of cases LookupExplicitNamespace is preferable.
 */
Oid
LookupNamespaceNoError(const char *nspname)
{
    /* check for pg_temp alias */
    if (strcmp(nspname, "pg_temp") == 0)
    {
        if (OidIsValid(myTempNamespace))
        {
            InvokeNamespaceSearchHook(myTempNamespace, true);
            return myTempNamespace;
        }

        /*
         * Since this is used only for looking up existing objects, there is
         * no point in trying to initialize the temp namespace here; and doing
         * so might create problems for some callers. Just report "not found".
         */
        return InvalidOid;
    }

    return get_namespace_oid(nspname, true);
}

/*
 * LookupExplicitNamespace
 *      Process an explicitly-specified schema name: look up the schema
 *      and verify we have USAGE (lookup) rights in it.
 *
 * Returns the namespace OID
 */
Oid
LookupExplicitNamespace(const char *nspname, bool missing_ok)
{
    Oid         namespaceId;
    AclResult   aclresult;

    /* check for pg_temp alias */
    if (strcmp(nspname, "pg_temp") == 0)
    {
        if (OidIsValid(myTempNamespace))
            return myTempNamespace;

        /*
         * Since this is used only for looking up existing objects, there is
         * no point in trying to initialize the temp namespace here; and doing
         * so might create problems for some callers --- just fall through.
         */
    }

    namespaceId = get_namespace_oid(nspname, missing_ok);
    if (missing_ok && !OidIsValid(namespaceId))
        return InvalidOid;

    aclresult = pg_namespace_aclcheck(namespaceId, GetUserId(), ACL_USAGE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, ACL_KIND_NAMESPACE,
                       nspname);
    /* Schema search hook for this lookup */
    InvokeNamespaceSearchHook(namespaceId, true);

    return namespaceId;
}

/*
 * LookupCreationNamespace
 *      Look up the schema and verify we have CREATE rights on it.
 *
 * This is just like LookupExplicitNamespace except for the different
 * permission check, and that we are willing to create pg_temp if needed.
 *
 * Note: calling this may result in a CommandCounterIncrement operation,
 * if we have to create or clean out the temp namespace.
 */
Oid
LookupCreationNamespace(const char *nspname)
{
    Oid         namespaceId;
    AclResult   aclresult;

    /* check for pg_temp alias */
    if (strcmp(nspname, "pg_temp") == 0)
    {
        /* Initialize temp namespace if first time through */
        if (!OidIsValid(myTempNamespace))
            InitTempTableNamespace();
        return myTempNamespace;
    }

    namespaceId = get_namespace_oid(nspname, false);

    aclresult = pg_namespace_aclcheck(namespaceId, GetUserId(), ACL_CREATE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, ACL_KIND_NAMESPACE,
                       nspname);

    return namespaceId;
}

/*
 * Common checks on switching namespaces.
 *
 * We complain if either the old or new namespaces is a temporary schema
 * (or temporary toast schema), or if either the old or new namespaces is the
 * TOAST schema.
 */
void
CheckSetNamespace(Oid oldNspOid, Oid nspOid)
{
    /* disallow renaming into or out of temp schemas */
    if (isAnyTempNamespace(nspOid) || isAnyTempNamespace(oldNspOid))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
            errmsg("cannot move objects into or out of temporary schemas")));

    /* same for TOAST schema */
    if (nspOid == PG_TOAST_NAMESPACE || oldNspOid == PG_TOAST_NAMESPACE)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot move objects into or out of TOAST schema")));
}

/*
 * QualifiedNameGetCreationNamespace
 *      Given a possibly-qualified name for an object (in List-of-Values
 *      format), determine what namespace the object should be created in.
 *      Also extract and return the object name (last component of list).
 *
 * Note: this does not apply any permissions check.  Callers must check
 * for CREATE rights on the selected namespace when appropriate.
 *
 * Note: calling this may result in a CommandCounterIncrement operation,
 * if we have to create or clean out the temp namespace.
 */
Oid
QualifiedNameGetCreationNamespace(List *names, char **objname_p)
{
    char       *schemaname;
    Oid         namespaceId;

    /* deconstruct the name list */
    DeconstructQualifiedName(names, &schemaname, objname_p);

    if (schemaname)
    {
        /* check for pg_temp alias */
        if (strcmp(schemaname, "pg_temp") == 0)
        {
            /* Initialize temp namespace if first time through */
            if (!OidIsValid(myTempNamespace))
                InitTempTableNamespace();
            return myTempNamespace;
        }
        /* use exact schema given */
        namespaceId = get_namespace_oid(schemaname, false);
        /* we do not check for USAGE rights here! */
    }
    else
    {
        /* use the default creation namespace */
        recomputeNamespacePath();
        if (activeTempCreationPending)
        {
            /* Need to initialize temp namespace */
            InitTempTableNamespace();
            return myTempNamespace;
        }
        namespaceId = activeCreationNamespace;
        if (!OidIsValid(namespaceId))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_SCHEMA),
                     errmsg("no schema has been selected to create in")));
    }

    return namespaceId;
}

/*
 * get_namespace_oid - given a namespace name, look up the OID
 *
 * If missing_ok is false, throw an error if namespace name not found.  If
 * true, just return InvalidOid.
 */
Oid
get_namespace_oid(const char *nspname, bool missing_ok)
{
    Oid         oid;

