DatabaseMysqlBase.php

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<?php
namespace Wikimedia\Rdbms;

use DateTime;
use DateTimeZone;
use Wikimedia;
use InvalidArgumentException;
use Exception;
use RuntimeException;
use stdClass;

abstract class DatabaseMysqlBase extends Database {
    protected $lastKnownReplicaPos;
    protected $lagDetectionMethod;
    protected $lagDetectionOptions = [];
    protected $useGTIDs = false;
    protected $sslKeyPath;
    protected $sslCertPath;
    protected $sslCAFile;
    protected $sslCAPath;
    protected $sslCiphers;
    protected $sqlMode;
    protected $utf8Mode;
    protected $defaultBigSelects = null;

    private $serverVersion = null;
    private $insertSelectIsSafe = null;
    private $replicationInfoRow = null;

    // Cache getServerId() for 24 hours
    const SERVER_ID_CACHE_TTL = 86400;

    const LAG_STALE_WARN_THRESHOLD = 0.100;

    function __construct( array $params ) {
        $this->lagDetectionMethod = $params['lagDetectionMethod'] ?? 'Seconds_Behind_Master';
        $this->lagDetectionOptions = $params['lagDetectionOptions'] ?? [];
        $this->useGTIDs = !empty( $params['useGTIDs' ] );
        foreach ( [ 'KeyPath', 'CertPath', 'CAFile', 'CAPath', 'Ciphers' ] as $name ) {
            $var = "ssl{$name}";
            if ( isset( $params[$var] ) ) {
                $this->$var = $params[$var];
            }
        }
        $this->sqlMode = $params['sqlMode'] ?? null;
        $this->utf8Mode = !empty( $params['utf8Mode'] );
        $this->insertSelectIsSafe = isset( $params['insertSelectIsSafe'] )
            ? (bool)$params['insertSelectIsSafe'] : null;

        parent::__construct( $params );
    }

    public function getType() {
        return 'mysql';
    }

    protected function open( $server, $user, $password, $dbName, $schema, $tablePrefix ) {
        # Close/unset connection handle
        $this->close();

        $this->server = $server;
        $this->user = $user;
        $this->password = $password;

        $this->installErrorHandler();
        try {
            $this->conn = $this->mysqlConnect( $this->server, $dbName );
        } catch ( Exception $ex ) {
            $this->restoreErrorHandler();
            throw $ex;
        }
        $error = $this->restoreErrorHandler();

        # Always log connection errors
        if ( !$this->conn ) {
            $error = $error ?: $this->lastError();
            $this->connLogger->error(
                "Error connecting to {db_server}: {error}",
                $this->getLogContext( [
                    'method' => __METHOD__,
                    'error' => $error,
                ] )
            );
            $this->connLogger->debug( "DB connection error\n" .
                "Server: $server, User: $user, Password: " .
                substr( $password, 0, 3 ) . "..., error: " . $error . "\n" );

            throw new DBConnectionError( $this, $error );
        }

        if ( strlen( $dbName ) ) {
            $this->selectDomain( new DatabaseDomain( $dbName, null, $tablePrefix ) );
        } else {
            $this->currentDomain = new DatabaseDomain( null, null, $tablePrefix );
        }

        // Tell the server what we're communicating with
        if ( !$this->connectInitCharset() ) {
            $error = $this->lastError();
            $this->queryLogger->error(
                "Error setting character set: {error}",
                $this->getLogContext( [
                    'method' => __METHOD__,
                    'error' => $this->lastError(),
                ] )
            );
            throw new DBConnectionError( $this, "Error setting character set: $error" );
        }

        // Abstract over any insane MySQL defaults
        $set = [ 'group_concat_max_len = 262144' ];
        // Set SQL mode, default is turning them all off, can be overridden or skipped with null
        if ( is_string( $this->sqlMode ) ) {
            $set[] = 'sql_mode = ' . $this->addQuotes( $this->sqlMode );
        }
        // Set any custom settings defined by site config
        // (e.g. https://dev.mysql.com/doc/refman/4.1/en/innodb-parameters.html)
        foreach ( $this->connectionVariables as $var => $val ) {
            // Escape strings but not numbers to avoid MySQL complaining
            if ( !is_int( $val ) && !is_float( $val ) ) {
                $val = $this->addQuotes( $val );
            }
            $set[] = $this->addIdentifierQuotes( $var ) . ' = ' . $val;
        }

        if ( $set ) {
            // Use doQuery() to avoid opening implicit transactions (DBO_TRX)
            $success = $this->doQuery( 'SET ' . implode( ', ', $set ) );
            if ( !$success ) {
                $error = $this->lastError();
                $this->queryLogger->error(
                    'Error setting MySQL variables on server {db_server}: {error}',
                    $this->getLogContext( [
                        'method' => __METHOD__,
                        'error' => $error,
                    ] )
                );
                throw new DBConnectionError( $this, "Error setting MySQL variables: $error" );
            }
        }

