nodeSetOp.c

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/*-------------------------------------------------------------------------
 *
 * nodeSetOp.c
 *    Routines to handle INTERSECT and EXCEPT selection
 *
 * The input of a SetOp node consists of tuples from two relations,
 * which have been combined into one dataset, with a junk attribute added
 * that shows which relation each tuple came from.  In SETOP_SORTED mode,
 * the input has furthermore been sorted according to all the grouping
 * columns (ie, all the non-junk attributes).  The SetOp node scans each
 * group of identical tuples to determine how many came from each input
 * relation.  Then it is a simple matter to emit the output demanded by the
 * SQL spec for INTERSECT, INTERSECT ALL, EXCEPT, or EXCEPT ALL.
 *
 * In SETOP_HASHED mode, the input is delivered in no particular order,
 * except that we know all the tuples from one input relation will come before
 * all the tuples of the other.  The planner guarantees that the first input
 * relation is the left-hand one for EXCEPT, and tries to make the smaller
 * input relation come first for INTERSECT.  We build a hash table in memory
 * with one entry for each group of identical tuples, and count the number of
 * tuples in the group from each relation.  After seeing all the input, we
 * scan the hashtable and generate the correct output using those counts.
 * We can avoid making hashtable entries for any tuples appearing only in the
 * second input relation, since they cannot result in any output.
 *
 * This node type is not used for UNION or UNION ALL, since those can be
 * implemented more cheaply (there's no need for the junk attribute to
 * identify the source relation).
 *
 * Note that SetOp does no qual checking nor projection.  The delivered
 * output tuples are just copies of the first-to-arrive tuple in each
 * input group.
 *
 *
 * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeSetOp.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "executor/executor.h"
#include "executor/nodeSetOp.h"
#include "utils/memutils.h"


/*
 * SetOpStatePerGroupData - per-group working state
 *
 * These values are working state that is initialized at the start of
 * an input tuple group and updated for each input tuple.
 *
 * In SETOP_SORTED mode, we need only one of these structs, and it's kept in
 * the plan state node.  In SETOP_HASHED mode, the hash table contains one
 * of these for each tuple group.
 */
typedef struct SetOpStatePerGroupData
{
    long        numLeft;        /* number of left-input dups in group */
    long        numRight;       /* number of right-input dups in group */
} SetOpStatePerGroupData;

/*
 * To implement hashed mode, we need a hashtable that stores a
 * representative tuple and the duplicate counts for each distinct set
 * of grouping columns.  We compute the hash key from the grouping columns.
 */
typedef struct SetOpHashEntryData *SetOpHashEntry;

typedef struct SetOpHashEntryData
{
    TupleHashEntryData shared;  /* common header for hash table entries */
    SetOpStatePerGroupData pergroup;
}   SetOpHashEntryData;


static TupleTableSlot *setop_retrieve_direct(SetOpState *setopstate);
static void setop_fill_hash_table(SetOpState *setopstate);
static TupleTableSlot *setop_retrieve_hash_table(SetOpState *setopstate);


/*
 * Initialize state for a new group of input values.
 */
static inline void
initialize_counts(SetOpStatePerGroup pergroup)
{
    pergroup->numLeft = pergroup->numRight = 0;
}

/*
 * Advance the appropriate counter for one input tuple.
 */
static inline void
advance_counts(SetOpStatePerGroup pergroup, int flag)
{
    if (flag)
        pergroup->numRight++;
    else
        pergroup->numLeft++;
}

/*
 * Fetch the "flag" column from an input tuple.
 * This is an integer column with value 0 for left side, 1 for right side.
 */
static int
fetch_tuple_flag(SetOpState *setopstate, TupleTableSlot *inputslot)
{
    SetOp      *node = (SetOp *) setopstate->ps.plan;
    int         flag;
    bool        isNull;

    flag = DatumGetInt32(slot_getattr(inputslot,
                                      node->flagColIdx,
                                      &isNull));
    Assert(!isNull);
    Assert(flag == 0 || flag == 1);
    return flag;
}

