Database.php

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<?php
namespace Wikimedia\Rdbms;
 
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Wikimedia\ScopedCallback;
use Wikimedia\Timestamp\ConvertibleTimestamp;
use MediaWiki;
use BagOStuff;
use HashBagOStuff;
use InvalidArgumentException;
use Exception;
use RuntimeException;
 
abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAwareInterface {
    const DEADLOCK_TRIES = 4;
    const DEADLOCK_DELAY_MIN = 500000;
    const DEADLOCK_DELAY_MAX = 1500000;
 
    const PING_TTL = 1.0;
    const PING_QUERY = 'SELECT 1 AS ping';
 
    const TINY_WRITE_SEC = .010;
    const SLOW_WRITE_SEC = .500;
    const SMALL_WRITE_ROWS = 100;
 
    protected $mLastQuery = '';
    protected $mLastWriteTime = false;
    protected $mPHPError = false;
    protected $mServer;
    protected $mUser;
    protected $mPassword;
    protected $mDBname;
    protected $tableAliases = [];
    protected $cliMode;
    protected $agent;
 
    protected $srvCache;
    protected $connLogger;
    protected $queryLogger;
    protected $errorLogger;
 
    protected $mConn = null;
    protected $mOpened = false;
 
    protected $mTrxIdleCallbacks = [];
    protected $mTrxPreCommitCallbacks = [];
    protected $mTrxEndCallbacks = [];
    protected $mTrxRecurringCallbacks = [];
    protected $mTrxEndCallbacksSuppressed = false;
 
    protected $mTablePrefix = '';
    protected $mSchema = '';
    protected $mFlags;
    protected $mLBInfo = [];
    protected $mDefaultBigSelects = null;
    protected $mSchemaVars = false;
    protected $mSessionVars = [];
    protected $preparedArgs;
    protected $htmlErrors;
    protected $delimiter = ';';
    protected $currentDomain;
 
    protected $mTrxLevel = 0;
    protected $mTrxShortId = '';
    private $mTrxTimestamp = null;
    private $mTrxReplicaLag = null;
    private $mTrxFname = null;
    private $mTrxDoneWrites = false;
    private $mTrxAutomatic = false;
    private $mTrxAtomicLevels = [];
    private $mTrxAutomaticAtomic = false;
    private $mTrxWriteCallers = [];
    private $mTrxWriteDuration = 0.0;
    private $mTrxWriteQueryCount = 0;
    private $mTrxWriteAdjDuration = 0.0;
    private $mTrxWriteAdjQueryCount = 0;
    private $mRTTEstimate = 0.0;
 
    private $mNamedLocksHeld = [];
    protected $mSessionTempTables = [];
 
    private $lazyMasterHandle;
 
    protected $lastPing = 0.0;
 
    private $priorFlags = [];
 
    protected $profiler;
    protected $trxProfiler;
 
    function __construct( array $params ) {
        $server = $params['host'];
        $user = $params['user'];
        $password = $params['password'];
        $dbName = $params['dbname'];
 
        $this->mSchema = $params['schema'];
        $this->mTablePrefix = $params['tablePrefix'];
 
        $this->cliMode = $params['cliMode'];
        // Agent name is added to SQL queries in a comment, so make sure it can't break out
        $this->agent = str_replace( '/', '-', $params['agent'] );
 
        $this->mFlags = $params['flags'];
        if ( $this->mFlags & self::DBO_DEFAULT ) {
            if ( $this->cliMode ) {
                $this->mFlags &= ~self::DBO_TRX;
            } else {
                $this->mFlags |= self::DBO_TRX;
            }
        }
 
        $this->mSessionVars = $params['variables'];
 
        $this->srvCache = isset( $params['srvCache'] )
            ? $params['srvCache']
            : new HashBagOStuff();
 
        $this->profiler = $params['profiler'];
        $this->trxProfiler = $params['trxProfiler'];
        $this->connLogger = $params['connLogger'];
        $this->queryLogger = $params['queryLogger'];
        $this->errorLogger = $params['errorLogger'];
 
        // Set initial dummy domain until open() sets the final DB/prefix
        $this->currentDomain = DatabaseDomain::newUnspecified();
 
        if ( $user ) {
            $this->open( $server, $user, $password, $dbName );
        } elseif ( $this->requiresDatabaseUser() ) {
            throw new InvalidArgumentException( "No database user provided." );
        }
 
        // Set the domain object after open() sets the relevant fields
        if ( $this->mDBname != '' ) {
            // Domains with server scope but a table prefix are not used by IDatabase classes
            $this->currentDomain = new DatabaseDomain( $this->mDBname, null, $this->mTablePrefix );
        }
    }
 
    final public static function factory( $dbType, $p = [] ) {
        static $canonicalDBTypes = [
            'mysql' => [ 'mysqli', 'mysql' ],
            'postgres' => [],
            'sqlite' => [],
            'oracle' => [],
            'mssql' => [],
        ];
        static $classAliases = [
            'DatabaseMssql' => DatabaseMssql::class,
            'DatabaseMysql' => DatabaseMysql::class,
            'DatabaseMysqli' => DatabaseMysqli::class,
            'DatabaseSqlite' => DatabaseSqlite::class,
            'DatabasePostgres' => DatabasePostgres::class
        ];
 
        $driver = false;
        $dbType = strtolower( $dbType );
        if ( isset( $canonicalDBTypes[$dbType] ) && $canonicalDBTypes[$dbType] ) {
            $possibleDrivers = $canonicalDBTypes[$dbType];
            if ( !empty( $p['driver'] ) ) {
                if ( in_array( $p['driver'], $possibleDrivers ) ) {
                    $driver = $p['driver'];
                } else {
                    throw new InvalidArgumentException( __METHOD__ .
                        " type '$dbType' does not support driver '{$p['driver']}'" );
                }
            } else {
                foreach ( $possibleDrivers as $posDriver ) {
                    if ( extension_loaded( $posDriver ) ) {
                        $driver = $posDriver;
                        break;
                    }
                }
            }
        } else {
            $driver = $dbType;
        }
 
        if ( $driver === false || $driver === '' ) {
            throw new InvalidArgumentException( __METHOD__ .
                " no viable database extension found for type '$dbType'" );
        }
 
        $class = 'Database' . ucfirst( $driver );
        if ( isset( $classAliases[$class] ) ) {
            $class = $classAliases[$class];
        }
 
        if ( class_exists( $class ) && is_subclass_of( $class, IDatabase::class ) ) {
            // Resolve some defaults for b/c
            $p['host'] = isset( $p['host'] ) ? $p['host'] : false;
            $p['user'] = isset( $p['user'] ) ? $p['user'] : false;
            $p['password'] = isset( $p['password'] ) ? $p['password'] : false;
            $p['dbname'] = isset( $p['dbname'] ) ? $p['dbname'] : false;
            $p['flags'] = isset( $p['flags'] ) ? $p['flags'] : 0;
            $p['variables'] = isset( $p['variables'] ) ? $p['variables'] : [];
            $p['tablePrefix'] = isset( $p['tablePrefix'] ) ? $p['tablePrefix'] : '';
            $p['schema'] = isset( $p['schema'] ) ? $p['schema'] : '';
            $p['cliMode'] = isset( $p['cliMode'] ) ? $p['cliMode'] : ( PHP_SAPI === 'cli' );
            $p['agent'] = isset( $p['agent'] ) ? $p['agent'] : '';
            if ( !isset( $p['connLogger'] ) ) {
                $p['connLogger'] = new \Psr\Log\NullLogger();
            }
            if ( !isset( $p['queryLogger'] ) ) {
                $p['queryLogger'] = new \Psr\Log\NullLogger();
            }
            $p['profiler'] = isset( $p['profiler'] ) ? $p['profiler'] : null;
            if ( !isset( $p['trxProfiler'] ) ) {
                $p['trxProfiler'] = new TransactionProfiler();
            }
            if ( !isset( $p['errorLogger'] ) ) {
                $p['errorLogger'] = function ( Exception $e ) {
                    trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
                };
            }
 
            $conn = new $class( $p );
        } else {
            $conn = null;
        }
 
        return $conn;
    }
 
    public function setLogger( LoggerInterface $logger ) {
        $this->queryLogger = $logger;
    }
 
    public function getServerInfo() {
        return $this->getServerVersion();
    }
 
    public function bufferResults( $buffer = null ) {
        $res = !$this->getFlag( self::DBO_NOBUFFER );
        if ( $buffer !== null ) {
            $buffer
                ? $this->clearFlag( self::DBO_NOBUFFER )
                : $this->setFlag( self::DBO_NOBUFFER );
        }
 
        return $res;
    }
 
    protected function ignoreErrors( $ignoreErrors = null ) {
        $res = $this->getFlag( self::DBO_IGNORE );
        if ( $ignoreErrors !== null ) {
            $ignoreErrors
                ? $this->setFlag( self::DBO_IGNORE )
                : $this->clearFlag( self::DBO_IGNORE );
        }
 
        return $res;
    }
 
    public function trxLevel() {
        return $this->mTrxLevel;
    }
 
    public function trxTimestamp() {
        return $this->mTrxLevel ? $this->mTrxTimestamp : null;
    }
 
    public function tablePrefix( $prefix = null ) {
        $old = $this->mTablePrefix;
        if ( $prefix !== null ) {
            $this->mTablePrefix = $prefix;
            $this->currentDomain = ( $this->mDBname != '' )
                ? new DatabaseDomain( $this->mDBname, null, $this->mTablePrefix )
                : DatabaseDomain::newUnspecified();
        }
 
        return $old;
    }
 
    public function dbSchema( $schema = null ) {
        $old = $this->mSchema;
        if ( $schema !== null ) {
            $this->mSchema = $schema;
        }
 
