function reportConnectionError(&$conn)
 {
     wfProfileIn(__METHOD__);
     if (!is_object($conn)) {
         // No last connection, probably due to all servers being too busy
         wfLogDBError("LB failure with no last connection\n");
         $conn = new Database();
         if ($this->mFailFunction) {
             $conn->failFunction($this->mFailFunction);
             $conn->reportConnectionError($this->mLastError);
         } else {
             // If all servers were busy, mLastError will contain something sensible
             throw new DBConnectionError($conn, $this->mLastError);
         }
     } else {
         if ($this->mFailFunction) {
             $conn->failFunction($this->mFailFunction);
         } else {
             $conn->failFunction(false);
         }
         $server = $conn->getProperty('mServer');
         wfLogDBError("Connection error: {$this->mLastError} ({$server})\n");
         $conn->reportConnectionError("{$this->mLastError} ({$server})");
     }
     wfProfileOut(__METHOD__);
 }

	/**
	 * Begin a transaction. If a transaction is already in progress, that transaction will be committed before the
	 * new transaction is started.
	 *
	 * Note that when the DBO_TRX flag is set (which is usually the case for web requests, but not for maintenance scripts),
	 * any previous database query will have started a transaction automatically.
	 *
	 * Nesting of transactions is not supported. Attempts to nest transactions will cause a warning, unless the current
	 * transaction was started automatically because of the DBO_TRX flag.
	 *
	 * @param $fname string
	 */
	final public function begin( $fname = __METHOD__ ) {
		global $wgDebugDBTransactions;

		if ( $this->mTrxLevel ) { // implicit commit
			if ( !$this->mTrxAutomatic ) {
				// We want to warn about inadvertently nested begin/commit pairs, but not about
				// auto-committing implicit transactions that were started by query() via DBO_TRX
				$msg = "$fname: Transaction already in progress (from {$this->mTrxFname}), " .
					" performing implicit commit!";
				wfWarn( $msg );
				wfLogDBError( $msg );
			} else {
				// if the transaction was automatic and has done write operations,
				// log it if $wgDebugDBTransactions is enabled.
				if ( $this->mTrxDoneWrites && $wgDebugDBTransactions ) {
					wfDebug( "$fname: Automatic transaction with writes in progress" .
						" (from {$this->mTrxFname}), performing implicit commit!\n"
					);
				}
			}

			$this->runOnTransactionPreCommitCallbacks();
			$this->doCommit( $fname );
			if ( $this->mTrxDoneWrites ) {
				Profiler::instance()->transactionWritingOut( $this->mServer, $this->mDBname );
			}
			$this->runOnTransactionIdleCallbacks();
		}

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

 /** Open an MSSQL database and return a resource handle to it
  *  NOTE: only $dbName is used, the other parameters are irrelevant for MSSQL databases
  */
 function open($server, $user, $password, $dbName)
 {
     wfProfileIn(__METHOD__);
     # Test for missing mysql.so
     # First try to load it
     if (!@extension_loaded('mssql')) {
         @dl('mssql.so');
     }
     # Fail now
     # Otherwise we get a suppressed fatal error, which is very hard to track down
     if (!function_exists('mssql_connect')) {
         throw new DBConnectionError($this, "MSSQL functions missing, have you compiled PHP with the --with-mssql option?\n");
     }
     $this->close();
     $this->mServer = $server;
     $this->mUser = $user;
     $this->mPassword = $password;
     $this->mDBname = $dbName;
     wfProfileIn("dbconnect-{$server}");
     # Try to connect up to three times
     # The kernel's default SYN retransmission period is far too slow for us,
     # so we use a short timeout plus a manual retry.
     $this->mConn = false;
     $max = 3;
     for ($i = 0; $i < $max && !$this->mConn; $i++) {
         if ($i > 1) {
             usleep(1000);
         }
         if ($this->mFlags & DBO_PERSISTENT) {
             @($this->mConn = mssql_pconnect($server, $user, $password));
         } else {
             # Create a new connection...
             @($this->mConn = mssql_connect($server, $user, $password, true));
         }
     }
     wfProfileOut("dbconnect-{$server}");
     if ($dbName != '') {
         if ($this->mConn !== false) {
             $success = @mssql_select_db($dbName, $this->mConn);
             if (!$success) {
                 $error = "Error selecting database {$dbName} on server {$this->mServer} " . "from client host " . wfHostname() . "\n";
                 wfLogDBError(" Error selecting database {$dbName} on server {$this->mServer} \n");
                 wfDebug($error);
             }
         } else {
             wfDebug("DB connection error\n");
             wfDebug("Server: {$server}, User: {$user}, Password: " . substr($password, 0, 3) . "...\n");
             $success = false;
         }
     } else {
         # Delay USE query
         $success = (bool) $this->mConn;
     }
     if (!$success) {
         $this->reportConnectionError();
     }
     $this->mOpened = $success;
     wfProfileOut(__METHOD__);
     return $success;
 }

