Database.php

Go to the documentation of this file.

<?php
define( 'DEADLOCK_TRIES', 4 );
define( 'DEADLOCK_DELAY_MIN', 500000 );
define( 'DEADLOCK_DELAY_MAX', 1500000 );

interface DatabaseType {
        function getType();

        function open( $server, $user, $password, $dbName );

        function fetchObject( $res );

        function fetchRow( $res );

        function numRows( $res );

        function numFields( $res );

        function fieldName( $res, $n );

        function insertId();

        function dataSeek( $res, $row );

        function lastErrno();

        function lastError();

        function fieldInfo( $table, $field );

        function indexInfo( $table, $index, $fname = 'Database::indexInfo' );

        function affectedRows();

        function strencode( $s );

        static function getSoftwareLink();

        function getServerVersion();

        function getServerInfo();
}

abstract class DatabaseBase implements DatabaseType {

# ------------------------------------------------------------------------------
# Variables
# ------------------------------------------------------------------------------

        protected $mLastQuery = '';
        protected $mDoneWrites = false;
        protected $mPHPError = false;

        protected $mServer, $mUser, $mPassword, $mDBname;

        protected $mConn = null;
        protected $mOpened = false;

        protected $trxIdleCallbacks = array();

        protected $mTablePrefix;
        protected $mFlags;
        protected $mTrxLevel = 0;
        protected $mErrorCount = 0;
        protected $mLBInfo = array();
        protected $mFakeSlaveLag = null, $mFakeMaster = false;
        protected $mDefaultBigSelects = null;
        protected $mSchemaVars = false;

        protected $preparedArgs;

        protected $htmlErrors;

        protected $delimiter = ';';

        private $mTrxFname = null;

        private $mTrxDoneWrites = false;

        private $mTrxAutomatic = false;

# ------------------------------------------------------------------------------
# Accessors
# ------------------------------------------------------------------------------
        # These optionally set a variable and return the previous state

        public function getServerInfo() {
                return $this->getServerVersion();
        }

        public function getDelimiter() {
                return $this->delimiter;
        }

        public function debug( $debug = null ) {
                return wfSetBit( $this->mFlags, DBO_DEBUG, $debug );
        }

        public function bufferResults( $buffer = null ) {
                if ( is_null( $buffer ) ) {
                        return !(bool)( $this->mFlags & DBO_NOBUFFER );
                } else {
                        return !wfSetBit( $this->mFlags, DBO_NOBUFFER, !$buffer );
                }
        }

        public function ignoreErrors( $ignoreErrors = null ) {
                return wfSetBit( $this->mFlags, DBO_IGNORE, $ignoreErrors );
        }

        public function trxLevel( $level = null ) {
                return wfSetVar( $this->mTrxLevel, $level );
        }

        public function errorCount( $count = null ) {
                return wfSetVar( $this->mErrorCount, $count );
        }

        public function tablePrefix( $prefix = null ) {
                return wfSetVar( $this->mTablePrefix, $prefix );
        }

        public function getLBInfo( $name = null ) {
                if ( is_null( $name ) ) {
                        return $this->mLBInfo;
                } else {
                        if ( array_key_exists( $name, $this->mLBInfo ) ) {
                                return $this->mLBInfo[$name];
                        } else {
                                return null;
                        }
                }
        }

        public function setLBInfo( $name, $value = null ) {
                if ( is_null( $value ) ) {
                        $this->mLBInfo = $name;
                } else {
                        $this->mLBInfo[$name] = $value;
                }
        }

        public function setFakeSlaveLag( $lag ) {
                $this->mFakeSlaveLag = $lag;
        }

        public function setFakeMaster( $enabled = true ) {
                $this->mFakeMaster = $enabled;
        }

        public function cascadingDeletes() {
                return false;
        }

        public function cleanupTriggers() {
                return false;
        }

        public function strictIPs() {
                return false;
        }

        public function realTimestamps() {
                return false;
        }

        public function implicitGroupby() {
                return true;
        }

        public function implicitOrderby() {
                return true;
        }

        public function searchableIPs() {
                return false;
        }

        public function functionalIndexes() {
                return false;
        }

        public function lastQuery() {
                return $this->mLastQuery;
        }

        public function doneWrites() {
                return $this->mDoneWrites;
        }

        public function isOpen() {
                return $this->mOpened;
        }

        public function setFlag( $flag ) {
                global $wgDebugDBTransactions;
                $this->mFlags |= $flag;
                if ( ( $flag & DBO_TRX) & $wgDebugDBTransactions ) {
                        wfDebug("Implicit transactions are now  disabled.\n");
                }
        }

        public function clearFlag( $flag ) {
                global $wgDebugDBTransactions;
                $this->mFlags &= ~$flag;
                if ( ( $flag & DBO_TRX ) && $wgDebugDBTransactions ) {
                        wfDebug("Implicit transactions are now disabled.\n");
                }
        }

        public function getFlag( $flag ) {
                return !!( $this->mFlags & $flag );
        }

        public function getProperty( $name ) {
                return $this->$name;
        }

        public function getWikiID() {
                if ( $this->mTablePrefix ) {
                        return "{$this->mDBname}-{$this->mTablePrefix}";
                } else {
                        return $this->mDBname;
                }
        }

        public function getSchemaPath() {
                global $IP;
                if ( file_exists( "$IP/maintenance/" . $this->getType() . "/tables.sql" ) ) {
                        return "$IP/maintenance/" . $this->getType() . "/tables.sql";
                } else {
                        return "$IP/maintenance/tables.sql";
                }
        }

# ------------------------------------------------------------------------------
# Other functions
# ------------------------------------------------------------------------------

        function __construct( $server = false, $user = false, $password = false, $dbName = false,
                $flags = 0, $tablePrefix = 'get from global'
        ) {
                global $wgDBprefix, $wgCommandLineMode, $wgDebugDBTransactions;

                $this->mFlags = $flags;

                if ( $this->mFlags & DBO_DEFAULT ) {
                        if ( $wgCommandLineMode ) {
                                $this->mFlags &= ~DBO_TRX;
                                if ( $wgDebugDBTransactions ) {
                                        wfDebug("Implicit transaction open disabled.\n");
                                }
                        } else {
                                $this->mFlags |= DBO_TRX;
                                if ( $wgDebugDBTransactions ) {
                                        wfDebug("Implicit transaction open enabled.\n");
                                }
                        }
                }

                if ( $tablePrefix == 'get from global' ) {
                        $this->mTablePrefix = $wgDBprefix;
                } else {
                        $this->mTablePrefix = $tablePrefix;
                }

                if ( $user ) {
                        $this->open( $server, $user, $password, $dbName );
                }
        }

        public function __sleep() {
                throw new MWException( 'Database serialization may cause problems, since the connection is not restored on wakeup.' );
        }

        public final static function factory( $dbType, $p = array() ) {
                $canonicalDBTypes = array(
                        'mysql', 'postgres', 'sqlite', 'oracle', 'mssql', 'ibm_db2'
                );
                $dbType = strtolower( $dbType );
                $class = 'Database' . ucfirst( $dbType );

                if( in_array( $dbType, $canonicalDBTypes ) || ( class_exists( $class ) && is_subclass_of( $class, 'DatabaseBase' ) ) ) {
                        return new $class(
                                isset( $p['host'] ) ? $p['host'] : false,
                                isset( $p['user'] ) ? $p['user'] : false,
                                isset( $p['password'] ) ? $p['password'] : false,
                                isset( $p['dbname'] ) ? $p['dbname'] : false,
                                isset( $p['flags'] ) ? $p['flags'] : 0,
                                isset( $p['tablePrefix'] ) ? $p['tablePrefix'] : 'get from global'
                        );
                } else {
                        return null;
                }
        }