        return $old;
    }
 
    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 setLazyMasterHandle( IDatabase $conn ) {
        $this->lazyMasterHandle = $conn;
    }
 
    protected function getLazyMasterHandle() {
        return $this->lazyMasterHandle;
    }
 
    public function implicitGroupby() {
        return true;
    }
 
    public function implicitOrderby() {
        return true;
    }
 
    public function lastQuery() {
        return $this->mLastQuery;
    }
 
    public function doneWrites() {
        return (bool)$this->mLastWriteTime;
    }
 
    public function lastDoneWrites() {
        return $this->mLastWriteTime ?: false;
    }
 
    public function writesPending() {
        return $this->mTrxLevel && $this->mTrxDoneWrites;
    }
 
    public function writesOrCallbacksPending() {
        return $this->mTrxLevel && (
            $this->mTrxDoneWrites || $this->mTrxIdleCallbacks || $this->mTrxPreCommitCallbacks
        );
    }
 
    public function pendingWriteQueryDuration( $type = self::ESTIMATE_TOTAL ) {
        if ( !$this->mTrxLevel ) {
            return false;
        } elseif ( !$this->mTrxDoneWrites ) {
            return 0.0;
        }
 
        switch ( $type ) {
            case self::ESTIMATE_DB_APPLY:
                $this->ping( $rtt );
                $rttAdjTotal = $this->mTrxWriteAdjQueryCount * $rtt;
                $applyTime = max( $this->mTrxWriteAdjDuration - $rttAdjTotal, 0 );
                // For omitted queries, make them count as something at least
                $omitted = $this->mTrxWriteQueryCount - $this->mTrxWriteAdjQueryCount;
                $applyTime += self::TINY_WRITE_SEC * $omitted;
 
                return $applyTime;
            default: // everything
                return $this->mTrxWriteDuration;
        }
    }
 
    public function pendingWriteCallers() {
        return $this->mTrxLevel ? $this->mTrxWriteCallers : [];
    }
 
    protected function pendingWriteAndCallbackCallers() {
        if ( !$this->mTrxLevel ) {
            return [];
        }
 
        $fnames = $this->mTrxWriteCallers;
        foreach ( [
            $this->mTrxIdleCallbacks,
            $this->mTrxPreCommitCallbacks,
            $this->mTrxEndCallbacks
        ] as $callbacks ) {
            foreach ( $callbacks as $callback ) {
                $fnames[] = $callback[1];
            }
        }
 
        return $fnames;
    }
 
    public function isOpen() {
        return $this->mOpened;
    }
 
    public function setFlag( $flag, $remember = self::REMEMBER_NOTHING ) {
        if ( $remember === self::REMEMBER_PRIOR ) {
            array_push( $this->priorFlags, $this->mFlags );
        }
        $this->mFlags |= $flag;
    }
 
    public function clearFlag( $flag, $remember = self::REMEMBER_NOTHING ) {
        if ( $remember === self::REMEMBER_PRIOR ) {
            array_push( $this->priorFlags, $this->mFlags );
        }
        $this->mFlags &= ~$flag;
    }
 
    public function restoreFlags( $state = self::RESTORE_PRIOR ) {
        if ( !$this->priorFlags ) {
            return;
        }
 
        if ( $state === self::RESTORE_INITIAL ) {
            $this->mFlags = reset( $this->priorFlags );
            $this->priorFlags = [];
        } else {
            $this->mFlags = array_pop( $this->priorFlags );
        }
    }
 
    public function getFlag( $flag ) {
        return !!( $this->mFlags & $flag );
    }
 
    public function getProperty( $name ) {
        return $this->$name;
    }
 
    public function getDomainID() {
        return $this->currentDomain->getId();
    }
 
    final public function getWikiID() {
        return $this->getDomainID();
    }
 
    abstract function indexInfo( $table, $index, $fname = __METHOD__ );
 
    abstract function strencode( $s );
 
    protected function installErrorHandler() {
        $this->mPHPError = false;
        $this->htmlErrors = ini_set( 'html_errors', '0' );
        set_error_handler( [ $this, 'connectionErrorLogger' ] );
    }
 
    protected function restoreErrorHandler() {
        restore_error_handler();
        if ( $this->htmlErrors !== false ) {
            ini_set( 'html_errors', $this->htmlErrors );
        }
 
        return $this->getLastPHPError();
    }
 
    protected function getLastPHPError() {
        if ( $this->mPHPError ) {
            $error = preg_replace( '!\[<a.*</a>\]!', '', $this->mPHPError );
            $error = preg_replace( '!^.*?:\s?(.*)$!', '$1', $error );
 
            return $error;
        }
 
        return false;
    }
 
    public function connectionErrorLogger( $errno, $errstr ) {
        $this->mPHPError = $errstr;
    }
 
    protected function getLogContext( array $extras = [] ) {
        return array_merge(
            [
                'db_server' => $this->mServer,
                'db_name' => $this->mDBname,
                'db_user' => $this->mUser,
            ],
            $extras
        );
    }
 
    public function close() {
        if ( $this->mConn ) {
            if ( $this->trxLevel() ) {
                $this->commit( __METHOD__, self::FLUSHING_INTERNAL );
            }
 
            $closed = $this->closeConnection();
            $this->mConn = false;
        } elseif ( $this->mTrxIdleCallbacks || $this->mTrxEndCallbacks ) { // sanity
            throw new RuntimeException( "Transaction callbacks still pending." );
        } else {
            $closed = true;
        }
        $this->mOpened = false;
 
        return $closed;
    }
 
    protected function assertOpen() {
        if ( !$this->isOpen() ) {
            throw new DBUnexpectedError( $this, "DB connection was already closed." );
        }
    }
 
    abstract protected function closeConnection();
 
    public function reportConnectionError( $error = 'Unknown error' ) {
        $myError = $this->lastError();
        if ( $myError ) {
            $error = $myError;
        }
 
        # New method
        throw new DBConnectionError( $this, $error );
    }
 
    abstract protected function doQuery( $sql );
 
    protected function isWriteQuery( $sql ) {
        return !preg_match(
            '/^(?:SELECT|BEGIN|ROLLBACK|COMMIT|SET|SHOW|EXPLAIN|\‍(SELECT)\b/i', $sql );
    }
 
    protected function getQueryVerb( $sql ) {
        return preg_match( '/^\s*([a-z]+)/i', $sql, $m ) ? strtoupper( $m[1] ) : null;
    }
 
    protected function isTransactableQuery( $sql ) {
        return !in_array(
            $this->getQueryVerb( $sql ),
            [ 'BEGIN', 'COMMIT', 'ROLLBACK', 'SHOW', 'SET', 'CREATE', 'ALTER' ],
            true
        );
    }
 
    protected function registerTempTableOperation( $sql ) {
        if ( preg_match(
            '/^CREATE\s+TEMPORARY\s+TABLE\s+(?:IF\s+NOT\s+EXISTS\s+)?[`"\']?(\w+)[`"\']?/i',
            $sql,
            $matches
        ) ) {
            $this->mSessionTempTables[$matches[1]] = 1;
 
            return true;
        } elseif ( preg_match(
            '/^DROP\s+(?:TEMPORARY\s+)?TABLE\s+(?:IF\s+EXISTS\s+)?[`"\']?(\w+)[`"\']?/i',
            $sql,
            $matches
        ) ) {
            unset( $this->mSessionTempTables[$matches[1]] );
 
            return true;
        } elseif ( preg_match(
            '/^(?:INSERT\s+(?:\w+\s+)?INTO|UPDATE|DELETE\s+FROM)\s+[`"\']?(\w+)[`"\']?/i',
            $sql,
            $matches
        ) ) {
            return isset( $this->mSessionTempTables[$matches[1]] );
        }
 
        return false;
    }
 
    public function query( $sql, $fname = __METHOD__, $tempIgnore = false ) {
        $priorWritesPending = $this->writesOrCallbacksPending();
        $this->mLastQuery = $sql;
 
        $isWrite = $this->isWriteQuery( $sql ) && !$this->registerTempTableOperation( $sql );
        if ( $isWrite ) {
            $reason = $this->getReadOnlyReason();
            if ( $reason !== false ) {
                throw new DBReadOnlyError( $this, "Database is read-only: $reason" );
            }
            # Set a flag indicating that writes have been done
            $this->mLastWriteTime = microtime( true );
        }
 
        // Add trace comment to the begin of the sql string, right after the operator.
        // Or, for one-word queries (like "BEGIN" or COMMIT") add it to the end (T44598)
        $commentedSql = preg_replace( '/\s|$/', " /* $fname {$this->agent} */ ", $sql, 1 );
 
        # Start implicit transactions that wrap the request if DBO_TRX is enabled
        if ( !$this->mTrxLevel && $this->getFlag( self::DBO_TRX )
            && $this->isTransactableQuery( $sql )
        ) {
            $this->begin( __METHOD__ . " ($fname)", self::TRANSACTION_INTERNAL );
            $this->mTrxAutomatic = true;
        }
 
        # Keep track of whether the transaction has write queries pending
        if ( $this->mTrxLevel && !$this->mTrxDoneWrites && $isWrite ) {
            $this->mTrxDoneWrites = true;
            $this->trxProfiler->transactionWritingIn(
                $this->mServer, $this->mDBname, $this->mTrxShortId );
        }
 
        if ( $this->getFlag( self::DBO_DEBUG ) ) {
            $this->queryLogger->debug( "{$this->mDBname} {$commentedSql}" );
        }
 