    oid = GetSysCacheOid1(NAMESPACENAME, CStringGetDatum(nspname));
    if (!OidIsValid(oid) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_SCHEMA),
                 errmsg("schema \"%s\" does not exist", nspname)));

    return oid;
}

/*
 * makeRangeVarFromNameList
 *      Utility routine to convert a qualified-name list into RangeVar form.
 */
RangeVar *
makeRangeVarFromNameList(List *names)
{
    RangeVar   *rel = makeRangeVar(NULL, NULL, -1);

    switch (list_length(names))
    {
        case 1:
            rel->relname = strVal(linitial(names));
            break;
        case 2:
            rel->schemaname = strVal(linitial(names));
            rel->relname = strVal(lsecond(names));
            break;
        case 3:
            rel->catalogname = strVal(linitial(names));
            rel->schemaname = strVal(lsecond(names));
            rel->relname = strVal(lthird(names));
            break;
        default:
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("improper relation name (too many dotted names): %s",
                        NameListToString(names))));
            break;
    }

    return rel;
}

/*
 * NameListToString
 *      Utility routine to convert a qualified-name list into a string.
 *
 * This is used primarily to form error messages, and so we do not quote
 * the list elements, for the sake of legibility.
 *
 * In most scenarios the list elements should always be Value strings,
 * but we also allow A_Star for the convenience of ColumnRef processing.
 */
char *
NameListToString(List *names)
{
    StringInfoData string;
    ListCell   *l;

    initStringInfo(&string);

    foreach(l, names)
    {
        Node       *name = (Node *) lfirst(l);

        if (l != list_head(names))
            appendStringInfoChar(&string, '.');

        if (IsA(name, String))
            appendStringInfoString(&string, strVal(name));
        else if (IsA(name, A_Star))
            appendStringInfoChar(&string, '*');
        else
            elog(ERROR, "unexpected node type in name list: %d",
                 (int) nodeTag(name));
    }

    return string.data;
}

/*
 * NameListToQuotedString
 *      Utility routine to convert a qualified-name list into a string.
 *
 * Same as above except that names will be double-quoted where necessary,
 * so the string could be re-parsed (eg, by textToQualifiedNameList).
 */
char *
NameListToQuotedString(List *names)
{
    StringInfoData string;
    ListCell   *l;

    initStringInfo(&string);

    foreach(l, names)
    {
        if (l != list_head(names))
            appendStringInfoChar(&string, '.');
        appendStringInfoString(&string, quote_identifier(strVal(lfirst(l))));
    }

    return string.data;
}

/*
 * isTempNamespace - is the given namespace my temporary-table namespace?
 */
bool
isTempNamespace(Oid namespaceId)
{
    if (OidIsValid(myTempNamespace) && myTempNamespace == namespaceId)
        return true;
    return false;
}

/*
 * isTempToastNamespace - is the given namespace my temporary-toast-table
 *      namespace?
 */
bool
isTempToastNamespace(Oid namespaceId)
{
    if (OidIsValid(myTempToastNamespace) && myTempToastNamespace == namespaceId)
        return true;
    return false;
}

/*
 * isTempOrTempToastNamespace - is the given namespace my temporary-table
 *      namespace or my temporary-toast-table namespace?
 */
bool
isTempOrTempToastNamespace(Oid namespaceId)
{
    if (OidIsValid(myTempNamespace) &&
     (myTempNamespace == namespaceId || myTempToastNamespace == namespaceId))
        return true;
    return false;
}

/*
 * isAnyTempNamespace - is the given namespace a temporary-table namespace
 * (either my own, or another backend's)?  Temporary-toast-table namespaces
 * are included, too.
 */
bool
isAnyTempNamespace(Oid namespaceId)
{
    bool        result;
    char       *nspname;

    /* True if the namespace name starts with "pg_temp_" or "pg_toast_temp_" */
    nspname = get_namespace_name(namespaceId);
    if (!nspname)
        return false;           /* no such namespace? */
    result = (strncmp(nspname, "pg_temp_", 8) == 0) ||
        (strncmp(nspname, "pg_toast_temp_", 14) == 0);
    pfree(nspname);
    return result;
}

/*
 * isOtherTempNamespace - is the given namespace some other backend's
 * temporary-table namespace (including temporary-toast-table namespaces)?
 *
 * Note: for most purposes in the C code, this function is obsolete.  Use
 * RELATION_IS_OTHER_TEMP() instead to detect non-local temp relations.
 */
bool
isOtherTempNamespace(Oid namespaceId)
{
    /* If it's my own temp namespace, say "false" */
    if (isTempOrTempToastNamespace(namespaceId))
        return false;
    /* Else, if it's any temp namespace, say "true" */
    return isAnyTempNamespace(namespaceId);
}

/*
 * GetTempNamespaceBackendId - if the given namespace is a temporary-table
 * namespace (either my own, or another backend's), return the BackendId
 * that owns it.  Temporary-toast-table namespaces are included, too.
 * If it isn't a temp namespace, return InvalidBackendId.
 */
int
GetTempNamespaceBackendId(Oid namespaceId)
{
    int         result;
    char       *nspname;