 /**
  * Begin a transaction. If a transaction is already in progress,
  * that transaction will be committed before the new transaction is started.
  *
  * Note that when the DBO_TRX flag is set (which is usually the case for web
  * requests, but not for maintenance scripts), any previous database query
  * will have started a transaction automatically.
  *
  * Nesting of transactions is not supported. Attempts to nest transactions
  * will cause a warning, unless the current transaction was started
  * automatically because of the DBO_TRX flag.
  *
  * @param string $fname
  * @throws DBError
  */
 public final function begin($fname = __METHOD__)
 {
     if ($this->mTrxLevel) {
         // implicit commit
         if ($this->mTrxAtomicLevels) {
             // If the current transaction was an automatic atomic one, then we definitely have
             // a problem. Same if there is any unclosed atomic level.
             $levels = implode(', ', $this->mTrxAtomicLevels);
             throw new DBUnexpectedError($this, "Got explicit BEGIN while atomic sections {$levels} are still open.");
         } elseif (!$this->mTrxAutomatic) {
             // We want to warn about inadvertently nested begin/commit pairs, but not about
             // auto-committing implicit transactions that were started by query() via DBO_TRX
             $msg = "{$fname}: Transaction already in progress (from {$this->mTrxFname}), " . " performing implicit commit!";
             wfWarn($msg);
             wfLogDBError($msg, $this->getLogContext(array('method' => __METHOD__, 'fname' => $fname)));
         } else {
             // if the transaction was automatic and has done write operations
             if ($this->mTrxDoneWrites) {
                 wfDebug("{$fname}: Automatic transaction with writes in progress" . " (from {$this->mTrxFname}), performing implicit commit!\n");
             }
         }
         $this->runOnTransactionPreCommitCallbacks();
         $writeTime = $this->pendingWriteQueryDuration();
         $this->doCommit($fname);
         if ($this->mTrxDoneWrites) {
             $this->mDoneWrites = microtime(true);
             $this->getTransactionProfiler()->transactionWritingOut($this->mServer, $this->mDBname, $this->mTrxShortId, $writeTime);
         }
         $this->runOnTransactionIdleCallbacks();
     }
     # Avoid fatals if close() was called
     $this->assertOpen();
     $this->doBegin($fname);
     $this->mTrxTimestamp = microtime(true);
     $this->mTrxFname = $fname;
     $this->mTrxDoneWrites = false;
     $this->mTrxAutomatic = false;
     $this->mTrxAutomaticAtomic = false;
     $this->mTrxAtomicLevels = array();
     $this->mTrxIdleCallbacks = array();
     $this->mTrxPreCommitCallbacks = array();
     $this->mTrxShortId = wfRandomString(12);
     $this->mTrxWriteDuration = 0.0;
     // First SELECT after BEGIN will establish the snapshot in REPEATABLE-READ.
     // Get an estimate of the slave lag before then, treating estimate staleness
     // as lag itself just to be safe
     $status = $this->getApproximateLagStatus();
     $this->mTrxSlaveLag = $status['lag'] + (microtime(true) - $status['since']);
 }