        protected function installErrorHandler() {
                $this->mPHPError = false;
                $this->htmlErrors = ini_set( 'html_errors', '0' );
                set_error_handler( array( $this, 'connectionErrorHandler' ) );
        }

        protected function restoreErrorHandler() {
                restore_error_handler();
                if ( $this->htmlErrors !== false ) {
                        ini_set( 'html_errors', $this->htmlErrors );
                }
                if ( $this->mPHPError ) {
                        $error = preg_replace( '!\[<a.*</a>\]!', '', $this->mPHPError );
                        $error = preg_replace( '!^.*?:\s?(.*)$!', '$1', $error );
                        return $error;
                } else {
                        return false;
                }
        }

        protected function connectionErrorHandler( $errno,  $errstr ) {
                $this->mPHPError = $errstr;
        }

        public function close() {
                $this->mOpened = false;
                if ( $this->mConn ) {
                        if ( $this->trxLevel() ) {
                                if ( !$this->mTrxAutomatic ) {
                                        wfWarn( "Transaction still in progress (from {$this->mTrxFname}), " .
                                                " performing implicit commit before closing connection!" );
                                }

                                $this->commit( __METHOD__, 'flush' );
                        }

                        $ret = $this->closeConnection();
                        $this->mConn = false;
                        return $ret;
                } else {
                        return true;
                }
        }

        protected abstract function closeConnection();

        function reportConnectionError( $error = 'Unknown error' ) {
                $myError = $this->lastError();
                if ( $myError ) {
                        $error = $myError;
                }

                # New method
                throw new DBConnectionError( $this, $error );
        }

        protected abstract function doQuery( $sql );

        public function isWriteQuery( $sql ) {
                return !preg_match( '/^(?:SELECT|BEGIN|ROLLBACK|COMMIT|SET|SHOW|EXPLAIN|\(SELECT)\b/i', $sql );
        }

        public function query( $sql, $fname = '', $tempIgnore = false ) {
                $isMaster = !is_null( $this->getLBInfo( 'master' ) );
                if ( !Profiler::instance()->isStub() ) {
                        # generalizeSQL will probably cut down the query to reasonable
                        # logging size most of the time. The substr is really just a sanity check.

                        if ( $isMaster ) {
                                $queryProf = 'query-m: ' . substr( DatabaseBase::generalizeSQL( $sql ), 0, 255 );
                                $totalProf = 'DatabaseBase::query-master';
                        } else {
                                $queryProf = 'query: ' . substr( DatabaseBase::generalizeSQL( $sql ), 0, 255 );
                                $totalProf = 'DatabaseBase::query';
                        }

                        wfProfileIn( $totalProf );
                        wfProfileIn( $queryProf );
                }

                $this->mLastQuery = $sql;
                if ( !$this->mDoneWrites && $this->isWriteQuery( $sql ) ) {
                        # Set a flag indicating that writes have been done
                        wfDebug( __METHOD__ . ": Writes done: $sql\n" );
                        $this->mDoneWrites = true;
                }

                # Add a comment for easy SHOW PROCESSLIST interpretation
                global $wgUser;
                if ( is_object( $wgUser ) && $wgUser->isItemLoaded( 'name' ) ) {
                        $userName = $wgUser->getName();
                        if ( mb_strlen( $userName ) > 15 ) {
                                $userName = mb_substr( $userName, 0, 15 ) . '...';
                        }
                        $userName = str_replace( '/', '', $userName );
                } else {
                        $userName = '';
                }
                $commentedSql = preg_replace( '/\s/', " /* $fname $userName */ ", $sql, 1 );

                # If DBO_TRX is set, start a transaction
                if ( ( $this->mFlags & DBO_TRX ) && !$this->mTrxLevel &&
                        $sql != 'BEGIN' && $sql != 'COMMIT' && $sql != 'ROLLBACK' )
                {
                        # Avoid establishing transactions for SHOW and SET statements too -
                        # that would delay transaction initializations to once connection
                        # is really used by application
                        $sqlstart = substr( $sql, 0, 10 ); // very much worth it, benchmark certified(tm)
                        if ( strpos( $sqlstart, "SHOW " ) !== 0 && strpos( $sqlstart, "SET " ) !== 0 ) {
                                global $wgDebugDBTransactions;
                                if ( $wgDebugDBTransactions ) {
                                        wfDebug("Implicit transaction start.\n");
                                }
                                $this->begin( __METHOD__ . " ($fname)" );
                                $this->mTrxAutomatic = true;
                        }
                }

                # Keep track of whether the transaction has write queries pending
                if ( $this->mTrxLevel && !$this->mTrxDoneWrites && $this->isWriteQuery( $sql ) ) {
                        $this->mTrxDoneWrites = true;
                }

                if ( $this->debug() ) {
                        static $cnt = 0;

                        $cnt++;
                        $sqlx = substr( $commentedSql, 0, 500 );
                        $sqlx = strtr( $sqlx, "\t\n", '  ' );

                        $master = $isMaster ? 'master' : 'slave';
                        wfDebug( "Query {$this->mDBname} ($cnt) ($master): $sqlx\n" );
                }

                if ( istainted( $sql ) & TC_MYSQL ) {
                        throw new MWException( 'Tainted query found' );
                }

                $queryId = MWDebug::query( $sql, $fname, $isMaster );

                # Do the query and handle errors
                $ret = $this->doQuery( $commentedSql );

                MWDebug::queryTime( $queryId );

                # Try reconnecting if the connection was lost
                if ( false === $ret && $this->wasErrorReissuable() ) {
                        # Transaction is gone, like it or not
                        $this->mTrxLevel = 0;
                        $this->trxIdleCallbacks = array(); // cancel
                        wfDebug( "Connection lost, reconnecting...\n" );

                        if ( $this->ping() ) {
                                wfDebug( "Reconnected\n" );
                                $sqlx = substr( $commentedSql, 0, 500 );
                                $sqlx = strtr( $sqlx, "\t\n", '  ' );
                                global $wgRequestTime;
                                $elapsed = round( microtime( true ) - $wgRequestTime, 3 );
                                if ( $elapsed < 300 ) {
                                        # Not a database error to lose a transaction after a minute or two
                                        wfLogDBError( "Connection lost and reconnected after {$elapsed}s, query: $sqlx\n" );
                                }
                                $ret = $this->doQuery( $commentedSql );
                        } else {
                                wfDebug( "Failed\n" );
                        }
                }

                if ( false === $ret ) {
                        $this->reportQueryError( $this->lastError(), $this->lastErrno(), $sql, $fname, $tempIgnore );
                }

                if ( !Profiler::instance()->isStub() ) {
                        wfProfileOut( $queryProf );
                        wfProfileOut( $totalProf );
                }

                return $this->resultObject( $ret );
        }

        public function reportQueryError( $error, $errno, $sql, $fname, $tempIgnore = false ) {
                # Ignore errors during error handling to avoid infinite recursion
                $ignore = $this->ignoreErrors( true );
                ++$this->mErrorCount;

                if ( $ignore || $tempIgnore ) {
                        wfDebug( "SQL ERROR (ignored): $error\n" );
                        $this->ignoreErrors( $ignore );
                } else {
                        $sql1line = str_replace( "\n", "\\n", $sql );
                        wfLogDBError( "$fname\t{$this->mServer}\t$errno\t$error\t$sql1line\n" );
                        wfDebug( "SQL ERROR: " . $error . "\n" );
                        throw new DBQueryError( $this, $error, $errno, $sql, $fname );
                }
        }

        protected function prepare( $sql, $func = 'DatabaseBase::prepare' ) {
                /* MySQL doesn't support prepared statements (yet), so just
                   pack up the query for reference. We'll manually replace
                   the bits later. */
                return array( 'query' => $sql, 'func' => $func );
        }

        protected function freePrepared( $prepared ) {
                /* No-op by default */
        }

        public function execute( $prepared, $args = null ) {
                if ( !is_array( $args ) ) {
                        # Pull the var args
                        $args = func_get_args();
                        array_shift( $args );
                }