        $this->opened = true;

        return true;
    }

    protected function connectInitCharset() {
        if ( $this->utf8Mode ) {
            // Tell the server we're communicating with it in UTF-8.
            // This may engage various charset conversions.
            return $this->mysqlSetCharset( 'utf8' );
        } else {
            return $this->mysqlSetCharset( 'binary' );
        }
    }

    protected function doSelectDomain( DatabaseDomain $domain ) {
        if ( $domain->getSchema() !== null ) {
            throw new DBExpectedError( $this, __CLASS__ . ": domain schemas are not supported." );
        }

        $database = $domain->getDatabase();
        // A null database means "don't care" so leave it as is and update the table prefix
        if ( $database === null ) {
            $this->currentDomain = new DatabaseDomain(
                $this->currentDomain->getDatabase(),
                null,
                $domain->getTablePrefix()
            );

            return true;
        }

        if ( $database !== $this->getDBname() ) {
            $sql = 'USE ' . $this->addIdentifierQuotes( $database );
            list( $res, $err, $errno ) =
                $this->executeQuery( $sql, __METHOD__, self::QUERY_IGNORE_DBO_TRX );

            if ( $res === false ) {
                $this->reportQueryError( $err, $errno, $sql, __METHOD__ );
                return false; // unreachable
            }
        }

        // Update that domain fields on success (no exception thrown)
        $this->currentDomain = $domain;

        return true;
    }

    abstract protected function mysqlConnect( $realServer, $dbName );

    abstract protected function mysqlSetCharset( $charset );

    public function freeResult( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }
        Wikimedia\suppressWarnings();
        $ok = $this->mysqlFreeResult( $res );
        Wikimedia\restoreWarnings();
        if ( !$ok ) {
            throw new DBUnexpectedError( $this, "Unable to free MySQL result" );
        }
    }

    abstract protected function mysqlFreeResult( $res );

    public function fetchObject( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }
        Wikimedia\suppressWarnings();
        $row = $this->mysqlFetchObject( $res );
        Wikimedia\restoreWarnings();

        $errno = $this->lastErrno();
        // Unfortunately, mysql_fetch_object does not reset the last errno.
        // Only check for CR_SERVER_LOST and CR_UNKNOWN_ERROR, as
        // these are the only errors mysql_fetch_object can cause.
        // See https://dev.mysql.com/doc/refman/5.0/en/mysql-fetch-row.html.
        if ( $errno == 2000 || $errno == 2013 ) {
            throw new DBUnexpectedError(
                $this,
                'Error in fetchObject(): ' . htmlspecialchars( $this->lastError() )
            );
        }

        return $row;
    }

    abstract protected function mysqlFetchObject( $res );

    public function fetchRow( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }
        Wikimedia\suppressWarnings();
        $row = $this->mysqlFetchArray( $res );
        Wikimedia\restoreWarnings();

        $errno = $this->lastErrno();
        // Unfortunately, mysql_fetch_array does not reset the last errno.
        // Only check for CR_SERVER_LOST and CR_UNKNOWN_ERROR, as
        // these are the only errors mysql_fetch_array can cause.
        // See https://dev.mysql.com/doc/refman/5.0/en/mysql-fetch-row.html.
        if ( $errno == 2000 || $errno == 2013 ) {
            throw new DBUnexpectedError(
                $this,
                'Error in fetchRow(): ' . htmlspecialchars( $this->lastError() )
            );
        }

        return $row;
    }

    abstract protected function mysqlFetchArray( $res );

    function numRows( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }
        Wikimedia\suppressWarnings();
        $n = !is_bool( $res ) ? $this->mysqlNumRows( $res ) : 0;
        Wikimedia\restoreWarnings();

        // Unfortunately, mysql_num_rows does not reset the last errno.
        // We are not checking for any errors here, since
        // there are no errors mysql_num_rows can cause.
        // See https://dev.mysql.com/doc/refman/5.0/en/mysql-fetch-row.html.
        // See https://phabricator.wikimedia.org/T44430
        return $n;
    }

    abstract protected function mysqlNumRows( $res );

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

        return $this->mysqlNumFields( $res );
    }

    abstract protected function mysqlNumFields( $res );

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

        return $this->mysqlFieldName( $res, $n );
    }

    abstract protected function mysqlFieldName( $res, $n );

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

        return $this->mysqlFieldType( $res, $n );
    }

    abstract protected function mysqlFieldType( $res, $n );