 public function reportQueryError($error, $errno, $sql, $fname, $tempIgnore = false)
 {
     if ($this->ignoreErrors() || $tempIgnore) {
         wfDebug("SQL ERROR (ignored): {$error}\n");
     } else {
         $sql1line = mb_substr(str_replace("\n", "\\n", $sql), 0, 5 * 1024);
         wfLogDBError("{fname}\t{db_server}\t{errno}\t{error}\t{sql1line}", $this->getLogContext(['method' => __METHOD__, 'errno' => $errno, 'error' => $error, 'sql1line' => $sql1line, 'fname' => $fname]));
         wfDebug("SQL ERROR: " . $error . "\n");
         throw new DBQueryError($this, $error, $errno, $sql, $fname);
     }
 }

	/**
	 * @param $server string
	 * @param $user string
	 * @param $password string
	 * @param $dbName string
	 * @return bool
	 * @throws DBConnectionError
	 */
	function open( $server, $user, $password, $dbName ) {
		global $wgAllDBsAreLocalhost, $wgDBmysql5, $wgSQLMode;
		wfProfileIn( __METHOD__ );

		# Debugging hack -- fake cluster
		if ( $wgAllDBsAreLocalhost ) {
			$realServer = 'localhost';
		} else {
			$realServer = $server;
		}
		$this->close();
		$this->mServer = $server;
		$this->mUser = $user;
		$this->mPassword = $password;
		$this->mDBname = $dbName;

		wfProfileIn( "dbconnect-$server" );

		# The kernel's default SYN retransmission period is far too slow for us,
		# so we use a short timeout plus a manual retry. Retrying means that a small
		# but finite rate of SYN packet loss won't cause user-visible errors.
		$this->mConn = false;
		$this->installErrorHandler();
		try {
			$this->mConn = $this->mysqlConnect( $realServer );
		} catch ( Exception $ex ) {
			wfProfileOut( "dbconnect-$server" );
			wfProfileOut( __METHOD__ );
			throw $ex;
		}
		$error = $this->restoreErrorHandler();

		wfProfileOut( "dbconnect-$server" );

		# Always log connection errors
		if ( !$this->mConn ) {
			if ( !$error ) {
				$error = $this->lastError();
			}
			wfLogDBError( "Error connecting to {$this->mServer}: $error\n" );
			wfDebug( "DB connection error\n" .
				"Server: $server, User: $user, Password: " .
				substr( $password, 0, 3 ) . "..., error: " . $error . "\n" );

			wfProfileOut( __METHOD__ );
			return $this->reportConnectionError( $error );
		}

		if ( $dbName != '' ) {
			wfSuppressWarnings();
			$success = $this->selectDB( $dbName );
			wfRestoreWarnings();
			if ( !$success ) {
				wfLogDBError( "Error selecting database $dbName on server {$this->mServer}\n" );
				wfDebug( "Error selecting database $dbName on server {$this->mServer} " .
					"from client host " . wfHostname() . "\n" );

				wfProfileOut( __METHOD__ );
				return $this->reportConnectionError( "Error selecting database $dbName" );
			}
		}

		// Tell the server we're communicating with it in UTF-8.
		// This may engage various charset conversions.
		if ( $wgDBmysql5 ) {
			$this->query( 'SET NAMES utf8', __METHOD__ );
		} else {
			$this->query( 'SET NAMES binary', __METHOD__ );
		}
		// Set SQL mode, default is turning them all off, can be overridden or skipped with null
		if ( is_string( $wgSQLMode ) ) {
			$mode = $this->addQuotes( $wgSQLMode );
			$this->query( "SET sql_mode = $mode", __METHOD__ );
		}