                $sql = $this->fillPrepared( $prepared['query'], $args );

                return $this->query( $sql, $prepared['func'] );
        }

        public function fillPrepared( $preparedQuery, $args ) {
                reset( $args );
                $this->preparedArgs =& $args;

                return preg_replace_callback( '/(\\\\[?!&]|[?!&])/',
                        array( &$this, 'fillPreparedArg' ), $preparedQuery );
        }

        protected function fillPreparedArg( $matches ) {
                switch( $matches[1] ) {
                        case '\\?': return '?';
                        case '\\!': return '!';
                        case '\\&': return '&';
                }

                list( /* $n */ , $arg ) = each( $this->preparedArgs );

                switch( $matches[1] ) {
                        case '?': return $this->addQuotes( $arg );
                        case '!': return $arg;
                        case '&':
                                # return $this->addQuotes( file_get_contents( $arg ) );
                                throw new DBUnexpectedError( $this, '& mode is not implemented. If it\'s really needed, uncomment the line above.' );
                        default:
                                throw new DBUnexpectedError( $this, 'Received invalid match. This should never happen!' );
                }
        }

        public function freeResult( $res ) {}

        public function selectField( $table, $var, $cond = '', $fname = 'DatabaseBase::selectField',
                $options = array() )
        {
                if ( !is_array( $options ) ) {
                        $options = array( $options );
                }

                $options['LIMIT'] = 1;

                $res = $this->select( $table, $var, $cond, $fname, $options );

                if ( $res === false || !$this->numRows( $res ) ) {
                        return false;
                }

                $row = $this->fetchRow( $res );

                if ( $row !== false ) {
                        return reset( $row );
                } else {
                        return false;
                }
        }

        public function makeSelectOptions( $options ) {
                $preLimitTail = $postLimitTail = '';
                $startOpts = '';

                $noKeyOptions = array();

                foreach ( $options as $key => $option ) {
                        if ( is_numeric( $key ) ) {
                                $noKeyOptions[$option] = true;
                        }
                }

                if ( isset( $options['GROUP BY'] ) ) {
                        $gb = is_array( $options['GROUP BY'] )
                                ? implode( ',', $options['GROUP BY'] )
                                : $options['GROUP BY'];
                        $preLimitTail .= " GROUP BY {$gb}";
                }

                if ( isset( $options['HAVING'] ) ) {
                        $having = is_array( $options['HAVING'] )
                                ? $this->makeList( $options['HAVING'], LIST_AND )
                                : $options['HAVING'];
                        $preLimitTail .= " HAVING {$having}";
                }

                if ( isset( $options['ORDER BY'] ) ) {
                        $ob = is_array( $options['ORDER BY'] )
                                ? implode( ',', $options['ORDER BY'] )
                                : $options['ORDER BY'];
                        $preLimitTail .= " ORDER BY {$ob}";
                }

                // if (isset($options['LIMIT'])) {
                //      $tailOpts .= $this->limitResult('', $options['LIMIT'],
                //              isset($options['OFFSET']) ? $options['OFFSET']
                //              : false);
                // }

                if ( isset( $noKeyOptions['FOR UPDATE'] ) ) {
                        $postLimitTail .= ' FOR UPDATE';
                }

                if ( isset( $noKeyOptions['LOCK IN SHARE MODE'] ) ) {
                        $postLimitTail .= ' LOCK IN SHARE MODE';
                }

                if ( isset( $noKeyOptions['DISTINCT'] ) || isset( $noKeyOptions['DISTINCTROW'] ) ) {
                        $startOpts .= 'DISTINCT';
                }

                # Various MySQL extensions
                if ( isset( $noKeyOptions['STRAIGHT_JOIN'] ) ) {
                        $startOpts .= ' /*! STRAIGHT_JOIN */';
                }

                if ( isset( $noKeyOptions['HIGH_PRIORITY'] ) ) {
                        $startOpts .= ' HIGH_PRIORITY';
                }

                if ( isset( $noKeyOptions['SQL_BIG_RESULT'] ) ) {
                        $startOpts .= ' SQL_BIG_RESULT';
                }

                if ( isset( $noKeyOptions['SQL_BUFFER_RESULT'] ) ) {
                        $startOpts .= ' SQL_BUFFER_RESULT';
                }

                if ( isset( $noKeyOptions['SQL_SMALL_RESULT'] ) ) {
                        $startOpts .= ' SQL_SMALL_RESULT';
                }

                if ( isset( $noKeyOptions['SQL_CALC_FOUND_ROWS'] ) ) {
                        $startOpts .= ' SQL_CALC_FOUND_ROWS';
                }

                if ( isset( $noKeyOptions['SQL_CACHE'] ) ) {
                        $startOpts .= ' SQL_CACHE';
                }

                if ( isset( $noKeyOptions['SQL_NO_CACHE'] ) ) {
                        $startOpts .= ' SQL_NO_CACHE';
                }

                if ( isset( $options['USE INDEX'] ) && ! is_array( $options['USE INDEX'] ) ) {
                        $useIndex = $this->useIndexClause( $options['USE INDEX'] );
                } else {
                        $useIndex = '';
                }

                return array( $startOpts, $useIndex, $preLimitTail, $postLimitTail );
        }

        public function select( $table, $vars, $conds = '', $fname = 'DatabaseBase::select',
                $options = array(), $join_conds = array() ) {
                $sql = $this->selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds );

                return $this->query( $sql, $fname );
        }

        public function selectSQLText( $table, $vars, $conds = '', $fname = 'DatabaseBase::select',
                $options = array(), $join_conds = array() )
        {
                if ( is_array( $vars ) ) {
                        $vars = implode( ',', $this->fieldNamesWithAlias( $vars ) );
                }