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

        return $this->mysqlDataSeek( $res, $row );
    }

    abstract protected function mysqlDataSeek( $res, $row );

    public function lastError() {
        if ( $this->conn ) {
            # Even if it's non-zero, it can still be invalid
            Wikimedia\suppressWarnings();
            $error = $this->mysqlError( $this->conn );
            if ( !$error ) {
                $error = $this->mysqlError();
            }
            Wikimedia\restoreWarnings();
        } else {
            $error = $this->mysqlError();
        }
        if ( $error ) {
            $error .= ' (' . $this->server . ')';
        }

        return $error;
    }

    abstract protected function mysqlError( $conn = null );

    protected function wasQueryTimeout( $error, $errno ) {
        // https://dev.mysql.com/doc/refman/8.0/en/client-error-reference.html
        // https://phabricator.wikimedia.org/T170638
        return in_array( $errno, [ 2062, 3024 ] );
    }

    public function replace( $table, $uniqueIndexes, $rows, $fname = __METHOD__ ) {
        $this->nativeReplace( $table, $rows, $fname );
    }

    protected function isInsertSelectSafe( array $insertOptions, array $selectOptions ) {
        $row = $this->getReplicationSafetyInfo();
        // For row-based-replication, the resulting changes will be relayed, not the query
        if ( $row->binlog_format === 'ROW' ) {
            return true;
        }
        // LIMIT requires ORDER BY on a unique key or it is non-deterministic
        if ( isset( $selectOptions['LIMIT'] ) ) {
            return false;
        }
        // In MySQL, an INSERT SELECT is only replication safe with row-based
        // replication or if innodb_autoinc_lock_mode is 0. When those
        // conditions aren't met, use non-native mode.
        // While we could try to determine if the insert is safe anyway by
        // checking if the target table has an auto-increment column that
        // isn't set in $varMap, that seems unlikely to be worth the extra
        // complexity.
        return (
            in_array( 'NO_AUTO_COLUMNS', $insertOptions ) ||
            (int)$row->innodb_autoinc_lock_mode === 0
        );
    }

    protected function getReplicationSafetyInfo() {
        if ( $this->replicationInfoRow === null ) {
            $this->replicationInfoRow = $this->selectRow(
                false,
                [
                    'innodb_autoinc_lock_mode' => '@@innodb_autoinc_lock_mode',
                    'binlog_format' => '@@binlog_format',
                ],
                [],
                __METHOD__
            );
        }

        return $this->replicationInfoRow;
    }

    public function estimateRowCount( $table, $var = '*', $conds = '',
        $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        $conds = $this->normalizeConditions( $conds, $fname );
        $column = $this->extractSingleFieldFromList( $var );
        if ( is_string( $column ) && !in_array( $column, [ '*', '1' ] ) ) {
            $conds[] = "$column IS NOT NULL";
        }

        $options['EXPLAIN'] = true;
        $res = $this->select( $table, $var, $conds, $fname, $options, $join_conds );
        if ( $res === false ) {
            return false;
        }
        if ( !$this->numRows( $res ) ) {
            return 0;
        }

        $rows = 1;
        foreach ( $res as $plan ) {
            $rows *= $plan->rows > 0 ? $plan->rows : 1; // avoid resetting to zero
        }

        return (int)$rows;
    }

    public function tableExists( $table, $fname = __METHOD__ ) {
        // Split database and table into proper variables as Database::tableName() returns
        // shared tables prefixed with their database, which do not work in SHOW TABLES statements
        list( $database, , $prefix, $table ) = $this->qualifiedTableComponents( $table );
        $tableName = "{$prefix}{$table}";

        if ( isset( $this->sessionTempTables[$tableName] ) ) {
            return true; // already known to exist and won't show in SHOW TABLES anyway
        }

        // We can't use buildLike() here, because it specifies an escape character
        // other than the backslash, which is the only one supported by SHOW TABLES
        $encLike = $this->escapeLikeInternal( $tableName, '\\' );

        // If the database has been specified (such as for shared tables), use "FROM"
        if ( $database !== '' ) {
            $encDatabase = $this->addIdentifierQuotes( $database );
            $query = "SHOW TABLES FROM $encDatabase LIKE '$encLike'";
        } else {
            $query = "SHOW TABLES LIKE '$encLike'";
        }

        return $this->query( $query, $fname )->numRows() > 0;
    }

    public function fieldInfo( $table, $field ) {
        $table = $this->tableName( $table );
        $res = $this->query( "SELECT * FROM $table LIMIT 1", __METHOD__, true );
        if ( !$res ) {
            return false;
        }
        $n = $this->mysqlNumFields( $res->result );
        for ( $i = 0; $i < $n; $i++ ) {
            $meta = $this->mysqlFetchField( $res->result, $i );
            if ( $field == $meta->name ) {
                return new MySQLField( $meta );
            }
        }

        return false;
    }

    abstract protected function mysqlFetchField( $res, $n );

    public function indexInfo( $table, $index, $fname = __METHOD__ ) {
        # SHOW INDEX works in MySQL 3.23.58, but SHOW INDEXES does not.
        # SHOW INDEX should work for 3.x and up:
        # https://dev.mysql.com/doc/mysql/en/SHOW_INDEX.html
        $table = $this->tableName( $table );
        $index = $this->indexName( $index );