/*
 * Initialize the hash table to empty.
 */
static void
build_hash_table(SetOpState *setopstate)
{
    SetOp      *node = (SetOp *) setopstate->ps.plan;

    Assert(node->strategy == SETOP_HASHED);
    Assert(node->numGroups > 0);

    setopstate->hashtable = BuildTupleHashTable(node->numCols,
                                                node->dupColIdx,
                                                setopstate->eqfunctions,
                                                setopstate->hashfunctions,
                                                node->numGroups,
                                                sizeof(SetOpHashEntryData),
                                                setopstate->tableContext,
                                                setopstate->tempContext);
}

/*
 * We've completed processing a tuple group.  Decide how many copies (if any)
 * of its representative row to emit, and store the count into numOutput.
 * This logic is straight from the SQL92 specification.
 */
static void
set_output_count(SetOpState *setopstate, SetOpStatePerGroup pergroup)
{
    SetOp      *plannode = (SetOp *) setopstate->ps.plan;

    switch (plannode->cmd)
    {
        case SETOPCMD_INTERSECT:
            if (pergroup->numLeft > 0 && pergroup->numRight > 0)
                setopstate->numOutput = 1;
            else
                setopstate->numOutput = 0;
            break;
        case SETOPCMD_INTERSECT_ALL:
            setopstate->numOutput =
                (pergroup->numLeft < pergroup->numRight) ?
                pergroup->numLeft : pergroup->numRight;
            break;
        case SETOPCMD_EXCEPT:
            if (pergroup->numLeft > 0 && pergroup->numRight == 0)
                setopstate->numOutput = 1;
            else
                setopstate->numOutput = 0;
            break;
        case SETOPCMD_EXCEPT_ALL:
            setopstate->numOutput =
                (pergroup->numLeft < pergroup->numRight) ?
                0 : (pergroup->numLeft - pergroup->numRight);
            break;
        default:
            elog(ERROR, "unrecognized set op: %d", (int) plannode->cmd);
            break;
    }
}


/* ----------------------------------------------------------------
 *      ExecSetOp
 * ----------------------------------------------------------------
 */
TupleTableSlot *                /* return: a tuple or NULL */
ExecSetOp(SetOpState *node)
{
    SetOp      *plannode = (SetOp *) node->ps.plan;
    TupleTableSlot *resultTupleSlot = node->ps.ps_ResultTupleSlot;

    /*
     * If the previously-returned tuple needs to be returned more than once,
     * keep returning it.
     */
    if (node->numOutput > 0)
    {
        node->numOutput--;
        return resultTupleSlot;
    }

    /* Otherwise, we're done if we are out of groups */
    if (node->setop_done)
        return NULL;

    /* Fetch the next tuple group according to the correct strategy */
    if (plannode->strategy == SETOP_HASHED)
    {
        if (!node->table_filled)
            setop_fill_hash_table(node);
        return setop_retrieve_hash_table(node);
    }
    else
        return setop_retrieve_direct(node);
}

/*
 * ExecSetOp for non-hashed case
 */
static TupleTableSlot *
setop_retrieve_direct(SetOpState *setopstate)
{
    SetOp      *node = (SetOp *) setopstate->ps.plan;
    PlanState  *outerPlan;
    SetOpStatePerGroup pergroup;
    TupleTableSlot *outerslot;
    TupleTableSlot *resultTupleSlot;

    /*
     * get state info from node
     */
    outerPlan = outerPlanState(setopstate);
    pergroup = setopstate->pergroup;
    resultTupleSlot = setopstate->ps.ps_ResultTupleSlot;