        # Avoid fatals if close() was called
        $this->assertOpen();
 
        # Send the query to the server
        $ret = $this->doProfiledQuery( $sql, $commentedSql, $isWrite, $fname );
 
        # Try reconnecting if the connection was lost
        if ( false === $ret && $this->wasErrorReissuable() ) {
            $recoverable = $this->canRecoverFromDisconnect( $sql, $priorWritesPending );
            # Stash the last error values before anything might clear them
            $lastError = $this->lastError();
            $lastErrno = $this->lastErrno();
            # Update state tracking to reflect transaction loss due to disconnection
            $this->handleSessionLoss();
            if ( $this->reconnect() ) {
                $msg = __METHOD__ . ": lost connection to {$this->getServer()}; reconnected";
                $this->connLogger->warning( $msg );
                $this->queryLogger->warning(
                    "$msg:\n" . ( new RuntimeException() )->getTraceAsString() );
 
                if ( !$recoverable ) {
                    # Callers may catch the exception and continue to use the DB
                    $this->reportQueryError( $lastError, $lastErrno, $sql, $fname );
                } else {
                    # Should be safe to silently retry the query
                    $ret = $this->doProfiledQuery( $sql, $commentedSql, $isWrite, $fname );
                }
            } else {
                $msg = __METHOD__ . ": lost connection to {$this->getServer()} permanently";
                $this->connLogger->error( $msg );
            }
        }
 
        if ( false === $ret ) {
            # Deadlocks cause the entire transaction to abort, not just the statement.
            # https://dev.mysql.com/doc/refman/5.7/en/innodb-error-handling.html
            # https://www.postgresql.org/docs/9.1/static/explicit-locking.html
            if ( $this->wasDeadlock() ) {
                if ( $this->explicitTrxActive() || $priorWritesPending ) {
                    $tempIgnore = false; // not recoverable
                }
                # Update state tracking to reflect transaction loss
                $this->handleSessionLoss();
            }
 
            $this->reportQueryError(
                $this->lastError(), $this->lastErrno(), $sql, $fname, $tempIgnore );
        }
 
        $res = $this->resultObject( $ret );
 
        return $res;
    }
 
    private function doProfiledQuery( $sql, $commentedSql, $isWrite, $fname ) {
        $isMaster = !is_null( $this->getLBInfo( 'master' ) );
        # 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( self::generalizeSQL( $sql ), 0, 255 );
        } else {
            $queryProf = 'query: ' . substr( self::generalizeSQL( $sql ), 0, 255 );
        }
 
        # Include query transaction state
        $queryProf .= $this->mTrxShortId ? " [TRX#{$this->mTrxShortId}]" : "";
 
        $startTime = microtime( true );
        if ( $this->profiler ) {
            call_user_func( [ $this->profiler, 'profileIn' ], $queryProf );
        }
        $ret = $this->doQuery( $commentedSql );
        if ( $this->profiler ) {
            call_user_func( [ $this->profiler, 'profileOut' ], $queryProf );
        }
        $queryRuntime = max( microtime( true ) - $startTime, 0.0 );
 
        unset( $queryProfSection ); // profile out (if set)
 
        if ( $ret !== false ) {
            $this->lastPing = $startTime;
            if ( $isWrite && $this->mTrxLevel ) {
                $this->updateTrxWriteQueryTime( $sql, $queryRuntime );
                $this->mTrxWriteCallers[] = $fname;
            }
        }
 
        if ( $sql === self::PING_QUERY ) {
            $this->mRTTEstimate = $queryRuntime;
        }
 
        $this->trxProfiler->recordQueryCompletion(
            $queryProf, $startTime, $isWrite, $this->affectedRows()
        );
        $this->queryLogger->debug( $sql, [
            'method' => $fname,
            'master' => $isMaster,
            'runtime' => $queryRuntime,
        ] );
 
        return $ret;
    }
 
    private function updateTrxWriteQueryTime( $sql, $runtime ) {
        // Whether this is indicative of replica DB runtime (except for RBR or ws_repl)
        $indicativeOfReplicaRuntime = true;
        if ( $runtime > self::SLOW_WRITE_SEC ) {
            $verb = $this->getQueryVerb( $sql );
            // insert(), upsert(), replace() are fast unless bulky in size or blocked on locks
            if ( $verb === 'INSERT' ) {
                $indicativeOfReplicaRuntime = $this->affectedRows() > self::SMALL_WRITE_ROWS;
            } elseif ( $verb === 'REPLACE' ) {
                $indicativeOfReplicaRuntime = $this->affectedRows() > self::SMALL_WRITE_ROWS / 2;
            }
        }
 
        $this->mTrxWriteDuration += $runtime;
        $this->mTrxWriteQueryCount += 1;
        if ( $indicativeOfReplicaRuntime ) {
            $this->mTrxWriteAdjDuration += $runtime;
            $this->mTrxWriteAdjQueryCount += 1;
        }
    }
 
    private function canRecoverFromDisconnect( $sql, $priorWritesPending ) {
        # Transaction dropped; this can mean lost writes, or REPEATABLE-READ snapshots.
        # Dropped connections also mean that named locks are automatically released.
        # Only allow error suppression in autocommit mode or when the lost transaction
        # didn't matter anyway (aside from DBO_TRX snapshot loss).
        if ( $this->mNamedLocksHeld ) {
            return false; // possible critical section violation
        } elseif ( $sql === 'COMMIT' ) {
            return !$priorWritesPending; // nothing written anyway? (T127428)
        } elseif ( $sql === 'ROLLBACK' ) {
            return true; // transaction lost...which is also what was requested :)
        } elseif ( $this->explicitTrxActive() ) {
            return false; // don't drop atomocity
        } elseif ( $priorWritesPending ) {
            return false; // prior writes lost from implicit transaction
        }
 
        return true;
    }
 
    private function handleSessionLoss() {
        $this->mTrxLevel = 0;
        $this->mTrxIdleCallbacks = []; // T67263
        $this->mTrxPreCommitCallbacks = []; // T67263
        $this->mSessionTempTables = [];
        $this->mNamedLocksHeld = [];
        try {
            // Handle callbacks in mTrxEndCallbacks
            $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
            $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
            return null;
        } catch ( Exception $e ) {
            // Already logged; move on...
            return $e;
        }
    }
 
    public function reportQueryError( $error, $errno, $sql, $fname, $tempIgnore = false ) {
        if ( $this->ignoreErrors() || $tempIgnore ) {
            $this->queryLogger->debug( "SQL ERROR (ignored): $error\n" );
        } else {
            $sql1line = mb_substr( str_replace( "\n", "\\n", $sql ), 0, 5 * 1024 );
            $this->queryLogger->error(
                "{fname}\t{db_server}\t{errno}\t{error}\t{sql1line}",
                $this->getLogContext( [
                    'method' => __METHOD__,
                    'errno' => $errno,
                    'error' => $error,
                    'sql1line' => $sql1line,
                    'fname' => $fname,
                ] )
            );
            $this->queryLogger->debug( "SQL ERROR: " . $error . "\n" );
            throw new DBQueryError( $this, $error, $errno, $sql, $fname );
        }
    }
 
    public function freeResult( $res ) {
    }
 
    public function selectField(
        $table, $var, $cond = '', $fname = __METHOD__, $options = []
    ) {
        if ( $var === '*' ) { // sanity
            throw new DBUnexpectedError( $this, "Cannot use a * field: got '$var'" );
        }
 
        if ( !is_array( $options ) ) {
            $options = [ $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 selectFieldValues(
        $table, $var, $cond = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        if ( $var === '*' ) { // sanity
            throw new DBUnexpectedError( $this, "Cannot use a * field" );
        } elseif ( !is_string( $var ) ) { // sanity
            throw new DBUnexpectedError( $this, "Cannot use an array of fields" );
        }
 
        if ( !is_array( $options ) ) {
            $options = [ $options ];
        }
 
        $res = $this->select( $table, $var, $cond, $fname, $options, $join_conds );
        if ( $res === false ) {
            return false;
        }
 
        $values = [];
        foreach ( $res as $row ) {
            $values[] = $row->$var;
        }
 
        return $values;
    }
 
    protected function makeSelectOptions( $options ) {
        $preLimitTail = $postLimitTail = '';
        $startOpts = '';
 
        $noKeyOptions = [];
 
        foreach ( $options as $key => $option ) {
            if ( is_numeric( $key ) ) {
                $noKeyOptions[$option] = true;
            }
        }
 
        $preLimitTail .= $this->makeGroupByWithHaving( $options );
 
        $preLimitTail .= $this->makeOrderBy( $options );
 
        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_string( $options['USE INDEX'] ) ) {
            $useIndex = $this->useIndexClause( $options['USE INDEX'] );
        } else {
            $useIndex = '';
        }
        if ( isset( $options['IGNORE INDEX'] ) && is_string( $options['IGNORE INDEX'] ) ) {
            $ignoreIndex = $this->ignoreIndexClause( $options['IGNORE INDEX'] );
        } else {
            $ignoreIndex = '';
        }
 
        return [ $startOpts, $useIndex, $preLimitTail, $postLimitTail, $ignoreIndex ];
    }
 
    protected function makeGroupByWithHaving( $options ) {
        $sql = '';
        if ( isset( $options['GROUP BY'] ) ) {
            $gb = is_array( $options['GROUP BY'] )
                ? implode( ',', $options['GROUP BY'] )
                : $options['GROUP BY'];
            $sql .= ' GROUP BY ' . $gb;
        }
        if ( isset( $options['HAVING'] ) ) {
            $having = is_array( $options['HAVING'] )
                ? $this->makeList( $options['HAVING'], self::LIST_AND )
                : $options['HAVING'];
            $sql .= ' HAVING ' . $having;
        }
 
        return $sql;
    }
 
    protected function makeOrderBy( $options ) {
        if ( isset( $options['ORDER BY'] ) ) {
            $ob = is_array( $options['ORDER BY'] )
                ? implode( ',', $options['ORDER BY'] )
                : $options['ORDER BY'];
 
            return ' ORDER BY ' . $ob;
        }
 
        return '';
    }
 
    public function select( $table, $vars, $conds = '', $fname = __METHOD__,
        $options = [], $join_conds = [] ) {
        $sql = $this->selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds );
 
        return $this->query( $sql, $fname );
    }
 
    public function selectSQLText( $table, $vars, $conds = '', $fname = __METHOD__,
        $options = [], $join_conds = []
    ) {
        if ( is_array( $vars ) ) {
            $vars = implode( ',', $this->fieldNamesWithAlias( $vars ) );
        }
 