                $options = (array)$options;

                if ( is_array( $table ) ) {
                        $useIndex = ( isset( $options['USE INDEX'] ) && is_array( $options['USE INDEX'] ) )
                                ? $options['USE INDEX']
                                : array();
                        if ( count( $join_conds ) || count( $useIndex ) ) {
                                $from = ' FROM ' .
                                        $this->tableNamesWithUseIndexOrJOIN( $table, $useIndex, $join_conds );
                        } else {
                                $from = ' FROM ' . implode( ',', $this->tableNamesWithAlias( $table ) );
                        }
                } elseif ( $table != '' ) {
                        if ( $table[0] == ' ' ) {
                                $from = ' FROM ' . $table;
                        } else {
                                $from = ' FROM ' . $this->tableName( $table );
                        }
                } else {
                        $from = '';
                }

                list( $startOpts, $useIndex, $preLimitTail, $postLimitTail ) = $this->makeSelectOptions( $options );

                if ( !empty( $conds ) ) {
                        if ( is_array( $conds ) ) {
                                $conds = $this->makeList( $conds, LIST_AND );
                        }
                        $sql = "SELECT $startOpts $vars $from $useIndex WHERE $conds $preLimitTail";
                } else {
                        $sql = "SELECT $startOpts $vars $from $useIndex $preLimitTail";
                }

                if ( isset( $options['LIMIT'] ) ) {
                        $sql = $this->limitResult( $sql, $options['LIMIT'],
                                isset( $options['OFFSET'] ) ? $options['OFFSET'] : false );
                }
                $sql = "$sql $postLimitTail";

                if ( isset( $options['EXPLAIN'] ) ) {
                        $sql = 'EXPLAIN ' . $sql;
                }

                return $sql;
        }

        public function selectRow( $table, $vars, $conds, $fname = 'DatabaseBase::selectRow',
                $options = array(), $join_conds = array() )
        {
                $options = (array)$options;
                $options['LIMIT'] = 1;
                $res = $this->select( $table, $vars, $conds, $fname, $options, $join_conds );

                if ( $res === false ) {
                        return false;
                }

                if ( !$this->numRows( $res ) ) {
                        return false;
                }

                $obj = $this->fetchObject( $res );

                return $obj;
        }

        public function estimateRowCount( $table, $vars = '*', $conds = '',
                $fname = 'DatabaseBase::estimateRowCount', $options = array() )
        {
                $rows = 0;
                $res = $this->select( $table, array( 'rowcount' => 'COUNT(*)' ), $conds, $fname, $options );

                if ( $res ) {
                        $row = $this->fetchRow( $res );
                        $rows = ( isset( $row['rowcount'] ) ) ? $row['rowcount'] : 0;
                }

                return $rows;
        }

        static function generalizeSQL( $sql ) {
                # This does the same as the regexp below would do, but in such a way
                # as to avoid crashing php on some large strings.
                # $sql = preg_replace ( "/'([^\\\\']|\\\\.)*'|\"([^\\\\\"]|\\\\.)*\"/", "'X'", $sql);

                $sql = str_replace ( "\\\\", '', $sql );
                $sql = str_replace ( "\\'", '', $sql );
                $sql = str_replace ( "\\\"", '', $sql );
                $sql = preg_replace ( "/'.*'/s", "'X'", $sql );
                $sql = preg_replace ( '/".*"/s', "'X'", $sql );

                # All newlines, tabs, etc replaced by single space
                $sql = preg_replace ( '/\s+/', ' ', $sql );

                # All numbers => N
                $sql = preg_replace ( '/-?[0-9]+/s', 'N', $sql );

                return $sql;
        }

        public function fieldExists( $table, $field, $fname = 'DatabaseBase::fieldExists' ) {
                $info = $this->fieldInfo( $table, $field );

                return (bool)$info;
        }

        public function indexExists( $table, $index, $fname = 'DatabaseBase::indexExists' ) {
                $info = $this->indexInfo( $table, $index, $fname );
                if ( is_null( $info ) ) {
                        return null;
                } else {
                        return $info !== false;
                }
        }

        public function tableExists( $table, $fname = __METHOD__ ) {
                $table = $this->tableName( $table );
                $old = $this->ignoreErrors( true );
                $res = $this->query( "SELECT 1 FROM $table LIMIT 1", $fname );
                $this->ignoreErrors( $old );

                return (bool)$res;
        }

        public function fieldType( $res, $index ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                return mysql_field_type( $res, $index );
        }

        public function indexUnique( $table, $index ) {
                $indexInfo = $this->indexInfo( $table, $index );

                if ( !$indexInfo ) {
                        return null;
                }

                return !$indexInfo[0]->Non_unique;
        }

        protected function makeInsertOptions( $options ) {
                return implode( ' ', $options );
        }

        public function insert( $table, $a, $fname = 'DatabaseBase::insert', $options = array() ) {
                # No rows to insert, easy just return now
                if ( !count( $a ) ) {
                        return true;
                }

                $table = $this->tableName( $table );

                if ( !is_array( $options ) ) {
                        $options = array( $options );
                }

                $options = $this->makeInsertOptions( $options );

                if ( isset( $a[0] ) && is_array( $a[0] ) ) {
                        $multi = true;
                        $keys = array_keys( $a[0] );
                } else {
                        $multi = false;
                        $keys = array_keys( $a );
                }

                $sql = 'INSERT ' . $options .
                        " INTO $table (" . implode( ',', $keys ) . ') VALUES ';

                if ( $multi ) {
                        $first = true;
                        foreach ( $a as $row ) {
                                if ( $first ) {
                                        $first = false;
                                } else {
                                        $sql .= ',';
                                }
                                $sql .= '(' . $this->makeList( $row ) . ')';
                        }
                } else {
                        $sql .= '(' . $this->makeList( $a ) . ')';
                }

                return (bool)$this->query( $sql, $fname );
        }

        protected function makeUpdateOptions( $options ) {
                if ( !is_array( $options ) ) {
                        $options = array( $options );
                }

                $opts = array();

                if ( in_array( 'LOW_PRIORITY', $options ) ) {
                        $opts[] = $this->lowPriorityOption();
                }

                if ( in_array( 'IGNORE', $options ) ) {
                        $opts[] = 'IGNORE';
                }

                return implode( ' ', $opts );
        }

        function update( $table, $values, $conds, $fname = 'DatabaseBase::update', $options = array() ) {
                $table = $this->tableName( $table );
                $opts = $this->makeUpdateOptions( $options );
                $sql = "UPDATE $opts $table SET " . $this->makeList( $values, LIST_SET );

                if ( $conds !== array() && $conds !== '*' ) {
                        $sql .= " WHERE " . $this->makeList( $conds, LIST_AND );
                }

                return $this->query( $sql, $fname );
        }

        public function makeList( $a, $mode = LIST_COMMA ) {
                if ( !is_array( $a ) ) {
                        throw new DBUnexpectedError( $this, 'DatabaseBase::makeList called with incorrect parameters' );
                }

                $first = true;
                $list = '';

                foreach ( $a as $field => $value ) {
                        if ( !$first ) {
                                if ( $mode == LIST_AND ) {
                                        $list .= ' AND ';
                                } elseif ( $mode == LIST_OR ) {
                                        $list .= ' OR ';
                                } else {
                                        $list .= ',';
                                }
                        } else {
                                $first = false;
                        }

                        if ( ( $mode == LIST_AND || $mode == LIST_OR ) && is_numeric( $field ) ) {
                                $list .= "($value)";
                        } elseif ( ( $mode == LIST_SET ) && is_numeric( $field ) ) {
                                $list .= "$value";
                        } elseif ( ( $mode == LIST_AND || $mode == LIST_OR ) && is_array( $value ) ) {
                                if ( count( $value ) == 0 ) {
                                        throw new MWException( __METHOD__ . ": empty input for field $field" );
                                } elseif ( count( $value ) == 1 ) {
                                        // Special-case single values, as IN isn't terribly efficient
                                        // Don't necessarily assume the single key is 0; we don't
                                        // enforce linear numeric ordering on other arrays here.
                                        $value = array_values( $value );
                                        $list .= $field . " = " . $this->addQuotes( $value[0] );
                                } else {
                                        $list .= $field . " IN (" . $this->makeList( $value ) . ") ";
                                }
                        } elseif ( $value === null ) {
                                if ( $mode == LIST_AND || $mode == LIST_OR ) {
                                        $list .= "$field IS ";
                                } elseif ( $mode == LIST_SET ) {
                                        $list .= "$field = ";
                                }
                                $list .= 'NULL';
                        } else {
                                if ( $mode == LIST_AND || $mode == LIST_OR || $mode == LIST_SET ) {
                                        $list .= "$field = ";
                                }
                                $list .= $mode == LIST_NAMES ? $value : $this->addQuotes( $value );
                        }
                }