        $sql = 'SHOW INDEX FROM ' . $table;
        $res = $this->query( $sql, $fname );

        if ( !$res ) {
            return null;
        }

        $result = [];

        foreach ( $res as $row ) {
            if ( $row->Key_name == $index ) {
                $result[] = $row;
            }
        }

        return $result ?: false;
    }

    public function strencode( $s ) {
        return $this->mysqlRealEscapeString( $s );
    }

    abstract protected function mysqlRealEscapeString( $s );

    public function addQuotes( $s ) {
        if ( is_bool( $s ) ) {
            // Parent would transform to int, which does not play nice with MySQL type juggling.
            // When searching for an int in a string column, the strings are cast to int, which
            // means false would match any string not starting with a number.
            $s = (string)(int)$s;
        }
        return parent::addQuotes( $s );
    }

    public function addIdentifierQuotes( $s ) {
        // Characters in the range \u0001-\uFFFF are valid in a quoted identifier
        // Remove NUL bytes and escape backticks by doubling
        return '`' . str_replace( [ "\0", '`' ], [ '', '``' ], $s ) . '`';
    }

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

    protected function doGetLag() {
        if ( $this->getLagDetectionMethod() === 'pt-heartbeat' ) {
            return $this->getLagFromPtHeartbeat();
        } else {
            return $this->getLagFromSlaveStatus();
        }
    }

    protected function getLagDetectionMethod() {
        return $this->lagDetectionMethod;
    }

    protected function getLagFromSlaveStatus() {
        $res = $this->query( 'SHOW SLAVE STATUS', __METHOD__ );
        $row = $res ? $res->fetchObject() : false;
        // If the server is not replicating, there will be no row
        if ( $row && strval( $row->Seconds_Behind_Master ) !== '' ) {
            return intval( $row->Seconds_Behind_Master );
        }

        return false;
    }

    protected function getLagFromPtHeartbeat() {
        $options = $this->lagDetectionOptions;

        $currentTrxInfo = $this->getRecordedTransactionLagStatus();
        if ( $currentTrxInfo ) {
            // There is an active transaction and the initial lag was already queried
            $staleness = microtime( true ) - $currentTrxInfo['since'];
            if ( $staleness > self::LAG_STALE_WARN_THRESHOLD ) {
                // Avoid returning higher and higher lag value due to snapshot age
                // given that the isolation level will typically be REPEATABLE-READ
                $this->queryLogger->warning(
                    "Using cached lag value for {db_server} due to active transaction",
                    $this->getLogContext( [
                        'method' => __METHOD__,
                        'age' => $staleness,
                        'trace' => ( new RuntimeException() )->getTraceAsString()
                    ] )
                );
            }

            return $currentTrxInfo['lag'];
        }

        if ( isset( $options['conds'] ) ) {
            // Best method for multi-DC setups: use logical channel names
            $data = $this->getHeartbeatData( $options['conds'] );
        } else {
            // Standard method: use master server ID (works with stock pt-heartbeat)
            $masterInfo = $this->getMasterServerInfo();
            if ( !$masterInfo ) {
                $this->queryLogger->error(
                    "Unable to query master of {db_server} for server ID",
                    $this->getLogContext( [
                        'method' => __METHOD__
                    ] )
                );

                return false; // could not get master server ID
            }

            $conds = [ 'server_id' => intval( $masterInfo['serverId'] ) ];
            $data = $this->getHeartbeatData( $conds );
        }

        list( $time, $nowUnix ) = $data;
        if ( $time !== null ) {
            // @time is in ISO format like "2015-09-25T16:48:10.000510"
            $dateTime = new DateTime( $time, new DateTimeZone( 'UTC' ) );
            $timeUnix = (int)$dateTime->format( 'U' ) + $dateTime->format( 'u' ) / 1e6;

            return max( $nowUnix - $timeUnix, 0.0 );
        }

        $this->queryLogger->error(
            "Unable to find pt-heartbeat row for {db_server}",
            $this->getLogContext( [
                'method' => __METHOD__
            ] )
        );

        return false;
    }

    protected function getMasterServerInfo() {
        $cache = $this->srvCache;
        $key = $cache->makeGlobalKey(
            'mysql',
            'master-info',
            // Using one key for all cluster replica DBs is preferable
            $this->getLBInfo( 'clusterMasterHost' ) ?: $this->getServer()
        );
        $fname = __METHOD__;

        return $cache->getWithSetCallback(
            $key,
            $cache::TTL_INDEFINITE,
            function () use ( $cache, $key, $fname ) {
                // Get and leave a lock key in place for a short period
                if ( !$cache->lock( $key, 0, 10 ) ) {
                    return false; // avoid master connection spike slams
                }

                $conn = $this->getLazyMasterHandle();
                if ( !$conn ) {
                    return false; // something is misconfigured
                }

                // Connect to and query the master; catch errors to avoid outages
                try {
                    $res = $conn->query( 'SELECT @@server_id AS id', $fname );
                    $row = $res ? $res->fetchObject() : false;
                    $id = $row ? (int)$row->id : 0;
                } catch ( DBError $e ) {
                    $id = 0;
                }