        $options = (array)$options;
        $useIndexes = ( isset( $options['USE INDEX'] ) && is_array( $options['USE INDEX'] ) )
            ? $options['USE INDEX']
            : [];
        $ignoreIndexes = (
            isset( $options['IGNORE INDEX'] ) &&
            is_array( $options['IGNORE INDEX'] )
        )
            ? $options['IGNORE INDEX']
            : [];
 
        if ( is_array( $table ) ) {
            $from = ' FROM ' .
                $this->tableNamesWithIndexClauseOrJOIN(
                    $table, $useIndexes, $ignoreIndexes, $join_conds );
        } elseif ( $table != '' ) {
            if ( $table[0] == ' ' ) {
                $from = ' FROM ' . $table;
            } else {
                $from = ' FROM ' .
                    $this->tableNamesWithIndexClauseOrJOIN(
                        [ $table ], $useIndexes, $ignoreIndexes, [] );
            }
        } else {
            $from = '';
        }
 
        list( $startOpts, $useIndex, $preLimitTail, $postLimitTail, $ignoreIndex ) =
            $this->makeSelectOptions( $options );
 
        if ( !empty( $conds ) ) {
            if ( is_array( $conds ) ) {
                $conds = $this->makeList( $conds, self::LIST_AND );
            }
            $sql = "SELECT $startOpts $vars $from $useIndex $ignoreIndex " .
                "WHERE $conds $preLimitTail";
        } else {
            $sql = "SELECT $startOpts $vars $from $useIndex $ignoreIndex $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 = __METHOD__,
        $options = [], $join_conds = []
    ) {
        $options = (array)$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 = __METHOD__, $options = []
    ) {
        $rows = 0;
        $res = $this->select( $table, [ 'rowcount' => 'COUNT(*)' ], $conds, $fname, $options );
 
        if ( $res ) {
            $row = $this->fetchRow( $res );
            $rows = ( isset( $row['rowcount'] ) ) ? (int)$row['rowcount'] : 0;
        }
 
        return $rows;
    }
 
    public function selectRowCount(
        $tables, $vars = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        $rows = 0;
        $sql = $this->selectSQLText( $tables, '1', $conds, $fname, $options, $join_conds );
        // The identifier quotes is primarily for MSSQL.
        $rowCountCol = $this->addIdentifierQuotes( "rowcount" );
        $tableName = $this->addIdentifierQuotes( "tmp_count" );
        $res = $this->query( "SELECT COUNT(*) AS $rowCountCol FROM ($sql) $tableName", $fname );
 
        if ( $res ) {
            $row = $this->fetchRow( $res );
            $rows = ( isset( $row['rowcount'] ) ) ? (int)$row['rowcount'] : 0;
        }
 
        return $rows;
    }
 
    protected 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,
        # except the ones surrounded by characters, e.g. l10n
        $sql = preg_replace( '/-?\d+(,-?\d+)+/s', 'N,...,N', $sql );
        $sql = preg_replace( '/(?<![a-zA-Z])-?\d+(?![a-zA-Z])/s', 'N', $sql );
 
        return $sql;
    }
 
    public function fieldExists( $table, $field, $fname = __METHOD__ ) {
        $info = $this->fieldInfo( $table, $field );
 
        return (bool)$info;
    }
 
    public function indexExists( $table, $index, $fname = __METHOD__ ) {
        if ( !$this->tableExists( $table ) ) {
            return null;
        }
 
        $info = $this->indexInfo( $table, $index, $fname );
        if ( is_null( $info ) ) {
            return null;
        } else {
            return $info !== false;
        }
    }
 
    public function tableExists( $table, $fname = __METHOD__ ) {
        $tableRaw = $this->tableName( $table, 'raw' );
        if ( isset( $this->mSessionTempTables[$tableRaw] ) ) {
            return true; // already known to exist
        }
 
        $table = $this->tableName( $table );
        $ignoreErrors = true;
        $res = $this->query( "SELECT 1 FROM $table LIMIT 1", $fname, $ignoreErrors );
 
        return (bool)$res;
    }
 
    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 = __METHOD__, $options = [] ) {
        # No rows to insert, easy just return now
        if ( !count( $a ) ) {
            return true;
        }
 
        $table = $this->tableName( $table );
 
        if ( !is_array( $options ) ) {
            $options = [ $options ];
        }
 
        $fh = null;
        if ( isset( $options['fileHandle'] ) ) {
            $fh = $options['fileHandle'];
        }
        $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 ) . ')';
        }
 
        if ( $fh !== null && false === fwrite( $fh, $sql ) ) {
            return false;
        } elseif ( $fh !== null ) {
            return true;
        }
 
        return (bool)$this->query( $sql, $fname );
    }
 
    protected function makeUpdateOptionsArray( $options ) {
        if ( !is_array( $options ) ) {
            $options = [ $options ];
        }
 
        $opts = [];
 
        if ( in_array( 'IGNORE', $options ) ) {
            $opts[] = 'IGNORE';
        }
 
        return $opts;
    }
 
    protected function makeUpdateOptions( $options ) {
        $opts = $this->makeUpdateOptionsArray( $options );
 
        return implode( ' ', $opts );
    }
 
    public function update( $table, $values, $conds, $fname = __METHOD__, $options = [] ) {
        $table = $this->tableName( $table );
        $opts = $this->makeUpdateOptions( $options );
        $sql = "UPDATE $opts $table SET " . $this->makeList( $values, self::LIST_SET );
 
        if ( $conds !== [] && $conds !== '*' ) {
            $sql .= " WHERE " . $this->makeList( $conds, self::LIST_AND );
        }
 
        return (bool)$this->query( $sql, $fname );
    }
 
    public function makeList( $a, $mode = self::LIST_COMMA ) {
        if ( !is_array( $a ) ) {
            throw new DBUnexpectedError( $this, __METHOD__ . ' called with incorrect parameters' );
        }
 
        $first = true;
        $list = '';
 
        foreach ( $a as $field => $value ) {
            if ( !$first ) {
                if ( $mode == self::LIST_AND ) {
                    $list .= ' AND ';
                } elseif ( $mode == self::LIST_OR ) {
                    $list .= ' OR ';
                } else {
                    $list .= ',';
                }
            } else {
                $first = false;
            }
 
            if ( ( $mode == self::LIST_AND || $mode == self::LIST_OR ) && is_numeric( $field ) ) {
                $list .= "($value)";
            } elseif ( $mode == self::LIST_SET && is_numeric( $field ) ) {
                $list .= "$value";
            } elseif (
                ( $mode == self::LIST_AND || $mode == self::LIST_OR ) && is_array( $value )
            ) {
                // Remove null from array to be handled separately if found
                $includeNull = false;
                foreach ( array_keys( $value, null, true ) as $nullKey ) {
                    $includeNull = true;
                    unset( $value[$nullKey] );
                }
                if ( count( $value ) == 0 && !$includeNull ) {
                    throw new InvalidArgumentException(
                        __METHOD__ . ": empty input for field $field" );
                } elseif ( count( $value ) == 0 ) {
                    // only check if $field is null
                    $list .= "$field IS NULL";
                } else {
                    // IN clause contains at least one valid element
                    if ( $includeNull ) {
                        // Group subconditions to ensure correct precedence
                        $list .= '(';
                    }
                    if ( 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 )[0];
                        $list .= $field . " = " . $this->addQuotes( $value );
                    } else {
                        $list .= $field . " IN (" . $this->makeList( $value ) . ") ";
                    }
                    // if null present in array, append IS NULL
                    if ( $includeNull ) {
                        $list .= " OR $field IS NULL)";
                    }
                }
            } elseif ( $value === null ) {
                if ( $mode == self::LIST_AND || $mode == self::LIST_OR ) {
                    $list .= "$field IS ";
                } elseif ( $mode == self::LIST_SET ) {
                    $list .= "$field = ";
                }
                $list .= 'NULL';
            } else {
                if (
                    $mode == self::LIST_AND || $mode == self::LIST_OR || $mode == self::LIST_SET
                ) {
                    $list .= "$field = ";
                }
                $list .= $mode == self::LIST_NAMES ? $value : $this->addQuotes( $value );
            }
        }
 
        return $list;
    }
 
    public function makeWhereFrom2d( $data, $baseKey, $subKey ) {
        $conds = [];
 
        foreach ( $data as $base => $sub ) {
            if ( count( $sub ) ) {
                $conds[] = $this->makeList(
                    [ $baseKey => $base, $subKey => array_keys( $sub ) ],
                    self::LIST_AND );
            }
        }
 
        if ( $conds ) {
            return $this->makeList( $conds, self::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 buildGroupConcatField(
        $delim, $table, $field, $conds = '', $join_conds = []
    ) {
        $fld = "GROUP_CONCAT($field SEPARATOR " . $this->addQuotes( $delim ) . ')';
 
        return '(' . $this->selectSQLText( $table, $fld, $conds, null, [], $join_conds ) . ')';
    }
 
    public function buildStringCast( $field ) {
        return $field;
    }
 
    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' ) {
        # 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 = explode( '.', $name, 3 );
        if ( count( $dbDetails ) == 3 ) {
            list( $database, $schema, $table ) = $dbDetails;
            # We don't want any prefix added in this case
            $prefix = '';
        } elseif ( count( $dbDetails ) == 2 ) {
            list( $database, $table ) = $dbDetails;
            # We don't want any prefix added in this case
            $prefix = '';
            # In dbs that support it, $database may actually be the schema
            # but that doesn't affect any of the functionality here
            $schema = '';
        } else {
            list( $table ) = $dbDetails;
            if ( isset( $this->tableAliases[$table] ) ) {
                $database = $this->tableAliases[$table]['dbname'];
                $schema = is_string( $this->tableAliases[$table]['schema'] )
                    ? $this->tableAliases[$table]['schema']
                    : $this->mSchema;
                $prefix = is_string( $this->tableAliases[$table]['prefix'] )
                    ? $this->tableAliases[$table]['prefix']
                    : $this->mTablePrefix;
            } else {
                $database = '';
                $schema = $this->mSchema; # Default schema
                $prefix = $this->mTablePrefix; # Default prefix
            }
        }
 