    /* See if the namespace name starts with "pg_temp_" or "pg_toast_temp_" */
    nspname = get_namespace_name(namespaceId);
    if (!nspname)
        return InvalidBackendId;    /* no such namespace? */
    if (strncmp(nspname, "pg_temp_", 8) == 0)
        result = atoi(nspname + 8);
    else if (strncmp(nspname, "pg_toast_temp_", 14) == 0)
        result = atoi(nspname + 14);
    else
        result = InvalidBackendId;
    pfree(nspname);
    return result;
}

/*
 * GetTempToastNamespace - get the OID of my temporary-toast-table namespace,
 * which must already be assigned.  (This is only used when creating a toast
 * table for a temp table, so we must have already done InitTempTableNamespace)
 */
Oid
GetTempToastNamespace(void)
{
    Assert(OidIsValid(myTempToastNamespace));
    return myTempToastNamespace;
}


/*
 * GetOverrideSearchPath - fetch current search path definition in form
 * used by PushOverrideSearchPath.
 *
 * The result structure is allocated in the specified memory context
 * (which might or might not be equal to CurrentMemoryContext); but any
 * junk created by revalidation calculations will be in CurrentMemoryContext.
 */
OverrideSearchPath *
GetOverrideSearchPath(MemoryContext context)
{
    OverrideSearchPath *result;
    List       *schemas;
    MemoryContext oldcxt;

    recomputeNamespacePath();

    oldcxt = MemoryContextSwitchTo(context);

    result = (OverrideSearchPath *) palloc0(sizeof(OverrideSearchPath));
    schemas = list_copy(activeSearchPath);
    while (schemas && linitial_oid(schemas) != activeCreationNamespace)
    {
        if (linitial_oid(schemas) == myTempNamespace)
            result->addTemp = true;
        else
        {
            Assert(linitial_oid(schemas) == PG_CATALOG_NAMESPACE);
            result->addCatalog = true;
        }
        schemas = list_delete_first(schemas);
    }
    result->schemas = schemas;

    MemoryContextSwitchTo(oldcxt);

    return result;
}

/*
 * CopyOverrideSearchPath - copy the specified OverrideSearchPath.
 *
 * The result structure is allocated in CurrentMemoryContext.
 */
OverrideSearchPath *
CopyOverrideSearchPath(OverrideSearchPath *path)
{
    OverrideSearchPath *result;

    result = (OverrideSearchPath *) palloc(sizeof(OverrideSearchPath));
    result->schemas = list_copy(path->schemas);
    result->addCatalog = path->addCatalog;
    result->addTemp = path->addTemp;

    return result;
}

/*
 * OverrideSearchPathMatchesCurrent - does path match current setting?
 */
bool
OverrideSearchPathMatchesCurrent(OverrideSearchPath *path)
{
    ListCell   *lc,
               *lcp;

    recomputeNamespacePath();

    /* We scan down the activeSearchPath to see if it matches the input. */
    lc = list_head(activeSearchPath);

    /* If path->addTemp, first item should be my temp namespace. */
    if (path->addTemp)
    {
        if (lc && lfirst_oid(lc) == myTempNamespace)
            lc = lnext(lc);
        else
            return false;
    }
    /* If path->addCatalog, next item should be pg_catalog. */
    if (path->addCatalog)
    {
        if (lc && lfirst_oid(lc) == PG_CATALOG_NAMESPACE)
            lc = lnext(lc);
        else
            return false;
    }
    /* We should now be looking at the activeCreationNamespace. */
    if (activeCreationNamespace != (lc ? lfirst_oid(lc) : InvalidOid))
        return false;
    /* The remainder of activeSearchPath should match path->schemas. */
    foreach(lcp, path->schemas)
    {
        if (lc && lfirst_oid(lc) == lfirst_oid(lcp))
            lc = lnext(lc);
        else
            return false;
    }
    if (lc)
        return false;
    return true;
}

/*
 * PushOverrideSearchPath - temporarily override the search path
 *
 * We allow nested overrides, hence the push/pop terminology.  The GUC
 * search_path variable is ignored while an override is active.
 *
 * It's possible that newpath->useTemp is set but there is no longer any
 * active temp namespace, if the path was saved during a transaction that
 * created a temp namespace and was later rolled back.  In that case we just
 * ignore useTemp.  A plausible alternative would be to create a new temp
 * namespace, but for existing callers that's not necessary because an empty
 * temp namespace wouldn't affect their results anyway.
 *
 * It's also worth noting that other schemas listed in newpath might not
 * exist anymore either.  We don't worry about this because OIDs that match
 * no existing namespace will simply not produce any hits during searches.
 */
void
PushOverrideSearchPath(OverrideSearchPath *newpath)
{
    OverrideStackEntry *entry;
    List       *oidlist;
    Oid         firstNS;
    MemoryContext oldcxt;

    /*
     * Copy the list for safekeeping, and insert implicitly-searched
     * namespaces as needed.  This code should track recomputeNamespacePath.
     */
    oldcxt = MemoryContextSwitchTo(TopMemoryContext);

    oidlist = list_copy(newpath->schemas);

    /*
     * Remember the first member of the explicit list.
     */
    if (oidlist == NIL)
        firstNS = InvalidOid;
    else
        firstNS = linitial_oid(oidlist);

    /*
     * Add any implicitly-searched namespaces to the list.  Note these go on
     * the front, not the back; also notice that we do not check USAGE
     * permissions for these.
     */
    if (newpath->addCatalog)
        oidlist = lcons_oid(PG_CATALOG_NAMESPACE, oidlist);

    if (newpath->addTemp && OidIsValid(myTempNamespace))
        oidlist = lcons_oid(myTempNamespace, oidlist);