                // Cache the ID if it was retrieved
                return $id ? [ 'serverId' => $id, 'asOf' => time() ] : false;
            }
        );
    }

    protected function getHeartbeatData( array $conds ) {
        // Query time and trip time are not counted
        $nowUnix = microtime( true );
        // Do not bother starting implicit transactions here
        $this->clearFlag( self::DBO_TRX, self::REMEMBER_PRIOR );
        try {
            $whereSQL = $this->makeList( $conds, self::LIST_AND );
            // Use ORDER BY for channel based queries since that field might not be UNIQUE.
            // Note: this would use "TIMESTAMPDIFF(MICROSECOND,ts,UTC_TIMESTAMP(6))" but the
            // percision field is not supported in MySQL <= 5.5.
            $res = $this->query(
                "SELECT ts FROM heartbeat.heartbeat WHERE $whereSQL ORDER BY ts DESC LIMIT 1",
                __METHOD__
            );
            $row = $res ? $res->fetchObject() : false;
        } finally {
            $this->restoreFlags();
        }

        return [ $row ? $row->ts : null, $nowUnix ];
    }

    protected function getApproximateLagStatus() {
        if ( $this->getLagDetectionMethod() === 'pt-heartbeat' ) {
            // Disable caching since this is fast enough and we don't wan't
            // to be *too* pessimistic by having both the cache TTL and the
            // pt-heartbeat interval count as lag in getSessionLagStatus()
            return parent::getApproximateLagStatus();
        }

        $key = $this->srvCache->makeGlobalKey( 'mysql-lag', $this->getServer() );
        $approxLag = $this->srvCache->get( $key );
        if ( !$approxLag ) {
            $approxLag = parent::getApproximateLagStatus();
            $this->srvCache->set( $key, $approxLag, 1 );
        }

        return $approxLag;
    }

    public function masterPosWait( DBMasterPos $pos, $timeout ) {
        if ( !( $pos instanceof MySQLMasterPos ) ) {
            throw new InvalidArgumentException( "Position not an instance of MySQLMasterPos" );
        }

        if ( $this->getLBInfo( 'is static' ) === true ) {
            return 0; // this is a copy of a read-only dataset with no master DB
        } elseif ( $this->lastKnownReplicaPos && $this->lastKnownReplicaPos->hasReached( $pos ) ) {
            return 0; // already reached this point for sure
        }

        // Call doQuery() directly, to avoid opening a transaction if DBO_TRX is set
        if ( $pos->getGTIDs() ) {
            // Ignore GTIDs from domains exclusive to the master DB (presumably inactive)
            $rpos = $this->getReplicaPos();
            $gtidsWait = $rpos ? MySQLMasterPos::getCommonDomainGTIDs( $pos, $rpos ) : [];
            if ( !$gtidsWait ) {
                $this->queryLogger->error(
                    "No GTIDs with the same domain between master ($pos) and replica ($rpos)",
                    $this->getLogContext( [
                        'method' => __METHOD__,
                    ] )
                );

                return -1; // $pos is from the wrong cluster?
            }
            // Wait on the GTID set (MariaDB only)
            $gtidArg = $this->addQuotes( implode( ',', $gtidsWait ) );
            if ( strpos( $gtidArg, ':' ) !== false ) {
                // MySQL GTIDs, e.g "source_id:transaction_id"
                $sql = "SELECT WAIT_FOR_EXECUTED_GTID_SET($gtidArg, $timeout)";
            } else {
                // MariaDB GTIDs, e.g."domain:server:sequence"
                $sql = "SELECT MASTER_GTID_WAIT($gtidArg, $timeout)";
            }
        } else {
            // Wait on the binlog coordinates
            $encFile = $this->addQuotes( $pos->getLogFile() );
            $encPos = intval( $pos->getLogPosition()[$pos::CORD_EVENT] );
            $sql = "SELECT MASTER_POS_WAIT($encFile, $encPos, $timeout)";
        }

        list( $res, $err ) = $this->executeQuery( $sql, __METHOD__, self::QUERY_IGNORE_DBO_TRX );
        $row = $res ? $this->fetchRow( $res ) : false;
        if ( !$row ) {
            throw new DBExpectedError( $this, "Replication wait failed: {$err}" );
        }

        // Result can be NULL (error), -1 (timeout), or 0+ per the MySQL manual
        $status = ( $row[0] !== null ) ? intval( $row[0] ) : null;
        if ( $status === null ) {
            if ( !$pos->getGTIDs() ) {
                // T126436: jobs programmed to wait on master positions might be referencing
                // binlogs with an old master hostname; this makes MASTER_POS_WAIT() return null.
                // Try to detect this case and treat the replica DB as having reached the given
                // position (any master switchover already requires that the new master be caught
                // up before the switch).
                $replicationPos = $this->getReplicaPos();
                if ( $replicationPos && !$replicationPos->channelsMatch( $pos ) ) {
                    $this->lastKnownReplicaPos = $replicationPos;
                    $status = 0;
                }
            }
        } elseif ( $status >= 0 ) {
            // Remember that this position was reached to save queries next time
            $this->lastKnownReplicaPos = $pos;
        }

        return $status;
    }

    public function getReplicaPos() {
        $now = microtime( true ); // as-of-time *before* fetching GTID variables

        if ( $this->useGTIDs() ) {
            // Try to use GTIDs, fallbacking to binlog positions if not possible
            $data = $this->getServerGTIDs( __METHOD__ );
            // Use gtid_slave_pos for MariaDB and gtid_executed for MySQL
            foreach ( [ 'gtid_slave_pos', 'gtid_executed' ] as $name ) {
                if ( isset( $data[$name] ) && strlen( $data[$name] ) ) {
                    return new MySQLMasterPos( $data[$name], $now );
                }
            }
        }