		$this->mOpened = true;
		wfProfileOut( __METHOD__ );
		return true;
	}

 /**
  * Begin a transaction. If a transaction is already in progress,
  * that transaction will be committed before the new transaction is started.
  *
  * Note that when the DBO_TRX flag is set (which is usually the case for web
  * requests, but not for maintenance scripts), any previous database query
  * will have started a transaction automatically.
  *
  * Nesting of transactions is not supported. Attempts to nest transactions
  * will cause a warning, unless the current transaction was started
  * automatically because of the DBO_TRX flag.
  *
  * @param string $fname
  * @throws DBError
  */
 public final function begin($fname = __METHOD__)
 {
     global $wgDebugDBTransactions;
     if ($this->mTrxLevel) {
         // implicit commit
         if (!$this->mTrxAtomicLevels->isEmpty()) {
             // If the current transaction was an automatic atomic one, then we definitely have
             // a problem. Same if there is any unclosed atomic level.
             throw new DBUnexpectedError($this, "Attempted to start explicit transaction when atomic levels are still open.");
         } elseif (!$this->mTrxAutomatic) {
             // We want to warn about inadvertently nested begin/commit pairs, but not about
             // auto-committing implicit transactions that were started by query() via DBO_TRX
             $msg = "{$fname}: Transaction already in progress (from {$this->mTrxFname}), " . " performing implicit commit!";
             wfWarn($msg);
             wfLogDBError($msg, $this->getLogContext(array('method' => __METHOD__, 'fname' => $fname)));
         } else {
             // if the transaction was automatic and has done write operations,
             // log it if $wgDebugDBTransactions is enabled.
             if ($this->mTrxDoneWrites && $wgDebugDBTransactions) {
                 wfDebug("{$fname}: Automatic transaction with writes in progress" . " (from {$this->mTrxFname}), performing implicit commit!\n");
             }
         }
         $this->runOnTransactionPreCommitCallbacks();
         $writeTime = $this->pendingWriteQueryDuration();
         $this->doCommit($fname);
         if ($this->mTrxDoneWrites) {
             $this->mDoneWrites = microtime(true);
             $this->getTransactionProfiler()->transactionWritingOut($this->mServer, $this->mDBname, $this->mTrxShortId, $writeTime);
         }
         $this->runOnTransactionIdleCallbacks();
     }
     # Avoid fatals if close() was called
     $this->assertOpen();
     $this->doBegin($fname);
     $this->mTrxTimestamp = microtime(true);
     $this->mTrxFname = $fname;
     $this->mTrxDoneWrites = false;
     $this->mTrxAutomatic = false;
     $this->mTrxAutomaticAtomic = false;
     $this->mTrxAtomicLevels = new SplStack();
     $this->mTrxIdleCallbacks = array();
     $this->mTrxPreCommitCallbacks = array();
     $this->mTrxShortId = wfRandomString(12);
     $this->mTrxWriteDuration = 0.0;
 }

 /**
  * @throws DBConnectionError
  * @return bool
  */
 private function reportConnectionError()
 {
     $conn = $this->mErrorConnection;
     // The connection which caused the error
     $context = array('method' => __METHOD__, 'last_error' => $this->mLastError);
     if (!is_object($conn)) {
         // No last connection, probably due to all servers being too busy
         wfLogDBError("LB failure with no last connection. Connection error: {last_error}", $context);
         // If all servers were busy, mLastError will contain something sensible
         throw new DBConnectionError(null, $this->mLastError);
     } else {
         $context['db_server'] = $conn->getProperty('mServer');
         wfLogDBError("Connection error: {last_error} ({db_server})", $context);
         $conn->reportConnectionError("{$this->mLastError} ({$context['db_server']})");
         // throws DBConnectionError
     }
     return false;
     /* not reached */
 }