    /*
     * Build the new stack entry, then insert it at the head of the list.
     */
    entry = (OverrideStackEntry *) palloc(sizeof(OverrideStackEntry));
    entry->searchPath = oidlist;
    entry->creationNamespace = firstNS;
    entry->nestLevel = GetCurrentTransactionNestLevel();

    overrideStack = lcons(entry, overrideStack);

    /* And make it active. */
    activeSearchPath = entry->searchPath;
    activeCreationNamespace = entry->creationNamespace;
    activeTempCreationPending = false;  /* XXX is this OK? */

    MemoryContextSwitchTo(oldcxt);
}

/*
 * PopOverrideSearchPath - undo a previous PushOverrideSearchPath
 *
 * Any push during a (sub)transaction will be popped automatically at abort.
 * But it's caller error if a push isn't popped in normal control flow.
 */
void
PopOverrideSearchPath(void)
{
    OverrideStackEntry *entry;

    /* Sanity checks. */
    if (overrideStack == NIL)
        elog(ERROR, "bogus PopOverrideSearchPath call");
    entry = (OverrideStackEntry *) linitial(overrideStack);
    if (entry->nestLevel != GetCurrentTransactionNestLevel())
        elog(ERROR, "bogus PopOverrideSearchPath call");

    /* Pop the stack and free storage. */
    overrideStack = list_delete_first(overrideStack);
    list_free(entry->searchPath);
    pfree(entry);

    /* Activate the next level down. */
    if (overrideStack)
    {
        entry = (OverrideStackEntry *) linitial(overrideStack);
        activeSearchPath = entry->searchPath;
        activeCreationNamespace = entry->creationNamespace;
        activeTempCreationPending = false;      /* XXX is this OK? */
    }
    else
    {
        /* If not baseSearchPathValid, this is useless but harmless */
        activeSearchPath = baseSearchPath;
        activeCreationNamespace = baseCreationNamespace;
        activeTempCreationPending = baseTempCreationPending;
    }
}


/*
 * get_collation_oid - find a collation by possibly qualified name
 */
Oid
get_collation_oid(List *name, bool missing_ok)
{
    char       *schemaname;
    char       *collation_name;
    int32       dbencoding = GetDatabaseEncoding();
    Oid         namespaceId;
    Oid         colloid;
    ListCell   *l;

    /* deconstruct the name list */
    DeconstructQualifiedName(name, &schemaname, &collation_name);

    if (schemaname)
    {
        /* use exact schema given */
        namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
        if (missing_ok && !OidIsValid(namespaceId))
            return InvalidOid;

        /* first try for encoding-specific entry, then any-encoding */
        colloid = GetSysCacheOid3(COLLNAMEENCNSP,
                                  PointerGetDatum(collation_name),
                                  Int32GetDatum(dbencoding),
                                  ObjectIdGetDatum(namespaceId));
        if (OidIsValid(colloid))
            return colloid;
        colloid = GetSysCacheOid3(COLLNAMEENCNSP,
                                  PointerGetDatum(collation_name),
                                  Int32GetDatum(-1),
                                  ObjectIdGetDatum(namespaceId));
        if (OidIsValid(colloid))
            return colloid;
    }
    else
    {
        /* search for it in search path */
        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
            namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            colloid = GetSysCacheOid3(COLLNAMEENCNSP,
                                      PointerGetDatum(collation_name),
                                      Int32GetDatum(dbencoding),
                                      ObjectIdGetDatum(namespaceId));
            if (OidIsValid(colloid))
                return colloid;
            colloid = GetSysCacheOid3(COLLNAMEENCNSP,
                                      PointerGetDatum(collation_name),
                                      Int32GetDatum(-1),
                                      ObjectIdGetDatum(namespaceId));
            if (OidIsValid(colloid))
                return colloid;
        }
    }

    /* Not found in path */
    if (!missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("collation \"%s\" for encoding \"%s\" does not exist",
                        NameListToString(name), GetDatabaseEncodingName())));
    return InvalidOid;
}

/*
 * get_conversion_oid - find a conversion by possibly qualified name
 */
Oid
get_conversion_oid(List *name, bool missing_ok)
{
    char       *schemaname;
    char       *conversion_name;
    Oid         namespaceId;
    Oid         conoid = InvalidOid;
    ListCell   *l;

    /* deconstruct the name list */
    DeconstructQualifiedName(name, &schemaname, &conversion_name);

    if (schemaname)
    {
        /* use exact schema given */
        namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
        if (missing_ok && !OidIsValid(namespaceId))
            conoid = InvalidOid;
        else
            conoid = GetSysCacheOid2(CONNAMENSP,
                                     PointerGetDatum(conversion_name),
                                     ObjectIdGetDatum(namespaceId));
    }
    else
    {
        /* search for it in search path */
        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
            namespaceId = lfirst_oid(l);

            if (namespaceId == myTempNamespace)
                continue;       /* do not look in temp namespace */

            conoid = GetSysCacheOid2(CONNAMENSP,
                                     PointerGetDatum(conversion_name),
                                     ObjectIdGetDatum(namespaceId));
            if (OidIsValid(conoid))
                return conoid;
        }
    }