                return $list;
        }

        public function makeWhereFrom2d( $data, $baseKey, $subKey ) {
                $conds = array();

                foreach ( $data as $base => $sub ) {
                        if ( count( $sub ) ) {
                                $conds[] = $this->makeList(
                                        array( $baseKey => $base, $subKey => array_keys( $sub ) ),
                                        LIST_AND );
                        }
                }

                if ( $conds ) {
                        return $this->makeList( $conds, LIST_OR );
                } else {
                        // Nothing to search for...
                        return false;
                }
        }

        public function aggregateValue( $valuedata, $valuename = 'value' ) {
                return $valuename;
        }

        public function bitNot( $field ) {
                return "(~$field)";
        }

        public function bitAnd( $fieldLeft, $fieldRight ) {
                return "($fieldLeft & $fieldRight)";
        }

        public function bitOr( $fieldLeft, $fieldRight ) {
                return "($fieldLeft | $fieldRight)";
        }

        public function buildConcat( $stringList ) {
                return 'CONCAT(' . implode( ',', $stringList ) . ')';
        }

        public function selectDB( $db ) {
                # Stub.  Shouldn't cause serious problems if it's not overridden, but
                # if your database engine supports a concept similar to MySQL's
                # databases you may as well.
                $this->mDBname = $db;
                return true;
        }

        public function getDBname() {
                return $this->mDBname;
        }

        public function getServer() {
                return $this->mServer;
        }

        public function tableName( $name, $format = 'quoted' ) {
                global $wgSharedDB, $wgSharedPrefix, $wgSharedTables;
                # Skip the entire process when we have a string quoted on both ends.
                # Note that we check the end so that we will still quote any use of
                # use of `database`.table. But won't break things if someone wants
                # to query a database table with a dot in the name.
                if ( $this->isQuotedIdentifier( $name ) ) {
                        return $name;
                }

                # Lets test for any bits of text that should never show up in a table
                # name. Basically anything like JOIN or ON which are actually part of
                # SQL queries, but may end up inside of the table value to combine
                # sql. Such as how the API is doing.
                # Note that we use a whitespace test rather than a \b test to avoid
                # any remote case where a word like on may be inside of a table name
                # surrounded by symbols which may be considered word breaks.
                if ( preg_match( '/(^|\s)(DISTINCT|JOIN|ON|AS)(\s|$)/i', $name ) !== 0 ) {
                        return $name;
                }

                # Split database and table into proper variables.
                # We reverse the explode so that database.table and table both output
                # the correct table.
                $dbDetails = array_reverse( explode( '.', $name, 2 ) );
                if ( isset( $dbDetails[1] ) ) {
                        list( $table, $database ) = $dbDetails;
                } else {
                        list( $table ) = $dbDetails;
                }
                $prefix = $this->mTablePrefix; # Default prefix

                # A database name has been specified in input. We don't want any
                # prefixes added.
                if ( isset( $database ) ) {
                        $prefix = '';
                }

                # Note that we use the long format because php will complain in in_array if
                # the input is not an array, and will complain in is_array if it is not set.
                if ( !isset( $database ) # Don't use shared database if pre selected.
                 && isset( $wgSharedDB ) # We have a shared database
                 && !$this->isQuotedIdentifier( $table ) # Paranoia check to prevent shared tables listing '`table`'
                 && isset( $wgSharedTables )
                 && is_array( $wgSharedTables )
                 && in_array( $table, $wgSharedTables ) ) { # A shared table is selected
                        $database = $wgSharedDB;
                        $prefix   = isset( $wgSharedPrefix ) ? $wgSharedPrefix : $prefix;
                }

                # Quote the $database and $table and apply the prefix if not quoted.
                if ( isset( $database ) ) {
                        if ( $format == 'quoted' && !$this->isQuotedIdentifier( $database ) ) {
                                $database = $this->addIdentifierQuotes( $database );
                        }
                }

                $table = "{$prefix}{$table}";
                if ( $format == 'quoted' && !$this->isQuotedIdentifier( $table ) ) {
                        $table = $this->addIdentifierQuotes( "{$table}" );
                }

                # Merge our database and table into our final table name.
                $tableName = ( isset( $database ) ? "{$database}.{$table}" : "{$table}" );

                return $tableName;
        }

        public function tableNames() {
                $inArray = func_get_args();
                $retVal = array();

                foreach ( $inArray as $name ) {
                        $retVal[$name] = $this->tableName( $name );
                }

                return $retVal;
        }

        public function tableNamesN() {
                $inArray = func_get_args();
                $retVal = array();

                foreach ( $inArray as $name ) {
                        $retVal[] = $this->tableName( $name );
                }

                return $retVal;
        }

        public function tableNameWithAlias( $name, $alias = false ) {
                if ( !$alias || $alias == $name ) {
                        return $this->tableName( $name );
                } else {
                        return $this->tableName( $name ) . ' ' . $this->addIdentifierQuotes( $alias );
                }
        }

        public function tableNamesWithAlias( $tables ) {
                $retval = array();
                foreach ( $tables as $alias => $table ) {
                        if ( is_numeric( $alias ) ) {
                                $alias = $table;
                        }
                        $retval[] = $this->tableNameWithAlias( $table, $alias );
                }
                return $retval;
        }

        public function fieldNameWithAlias( $name, $alias = false ) {
                if ( !$alias || (string)$alias === (string)$name ) {
                        return $name;
                } else {
                        return $name . ' AS ' . $alias; //PostgreSQL needs AS
                }
        }

        public function fieldNamesWithAlias( $fields ) {
                $retval = array();
                foreach ( $fields as $alias => $field ) {
                        if ( is_numeric( $alias ) ) {
                                $alias = $field;
                        }
                        $retval[] = $this->fieldNameWithAlias( $field, $alias );
                }
                return $retval;
        }

        protected function tableNamesWithUseIndexOrJOIN(
                $tables, $use_index = array(), $join_conds = array()
        ) {
                $ret = array();
                $retJOIN = array();
                $use_index = (array)$use_index;
                $join_conds = (array)$join_conds;

                foreach ( $tables as $alias => $table ) {
                        if ( !is_string( $alias ) ) {
                                // No alias? Set it equal to the table name
                                $alias = $table;
                        }
                        // Is there a JOIN clause for this table?
                        if ( isset( $join_conds[$alias] ) ) {
                                list( $joinType, $conds ) = $join_conds[$alias];
                                $tableClause = $joinType;
                                $tableClause .= ' ' . $this->tableNameWithAlias( $table, $alias );
                                if ( isset( $use_index[$alias] ) ) { // has USE INDEX?
                                        $use = $this->useIndexClause( implode( ',', (array)$use_index[$alias] ) );
                                        if ( $use != '' ) {
                                                $tableClause .= ' ' . $use;
                                        }
                                }
                                $on = $this->makeList( (array)$conds, LIST_AND );
                                if ( $on != '' ) {
                                        $tableClause .= ' ON (' . $on . ')';
                                }

                                $retJOIN[] = $tableClause;
                        // Is there an INDEX clause for this table?
                        } elseif ( isset( $use_index[$alias] ) ) {
                                $tableClause = $this->tableNameWithAlias( $table, $alias );
                                $tableClause .= ' ' . $this->useIndexClause(
                                        implode( ',', (array)$use_index[$alias] ) );