 /**
  * Begin a transaction. If a transaction is already in progress,
  * that transaction will be committed before the new transaction is started.
  *
  * Note that when the DBO_TRX flag is set (which is usually the case for web
  * requests, but not for maintenance scripts), any previous database query
  * will have started a transaction automatically.
  *
  * Nesting of transactions is not supported. Attempts to nest transactions
  * will cause a warning, unless the current transaction was started
  * automatically because of the DBO_TRX flag.
  *
  * @param string $fname
  * @throws DBError
  */
 public final function begin($fname = __METHOD__)
 {
     global $wgDebugDBTransactions;
     if ($this->mTrxLevel) {
         // implicit commit
         if (!$this->mTrxAtomicLevels->isEmpty()) {
             // If the current transaction was an automatic atomic one, then we definitely have
             // a problem. Same if there is any unclosed atomic level.
             throw new DBUnexpectedError($this, "Attempted to start explicit transaction when atomic levels are still open.");
         } elseif (!$this->mTrxAutomatic) {
             // We want to warn about inadvertently nested begin/commit pairs, but not about
             // auto-committing implicit transactions that were started by query() via DBO_TRX
             $msg = "{$fname}: Transaction already in progress (from {$this->mTrxFname}), " . " performing implicit commit!";
             wfWarn($msg);
             wfLogDBError($msg);
         } else {
             // if the transaction was automatic and has done write operations,
             // log it if $wgDebugDBTransactions is enabled.
             if ($this->mTrxDoneWrites && $wgDebugDBTransactions) {
                 wfDebug("{$fname}: Automatic transaction with writes in progress" . " (from {$this->mTrxFname}), performing implicit commit!\n");
             }
         }
         $this->runOnTransactionPreCommitCallbacks();
         $this->doCommit($fname);
         if ($this->mTrxDoneWrites) {
             Profiler::instance()->transactionWritingOut($this->mServer, $this->mDBname);
         }
         $this->runOnTransactionIdleCallbacks();
     }
     $this->doBegin($fname);
     $this->mTrxFname = $fname;
     $this->mTrxDoneWrites = false;
     $this->mTrxAutomatic = false;
     $this->mTrxAutomaticAtomic = false;
     $this->mTrxAtomicLevels = new SplStack();
     $this->mTrxIdleCallbacks = array();
     $this->mTrxPreCommitCallbacks = array();
 }

 /**
  * @param $server string
  * @param $user string
  * @param $password string
  * @param $dbName string
  * @return bool
  * @throws DBConnectionError
  */
 function open($server, $user, $password, $dbName)
 {
     global $wgAllDBsAreLocalhost, $wgDBmysql5, $wgSQLMode;
     wfProfileIn(__METHOD__);
     # Load mysql.so if we don't have it
     wfDl('mysql');
     # Fail now
     # Otherwise we get a suppressed fatal error, which is very hard to track down
     if (!function_exists('mysql_connect')) {
         throw new DBConnectionError($this, "MySQL functions missing, have you compiled PHP with the --with-mysql option?\n");
     }
     # Debugging hack -- fake cluster
     if ($wgAllDBsAreLocalhost) {
         $realServer = 'localhost';
     } else {
         $realServer = $server;
     }
     $this->close();
     $this->mServer = $server;
     $this->mUser = $user;
     $this->mPassword = $password;
     $this->mDBname = $dbName;
     $connFlags = 0;
     if ($this->mFlags & DBO_SSL) {
         $connFlags |= MYSQL_CLIENT_SSL;
     }
     if ($this->mFlags & DBO_COMPRESS) {
         $connFlags |= MYSQL_CLIENT_COMPRESS;
     }
     wfProfileIn("dbconnect-{$server}");
     # The kernel's default SYN retransmission period is far too slow for us,
     # so we use a short timeout plus a manual retry. Retrying means that a small
     # but finite rate of SYN packet loss won't cause user-visible errors.
     $this->mConn = false;
     if (ini_get('mysql.connect_timeout') <= 3) {
         $numAttempts = 2;
     } else {
         $numAttempts = 1;
     }
     $this->installErrorHandler();
     for ($i = 0; $i < $numAttempts && !$this->mConn; $i++) {
         if ($i > 1) {
             usleep(1000);
         }
         if ($this->mFlags & DBO_PERSISTENT) {
             $this->mConn = mysql_pconnect($realServer, $user, $password, $connFlags);
         } else {
             # Create a new connection...
             $this->mConn = mysql_connect($realServer, $user, $password, true, $connFlags);
         }
         #if ( $this->mConn === false ) {
         #$iplus = $i + 1;
         #wfLogDBError("Connect loop error $iplus of $max ($server): " . mysql_errno() . " - " . mysql_error()."\n");
         #}
     }
     $error = $this->restoreErrorHandler();
     wfProfileOut("dbconnect-{$server}");
     # Always log connection errors
     if (!$this->mConn) {
         if (!$error) {
             $error = $this->lastError();
         }
         wfLogDBError("Error connecting to {$this->mServer}: {$error}\n");
         wfDebug("DB connection error\n" . "Server: {$server}, User: {$user}, Password: " . substr($password, 0, 3) . "..., error: " . $error . "\n");
         wfProfileOut(__METHOD__);
         $this->reportConnectionError($error);
     }
     if ($dbName != '') {
         wfSuppressWarnings();
         $success = mysql_select_db($dbName, $this->mConn);
         wfRestoreWarnings();
         if (!$success) {
             wfLogDBError("Error selecting database {$dbName} on server {$this->mServer}\n");
             wfDebug("Error selecting database {$dbName} on server {$this->mServer} " . "from client host " . wfHostname() . "\n");
             wfProfileOut(__METHOD__);
             $this->reportConnectionError("Error selecting database {$dbName}");
         }
     }
     // Tell the server we're communicating with it in UTF-8.
     // This may engage various charset conversions.
     if ($wgDBmysql5) {
         $this->query('SET NAMES utf8', __METHOD__);
     } else {
         $this->query('SET NAMES binary', __METHOD__);
     }
     // Set SQL mode, default is turning them all off, can be overridden or skipped with null
     if (is_string($wgSQLMode)) {
         $mode = $this->addQuotes($wgSQLMode);
         $this->query("SET sql_mode = {$mode}", __METHOD__);
     }
     $this->mOpened = true;
     wfProfileOut(__METHOD__);
//.........这里部分代码省略.........