    /*
     * We loop retrieving groups until we find one we should return
     */
    while (!setopstate->setop_done)
    {
        /*
         * If we don't already have the first tuple of the new group, fetch it
         * from the outer plan.
         */
        if (setopstate->grp_firstTuple == NULL)
        {
            outerslot = ExecProcNode(outerPlan);
            if (!TupIsNull(outerslot))
            {
                /* Make a copy of the first input tuple */
                setopstate->grp_firstTuple = ExecCopySlotTuple(outerslot);
            }
            else
            {
                /* outer plan produced no tuples at all */
                setopstate->setop_done = true;
                return NULL;
            }
        }

        /*
         * Store the copied first input tuple in the tuple table slot reserved
         * for it.  The tuple will be deleted when it is cleared from the
         * slot.
         */
        ExecStoreTuple(setopstate->grp_firstTuple,
                       resultTupleSlot,
                       InvalidBuffer,
                       true);
        setopstate->grp_firstTuple = NULL;      /* don't keep two pointers */

        /* Initialize working state for a new input tuple group */
        initialize_counts(pergroup);

        /* Count the first input tuple */
        advance_counts(pergroup,
                       fetch_tuple_flag(setopstate, resultTupleSlot));

        /*
         * Scan the outer plan until we exhaust it or cross a group boundary.
         */
        for (;;)
        {
            outerslot = ExecProcNode(outerPlan);
            if (TupIsNull(outerslot))
            {
                /* no more outer-plan tuples available */
                setopstate->setop_done = true;
                break;
            }

            /*
             * Check whether we've crossed a group boundary.
             */
            if (!execTuplesMatch(resultTupleSlot,
                                 outerslot,
                                 node->numCols, node->dupColIdx,
                                 setopstate->eqfunctions,
                                 setopstate->tempContext))
            {
                /*
                 * Save the first input tuple of the next group.
                 */
                setopstate->grp_firstTuple = ExecCopySlotTuple(outerslot);
                break;
            }

            /* Still in same group, so count this tuple */
            advance_counts(pergroup,
                           fetch_tuple_flag(setopstate, outerslot));
        }

        /*
         * Done scanning input tuple group.  See if we should emit any copies
         * of result tuple, and if so return the first copy.
         */
        set_output_count(setopstate, pergroup);

        if (setopstate->numOutput > 0)
        {
            setopstate->numOutput--;
            return resultTupleSlot;
        }
    }

    /* No more groups */
    ExecClearTuple(resultTupleSlot);
    return NULL;
}

/*
 * ExecSetOp for hashed case: phase 1, read input and build hash table
 */
static void
setop_fill_hash_table(SetOpState *setopstate)
{
    SetOp      *node = (SetOp *) setopstate->ps.plan;
    PlanState  *outerPlan;
    int         firstFlag;
    bool in_first_rel PG_USED_FOR_ASSERTS_ONLY;

    /*
     * get state info from node
     */
    outerPlan = outerPlanState(setopstate);
    firstFlag = node->firstFlag;
    /* verify planner didn't mess up */
    Assert(firstFlag == 0 ||
           (firstFlag == 1 &&
            (node->cmd == SETOPCMD_INTERSECT ||
             node->cmd == SETOPCMD_INTERSECT_ALL)));

    /*
     * Process each outer-plan tuple, and then fetch the next one, until we
     * exhaust the outer plan.
     */
    in_first_rel = true;
    for (;;)
    {
        TupleTableSlot *outerslot;
        int         flag;
        SetOpHashEntry entry;
        bool        isnew;

        outerslot = ExecProcNode(outerPlan);
        if (TupIsNull(outerslot))
            break;

        /* Identify whether it's left or right input */
        flag = fetch_tuple_flag(setopstate, outerslot);

        if (flag == firstFlag)
        {
            /* (still) in first input relation */
            Assert(in_first_rel);

            /* Find or build hashtable entry for this tuple's group */
            entry = (SetOpHashEntry)
                LookupTupleHashEntry(setopstate->hashtable, outerslot, &isnew);