                                $ret[] = $tableClause;
                        } else {
                                $tableClause = $this->tableNameWithAlias( $table, $alias );

                                $ret[] = $tableClause;
                        }
                }

                // We can't separate explicit JOIN clauses with ',', use ' ' for those
                $straightJoins = !empty( $ret ) ? implode( ',', $ret ) : "";
                $otherJoins = !empty( $retJOIN ) ? implode( ' ', $retJOIN ) : "";

                // Compile our final table clause
                return implode( ' ', array( $straightJoins, $otherJoins ) );
        }

        protected function indexName( $index ) {
                // Backwards-compatibility hack
                $renamed = array(
                        'ar_usertext_timestamp' => 'usertext_timestamp',
                        'un_user_id'            => 'user_id',
                        'un_user_ip'            => 'user_ip',
                );

                if ( isset( $renamed[$index] ) ) {
                        return $renamed[$index];
                } else {
                        return $index;
                }
        }

        public function addQuotes( $s ) {
                if ( $s === null ) {
                        return 'NULL';
                } else {
                        # This will also quote numeric values. This should be harmless,
                        # and protects against weird problems that occur when they really
                        # _are_ strings such as article titles and string->number->string
                        # conversion is not 1:1.
                        return "'" . $this->strencode( $s ) . "'";
                }
        }

        public function addIdentifierQuotes( $s ) {
                return '"' . str_replace( '"', '""', $s ) . '"';
        }

        public function isQuotedIdentifier( $name ) {
                return $name[0] == '"' && substr( $name, -1, 1 ) == '"';
        }

        protected function escapeLikeInternal( $s ) {
                $s = str_replace( '\\', '\\\\', $s );
                $s = $this->strencode( $s );
                $s = str_replace( array( '%', '_' ), array( '\%', '\_' ), $s );

                return $s;
        }

        public function buildLike() {
                $params = func_get_args();

                if ( count( $params ) > 0 && is_array( $params[0] ) ) {
                        $params = $params[0];
                }

                $s = '';

                foreach ( $params as $value ) {
                        if ( $value instanceof LikeMatch ) {
                                $s .= $value->toString();
                        } else {
                                $s .= $this->escapeLikeInternal( $value );
                        }
                }

                return " LIKE '" . $s . "' ";
        }

        public function anyChar() {
                return new LikeMatch( '_' );
        }

        public function anyString() {
                return new LikeMatch( '%' );
        }

        public function nextSequenceValue( $seqName ) {
                return null;
        }

        public function useIndexClause( $index ) {
                return '';
        }

        public function replace( $table, $uniqueIndexes, $rows, $fname = 'DatabaseBase::replace' ) {
                $quotedTable = $this->tableName( $table );

                if ( count( $rows ) == 0 ) {
                        return;
                }

                # Single row case
                if ( !is_array( reset( $rows ) ) ) {
                        $rows = array( $rows );
                }

                foreach( $rows as $row ) {
                        # Delete rows which collide
                        if ( $uniqueIndexes ) {
                                $sql = "DELETE FROM $quotedTable WHERE ";
                                $first = true;
                                foreach ( $uniqueIndexes as $index ) {
                                        if ( $first ) {
                                                $first = false;
                                                $sql .= '( ';
                                        } else {
                                                $sql .= ' ) OR ( ';
                                        }
                                        if ( is_array( $index ) ) {
                                                $first2 = true;
                                                foreach ( $index as $col ) {
                                                        if ( $first2 ) {
                                                                $first2 = false;
                                                        } else {
                                                                $sql .= ' AND ';
                                                        }
                                                        $sql .= $col . '=' . $this->addQuotes( $row[$col] );
                                                }
                                        } else {
                                                $sql .= $index . '=' . $this->addQuotes( $row[$index] );
                                        }
                                }
                                $sql .= ' )';
                                $this->query( $sql, $fname );
                        }

                        # Now insert the row
                        $this->insert( $table, $row );
                }
        }

        protected function nativeReplace( $table, $rows, $fname ) {
                $table = $this->tableName( $table );

                # Single row case
                if ( !is_array( reset( $rows ) ) ) {
                        $rows = array( $rows );
                }

                $sql = "REPLACE INTO $table (" . implode( ',', array_keys( $rows[0] ) ) . ') VALUES ';
                $first = true;

                foreach ( $rows as $row ) {
                        if ( $first ) {
                                $first = false;
                        } else {
                                $sql .= ',';
                        }

                        $sql .= '(' . $this->makeList( $row ) . ')';
                }

                return $this->query( $sql, $fname );
        }

        public function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds,
                $fname = 'DatabaseBase::deleteJoin' )
        {
                if ( !$conds ) {
                        throw new DBUnexpectedError( $this,
                                'DatabaseBase::deleteJoin() called with empty $conds' );
                }

                $delTable = $this->tableName( $delTable );
                $joinTable = $this->tableName( $joinTable );
                $sql = "DELETE FROM $delTable WHERE $delVar IN (SELECT $joinVar FROM $joinTable ";
                if ( $conds != '*' ) {
                        $sql .= 'WHERE ' . $this->makeList( $conds, LIST_AND );
                }
                $sql .= ')';

                $this->query( $sql, $fname );
        }

        public function textFieldSize( $table, $field ) {
                $table = $this->tableName( $table );
                $sql = "SHOW COLUMNS FROM $table LIKE \"$field\";";
                $res = $this->query( $sql, 'DatabaseBase::textFieldSize' );
                $row = $this->fetchObject( $res );

                $m = array();

                if ( preg_match( '/\((.*)\)/', $row->Type, $m ) ) {
                        $size = $m[1];
                } else {
                        $size = -1;
                }

                return $size;
        }

        public function lowPriorityOption() {
                return '';
        }

        public function delete( $table, $conds, $fname = 'DatabaseBase::delete' ) {
                if ( !$conds ) {
                        throw new DBUnexpectedError( $this, 'DatabaseBase::delete() called with no conditions' );
                }

                $table = $this->tableName( $table );
                $sql = "DELETE FROM $table";

                if ( $conds != '*' ) {
                        $sql .= ' WHERE ' . $this->makeList( $conds, LIST_AND );
                }

                return $this->query( $sql, $fname );
        }

        public function insertSelect( $destTable, $srcTable, $varMap, $conds,
                $fname = 'DatabaseBase::insertSelect',
                $insertOptions = array(), $selectOptions = array() )
        {
                $destTable = $this->tableName( $destTable );

                if ( is_array( $insertOptions ) ) {
                        $insertOptions = implode( ' ', $insertOptions );
                }

                if ( !is_array( $selectOptions ) ) {
                        $selectOptions = array( $selectOptions );
                }

                list( $startOpts, $useIndex, $tailOpts ) = $this->makeSelectOptions( $selectOptions );

                if ( is_array( $srcTable ) ) {
                        $srcTable =  implode( ',', array_map( array( &$this, 'tableName' ), $srcTable ) );
                } else {
                        $srcTable = $this->tableName( $srcTable );
                }

                $sql = "INSERT $insertOptions INTO $destTable (" . implode( ',', array_keys( $varMap ) ) . ')' .
                        " SELECT $startOpts " . implode( ',', $varMap ) .
                        " FROM $srcTable $useIndex ";

                if ( $conds != '*' ) {
                        if ( is_array( $conds ) ) {
                                $conds = $this->makeList( $conds, LIST_AND );
                        }
                        $sql .= " WHERE $conds";
                }