        # Quote $table and apply the prefix if not quoted.
        # $tableName might be empty if this is called from Database::replaceVars()
        $tableName = "{$prefix}{$table}";
        if ( $format === 'quoted'
            && !$this->isQuotedIdentifier( $tableName )
            && $tableName !== ''
        ) {
            $tableName = $this->addIdentifierQuotes( $tableName );
        }
 
        # Quote $schema and $database and merge them with the table name if needed
        $tableName = $this->prependDatabaseOrSchema( $schema, $tableName, $format );
        $tableName = $this->prependDatabaseOrSchema( $database, $tableName, $format );
 
        return $tableName;
    }
 
    private function prependDatabaseOrSchema( $namespace, $relation, $format ) {
        if ( strlen( $namespace ) ) {
            if ( $format === 'quoted' && !$this->isQuotedIdentifier( $namespace ) ) {
                $namespace = $this->addIdentifierQuotes( $namespace );
            }
            $relation = $namespace . '.' . $relation;
        }
 
        return $relation;
    }
 
    public function tableNames() {
        $inArray = func_get_args();
        $retVal = [];
 
        foreach ( $inArray as $name ) {
            $retVal[$name] = $this->tableName( $name );
        }
 
        return $retVal;
    }
 
    public function tableNamesN() {
        $inArray = func_get_args();
        $retVal = [];
 
        foreach ( $inArray as $name ) {
            $retVal[] = $this->tableName( $name );
        }
 
        return $retVal;
    }
 
    protected function tableNameWithAlias( $name, $alias = false ) {
        if ( !$alias || $alias == $name ) {
            return $this->tableName( $name );
        } else {
            return $this->tableName( $name ) . ' ' . $this->addIdentifierQuotes( $alias );
        }
    }
 
    protected function tableNamesWithAlias( $tables ) {
        $retval = [];
        foreach ( $tables as $alias => $table ) {
            if ( is_numeric( $alias ) ) {
                $alias = $table;
            }
            $retval[] = $this->tableNameWithAlias( $table, $alias );
        }
 
        return $retval;
    }
 
    protected function fieldNameWithAlias( $name, $alias = false ) {
        if ( !$alias || (string)$alias === (string)$name ) {
            return $name;
        } else {
            return $name . ' AS ' . $this->addIdentifierQuotes( $alias ); // PostgreSQL needs AS
        }
    }
 
    protected function fieldNamesWithAlias( $fields ) {
        $retval = [];
        foreach ( $fields as $alias => $field ) {
            if ( is_numeric( $alias ) ) {
                $alias = $field;
            }
            $retval[] = $this->fieldNameWithAlias( $field, $alias );
        }
 
        return $retval;
    }
 
    protected function tableNamesWithIndexClauseOrJOIN(
        $tables, $use_index = [], $ignore_index = [], $join_conds = []
    ) {
        $ret = [];
        $retJOIN = [];
        $use_index = (array)$use_index;
        $ignore_index = (array)$ignore_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;
                    }
                }
                if ( isset( $ignore_index[$alias] ) ) { // has IGNORE INDEX?
                    $ignore = $this->ignoreIndexClause(
                        implode( ',', (array)$ignore_index[$alias] ) );
                    if ( $ignore != '' ) {
                        $tableClause .= ' ' . $ignore;
                    }
                }
                $on = $this->makeList( (array)$conds, self::LIST_AND );
                if ( $on != '' ) {
                    $tableClause .= ' ON (' . $on . ')';
                }
 
                $retJOIN[] = $tableClause;
            } elseif ( isset( $use_index[$alias] ) ) {
                // Is there an INDEX clause for this table?
                $tableClause = $this->tableNameWithAlias( $table, $alias );
                $tableClause .= ' ' . $this->useIndexClause(
                        implode( ',', (array)$use_index[$alias] )
                    );
 
                $ret[] = $tableClause;
            } elseif ( isset( $ignore_index[$alias] ) ) {
                // Is there an INDEX clause for this table?
                $tableClause = $this->tableNameWithAlias( $table, $alias );
                $tableClause .= ' ' . $this->ignoreIndexClause(
                        implode( ',', (array)$ignore_index[$alias] )
                    );
 
                $ret[] = $tableClause;
            } else {
                $tableClause = $this->tableNameWithAlias( $table, $alias );
 
                $ret[] = $tableClause;
            }
        }
 
        // We can't separate explicit JOIN clauses with ',', use ' ' for those
        $implicitJoins = !empty( $ret ) ? implode( ',', $ret ) : "";
        $explicitJoins = !empty( $retJOIN ) ? implode( ' ', $retJOIN ) : "";
 
        // Compile our final table clause
        return implode( ' ', [ $implicitJoins, $explicitJoins ] );
    }
 
    protected function indexName( $index ) {
        return $index;
    }
 
    public function addQuotes( $s ) {
        if ( $s instanceof Blob ) {
            $s = $s->fetch();
        }
        if ( $s === null ) {
            return 'NULL';
        } elseif ( is_bool( $s ) ) {
            return (int)$s;
        } 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, $escapeChar = '`' ) {
        return str_replace( [ $escapeChar, '%', '_' ],
            [ "{$escapeChar}{$escapeChar}", "{$escapeChar}%", "{$escapeChar}_" ],
            $s );
    }
 
    public function buildLike() {
        $params = func_get_args();
 
        if ( count( $params ) > 0 && is_array( $params[0] ) ) {
            $params = $params[0];
        }
 
        $s = '';
 
        // We use ` instead of \ as the default LIKE escape character, since addQuotes()
        // may escape backslashes, creating problems of double escaping. The `
        // character has good cross-DBMS compatibility, avoiding special operators
        // in MS SQL like ^ and %
        $escapeChar = '`';
 
        foreach ( $params as $value ) {
            if ( $value instanceof LikeMatch ) {
                $s .= $value->toString();
            } else {
                $s .= $this->escapeLikeInternal( $value, $escapeChar );
            }
        }
 
        return ' LIKE ' . $this->addQuotes( $s ) . ' ESCAPE ' . $this->addQuotes( $escapeChar ) . ' ';
    }
 
    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 ignoreIndexClause( $index ) {
        return '';
    }
 
    public function replace( $table, $uniqueIndexes, $rows, $fname = __METHOD__ ) {
        $quotedTable = $this->tableName( $table );
 
        if ( count( $rows ) == 0 ) {
            return;
        }
 
        # Single row case
        if ( !is_array( reset( $rows ) ) ) {
            $rows = [ $rows ];
        }
 
        // @FXIME: this is not atomic, but a trx would break affectedRows()
        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, $fname );
        }
    }
 
    protected function nativeReplace( $table, $rows, $fname ) {
        $table = $this->tableName( $table );
 
        # Single row case
        if ( !is_array( reset( $rows ) ) ) {
            $rows = [ $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 upsert( $table, array $rows, array $uniqueIndexes, array $set,
        $fname = __METHOD__
    ) {
        if ( !count( $rows ) ) {
            return true; // nothing to do
        }
 
        if ( !is_array( reset( $rows ) ) ) {
            $rows = [ $rows ];
        }
 
        if ( count( $uniqueIndexes ) ) {
            $clauses = []; // list WHERE clauses that each identify a single row
            foreach ( $rows as $row ) {
                foreach ( $uniqueIndexes as $index ) {
                    $index = is_array( $index ) ? $index : [ $index ]; // columns
                    $rowKey = []; // unique key to this row
                    foreach ( $index as $column ) {
                        $rowKey[$column] = $row[$column];
                    }
                    $clauses[] = $this->makeList( $rowKey, self::LIST_AND );
                }
            }
            $where = [ $this->makeList( $clauses, self::LIST_OR ) ];
        } else {
            $where = false;
        }
 
        $useTrx = !$this->mTrxLevel;
        if ( $useTrx ) {
            $this->begin( $fname, self::TRANSACTION_INTERNAL );
        }
        try {
            # Update any existing conflicting row(s)
            if ( $where !== false ) {
                $ok = $this->update( $table, $set, $where, $fname );
            } else {
                $ok = true;
            }
            # Now insert any non-conflicting row(s)
            $ok = $this->insert( $table, $rows, $fname, [ 'IGNORE' ] ) && $ok;
        } catch ( Exception $e ) {
            if ( $useTrx ) {
                $this->rollback( $fname, self::FLUSHING_INTERNAL );
            }
            throw $e;
        }
        if ( $useTrx ) {
            $this->commit( $fname, self::FLUSHING_INTERNAL );
        }
 
        return $ok;
    }
 
    public function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds,
        $fname = __METHOD__
    ) {
        if ( !$conds ) {
            throw new DBUnexpectedError( $this, __METHOD__ . ' 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, self::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, __METHOD__ );
        $row = $this->fetchObject( $res );
 
        $m = [];
 
        if ( preg_match( '/\‍((.*)\‍)/', $row->Type, $m ) ) {
            $size = $m[1];
        } else {
            $size = -1;
        }
 
        return $size;
    }
 
    public function delete( $table, $conds, $fname = __METHOD__ ) {
        if ( !$conds ) {
            throw new DBUnexpectedError( $this, __METHOD__ . ' called with no conditions' );
        }
 