            /* If new tuple group, initialize counts */
            if (isnew)
                initialize_counts(&entry->pergroup);

            /* Advance the counts */
            advance_counts(&entry->pergroup, flag);
        }
        else
        {
            /* reached second relation */
            in_first_rel = false;

            /* For tuples not seen previously, do not make hashtable entry */
            entry = (SetOpHashEntry)
                LookupTupleHashEntry(setopstate->hashtable, outerslot, NULL);

            /* Advance the counts if entry is already present */
            if (entry)
                advance_counts(&entry->pergroup, flag);
        }

        /* Must reset temp context after each hashtable lookup */
        MemoryContextReset(setopstate->tempContext);
    }

    setopstate->table_filled = true;
    /* Initialize to walk the hash table */
    ResetTupleHashIterator(setopstate->hashtable, &setopstate->hashiter);
}

/*
 * ExecSetOp for hashed case: phase 2, retrieving groups from hash table
 */
static TupleTableSlot *
setop_retrieve_hash_table(SetOpState *setopstate)
{
    SetOpHashEntry entry;
    TupleTableSlot *resultTupleSlot;

    /*
     * get state info from node
     */
    resultTupleSlot = setopstate->ps.ps_ResultTupleSlot;

    /*
     * We loop retrieving groups until we find one we should return
     */
    while (!setopstate->setop_done)
    {
        /*
         * Find the next entry in the hash table
         */
        entry = (SetOpHashEntry) ScanTupleHashTable(&setopstate->hashiter);
        if (entry == NULL)
        {
            /* No more entries in hashtable, so done */
            setopstate->setop_done = true;
            return NULL;
        }

        /*
         * See if we should emit any copies of this tuple, and if so return
         * the first copy.
         */
        set_output_count(setopstate, &entry->pergroup);

        if (setopstate->numOutput > 0)
        {
            setopstate->numOutput--;
            return ExecStoreMinimalTuple(entry->shared.firstTuple,
                                         resultTupleSlot,
                                         false);
        }
    }

    /* No more groups */
    ExecClearTuple(resultTupleSlot);
    return NULL;
}

/* ----------------------------------------------------------------
 *      ExecInitSetOp
 *
 *      This initializes the setop node state structures and
 *      the node's subplan.
 * ----------------------------------------------------------------
 */
SetOpState *
ExecInitSetOp(SetOp *node, EState *estate, int eflags)
{
    SetOpState *setopstate;

    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));

    /*
     * create state structure
     */
    setopstate = makeNode(SetOpState);
    setopstate->ps.plan = (Plan *) node;
    setopstate->ps.state = estate;

    setopstate->eqfunctions = NULL;
    setopstate->hashfunctions = NULL;
    setopstate->setop_done = false;
    setopstate->numOutput = 0;
    setopstate->pergroup = NULL;
    setopstate->grp_firstTuple = NULL;
    setopstate->hashtable = NULL;
    setopstate->tableContext = NULL;

    /*
     * Miscellaneous initialization
     *
     * SetOp nodes have no ExprContext initialization because they never call
     * ExecQual or ExecProject.  But they do need a per-tuple memory context
     * anyway for calling execTuplesMatch.
     */
    setopstate->tempContext =
        AllocSetContextCreate(CurrentMemoryContext,
                              "SetOp",
                              ALLOCSET_DEFAULT_MINSIZE,
                              ALLOCSET_DEFAULT_INITSIZE,
                              ALLOCSET_DEFAULT_MAXSIZE);

    /*
     * If hashing, we also need a longer-lived context to store the hash
     * table.  The table can't just be kept in the per-query context because
     * we want to be able to throw it away in ExecReScanSetOp.
     */
    if (node->strategy == SETOP_HASHED)
        setopstate->tableContext =
            AllocSetContextCreate(CurrentMemoryContext,
                                  "SetOp hash table",
                                  ALLOCSET_DEFAULT_MINSIZE,
                                  ALLOCSET_DEFAULT_INITSIZE,
                                  ALLOCSET_DEFAULT_MAXSIZE);