 /**
  * @param $error
  * @param $errno
  * @param $sql
  * @param string $fname
  * @param bool $tempIgnore
  */
 function reportQueryError($error, $errno, $sql, $fname, $tempIgnore = false)
 {
     global $wgCommandLineMode, $wgFullyInitialised;
     # Ignore errors during error handling to avoid infinite recursion
     $ignore = $this->ignoreErrors(true);
     $this->mErrorCount++;
     if ($ignore || $tempIgnore) {
         wfDebug("SQL ERROR (ignored): " . $error . "\n");
     } else {
         $sql1line = str_replace("\n", "\\n", $sql);
         wfLogDBError("{$fname}\t{$this->mServer}\t{$errno}\t{$error}\t{$sql1line}\n");
         wfDebug("SQL ERROR: " . $error . "\n");
         if ($wgCommandLineMode || !$this->mOut || empty($wgFullyInitialised)) {
             $message = "A database error has occurred\n" . "Query: {$sql}\n" . "Function: {$fname}\n" . "Error: {$errno} {$error}\n";
             if (!$wgCommandLineMode) {
                 $message = nl2br($message);
             }
             wfDebugDieBacktrace($message);
         } else {
             // this calls wfAbruptExit()
             $this->mOut->databaseError($fname, $sql, $error, $errno);
         }
     }
     $this->ignoreErrors($ignore);
 }