        $table = $this->tableName( $table );
        $sql = "DELETE FROM $table";
 
        if ( $conds != '*' ) {
            if ( is_array( $conds ) ) {
                $conds = $this->makeList( $conds, self::LIST_AND );
            }
            $sql .= ' WHERE ' . $conds;
        }
 
        return $this->query( $sql, $fname );
    }
 
    public function insertSelect(
        $destTable, $srcTable, $varMap, $conds,
        $fname = __METHOD__, $insertOptions = [], $selectOptions = []
    ) {
        if ( $this->cliMode ) {
            // For massive migrations with downtime, we don't want to select everything
            // into memory and OOM, so do all this native on the server side if possible.
            return $this->nativeInsertSelect(
                $destTable,
                $srcTable,
                $varMap,
                $conds,
                $fname,
                $insertOptions,
                $selectOptions
            );
        }
 
        // For web requests, do a locking SELECT and then INSERT. This puts the SELECT burden
        // on only the master (without needing row-based-replication). It also makes it easy to
        // know how big the INSERT is going to be.
        $fields = [];
        foreach ( $varMap as $dstColumn => $sourceColumnOrSql ) {
            $fields[] = $this->fieldNameWithAlias( $sourceColumnOrSql, $dstColumn );
        }
        $selectOptions[] = 'FOR UPDATE';
        $res = $this->select( $srcTable, implode( ',', $fields ), $conds, $fname, $selectOptions );
        if ( !$res ) {
            return false;
        }
 
        $rows = [];
        foreach ( $res as $row ) {
            $rows[] = (array)$row;
        }
 
        return $this->insert( $destTable, $rows, $fname, $insertOptions );
    }
 
    protected function nativeInsertSelect( $destTable, $srcTable, $varMap, $conds,
        $fname = __METHOD__,
        $insertOptions = [], $selectOptions = []
    ) {
        $destTable = $this->tableName( $destTable );
 
        if ( !is_array( $insertOptions ) ) {
            $insertOptions = [ $insertOptions ];
        }
 
        $insertOptions = $this->makeInsertOptions( $insertOptions );
 
        if ( !is_array( $selectOptions ) ) {
            $selectOptions = [ $selectOptions ];
        }
 
        list( $startOpts, $useIndex, $tailOpts, $ignoreIndex ) = $this->makeSelectOptions(
            $selectOptions );
 
        if ( is_array( $srcTable ) ) {
            $srcTable = implode( ',', array_map( [ $this, 'tableName' ], $srcTable ) );
        } else {
            $srcTable = $this->tableName( $srcTable );
        }
 
        $sql = "INSERT $insertOptions" .
            " INTO $destTable (" . implode( ',', array_keys( $varMap ) ) . ')' .
            " SELECT $startOpts " . implode( ',', $varMap ) .
            " FROM $srcTable $useIndex $ignoreIndex ";
 
        if ( $conds != '*' ) {
            if ( is_array( $conds ) ) {
                $conds = $this->makeList( $conds, self::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, self::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 wasConnectionError( $errno ) {
        return false;
    }
 
    public function deadlockLoop() {
        $args = func_get_args();
        $function = array_shift( $args );
        $tries = self::DEADLOCK_TRIES;
 
        $this->begin( __METHOD__ );
 
        $retVal = null;
        $e = null;
        do {
            try {
                $retVal = call_user_func_array( $function, $args );
                break;
            } catch ( DBQueryError $e ) {
                if ( $this->wasDeadlock() ) {
                    // Retry after a randomized delay
                    usleep( mt_rand( self::DEADLOCK_DELAY_MIN, self::DEADLOCK_DELAY_MAX ) );
                } else {
                    // Throw the error back up
                    throw $e;
                }
            }
        } while ( --$tries > 0 );
 
        if ( $tries <= 0 ) {
            // Too many deadlocks; give up
            $this->rollback( __METHOD__ );
            throw $e;
        } else {
            $this->commit( __METHOD__ );
 
            return $retVal;
        }
    }
 
    public function masterPosWait( DBMasterPos $pos, $timeout ) {
        # Real waits are implemented in the subclass.
        return 0;
    }
 
    public function getReplicaPos() {
        # Stub
        return false;
    }
 
    public function getMasterPos() {
        # Stub
        return false;
    }
 
    public function serverIsReadOnly() {
        return false;
    }
 
    final public function onTransactionResolution( callable $callback, $fname = __METHOD__ ) {
        if ( !$this->mTrxLevel ) {
            throw new DBUnexpectedError( $this, "No transaction is active." );
        }
        $this->mTrxEndCallbacks[] = [ $callback, $fname ];
    }
 
    final public function onTransactionIdle( callable $callback, $fname = __METHOD__ ) {
        $this->mTrxIdleCallbacks[] = [ $callback, $fname ];
        if ( !$this->mTrxLevel ) {
            $this->runOnTransactionIdleCallbacks( self::TRIGGER_IDLE );
        }
    }
 
    final public function onTransactionPreCommitOrIdle( callable $callback, $fname = __METHOD__ ) {
        if ( $this->mTrxLevel ) {
            $this->mTrxPreCommitCallbacks[] = [ $callback, $fname ];
        } else {
            // If no transaction is active, then make one for this callback
            $this->startAtomic( __METHOD__ );
            try {
                call_user_func( $callback );
                $this->endAtomic( __METHOD__ );
            } catch ( Exception $e ) {
                $this->rollback( __METHOD__, self::FLUSHING_INTERNAL );
                throw $e;
            }
        }
    }
 
    final public function setTransactionListener( $name, callable $callback = null ) {
        if ( $callback ) {
            $this->mTrxRecurringCallbacks[$name] = $callback;
        } else {
            unset( $this->mTrxRecurringCallbacks[$name] );
        }
    }
 
    final public function setTrxEndCallbackSuppression( $suppress ) {
        $this->mTrxEndCallbacksSuppressed = $suppress;
    }
 
    public function runOnTransactionIdleCallbacks( $trigger ) {
        if ( $this->mTrxEndCallbacksSuppressed ) {
            return;
        }
 
        $autoTrx = $this->getFlag( self::DBO_TRX ); // automatic begin() enabled?
        $e = null; // first exception
        do { // callbacks may add callbacks :)
            $callbacks = array_merge(
                $this->mTrxIdleCallbacks,
                $this->mTrxEndCallbacks // include "transaction resolution" callbacks
            );
            $this->mTrxIdleCallbacks = []; // consumed (and recursion guard)
            $this->mTrxEndCallbacks = []; // consumed (recursion guard)
            foreach ( $callbacks as $callback ) {
                try {
                    list( $phpCallback ) = $callback;
                    $this->clearFlag( self::DBO_TRX ); // make each query its own transaction
                    call_user_func_array( $phpCallback, [ $trigger ] );
                    if ( $autoTrx ) {
                        $this->setFlag( self::DBO_TRX ); // restore automatic begin()
                    } else {
                        $this->clearFlag( self::DBO_TRX ); // restore auto-commit
                    }
                } catch ( Exception $ex ) {
                    call_user_func( $this->errorLogger, $ex );
                    $e = $e ?: $ex;
                    // Some callbacks may use startAtomic/endAtomic, so make sure
                    // their transactions are ended so other callbacks don't fail
                    if ( $this->trxLevel() ) {
                        $this->rollback( __METHOD__, self::FLUSHING_INTERNAL );
                    }
                }
            }
        } while ( count( $this->mTrxIdleCallbacks ) );
 
        if ( $e instanceof Exception ) {
            throw $e; // re-throw any first exception
        }
    }
 
    public function runOnTransactionPreCommitCallbacks() {
        $e = null; // first exception
        do { // callbacks may add callbacks :)
            $callbacks = $this->mTrxPreCommitCallbacks;
            $this->mTrxPreCommitCallbacks = []; // consumed (and recursion guard)
            foreach ( $callbacks as $callback ) {
                try {
                    list( $phpCallback ) = $callback;
                    call_user_func( $phpCallback );
                } catch ( Exception $ex ) {
                    call_user_func( $this->errorLogger, $ex );
                    $e = $e ?: $ex;
                }
            }
        } while ( count( $this->mTrxPreCommitCallbacks ) );
 
        if ( $e instanceof Exception ) {
            throw $e; // re-throw any first exception
        }
    }
 
    public function runTransactionListenerCallbacks( $trigger ) {
        if ( $this->mTrxEndCallbacksSuppressed ) {
            return;
        }
 
        $e = null; // first exception
 
        foreach ( $this->mTrxRecurringCallbacks as $phpCallback ) {
            try {
                $phpCallback( $trigger, $this );
            } catch ( Exception $ex ) {
                call_user_func( $this->errorLogger, $ex );
                $e = $e ?: $ex;
            }
        }
 
        if ( $e instanceof Exception ) {
            throw $e; // re-throw any first exception
        }
    }
 
    final public function startAtomic( $fname = __METHOD__ ) {
        if ( !$this->mTrxLevel ) {
            $this->begin( $fname, self::TRANSACTION_INTERNAL );
            // If DBO_TRX is set, a series of startAtomic/endAtomic pairs will result
            // in all changes being in one transaction to keep requests transactional.
            if ( !$this->getFlag( self::DBO_TRX ) ) {
                $this->mTrxAutomaticAtomic = true;
            }
        }
 