    /*
     * Tuple table initialization
     */
    ExecInitResultTupleSlot(estate, &setopstate->ps);

    /*
     * initialize child nodes
     *
     * If we are hashing then the child plan does not need to handle REWIND
     * efficiently; see ExecReScanSetOp.
     */
    if (node->strategy == SETOP_HASHED)
        eflags &= ~EXEC_FLAG_REWIND;
    outerPlanState(setopstate) = ExecInitNode(outerPlan(node), estate, eflags);

    /*
     * setop nodes do no projections, so initialize projection info for this
     * node appropriately
     */
    ExecAssignResultTypeFromTL(&setopstate->ps);
    setopstate->ps.ps_ProjInfo = NULL;

    /*
     * Precompute fmgr lookup data for inner loop. We need both equality and
     * hashing functions to do it by hashing, but only equality if not
     * hashing.
     */
    if (node->strategy == SETOP_HASHED)
        execTuplesHashPrepare(node->numCols,
                              node->dupOperators,
                              &setopstate->eqfunctions,
                              &setopstate->hashfunctions);
    else
        setopstate->eqfunctions =
            execTuplesMatchPrepare(node->numCols,
                                   node->dupOperators);

    if (node->strategy == SETOP_HASHED)
    {
        build_hash_table(setopstate);
        setopstate->table_filled = false;
    }
    else
    {
        setopstate->pergroup =
            (SetOpStatePerGroup) palloc0(sizeof(SetOpStatePerGroupData));
    }

    return setopstate;
}

/* ----------------------------------------------------------------
 *      ExecEndSetOp
 *
 *      This shuts down the subplan and frees resources allocated
 *      to this node.
 * ----------------------------------------------------------------
 */
void
ExecEndSetOp(SetOpState *node)
{
    /* clean up tuple table */
    ExecClearTuple(node->ps.ps_ResultTupleSlot);

    /* free subsidiary stuff including hashtable */
    MemoryContextDelete(node->tempContext);
    if (node->tableContext)
        MemoryContextDelete(node->tableContext);

    ExecEndNode(outerPlanState(node));
}


void
ExecReScanSetOp(SetOpState *node)
{
    ExecClearTuple(node->ps.ps_ResultTupleSlot);
    node->setop_done = false;
    node->numOutput = 0;

    if (((SetOp *) node->ps.plan)->strategy == SETOP_HASHED)
    {
        /*
         * In the hashed case, if we haven't yet built the hash table then we
         * can just return; nothing done yet, so nothing to undo. If subnode's
         * chgParam is not NULL then it will be re-scanned by ExecProcNode,
         * else no reason to re-scan it at all.
         */
        if (!node->table_filled)
            return;

        /*
         * If we do have the hash table and the subplan does not have any
         * parameter changes, then we can just rescan the existing hash table;
         * no need to build it again.
         */
        if (node->ps.lefttree->chgParam == NULL)
        {
            ResetTupleHashIterator(node->hashtable, &node->hashiter);
            return;
        }
    }

    /* Release first tuple of group, if we have made a copy */
    if (node->grp_firstTuple != NULL)
    {
        heap_freetuple(node->grp_firstTuple);
        node->grp_firstTuple = NULL;
    }

    /* Release any hashtable storage */
    if (node->tableContext)
        MemoryContextResetAndDeleteChildren(node->tableContext);

    /* And rebuild empty hashtable if needed */
    if (((SetOp *) node->ps.plan)->strategy == SETOP_HASHED)
    {
        build_hash_table(node);
        node->table_filled = false;
    }

    /*
     * if chgParam of subnode is not null then plan will be re-scanned by
     * first ExecProcNode.
     */
    if (node->ps.lefttree->chgParam == NULL)
        ExecReScan(node->ps.lefttree);
}