 /**
  * @param string $server
  * @param string $user
  * @param string $password
  * @param string $dbName
  * @throws Exception|DBConnectionError
  * @return bool
  */
 function open($server, $user, $password, $dbName)
 {
     global $wgAllDBsAreLocalhost, $wgSQLMode;
     # Debugging hack -- fake cluster
     if ($wgAllDBsAreLocalhost) {
         $realServer = 'localhost';
     } else {
         $realServer = $server;
     }
     $this->close();
     $this->mServer = $server;
     $this->mUser = $user;
     $this->mPassword = $password;
     $this->mDBname = $dbName;
     # The kernel's default SYN retransmission period is far too slow for us,
     # so we use a short timeout plus a manual retry. Retrying means that a small
     # but finite rate of SYN packet loss won't cause user-visible errors.
     $this->mConn = false;
     $this->installErrorHandler();
     try {
         $this->mConn = $this->mysqlConnect($realServer);
     } catch (Exception $ex) {
         $this->restoreErrorHandler();
         throw $ex;
     }
     $error = $this->restoreErrorHandler();
     # Always log connection errors
     if (!$this->mConn) {
         if (!$error) {
             $error = $this->lastError();
         }
         wfLogDBError("Error connecting to {db_server}: {error}", $this->getLogContext(array('method' => __METHOD__, 'error' => $error)));
         wfDebug("DB connection error\n" . "Server: {$server}, User: {$user}, Password: " . substr($password, 0, 3) . "..., error: " . $error . "\n");
         $this->reportConnectionError($error);
     }
     if ($dbName != '') {
         wfSuppressWarnings();
         $success = $this->selectDB($dbName);
         wfRestoreWarnings();
         if (!$success) {
             wfLogDBError("Error selecting database {db_name} on server {db_server}", $this->getLogContext(array('method' => __METHOD__)));
             wfDebug("Error selecting database {$dbName} on server {$this->mServer} " . "from client host " . wfHostname() . "\n");
             $this->reportConnectionError("Error selecting database {$dbName}");
         }
     }
     // Tell the server what we're communicating with
     if (!$this->connectInitCharset()) {
         $this->reportConnectionError("Error setting character set");
     }
     // Abstract over any insane MySQL defaults
     $set = array('group_concat_max_len = 262144');
     // Set SQL mode, default is turning them all off, can be overridden or skipped with null
     if (is_string($wgSQLMode)) {
         $set[] = 'sql_mode = ' . $this->addQuotes($wgSQLMode);
     }
     if ($set) {
         // Use doQuery() to avoid opening implicit transactions (DBO_TRX)
         $success = $this->doQuery('SET ' . implode(', ', $set), __METHOD__);
         if (!$success) {
             wfLogDBError('Error setting MySQL variables on server {db_server} (check $wgSQLMode)', $this->getLogContext(array('method' => __METHOD__)));
             $this->reportConnectionError('Error setting MySQL variables on server {db_server} (check $wgSQLMode)');
         }
     }
     $this->mOpened = true;
     return true;
 }

 /**
  * @param $conn
  * @throws DBConnectionError
  */
 function reportConnectionError(&$conn)
 {
     if (!is_object($conn)) {
         // No last connection, probably due to all servers being too busy
         wfLogDBError("LB failure with no last connection. Connection error: {$this->mLastError}\n");
         $conn = new Database();
         // If all servers were busy, mLastError will contain something sensible
         throw new DBConnectionError($conn, $this->mLastError);
     } else {
         $server = $conn->getProperty('mServer');
         wfLogDBError("Connection error: {$this->mLastError} ({$server})\n");
         $conn->reportConnectionError("{$this->mLastError} ({$server})");
     }
 }

 /**
  * @param $conn DatabaseBase
  * @param $threshold
  * @return int
  */
 function postConnectionBackoff($conn, $threshold)
 {
     if (!$threshold) {
         return 0;
     }
     $status = $conn->getMysqlStatus("Thread%");
     if ($status['Threads_running'] > $threshold) {
         $server = $conn->getProperty('mServer');
         wfLogDBError("LB backoff from {$server} - Threads_running = {$status['Threads_running']}\n");
         return $status['Threads_connected'];
     } else {
         return 0;
     }
 }