        $this->mTrxAtomicLevels[] = $fname;
    }
 
    final public function endAtomic( $fname = __METHOD__ ) {
        if ( !$this->mTrxLevel ) {
            throw new DBUnexpectedError( $this, "No atomic transaction is open (got $fname)." );
        }
        if ( !$this->mTrxAtomicLevels ||
            array_pop( $this->mTrxAtomicLevels ) !== $fname
        ) {
            throw new DBUnexpectedError( $this, "Invalid atomic section ended (got $fname)." );
        }
 
        if ( !$this->mTrxAtomicLevels && $this->mTrxAutomaticAtomic ) {
            $this->commit( $fname, self::FLUSHING_INTERNAL );
        }
    }
 
    final public function doAtomicSection( $fname, callable $callback ) {
        $this->startAtomic( $fname );
        try {
            $res = call_user_func_array( $callback, [ $this, $fname ] );
        } catch ( Exception $e ) {
            $this->rollback( $fname, self::FLUSHING_INTERNAL );
            throw $e;
        }
        $this->endAtomic( $fname );
 
        return $res;
    }
 
    final public function begin( $fname = __METHOD__, $mode = self::TRANSACTION_EXPLICIT ) {
        // Protect against mismatched atomic section, transaction nesting, and snapshot loss
        if ( $this->mTrxLevel ) {
            if ( $this->mTrxAtomicLevels ) {
                $levels = implode( ', ', $this->mTrxAtomicLevels );
                $msg = "$fname: Got explicit BEGIN while atomic section(s) $levels are open.";
                throw new DBUnexpectedError( $this, $msg );
            } elseif ( !$this->mTrxAutomatic ) {
                $msg = "$fname: Explicit transaction already active (from {$this->mTrxFname}).";
                throw new DBUnexpectedError( $this, $msg );
            } else {
                // @TODO: make this an exception at some point
                $msg = "$fname: Implicit transaction already active (from {$this->mTrxFname}).";
                $this->queryLogger->error( $msg );
                return; // join the main transaction set
            }
        } elseif ( $this->getFlag( self::DBO_TRX ) && $mode !== self::TRANSACTION_INTERNAL ) {
            // @TODO: make this an exception at some point
            $msg = "$fname: Implicit transaction expected (DBO_TRX set).";
            $this->queryLogger->error( $msg );
            return; // let any writes be in the main transaction
        }
 
        // Avoid fatals if close() was called
        $this->assertOpen();
 
        $this->doBegin( $fname );
        $this->mTrxTimestamp = microtime( true );
        $this->mTrxFname = $fname;
        $this->mTrxDoneWrites = false;
        $this->mTrxAutomaticAtomic = false;
        $this->mTrxAtomicLevels = [];
        $this->mTrxShortId = sprintf( '%06x', mt_rand( 0, 0xffffff ) );
        $this->mTrxWriteDuration = 0.0;
        $this->mTrxWriteQueryCount = 0;
        $this->mTrxWriteAdjDuration = 0.0;
        $this->mTrxWriteAdjQueryCount = 0;
        $this->mTrxWriteCallers = [];
        // First SELECT after BEGIN will establish the snapshot in REPEATABLE-READ.
        // Get an estimate of the replica DB lag before then, treating estimate staleness
        // as lag itself just to be safe
        $status = $this->getApproximateLagStatus();
        $this->mTrxReplicaLag = $status['lag'] + ( microtime( true ) - $status['since'] );
        // T147697: make explicitTrxActive() return true until begin() finishes. This way, no
        // caller will think its OK to muck around with the transaction just because startAtomic()
        // has not yet completed (e.g. setting mTrxAtomicLevels).
        $this->mTrxAutomatic = ( $mode === self::TRANSACTION_INTERNAL );
    }
 
    protected function doBegin( $fname ) {
        $this->query( 'BEGIN', $fname );
        $this->mTrxLevel = 1;
    }
 
    final public function commit( $fname = __METHOD__, $flush = '' ) {
        if ( $this->mTrxLevel && $this->mTrxAtomicLevels ) {
            // There are still atomic sections open. This cannot be ignored
            $levels = implode( ', ', $this->mTrxAtomicLevels );
            throw new DBUnexpectedError(
                $this,
                "$fname: Got COMMIT while atomic sections $levels are still open."
            );
        }
 
        if ( $flush === self::FLUSHING_INTERNAL || $flush === self::FLUSHING_ALL_PEERS ) {
            if ( !$this->mTrxLevel ) {
                return; // nothing to do
            } elseif ( !$this->mTrxAutomatic ) {
                throw new DBUnexpectedError(
                    $this,
                    "$fname: Flushing an explicit transaction, getting out of sync."
                );
            }
        } else {
            if ( !$this->mTrxLevel ) {
                $this->queryLogger->error(
                    "$fname: No transaction to commit, something got out of sync." );
                return; // nothing to do
            } elseif ( $this->mTrxAutomatic ) {
                // @TODO: make this an exception at some point
                $msg = "$fname: Explicit commit of implicit transaction.";
                $this->queryLogger->error( $msg );
                return; // wait for the main transaction set commit round
            }
        }
 
        // Avoid fatals if close() was called
        $this->assertOpen();
 
        $this->runOnTransactionPreCommitCallbacks();
        $writeTime = $this->pendingWriteQueryDuration( self::ESTIMATE_DB_APPLY );
        $this->doCommit( $fname );
        if ( $this->mTrxDoneWrites ) {
            $this->mLastWriteTime = microtime( true );
            $this->trxProfiler->transactionWritingOut(
                $this->mServer, $this->mDBname, $this->mTrxShortId, $writeTime );
        }
 
        $this->runOnTransactionIdleCallbacks( self::TRIGGER_COMMIT );
        $this->runTransactionListenerCallbacks( self::TRIGGER_COMMIT );
    }
 
    protected function doCommit( $fname ) {
        if ( $this->mTrxLevel ) {
            $this->query( 'COMMIT', $fname );
            $this->mTrxLevel = 0;
        }
    }
 
    final public function rollback( $fname = __METHOD__, $flush = '' ) {
        if ( $flush === self::FLUSHING_INTERNAL || $flush === self::FLUSHING_ALL_PEERS ) {
            if ( !$this->mTrxLevel ) {
                return; // nothing to do
            }
        } else {
            if ( !$this->mTrxLevel ) {
                $this->queryLogger->error(
                    "$fname: No transaction to rollback, something got out of sync." );
                return; // nothing to do
            } elseif ( $this->getFlag( self::DBO_TRX ) ) {
                throw new DBUnexpectedError(
                    $this,
                    "$fname: Expected mass rollback of all peer databases (DBO_TRX set)."
                );
            }
        }
 
        // Avoid fatals if close() was called
        $this->assertOpen();
 
        $this->doRollback( $fname );
        $this->mTrxAtomicLevels = [];
        if ( $this->mTrxDoneWrites ) {
            $this->trxProfiler->transactionWritingOut(
                $this->mServer, $this->mDBname, $this->mTrxShortId );
        }
 
        $this->mTrxIdleCallbacks = []; // clear
        $this->mTrxPreCommitCallbacks = []; // clear
        $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
        $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
    }
 
    protected function doRollback( $fname ) {
        if ( $this->mTrxLevel ) {
            # Disconnects cause rollback anyway, so ignore those errors
            $ignoreErrors = true;
            $this->query( 'ROLLBACK', $fname, $ignoreErrors );
            $this->mTrxLevel = 0;
        }
    }
 
    public function flushSnapshot( $fname = __METHOD__ ) {
        if ( $this->writesOrCallbacksPending() || $this->explicitTrxActive() ) {
            // This only flushes transactions to clear snapshots, not to write data
            $fnames = implode( ', ', $this->pendingWriteAndCallbackCallers() );
            throw new DBUnexpectedError(
                $this,
                "$fname: Cannot flush snapshot because writes are pending ($fnames)."
            );
        }
 
        $this->commit( $fname, self::FLUSHING_INTERNAL );
    }
 
    public function explicitTrxActive() {
        return $this->mTrxLevel && ( $this->mTrxAtomicLevels || !$this->mTrxAutomatic );
    }
 
    public function duplicateTableStructure(
        $oldName, $newName, $temporary = false, $fname = __METHOD__
    ) {
        throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
    }
 
    public function listTables( $prefix = null, $fname = __METHOD__ ) {
        throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
    }
 
    public function listViews( $prefix = null, $fname = __METHOD__ ) {
        throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
    }
 
    public function timestamp( $ts = 0 ) {
        $t = new ConvertibleTimestamp( $ts );
        // Let errors bubble up to avoid putting garbage in the DB
        return $t->getTimestamp( TS_MW );
    }
 
    public function timestampOrNull( $ts = null ) {
        if ( is_null( $ts ) ) {
            return null;
        } else {
            return $this->timestamp( $ts );
        }
    }
 
    protected function resultObject( $result ) {
        if ( !$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( &$rtt = null ) {
        // Avoid hitting the server if it was hit recently
        if ( $this->isOpen() && ( microtime( true ) - $this->lastPing ) < self::PING_TTL ) {
            if ( !func_num_args() || $this->mRTTEstimate > 0 ) {
                $rtt = $this->mRTTEstimate;
                return true; // don't care about $rtt
            }
        }
 