    /* Not found in path */
    if (!OidIsValid(conoid) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("conversion \"%s\" does not exist",
                        NameListToString(name))));
    return conoid;
}

/*
 * FindDefaultConversionProc - find default encoding conversion proc
 */
Oid
FindDefaultConversionProc(int32 for_encoding, int32 to_encoding)
{
    Oid         proc;
    ListCell   *l;

    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);

        if (namespaceId == myTempNamespace)
            continue;           /* do not look in temp namespace */

        proc = FindDefaultConversion(namespaceId, for_encoding, to_encoding);
        if (OidIsValid(proc))
            return proc;
    }

    /* Not found in path */
    return InvalidOid;
}

/*
 * recomputeNamespacePath - recompute path derived variables if needed.
 */
static void
recomputeNamespacePath(void)
{
    Oid         roleid = GetUserId();
    char       *rawname;
    List       *namelist;
    List       *oidlist;
    List       *newpath;
    ListCell   *l;
    bool        temp_missing;
    Oid         firstNS;
    MemoryContext oldcxt;

    /* Do nothing if an override search spec is active. */
    if (overrideStack)
        return;

    /* Do nothing if path is already valid. */
    if (baseSearchPathValid && namespaceUser == roleid)
        return;

    /* Need a modifiable copy of namespace_search_path string */
    rawname = pstrdup(namespace_search_path);

    /* Parse string into list of identifiers */
    if (!SplitIdentifierString(rawname, ',', &namelist))
    {
        /* syntax error in name list */
        /* this should not happen if GUC checked check_search_path */
        elog(ERROR, "invalid list syntax");
    }

    /*
     * Convert the list of names to a list of OIDs.  If any names are not
     * recognizable or we don't have read access, just leave them out of the
     * list.  (We can't raise an error, since the search_path setting has
     * already been accepted.)  Don't make duplicate entries, either.
     */
    oidlist = NIL;
    temp_missing = false;
    foreach(l, namelist)
    {
        char       *curname = (char *) lfirst(l);
        Oid         namespaceId;

        if (strcmp(curname, "$user") == 0)
        {
            /* $user --- substitute namespace matching user name, if any */
            HeapTuple   tuple;

            tuple = SearchSysCache1(AUTHOID, ObjectIdGetDatum(roleid));
            if (HeapTupleIsValid(tuple))
            {
                char       *rname;

                rname = NameStr(((Form_pg_authid) GETSTRUCT(tuple))->rolname);
                namespaceId = get_namespace_oid(rname, true);
                ReleaseSysCache(tuple);
                if (OidIsValid(namespaceId) &&
                    !list_member_oid(oidlist, namespaceId) &&
                    pg_namespace_aclcheck(namespaceId, roleid,
                                          ACL_USAGE) == ACLCHECK_OK &&
                    InvokeNamespaceSearchHook(namespaceId, false))
                    oidlist = lappend_oid(oidlist, namespaceId);
            }
        }
        else if (strcmp(curname, "pg_temp") == 0)
        {
            /* pg_temp --- substitute temp namespace, if any */
            if (OidIsValid(myTempNamespace))
            {
                if (!list_member_oid(oidlist, myTempNamespace) &&
                    InvokeNamespaceSearchHook(myTempNamespace, false))
                    oidlist = lappend_oid(oidlist, myTempNamespace);
            }
            else
            {
                /* If it ought to be the creation namespace, set flag */
                if (oidlist == NIL)
                    temp_missing = true;
            }
        }
        else
        {
            /* normal namespace reference */
            namespaceId = get_namespace_oid(curname, true);
            if (OidIsValid(namespaceId) &&
                !list_member_oid(oidlist, namespaceId) &&
                pg_namespace_aclcheck(namespaceId, roleid,
                                      ACL_USAGE) == ACLCHECK_OK &&
                InvokeNamespaceSearchHook(namespaceId, false))
                oidlist = lappend_oid(oidlist, namespaceId);
        }
    }

    /*
     * Remember the first member of the explicit list.  (Note: this is
     * nominally wrong if temp_missing, but we need it anyway to distinguish
     * explicit from implicit mention of pg_catalog.)
     */
    if (oidlist == NIL)
        firstNS = InvalidOid;
    else
        firstNS = linitial_oid(oidlist);

    /*
     * Add any implicitly-searched namespaces to the list.  Note these go on
     * the front, not the back; also notice that we do not check USAGE
     * permissions for these.
     */
    if (!list_member_oid(oidlist, PG_CATALOG_NAMESPACE))
        oidlist = lcons_oid(PG_CATALOG_NAMESPACE, oidlist);

    if (OidIsValid(myTempNamespace) &&
        !list_member_oid(oidlist, myTempNamespace))
        oidlist = lcons_oid(myTempNamespace, oidlist);

    /*
     * Now that we've successfully built the new list of namespace OIDs, save
     * it in permanent storage.
     */
    oldcxt = MemoryContextSwitchTo(TopMemoryContext);
    newpath = list_copy(oidlist);
    MemoryContextSwitchTo(oldcxt);

    /* Now safe to assign to state variables. */
    list_free(baseSearchPath);
    baseSearchPath = newpath;
    baseCreationNamespace = firstNS;
    baseTempCreationPending = temp_missing;

    /* Mark the path valid. */
    baseSearchPathValid = true;
    namespaceUser = roleid;