        $data = $this->getServerRoleStatus( 'SLAVE', __METHOD__ );
        if ( $data && strlen( $data['Relay_Master_Log_File'] ) ) {
            return new MySQLMasterPos(
                "{$data['Relay_Master_Log_File']}/{$data['Exec_Master_Log_Pos']}",
                $now
            );
        }

        return false;
    }

    public function getMasterPos() {
        $now = microtime( true ); // as-of-time *before* fetching GTID variables

        $pos = false;
        if ( $this->useGTIDs() ) {
            // Try to use GTIDs, fallbacking to binlog positions if not possible
            $data = $this->getServerGTIDs( __METHOD__ );
            // Use gtid_binlog_pos for MariaDB and gtid_executed for MySQL
            foreach ( [ 'gtid_binlog_pos', 'gtid_executed' ] as $name ) {
                if ( isset( $data[$name] ) && strlen( $data[$name] ) ) {
                    $pos = new MySQLMasterPos( $data[$name], $now );
                    break;
                }
            }
            // Filter domains that are inactive or not relevant to the session
            if ( $pos ) {
                $pos->setActiveOriginServerId( $this->getServerId() );
                $pos->setActiveOriginServerUUID( $this->getServerUUID() );
                if ( isset( $data['gtid_domain_id'] ) ) {
                    $pos->setActiveDomain( $data['gtid_domain_id'] );
                }
            }
        }

        if ( !$pos ) {
            $data = $this->getServerRoleStatus( 'MASTER', __METHOD__ );
            if ( $data && strlen( $data['File'] ) ) {
                $pos = new MySQLMasterPos( "{$data['File']}/{$data['Position']}", $now );
            }
        }

        return $pos;
    }

    protected function getServerId() {
        $fname = __METHOD__;
        return $this->srvCache->getWithSetCallback(
            $this->srvCache->makeGlobalKey( 'mysql-server-id', $this->getServer() ),
            self::SERVER_ID_CACHE_TTL,
            function () use ( $fname ) {
                $res = $this->query( "SELECT @@server_id AS id", $fname );
                return intval( $this->fetchObject( $res )->id );
            }
        );
    }

    protected function getServerUUID() {
        return $this->srvCache->getWithSetCallback(
            $this->srvCache->makeGlobalKey( 'mysql-server-uuid', $this->getServer() ),
            self::SERVER_ID_CACHE_TTL,
            function () {
                $res = $this->query( "SHOW GLOBAL VARIABLES LIKE 'server_uuid'" );
                $row = $this->fetchObject( $res );

                return $row ? $row->Value : null;
            }
        );
    }

    protected function getServerGTIDs( $fname = __METHOD__ ) {
        $map = [];
        // Get global-only variables like gtid_executed
        $res = $this->query( "SHOW GLOBAL VARIABLES LIKE 'gtid_%'", $fname );
        foreach ( $res as $row ) {
            $map[$row->Variable_name] = $row->Value;
        }
        // Get session-specific (e.g. gtid_domain_id since that is were writes will log)
        $res = $this->query( "SHOW SESSION VARIABLES LIKE 'gtid_%'", $fname );
        foreach ( $res as $row ) {
            $map[$row->Variable_name] = $row->Value;
        }

        return $map;
    }

    protected function getServerRoleStatus( $role, $fname = __METHOD__ ) {
        return $this->query( "SHOW $role STATUS", $fname )->fetchRow() ?: [];
    }

    public function serverIsReadOnly() {
        $res = $this->query( "SHOW GLOBAL VARIABLES LIKE 'read_only'", __METHOD__ );
        $row = $this->fetchObject( $res );

        return $row ? ( strtolower( $row->Value ) === 'on' ) : false;
    }

    function useIndexClause( $index ) {
        return "FORCE INDEX (" . $this->indexName( $index ) . ")";
    }

    function ignoreIndexClause( $index ) {
        return "IGNORE INDEX (" . $this->indexName( $index ) . ")";
    }

    function lowPriorityOption() {
        return 'LOW_PRIORITY';
    }

    public function getSoftwareLink() {
        // MariaDB includes its name in its version string; this is how MariaDB's version of
        // the mysql command-line client identifies MariaDB servers (see mariadb_connection()
        // in libmysql/libmysql.c).
        $version = $this->getServerVersion();
        if ( strpos( $version, 'MariaDB' ) !== false || strpos( $version, '-maria-' ) !== false ) {
            return '[{{int:version-db-mariadb-url}} MariaDB]';
        }