                $sql .= " $tailOpts";

                return $this->query( $sql, $fname );
        }

        public function limitResult( $sql, $limit, $offset = false ) {
                if ( !is_numeric( $limit ) ) {
                        throw new DBUnexpectedError( $this, "Invalid non-numeric limit passed to limitResult()\n" );
                }
                return "$sql LIMIT "
                        . ( ( is_numeric( $offset ) && $offset != 0 ) ? "{$offset}," : "" )
                        . "{$limit} ";
        }

        public function unionSupportsOrderAndLimit() {
                return true; // True for almost every DB supported
        }

        public function unionQueries( $sqls, $all ) {
                $glue = $all ? ') UNION ALL (' : ') UNION (';
                return '(' . implode( $glue, $sqls ) . ')';
        }

        public function conditional( $cond, $trueVal, $falseVal ) {
                if ( is_array( $cond ) ) {
                        $cond = $this->makeList( $cond, LIST_AND );
                }
                return " (CASE WHEN $cond THEN $trueVal ELSE $falseVal END) ";
        }

        public function strreplace( $orig, $old, $new ) {
                return "REPLACE({$orig}, {$old}, {$new})";
        }

        public function getServerUptime() {
                return 0;
        }

        public function wasDeadlock() {
                return false;
        }

        public function wasLockTimeout() {
                return false;
        }

        public function wasErrorReissuable() {
                return false;
        }

        public function wasReadOnlyError() {
                return false;
        }

        public function deadlockLoop() {
                $this->begin( __METHOD__ );
                $args = func_get_args();
                $function = array_shift( $args );
                $oldIgnore = $this->ignoreErrors( true );
                $tries = DEADLOCK_TRIES;

                if ( is_array( $function ) ) {
                        $fname = $function[0];
                } else {
                        $fname = $function;
                }

                do {
                        $retVal = call_user_func_array( $function, $args );
                        $error = $this->lastError();
                        $errno = $this->lastErrno();
                        $sql = $this->lastQuery();

                        if ( $errno ) {
                                if ( $this->wasDeadlock() ) {
                                        # Retry
                                        usleep( mt_rand( DEADLOCK_DELAY_MIN, DEADLOCK_DELAY_MAX ) );
                                } else {
                                        $this->reportQueryError( $error, $errno, $sql, $fname );
                                }
                        }
                } while ( $this->wasDeadlock() && --$tries > 0 );

                $this->ignoreErrors( $oldIgnore );

                if ( $tries <= 0 ) {
                        $this->rollback( __METHOD__ );
                        $this->reportQueryError( $error, $errno, $sql, $fname );
                        return false;
                } else {
                        $this->commit( __METHOD__ );
                        return $retVal;
                }
        }

        public function masterPosWait( DBMasterPos $pos, $timeout ) {
                wfProfileIn( __METHOD__ );

                if ( !is_null( $this->mFakeSlaveLag ) ) {
                        $wait = intval( ( $pos->pos - microtime( true ) + $this->mFakeSlaveLag ) * 1e6 );

                        if ( $wait > $timeout * 1e6 ) {
                                wfDebug( "Fake slave timed out waiting for $pos ($wait us)\n" );
                                wfProfileOut( __METHOD__ );
                                return -1;
                        } elseif ( $wait > 0 ) {
                                wfDebug( "Fake slave waiting $wait us\n" );
                                usleep( $wait );
                                wfProfileOut( __METHOD__ );
                                return 1;
                        } else {
                                wfDebug( "Fake slave up to date ($wait us)\n" );
                                wfProfileOut( __METHOD__ );
                                return 0;
                        }
                }

                wfProfileOut( __METHOD__ );

                # Real waits are implemented in the subclass.
                return 0;
        }

        public function getSlavePos() {
                if ( !is_null( $this->mFakeSlaveLag ) ) {
                        $pos = new MySQLMasterPos( 'fake', microtime( true ) - $this->mFakeSlaveLag );
                        wfDebug( __METHOD__ . ": fake slave pos = $pos\n" );
                        return $pos;
                } else {
                        # Stub
                        return false;
                }
        }

        public function getMasterPos() {
                if ( $this->mFakeMaster ) {
                        return new MySQLMasterPos( 'fake', microtime( true ) );
                } else {
                        return false;
                }
        }

        final public function onTransactionIdle( Closure $callback ) {
                if ( $this->mTrxLevel ) {
                        $this->trxIdleCallbacks[] = $callback;
                } else {
                        $callback();
                }
        }

        protected function runOnTransactionIdleCallbacks() {
                $e = null; // last exception
                do { // callbacks may add callbacks :)
                        $callbacks = $this->trxIdleCallbacks;
                        $this->trxIdleCallbacks = array(); // recursion guard
                        foreach ( $callbacks as $callback ) {
                                try {
                                        $callback();
                                } catch ( Exception $e ) {}
                        }
                } while ( count( $this->trxIdleCallbacks ) );

                if ( $e instanceof Exception ) {
                        throw $e; // re-throw any last exception
                }
        }

        final public function begin( $fname = 'DatabaseBase::begin' ) {
                global $wgDebugDBTransactions;

                if ( $this->mTrxLevel ) { // implicit commit
                        if ( !$this->mTrxAutomatic ) {
                                // We want to warn about inadvertently nested begin/commit pairs, but not about auto-committing
                                // implicit transactions that were started by query() because DBO_TRX was set.

                                wfWarn( "$fname: Transaction already in progress (from {$this->mTrxFname}), " .
                                        " performing implicit commit!" );
                        } else {
                                // if the transaction was automatic and has done write operations,
                                // log it if $wgDebugDBTransactions is enabled.

                                if ( $this->mTrxDoneWrites && $wgDebugDBTransactions ) {
                                        wfDebug( "$fname: Automatic transaction with writes in progress (from {$this->mTrxFname}), " .
                                                " performing implicit commit!\n" );
                                }
                        }

                        $this->doCommit( $fname );
                        $this->runOnTransactionIdleCallbacks();
                }

                $this->doBegin( $fname );
                $this->mTrxFname = $fname;
                $this->mTrxDoneWrites = false;
                $this->mTrxAutomatic = false;
        }

        protected function doBegin( $fname ) {
                $this->query( 'BEGIN', $fname );
                $this->mTrxLevel = 1;
        }

        final public function commit( $fname = 'DatabaseBase::commit', $flush = '' ) {
                if ( $flush != 'flush' ) {
                        if ( !$this->mTrxLevel ) {
                                wfWarn( "$fname: No transaction to commit, something got out of sync!" );
                        } elseif( $this->mTrxAutomatic ) {
                                wfWarn( "$fname: Explicit commit of implicit transaction. Something may be out of sync!" );
                        }
                } else {
                        if ( !$this->mTrxLevel ) {
                                return; // nothing to do
                        } elseif( !$this->mTrxAutomatic ) {
                                wfWarn( "$fname: Flushing an explicit transaction, getting out of sync!" );
                        }
                }