    /* And make it active. */
    activeSearchPath = baseSearchPath;
    activeCreationNamespace = baseCreationNamespace;
    activeTempCreationPending = baseTempCreationPending;

    /* Clean up. */
    pfree(rawname);
    list_free(namelist);
    list_free(oidlist);
}

/*
 * InitTempTableNamespace
 *      Initialize temp table namespace on first use in a particular backend
 */
static void
InitTempTableNamespace(void)
{
    char        namespaceName[NAMEDATALEN];
    Oid         namespaceId;
    Oid         toastspaceId;

    Assert(!OidIsValid(myTempNamespace));

    /*
     * First, do permission check to see if we are authorized to make temp
     * tables.  We use a nonstandard error message here since "databasename:
     * permission denied" might be a tad cryptic.
     *
     * Note that ACL_CREATE_TEMP rights are rechecked in pg_namespace_aclmask;
     * that's necessary since current user ID could change during the session.
     * But there's no need to make the namespace in the first place until a
     * temp table creation request is made by someone with appropriate rights.
     */
    if (pg_database_aclcheck(MyDatabaseId, GetUserId(),
                             ACL_CREATE_TEMP) != ACLCHECK_OK)
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied to create temporary tables in database \"%s\"",
                        get_database_name(MyDatabaseId))));

    /*
     * Do not allow a Hot Standby slave session to make temp tables.  Aside
     * from problems with modifying the system catalogs, there is a naming
     * conflict: pg_temp_N belongs to the session with BackendId N on the
     * master, not to a slave session with the same BackendId.  We should not
     * be able to get here anyway due to XactReadOnly checks, but let's just
     * make real sure.  Note that this also backstops various operations that
     * allow XactReadOnly transactions to modify temp tables; they'd need
     * RecoveryInProgress checks if not for this.
     */
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
                 errmsg("cannot create temporary tables during recovery")));

    /* Parallel workers can't create temporary tables, either. */
    if (IsParallelWorker())
        ereport(ERROR,
                (errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
                 errmsg("cannot create temporary tables in parallel mode")));

    snprintf(namespaceName, sizeof(namespaceName), "pg_temp_%d", MyBackendId);

    namespaceId = get_namespace_oid(namespaceName, true);
    if (!OidIsValid(namespaceId))
    {
        /*
         * First use of this temp namespace in this database; create it. The
         * temp namespaces are always owned by the superuser.  We leave their
         * permissions at default --- i.e., no access except to superuser ---
         * to ensure that unprivileged users can't peek at other backends'
         * temp tables.  This works because the places that access the temp
         * namespace for my own backend skip permissions checks on it.
         */
        namespaceId = NamespaceCreate(namespaceName, BOOTSTRAP_SUPERUSERID,
                                      true);
        /* Advance command counter to make namespace visible */
        CommandCounterIncrement();
    }
    else
    {
        /*
         * If the namespace already exists, clean it out (in case the former
         * owner crashed without doing so).
         */
        RemoveTempRelations(namespaceId);
    }

    /*
     * If the corresponding toast-table namespace doesn't exist yet, create
     * it. (We assume there is no need to clean it out if it does exist, since
     * dropping a parent table should make its toast table go away.)
     */
    snprintf(namespaceName, sizeof(namespaceName), "pg_toast_temp_%d",
             MyBackendId);

    toastspaceId = get_namespace_oid(namespaceName, true);
    if (!OidIsValid(toastspaceId))
    {
        toastspaceId = NamespaceCreate(namespaceName, BOOTSTRAP_SUPERUSERID,
                                       true);
        /* Advance command counter to make namespace visible */
        CommandCounterIncrement();
    }

    /*
     * Okay, we've prepared the temp namespace ... but it's not committed yet,
     * so all our work could be undone by transaction rollback.  Set flag for
     * AtEOXact_Namespace to know what to do.
     */
    myTempNamespace = namespaceId;
    myTempToastNamespace = toastspaceId;

    /* It should not be done already. */
    AssertState(myTempNamespaceSubID == InvalidSubTransactionId);
    myTempNamespaceSubID = GetCurrentSubTransactionId();

    baseSearchPathValid = false;    /* need to rebuild list */
}

/*
 * End-of-transaction cleanup for namespaces.
 */
void
AtEOXact_Namespace(bool isCommit, bool parallel)
{
    /*
     * If we abort the transaction in which a temp namespace was selected,
     * we'll have to do any creation or cleanout work over again.  So, just
     * forget the namespace entirely until next time.  On the other hand, if
     * we commit then register an exit callback to clean out the temp tables
     * at backend shutdown.  (We only want to register the callback once per
     * session, so this is a good place to do it.)
     */
    if (myTempNamespaceSubID != InvalidSubTransactionId && !parallel)
    {
        if (isCommit)
            before_shmem_exit(RemoveTempRelationsCallback, 0);
        else
        {
            myTempNamespace = InvalidOid;
            myTempToastNamespace = InvalidOid;
            baseSearchPathValid = false;        /* need to rebuild list */
        }
        myTempNamespaceSubID = InvalidSubTransactionId;
    }