        // Percona Server's version suffix is not very distinctive, and @@version_comment
        // doesn't give the necessary info for source builds, so assume the server is MySQL.
        // (Even Percona's version of mysql doesn't try to make the distinction.)
        return '[{{int:version-db-mysql-url}} MySQL]';
    }

    public function getServerVersion() {
        // Not using mysql_get_server_info() or similar for consistency: in the handshake,
        // MariaDB 10 adds the prefix "5.5.5-", and only some newer client libraries strip
        // it off (see RPL_VERSION_HACK in include/mysql_com.h).
        if ( $this->serverVersion === null ) {
            $this->serverVersion = $this->selectField( '', 'VERSION()', '', __METHOD__ );
        }
        return $this->serverVersion;
    }

    public function setSessionOptions( array $options ) {
        if ( isset( $options['connTimeout'] ) ) {
            $timeout = (int)$options['connTimeout'];
            $this->query( "SET net_read_timeout=$timeout" );
            $this->query( "SET net_write_timeout=$timeout" );
        }
    }

    public function streamStatementEnd( &$sql, &$newLine ) {
        if ( strtoupper( substr( $newLine, 0, 9 ) ) == 'DELIMITER' ) {
            preg_match( '/^DELIMITER\s+(\S+)/', $newLine, $m );
            $this->delimiter = $m[1];
            $newLine = '';
        }

        return parent::streamStatementEnd( $sql, $newLine );
    }

    public function lockIsFree( $lockName, $method ) {
        if ( !parent::lockIsFree( $lockName, $method ) ) {
            return false; // already held
        }

        $encName = $this->addQuotes( $this->makeLockName( $lockName ) );
        $result = $this->query( "SELECT IS_FREE_LOCK($encName) AS lockstatus", $method );
        $row = $this->fetchObject( $result );

        return ( $row->lockstatus == 1 );
    }

    public function lock( $lockName, $method, $timeout = 5 ) {
        $encName = $this->addQuotes( $this->makeLockName( $lockName ) );
        $result = $this->query( "SELECT GET_LOCK($encName, $timeout) AS lockstatus", $method );
        $row = $this->fetchObject( $result );

        if ( $row->lockstatus == 1 ) {
            parent::lock( $lockName, $method, $timeout ); // record
            return true;
        }

        $this->queryLogger->info( __METHOD__ . " failed to acquire lock '{lockname}'",
            [ 'lockname' => $lockName ] );

        return false;
    }

    public function unlock( $lockName, $method ) {
        $encName = $this->addQuotes( $this->makeLockName( $lockName ) );
        $result = $this->query( "SELECT RELEASE_LOCK($encName) as lockstatus", $method );
        $row = $this->fetchObject( $result );

        if ( $row->lockstatus == 1 ) {
            parent::unlock( $lockName, $method ); // record
            return true;
        }

        $this->queryLogger->warning( __METHOD__ . " failed to release lock '$lockName'\n" );

        return false;
    }

    private function makeLockName( $lockName ) {
        // https://dev.mysql.com/doc/refman/5.7/en/miscellaneous-functions.html#function_get-lock
        // Newer version enforce a 64 char length limit.
        return ( strlen( $lockName ) > 64 ) ? sha1( $lockName ) : $lockName;
    }

    public function namedLocksEnqueue() {
        return true;
    }

    public function tableLocksHaveTransactionScope() {
        return false; // tied to TCP connection
    }

    protected function doLockTables( array $read, array $write, $method ) {
        $items = [];
        foreach ( $write as $table ) {
            $items[] = $this->tableName( $table ) . ' WRITE';
        }
        foreach ( $read as $table ) {
            $items[] = $this->tableName( $table ) . ' READ';
        }

        $sql = "LOCK TABLES " . implode( ',', $items );
        $this->query( $sql, $method );

        return true;
    }

    protected function doUnlockTables( $method ) {
        $this->query( "UNLOCK TABLES", $method );

        return true;
    }

    public function setBigSelects( $value = true ) {
        if ( $value === 'default' ) {
            if ( $this->defaultBigSelects === null ) {
                # Function hasn't been called before so it must already be set to the default
                return;
            } else {
                $value = $this->defaultBigSelects;
            }
        } elseif ( $this->defaultBigSelects === null ) {
            $this->defaultBigSelects =
                (bool)$this->selectField( false, '@@sql_big_selects', '', __METHOD__ );
        }
        $encValue = $value ? '1' : '0';
        $this->query( "SET sql_big_selects=$encValue", __METHOD__ );
    }

    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 $delTable FROM $delTable, $joinTable WHERE $delVar=$joinVar ";

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

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

    public function upsert(
        $table, array $rows, $uniqueIndexes, array $set, $fname = __METHOD__
    ) {
        if ( $rows === [] ) {
            return true; // nothing to do
        }

        if ( !is_array( reset( $rows ) ) ) {
            $rows = [ $rows ];
        }

        $table = $this->tableName( $table );
        $columns = array_keys( $rows[0] );