                $this->doCommit( $fname );
                $this->runOnTransactionIdleCallbacks();
        }

        protected function doCommit( $fname ) {
                if ( $this->mTrxLevel ) {
                        $this->query( 'COMMIT', $fname );
                        $this->mTrxLevel = 0;
                }
        }

        final public function rollback( $fname = 'DatabaseBase::rollback' ) {
                if ( !$this->mTrxLevel ) {
                        wfWarn( "$fname: No transaction to rollback, something got out of sync!" );
                }
                $this->doRollback( $fname );
                $this->trxIdleCallbacks = array(); // cancel
        }

        protected function doRollback( $fname ) {
                if ( $this->mTrxLevel ) {
                        $this->query( 'ROLLBACK', $fname, true );
                        $this->mTrxLevel = 0;
                }
        }

        public function duplicateTableStructure( $oldName, $newName, $temporary = false,
                $fname = 'DatabaseBase::duplicateTableStructure' )
        {
                throw new MWException(
                        'DatabaseBase::duplicateTableStructure is not implemented in descendant class' );
        }

        function listTables( $prefix = null, $fname = 'DatabaseBase::listTables' ) {
                throw new MWException( 'DatabaseBase::listTables is not implemented in descendant class' );
        }

        public function timestamp( $ts = 0 ) {
                return wfTimestamp( TS_MW, $ts );
        }

        public function timestampOrNull( $ts = null ) {
                if ( is_null( $ts ) ) {
                        return null;
                } else {
                        return $this->timestamp( $ts );
                }
        }

        public function resultObject( $result ) {
                if ( empty( $result ) ) {
                        return false;
                } elseif ( $result instanceof ResultWrapper ) {
                        return $result;
                } elseif ( $result === true ) {
                        // Successful write query
                        return $result;
                } else {
                        return new ResultWrapper( $this, $result );
                }
        }

        public function ping() {
                # Stub.  Not essential to override.
                return true;
        }

        public function getLag() {
                return intval( $this->mFakeSlaveLag );
        }

        function maxListLen() {
                return 0;
        }

        public function encodeBlob( $b ) {
                return $b;
        }

        public function decodeBlob( $b ) {
                return $b;
        }

        public function setSessionOptions( array $options ) {}

        public function sourceFile(
                $filename, $lineCallback = false, $resultCallback = false, $fname = false
        ) {
                wfSuppressWarnings();
                $fp = fopen( $filename, 'r' );
                wfRestoreWarnings();

                if ( false === $fp ) {
                        throw new MWException( "Could not open \"{$filename}\".\n" );
                }

                if ( !$fname ) {
                        $fname = __METHOD__ . "( $filename )";
                }

                try {
                        $error = $this->sourceStream( $fp, $lineCallback, $resultCallback, $fname );
                }
                catch ( MWException $e ) {
                        fclose( $fp );
                        throw $e;
                }

                fclose( $fp );

                return $error;
        }

        public function patchPath( $patch ) {
                global $IP;

                $dbType = $this->getType();
                if ( file_exists( "$IP/maintenance/$dbType/archives/$patch" ) ) {
                        return "$IP/maintenance/$dbType/archives/$patch";
                } else {
                        return "$IP/maintenance/archives/$patch";
                }
        }

        public function setSchemaVars( $vars ) {
                $this->mSchemaVars = $vars;
        }

        public function sourceStream( $fp, $lineCallback = false, $resultCallback = false,
                $fname = 'DatabaseBase::sourceStream', $inputCallback = false )
        {
                $cmd = '';

                while ( !feof( $fp ) ) {
                        if ( $lineCallback ) {
                                call_user_func( $lineCallback );
                        }

                        $line = trim( fgets( $fp ) );

                        if ( $line == '' ) {
                                continue;
                        }

                        if ( '-' == $line[0] && '-' == $line[1] ) {
                                continue;
                        }

                        if ( $cmd != '' ) {
                                $cmd .= ' ';
                        }

                        $done = $this->streamStatementEnd( $cmd, $line );

                        $cmd .= "$line\n";

                        if ( $done || feof( $fp ) ) {
                                $cmd = $this->replaceVars( $cmd );
                                if ( $inputCallback ) {
                                        call_user_func( $inputCallback, $cmd );
                                }
                                $res = $this->query( $cmd, $fname );

                                if ( $resultCallback ) {
                                        call_user_func( $resultCallback, $res, $this );
                                }

                                if ( false === $res ) {
                                        $err = $this->lastError();
                                        return "Query \"{$cmd}\" failed with error code \"$err\".\n";
                                }

                                $cmd = '';
                        }
                }

                return true;
        }

        public function streamStatementEnd( &$sql, &$newLine ) {
                if ( $this->delimiter ) {
                        $prev = $newLine;
                        $newLine = preg_replace( '/' . preg_quote( $this->delimiter, '/' ) . '$/', '', $newLine );
                        if ( $newLine != $prev ) {
                                return true;
                        }
                }
                return false;
        }

        protected function replaceSchemaVars( $ins ) {
                $vars = $this->getSchemaVars();
                foreach ( $vars as $var => $value ) {
                        // replace '{$var}'
                        $ins = str_replace( '\'{$' . $var . '}\'', $this->addQuotes( $value ), $ins );
                        // replace `{$var}`
                        $ins = str_replace( '`{$' . $var . '}`', $this->addIdentifierQuotes( $value ), $ins );
                        // replace /*$var*/
                        $ins = str_replace( '/*$' . $var . '*/', $this->strencode( $value ) , $ins );
                }
                return $ins;
        }

        protected function replaceVars( $ins ) {
                $ins = $this->replaceSchemaVars( $ins );

                // Table prefixes
                $ins = preg_replace_callback( '!/\*(?:\$wgDBprefix|_)\*/([a-zA-Z_0-9]*)!',
                        array( $this, 'tableNameCallback' ), $ins );

                // Index names
                $ins = preg_replace_callback( '!/\*i\*/([a-zA-Z_0-9]*)!',
                        array( $this, 'indexNameCallback' ), $ins );

                return $ins;
        }

        protected function getSchemaVars() {
                if ( $this->mSchemaVars ) {
                        return $this->mSchemaVars;
                } else {
                        return $this->getDefaultSchemaVars();
                }
        }

        protected function getDefaultSchemaVars() {
                return array();
        }

        protected function tableNameCallback( $matches ) {
                return $this->tableName( $matches[1] );
        }

        protected function indexNameCallback( $matches ) {
                return $this->indexName( $matches[1] );
        }

        public function lockIsFree( $lockName, $method ) {
                return true;
        }

        public function lock( $lockName, $method, $timeout = 5 ) {
                return true;
        }

        public function unlock( $lockName, $method ) {
                return true;
        }

        public function lockTables( $read, $write, $method, $lowPriority = true ) {
                return true;
        }

        public function unlockTables( $method ) {
                return true;
        }

        public function dropTable( $tableName, $fName = 'DatabaseBase::dropTable' ) {
                if( !$this->tableExists( $tableName, $fName ) ) {
                        return false;
                }
                $sql = "DROP TABLE " . $this->tableName( $tableName );
                if( $this->cascadingDeletes() ) {
                        $sql .= " CASCADE";
                }
                return $this->query( $sql, $fName );
        }

        public function getSearchEngine() {
                return 'SearchEngineDummy';
        }

        public function getInfinity() {
                return 'infinity';
        }

        public function encodeExpiry( $expiry ) {
                return ( $expiry == '' || $expiry == 'infinity' || $expiry == $this->getInfinity() )
                        ? $this->getInfinity()
                        : $this->timestamp( $expiry );
        }

        public function decodeExpiry( $expiry, $format = TS_MW ) {
                return ( $expiry == '' || $expiry == $this->getInfinity() )
                        ? 'infinity'
                        : wfTimestamp( $format, $expiry );
        }

        public function setBigSelects( $value = true ) {
                // no-op
        }

        public function __toString() {
                return (string)$this->mConn;
        }
}