    /*
     * Clean up if someone failed to do PopOverrideSearchPath
     */
    if (overrideStack)
    {
        if (isCommit)
            elog(WARNING, "leaked override search path");
        while (overrideStack)
        {
            OverrideStackEntry *entry;

            entry = (OverrideStackEntry *) linitial(overrideStack);
            overrideStack = list_delete_first(overrideStack);
            list_free(entry->searchPath);
            pfree(entry);
        }
        /* If not baseSearchPathValid, this is useless but harmless */
        activeSearchPath = baseSearchPath;
        activeCreationNamespace = baseCreationNamespace;
        activeTempCreationPending = baseTempCreationPending;
    }
}

/*
 * AtEOSubXact_Namespace
 *
 * At subtransaction commit, propagate the temp-namespace-creation
 * flag to the parent subtransaction.
 *
 * At subtransaction abort, forget the flag if we set it up.
 */
void
AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
                      SubTransactionId parentSubid)
{
    OverrideStackEntry *entry;

    if (myTempNamespaceSubID == mySubid)
    {
        if (isCommit)
            myTempNamespaceSubID = parentSubid;
        else
        {
            myTempNamespaceSubID = InvalidSubTransactionId;
            /* TEMP namespace creation failed, so reset state */
            myTempNamespace = InvalidOid;
            myTempToastNamespace = InvalidOid;
            baseSearchPathValid = false;        /* need to rebuild list */
        }
    }

    /*
     * Clean up if someone failed to do PopOverrideSearchPath
     */
    while (overrideStack)
    {
        entry = (OverrideStackEntry *) linitial(overrideStack);
        if (entry->nestLevel < GetCurrentTransactionNestLevel())
            break;
        if (isCommit)
            elog(WARNING, "leaked override search path");
        overrideStack = list_delete_first(overrideStack);
        list_free(entry->searchPath);
        pfree(entry);
    }

    /* Activate the next level down. */
    if (overrideStack)
    {
        entry = (OverrideStackEntry *) linitial(overrideStack);
        activeSearchPath = entry->searchPath;
        activeCreationNamespace = entry->creationNamespace;
        activeTempCreationPending = false;      /* XXX is this OK? */
    }
    else
    {
        /* If not baseSearchPathValid, this is useless but harmless */
        activeSearchPath = baseSearchPath;
        activeCreationNamespace = baseCreationNamespace;
        activeTempCreationPending = baseTempCreationPending;
    }
}

/*
 * Remove all relations in the specified temp namespace.
 *
 * This is called at backend shutdown (if we made any temp relations).
 * It is also called when we begin using a pre-existing temp namespace,
 * in order to clean out any relations that might have been created by
 * a crashed backend.
 */
static void
RemoveTempRelations(Oid tempNamespaceId)
{
    ObjectAddress object;

    /*
     * We want to get rid of everything in the target namespace, but not the
     * namespace itself (deleting it only to recreate it later would be a
     * waste of cycles).  We do this by finding everything that has a
     * dependency on the namespace.
     */
    object.classId = NamespaceRelationId;
    object.objectId = tempNamespaceId;
    object.objectSubId = 0;

    deleteWhatDependsOn(&object, false);
}

/*
 * Callback to remove temp relations at backend exit.
 */
static void
RemoveTempRelationsCallback(int code, Datum arg)
{
    if (OidIsValid(myTempNamespace))    /* should always be true */
    {
        /* Need to ensure we have a usable transaction. */
        AbortOutOfAnyTransaction();
        StartTransactionCommand();

        RemoveTempRelations(myTempNamespace);

        CommitTransactionCommand();
    }
}

/*
 * Remove all temp tables from the temporary namespace.
 */
void
ResetTempTableNamespace(void)
{
    if (OidIsValid(myTempNamespace))
        RemoveTempRelations(myTempNamespace);
}


/*
 * Routines for handling the GUC variable 'search_path'.
 */

/* check_hook: validate new search_path value */
bool
check_search_path(char **newval, void **extra, GucSource source)
{
    char       *rawname;
    List       *namelist;

    /* Need a modifiable copy of string */
    rawname = pstrdup(*newval);

    /* Parse string into list of identifiers */
    if (!SplitIdentifierString(rawname, ',', &namelist))
    {
        /* syntax error in name list */
        GUC_check_errdetail("List syntax is invalid.");
        pfree(rawname);
        list_free(namelist);
        return false;
    }

    /*
     * We used to try to check that the named schemas exist, but there are
     * many valid use-cases for having search_path settings that include
     * schemas that don't exist; and often, we are not inside a transaction
     * here and so can't consult the system catalogs anyway.  So now, the only
     * requirement is syntactic validity of the identifier list.
     */

    pfree(rawname);
    list_free(namelist);

    return true;
}

/* assign_hook: do extra actions as needed */
void
assign_search_path(const char *newval, void *extra)
{
    /*
     * We mark the path as needing recomputation, but don't do anything until
     * it's needed.  This avoids trying to do database access during GUC
     * initialization, or outside a transaction.
     */
    baseSearchPathValid = false;
}