        $sql = "INSERT INTO $table (" . implode( ',', $columns ) . ') VALUES ';
        $rowTuples = [];
        foreach ( $rows as $row ) {
            $rowTuples[] = '(' . $this->makeList( $row ) . ')';
        }
        $sql .= implode( ',', $rowTuples );
        $sql .= " ON DUPLICATE KEY UPDATE " . $this->makeList( $set, self::LIST_SET );

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

        return true;
    }

    public function getServerUptime() {
        $vars = $this->getMysqlStatus( 'Uptime' );

        return (int)$vars['Uptime'];
    }

    public function wasDeadlock() {
        return $this->lastErrno() == 1213;
    }

    public function wasLockTimeout() {
        return $this->lastErrno() == 1205;
    }

    public function wasReadOnlyError() {
        return $this->lastErrno() == 1223 ||
            ( $this->lastErrno() == 1290 && strpos( $this->lastError(), '--read-only' ) !== false );
    }

    public function wasConnectionError( $errno ) {
        return $errno == 2013 || $errno == 2006;
    }

    protected function wasKnownStatementRollbackError() {
        $errno = $this->lastErrno();

        if ( $errno === 1205 ) { // lock wait timeout
            // Note that this is uncached to avoid stale values of SET is used
            $row = $this->selectRow(
                false,
                [ 'innodb_rollback_on_timeout' => '@@innodb_rollback_on_timeout' ],
                [],
                __METHOD__
            );
            // https://dev.mysql.com/doc/refman/5.7/en/innodb-error-handling.html
            // https://dev.mysql.com/doc/refman/5.5/en/innodb-parameters.html
            return $row->innodb_rollback_on_timeout ? false : true;
        }

        // See https://dev.mysql.com/doc/refman/5.5/en/error-messages-server.html
        return in_array( $errno, [ 1022, 1062, 1216, 1217, 1137, 1146, 1051, 1054 ], true );
    }

    public function duplicateTableStructure(
        $oldName, $newName, $temporary = false, $fname = __METHOD__
    ) {
        $tmp = $temporary ? 'TEMPORARY ' : '';
        $newName = $this->addIdentifierQuotes( $newName );
        $oldName = $this->addIdentifierQuotes( $oldName );
        $query = "CREATE $tmp TABLE $newName (LIKE $oldName)";

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

    public function listTables( $prefix = null, $fname = __METHOD__ ) {
        $result = $this->query( "SHOW TABLES", $fname );

        $endArray = [];

        foreach ( $result as $table ) {
            $vars = get_object_vars( $table );
            $table = array_pop( $vars );

            if ( !$prefix || strpos( $table, $prefix ) === 0 ) {
                $endArray[] = $table;
            }
        }

        return $endArray;
    }

    public function dropTable( $tableName, $fName = __METHOD__ ) {
        if ( !$this->tableExists( $tableName, $fName ) ) {
            return false;
        }

        return $this->query( "DROP TABLE IF EXISTS " . $this->tableName( $tableName ), $fName );
    }

    private function getMysqlStatus( $which = "%" ) {
        $res = $this->query( "SHOW STATUS LIKE '{$which}'" );
        $status = [];

        foreach ( $res as $row ) {
            $status[$row->Variable_name] = $row->Value;
        }

        return $status;
    }

    public function listViews( $prefix = null, $fname = __METHOD__ ) {
        // The name of the column containing the name of the VIEW
        $propertyName = 'Tables_in_' . $this->getDBname();

        // Query for the VIEWS
        $res = $this->query( 'SHOW FULL TABLES WHERE TABLE_TYPE = "VIEW"' );
        $allViews = [];
        foreach ( $res as $row ) {
            array_push( $allViews, $row->$propertyName );
        }

        if ( is_null( $prefix ) || $prefix === '' ) {
            return $allViews;
        }

        $filteredViews = [];
        foreach ( $allViews as $viewName ) {
            // Does the name of this VIEW start with the table-prefix?
            if ( strpos( $viewName, $prefix ) === 0 ) {
                array_push( $filteredViews, $viewName );
            }
        }

        return $filteredViews;
    }

    public function isView( $name, $prefix = null ) {
        return in_array( $name, $this->listViews( $prefix ) );
    }

    protected function isTransactableQuery( $sql ) {
        return parent::isTransactableQuery( $sql ) &&
            !preg_match( '/^SELECT\s+(GET|RELEASE|IS_FREE)_LOCK\(/', $sql );
    }

    public function buildStringCast( $field ) {
        return "CAST( $field AS BINARY )";
    }

    public function buildIntegerCast( $field ) {
        return 'CAST( ' . $field . ' AS SIGNED )';
    }

    /*
     * @return bool Whether GTID support is used (mockable for testing)
     */
    protected function useGTIDs() {
        return $this->useGTIDs;
    }
}

class_alias( DatabaseMysqlBase::class, 'DatabaseMysqlBase' );