        // This will reconnect if possible or return false if not
        $this->clearFlag( self::DBO_TRX, self::REMEMBER_PRIOR );
        $ok = ( $this->query( self::PING_QUERY, __METHOD__, true ) !== false );
        $this->restoreFlags( self::RESTORE_PRIOR );
 
        if ( $ok ) {
            $rtt = $this->mRTTEstimate;
        }
 
        return $ok;
    }
 
    protected function reconnect() {
        $this->closeConnection();
        $this->mOpened = false;
        $this->mConn = false;
        try {
            $this->open( $this->mServer, $this->mUser, $this->mPassword, $this->mDBname );
            $this->lastPing = microtime( true );
            $ok = true;
        } catch ( DBConnectionError $e ) {
            $ok = false;
        }
 
        return $ok;
    }
 
    public function getSessionLagStatus() {
        return $this->getTransactionLagStatus() ?: $this->getApproximateLagStatus();
    }
 
    protected function getTransactionLagStatus() {
        return $this->mTrxLevel
            ? [ 'lag' => $this->mTrxReplicaLag, 'since' => $this->trxTimestamp() ]
            : null;
    }
 
    protected function getApproximateLagStatus() {
        return [
            'lag'   => $this->getLBInfo( 'replica' ) ? $this->getLag() : 0,
            'since' => microtime( true )
        ];
    }
 
    public static function getCacheSetOptions( IDatabase $db1 ) {
        $res = [ 'lag' => 0, 'since' => INF, 'pending' => false ];
        foreach ( func_get_args() as $db ) {
            $status = $db->getSessionLagStatus();
            if ( $status['lag'] === false ) {
                $res['lag'] = false;
            } elseif ( $res['lag'] !== false ) {
                $res['lag'] = max( $res['lag'], $status['lag'] );
            }
            $res['since'] = min( $res['since'], $status['since'] );
            $res['pending'] = $res['pending'] ?: $db->writesPending();
        }
 
        return $res;
    }
 
    public function getLag() {
        return 0;
    }
 
    public function maxListLen() {
        return 0;
    }
 
    public function encodeBlob( $b ) {
        return $b;
    }
 
    public function decodeBlob( $b ) {
        if ( $b instanceof Blob ) {
            $b = $b->fetch();
        }
        return $b;
    }
 
    public function setSessionOptions( array $options ) {
    }
 
    public function sourceFile(
        $filename,
        callable $lineCallback = null,
        callable $resultCallback = null,
        $fname = false,
        callable $inputCallback = null
    ) {
        MediaWiki\suppressWarnings();
        $fp = fopen( $filename, 'r' );
        MediaWiki\restoreWarnings();
 
        if ( false === $fp ) {
            throw new RuntimeException( "Could not open \"{$filename}\".\n" );
        }
 
        if ( !$fname ) {
            $fname = __METHOD__ . "( $filename )";
        }
 
        try {
            $error = $this->sourceStream(
                $fp, $lineCallback, $resultCallback, $fname, $inputCallback );
        } catch ( Exception $e ) {
            fclose( $fp );
            throw $e;
        }
 
        fclose( $fp );
 
        return $error;
    }
 
    public function setSchemaVars( $vars ) {
        $this->mSchemaVars = $vars;
    }
 
    public function sourceStream(
        $fp,
        callable $lineCallback = null,
        callable $resultCallback = null,
        $fname = __METHOD__,
        callable $inputCallback = null
    ) {
        $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 replaceVars( $ins ) {
        $vars = $this->getSchemaVars();
        return preg_replace_callback(
            '!
                /\* (\$wgDBprefix|[_i]) \*/ (\w*) | # 1-2. tableName, indexName
                \'\{\$ (\w+) }\'                  | # 3. addQuotes
                `\{\$ (\w+) }`                    | # 4. addIdentifierQuotes
                /\*\$ (\w+) \*/                     # 5. leave unencoded
            !x',
            function ( $m ) use ( $vars ) {
                // Note: Because of <https://bugs.php.net/bug.php?id=51881>,
                // check for both nonexistent keys *and* the empty string.
                if ( isset( $m[1] ) && $m[1] !== '' ) {
                    if ( $m[1] === 'i' ) {
                        return $this->indexName( $m[2] );
                    } else {
                        return $this->tableName( $m[2] );
                    }
                } elseif ( isset( $m[3] ) && $m[3] !== '' && array_key_exists( $m[3], $vars ) ) {
                    return $this->addQuotes( $vars[$m[3]] );
                } elseif ( isset( $m[4] ) && $m[4] !== '' && array_key_exists( $m[4], $vars ) ) {
                    return $this->addIdentifierQuotes( $vars[$m[4]] );
                } elseif ( isset( $m[5] ) && $m[5] !== '' && array_key_exists( $m[5], $vars ) ) {
                    return $vars[$m[5]];
                } else {
                    return $m[0];
                }
            },
            $ins
        );
    }
 
    protected function getSchemaVars() {
        if ( $this->mSchemaVars ) {
            return $this->mSchemaVars;
        } else {
            return $this->getDefaultSchemaVars();
        }
    }
 
    protected function getDefaultSchemaVars() {
        return [];
    }
 
    public function lockIsFree( $lockName, $method ) {
        return true;
    }
 
    public function lock( $lockName, $method, $timeout = 5 ) {
        $this->mNamedLocksHeld[$lockName] = 1;
 
        return true;
    }
 
    public function unlock( $lockName, $method ) {
        unset( $this->mNamedLocksHeld[$lockName] );
 
        return true;
    }
 
    public function getScopedLockAndFlush( $lockKey, $fname, $timeout ) {
        if ( $this->writesOrCallbacksPending() ) {
            // This only flushes transactions to clear snapshots, not to write data
            $fnames = implode( ', ', $this->pendingWriteAndCallbackCallers() );
            throw new DBUnexpectedError(
                $this,
                "$fname: Cannot flush pre-lock snapshot because writes are pending ($fnames)."
            );
        }
 
        if ( !$this->lock( $lockKey, $fname, $timeout ) ) {
            return null;
        }
 
        $unlocker = new ScopedCallback( function () use ( $lockKey, $fname ) {
            if ( $this->trxLevel() ) {
                // There is a good chance an exception was thrown, causing any early return
                // from the caller. Let any error handler get a chance to issue rollback().
                // If there isn't one, let the error bubble up and trigger server-side rollback.
                $this->onTransactionResolution(
                    function () use ( $lockKey, $fname ) {
                        $this->unlock( $lockKey, $fname );
                    },
                    $fname
                );
            } else {
                $this->unlock( $lockKey, $fname );
            }
        } );
 
        $this->commit( $fname, self::FLUSHING_INTERNAL );
 
        return $unlocker;
    }
 
    public function namedLocksEnqueue() {
        return false;
    }
 
    public function tableLocksHaveTransactionScope() {
        return true;
    }
 
    final public function lockTables( array $read, array $write, $method ) {
        if ( $this->writesOrCallbacksPending() ) {
            throw new DBUnexpectedError( $this, "Transaction writes or callbacks still pending." );
        }
 
        if ( $this->tableLocksHaveTransactionScope() ) {
            $this->startAtomic( $method );
        }
 
        return $this->doLockTables( $read, $write, $method );
    }
 
    protected function doLockTables( array $read, array $write, $method ) {
        return true;
    }
 
    final public function unlockTables( $method ) {
        if ( $this->tableLocksHaveTransactionScope() ) {
            $this->endAtomic( $method );
 
            return true; // locks released on COMMIT/ROLLBACK
        }
 
        return $this->doUnlockTables( $method );
    }
 
    protected function doUnlockTables( $method ) {
        return true;
    }
 
    public function dropTable( $tableName, $fName = __METHOD__ ) {
        if ( !$this->tableExists( $tableName, $fName ) ) {
            return false;
        }
        $sql = "DROP TABLE " . $this->tableName( $tableName ) . " CASCADE";
 
        return $this->query( $sql, $fName );
    }
 
    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 ) {
        if ( $expiry == '' || $expiry == 'infinity' || $expiry == $this->getInfinity() ) {
            return 'infinity';
        }
 
        return ConvertibleTimestamp::convert( $format, $expiry );
    }
 
    public function setBigSelects( $value = true ) {
        // no-op
    }
 
    public function isReadOnly() {
        return ( $this->getReadOnlyReason() !== false );
    }
 
    protected function getReadOnlyReason() {
        $reason = $this->getLBInfo( 'readOnlyReason' );
 
        return is_string( $reason ) ? $reason : false;
    }
 
    public function setTableAliases( array $aliases ) {
        $this->tableAliases = $aliases;
    }
 
    protected function requiresDatabaseUser() {
        return true;
    }
 
    protected function getBindingHandle() {
        if ( !$this->mConn ) {
            throw new DBUnexpectedError(
                $this,
                'DB connection was already closed or the connection dropped.'
            );
        }
 
        return $this->mConn;
    }
 
    public function __toString() {
        return (string)$this->mConn;
    }
 
    public function __clone() {
        $this->connLogger->warning(
            "Cloning " . static::class . " is not recomended; forking connection:\n" .
            ( new RuntimeException() )->getTraceAsString()
        );
 
        if ( $this->isOpen() ) {
            // Open a new connection resource without messing with the old one
            $this->mOpened = false;
            $this->mConn = false;
            $this->mTrxEndCallbacks = []; // don't copy
            $this->handleSessionLoss(); // no trx or locks anymore
            $this->open( $this->mServer, $this->mUser, $this->mPassword, $this->mDBname );
            $this->lastPing = microtime( true );
        }
    }
 
    public function __sleep() {
        throw new RuntimeException( 'Database serialization may cause problems, since ' .
            'the connection is not restored on wakeup.' );
    }
 
    public function __destruct() {
        if ( $this->mTrxLevel && $this->mTrxDoneWrites ) {
            trigger_error( "Uncommitted DB writes (transaction from {$this->mTrxFname})." );
        }
 
        $danglingWriters = $this->pendingWriteAndCallbackCallers();
        if ( $danglingWriters ) {
            $fnames = implode( ', ', $danglingWriters );
            trigger_error( "DB transaction writes or callbacks still pending ($fnames)." );
        }
 
        if ( $this->mConn ) {
            // Avoid connection leaks for sanity. Normally, resources close at script completion.
            // The connection might already be closed in zend/hhvm by now, so suppress warnings.
            \MediaWiki\suppressWarnings();
            $this->closeConnection();
            \MediaWiki\restoreWarnings();
            $this->mConn = false;
            $this->mOpened = false;
        }
    }
}
 
class_alias( Database::class, 'DatabaseBase' ); // b/c for old name
class_alias( Database::class, 'Database' ); // b/c global alias