/*
 * InitializeSearchPath: initialize module during InitPostgres.
 *
 * This is called after we are up enough to be able to do catalog lookups.
 */
void
InitializeSearchPath(void)
{
    if (IsBootstrapProcessingMode())
    {
        /*
         * In bootstrap mode, the search path must be 'pg_catalog' so that
         * tables are created in the proper namespace; ignore the GUC setting.
         */
        MemoryContext oldcxt;

        oldcxt = MemoryContextSwitchTo(TopMemoryContext);
        baseSearchPath = list_make1_oid(PG_CATALOG_NAMESPACE);
        MemoryContextSwitchTo(oldcxt);
        baseCreationNamespace = PG_CATALOG_NAMESPACE;
        baseTempCreationPending = false;
        baseSearchPathValid = true;
        namespaceUser = GetUserId();
        activeSearchPath = baseSearchPath;
        activeCreationNamespace = baseCreationNamespace;
        activeTempCreationPending = baseTempCreationPending;
    }
    else
    {
        /*
         * In normal mode, arrange for a callback on any syscache invalidation
         * of pg_namespace rows.
         */
        CacheRegisterSyscacheCallback(NAMESPACEOID,
                                      NamespaceCallback,
                                      (Datum) 0);
        /* Force search path to be recomputed on next use */
        baseSearchPathValid = false;
    }
}

/*
 * NamespaceCallback
 *      Syscache inval callback function
 */
static void
NamespaceCallback(Datum arg, int cacheid, uint32 hashvalue)
{
    /* Force search path to be recomputed on next use */
    baseSearchPathValid = false;
}

/*
 * Fetch the active search path. The return value is a palloc'ed list
 * of OIDs; the caller is responsible for freeing this storage as
 * appropriate.
 *
 * The returned list includes the implicitly-prepended namespaces only if
 * includeImplicit is true.
 *
 * Note: calling this may result in a CommandCounterIncrement operation,
 * if we have to create or clean out the temp namespace.
 */
List *
fetch_search_path(bool includeImplicit)
{
    List       *result;

    recomputeNamespacePath();

    /*
     * If the temp namespace should be first, force it to exist.  This is so
     * that callers can trust the result to reflect the actual default
     * creation namespace.  It's a bit bogus to do this here, since
     * current_schema() is supposedly a stable function without side-effects,
     * but the alternatives seem worse.
     */
    if (activeTempCreationPending)
    {
        InitTempTableNamespace();
        recomputeNamespacePath();
    }

    result = list_copy(activeSearchPath);
    if (!includeImplicit)
    {
        while (result && linitial_oid(result) != activeCreationNamespace)
            result = list_delete_first(result);
    }

    return result;
}

/*
 * Fetch the active search path into a caller-allocated array of OIDs.
 * Returns the number of path entries.  (If this is more than sarray_len,
 * then the data didn't fit and is not all stored.)
 *
 * The returned list always includes the implicitly-prepended namespaces,
 * but never includes the temp namespace.  (This is suitable for existing
 * users, which would want to ignore the temp namespace anyway.)  This
 * definition allows us to not worry about initializing the temp namespace.
 */
int
fetch_search_path_array(Oid *sarray, int sarray_len)
{
    int         count = 0;
    ListCell   *l;

    recomputeNamespacePath();

    foreach(l, activeSearchPath)
    {
        Oid         namespaceId = lfirst_oid(l);

        if (namespaceId == myTempNamespace)
            continue;           /* do not include temp namespace */

        if (count < sarray_len)
            sarray[count] = namespaceId;
        count++;
    }

    return count;
}


/*
 * Export the FooIsVisible functions as SQL-callable functions.
 *
 * Note: as of Postgres 8.4, these will silently return NULL if called on
 * a nonexistent object OID, rather than failing.  This is to avoid race
 * condition errors when a query that's scanning a catalog using an MVCC
 * snapshot uses one of these functions.  The underlying IsVisible functions
 * always use an up-to-date snapshot and so might see the object as already
 * gone when it's still visible to the transaction snapshot.  (There is no race
 * condition in the current coding because we don't accept sinval messages
 * between the SearchSysCacheExists test and the subsequent lookup.)
 */

Datum
pg_table_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(RelationIsVisible(oid));
}

Datum
pg_type_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(TYPEOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(TypeIsVisible(oid));
}

Datum
pg_function_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(PROCOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(FunctionIsVisible(oid));
}

Datum
pg_operator_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(OPEROID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(OperatorIsVisible(oid));
}

Datum
pg_opclass_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(CLAOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(OpclassIsVisible(oid));
}

Datum
pg_opfamily_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(OPFAMILYOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(OpfamilyIsVisible(oid));
}

Datum
pg_collation_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(COLLOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(CollationIsVisible(oid));
}

Datum
pg_conversion_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(CONVOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(ConversionIsVisible(oid));
}

Datum
pg_ts_parser_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(TSPARSEROID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(TSParserIsVisible(oid));
}

Datum
pg_ts_dict_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(TSDICTOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(TSDictionaryIsVisible(oid));
}

Datum
pg_ts_template_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(TSTEMPLATEOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(TSTemplateIsVisible(oid));
}

Datum
pg_ts_config_is_visible(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    if (!SearchSysCacheExists1(TSCONFIGOID, ObjectIdGetDatum(oid)))
        PG_RETURN_NULL();

    PG_RETURN_BOOL(TSConfigIsVisible(oid));
}

Datum
pg_my_temp_schema(PG_FUNCTION_ARGS)
{
    PG_RETURN_OID(myTempNamespace);
}

Datum
pg_is_other_temp_schema(PG_FUNCTION_ARGS)
{
    Oid         oid = PG_GETARG_OID(0);

    PG_RETURN_BOOL(isOtherTempNamespace(oid));
}