 function open($server, $user, $password, $dbName)
 {
     global $wgAllDBsAreLocalhost;
     wfProfileIn(__METHOD__);
     # Test for missing mysql.so
     # First try to load it
     if (!@extension_loaded('mysql')) {
         @dl('mysql.so');
     }
     # Fail now
     # Otherwise we get a suppressed fatal error, which is very hard to track down
     if (!function_exists('mysql_connect')) {
         throw new DBConnectionError($this, "MySQL functions missing, have you compiled PHP with the --with-mysql option?\n");
     }
     # Debugging hack -- fake cluster
     if ($wgAllDBsAreLocalhost) {
         $realServer = 'localhost';
     } else {
         $realServer = $server;
     }
     $this->close();
     $this->mServer = $server;
     $this->mUser = $user;
     $this->mPassword = $password;
     $this->mDBname = $dbName;
     $success = false;
     wfProfileIn("dbconnect-{$server}");
     # The kernel's default SYN retransmission period is far too slow for us,
     # so we use a short timeout plus a manual retry. Retrying means that a small
     # but finite rate of SYN packet loss won't cause user-visible errors.
     $this->mConn = false;
     if (ini_get('mysql.connect_timeout') <= 3) {
         $numAttempts = 2;
     } else {
         $numAttempts = 1;
     }
     $this->installErrorHandler();
     for ($i = 0; $i < $numAttempts && !$this->mConn; $i++) {
         if ($i > 1) {
             usleep(1000);
         }
         if ($this->mFlags & DBO_PERSISTENT) {
             $this->mConn = mysql_pconnect($realServer, $user, $password);
         } else {
             # Create a new connection...
             $this->mConn = mysql_connect($realServer, $user, $password, true);
         }
         if ($this->mConn === false) {
             #$iplus = $i + 1;
             #wfLogDBError("Connect loop error $iplus of $max ($server): " . mysql_errno() . " - " . mysql_error()."\n");
         }
     }
     $phpError = $this->restoreErrorHandler();
     # Always log connection errors
     if (!$this->mConn) {
         $error = $this->lastError();
         if (!$error) {
             $error = $phpError;
         }
         wfLogDBError("Error connecting to {$this->mServer}: {$error}\n");
         wfDebug("DB connection error\n");
         wfDebug("Server: {$server}, User: {$user}, Password: " . substr($password, 0, 3) . "..., error: " . mysql_error() . "\n");
         $success = false;
     }
     wfProfileOut("dbconnect-{$server}");
     if ($dbName != '' && $this->mConn !== false) {
         $success = @mysql_select_db($dbName, $this->mConn);
         if (!$success) {
             $error = "Error selecting database {$dbName} on server {$this->mServer} " . "from client host " . wfHostname() . "\n";
             wfLogDBError(" Error selecting database {$dbName} on server {$this->mServer} \n");
             wfDebug($error);
         }
     } else {
         # Delay USE query
         $success = (bool) $this->mConn;
     }
     if ($success) {
         $version = $this->getServerVersion();
         if (version_compare($version, '4.1') >= 0) {
             // Tell the server we're communicating with it in UTF-8.
             // This may engage various charset conversions.
             global $wgDBmysql5;
             if ($wgDBmysql5) {
                 $this->query('SET NAMES utf8', __METHOD__);
             }
             // Turn off strict mode
             $this->query("SET sql_mode = ''", __METHOD__);
         }
         // Turn off strict mode if it is on
     } else {
         $this->reportConnectionError($phpError);
     }
     $this->mOpened = $success;
     wfProfileOut(__METHOD__);
     return $success;
 }

 /**
  * @return bool|float
  */
 protected function getLagFromPtHeartbeat()
 {
     $masterInfo = $this->getMasterServerInfo();
     if (!$masterInfo) {
         wfLogDBError("Unable to query master of {db_server} for server ID", $this->getLogContext(array('method' => __METHOD__)));
         return false;
         // could not get master server ID
     }
     list($time, $nowUnix) = $this->getHeartbeatData($masterInfo['serverId']);
     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') + $dateTime->format('u') / 1000000.0;
         return max($nowUnix - $timeUnix, 0.0);
     }
     wfLogDBError("Unable to find pt-heartbeat row for {db_server}", $this->getLogContext(array('method' => __METHOD__)));
     return false;
 }

 /**
  * @param $error
  * @param $errno
  * @param $sql
  * @param string $fname
  * @param bool $tempIgnore
  */
 function reportQueryError($error, $errno, $sql, $fname, $tempIgnore = false)
 {
     global $wgCommandLineMode, $wgFullyInitialised, $wgColorErrors;
     # Ignore errors during error handling to avoid infinite recursion
     $ignore = $this->ignoreErrors(true);
     ++$this->mErrorCount;
     if ($ignore || $tempIgnore) {
         wfDebug("SQL ERROR (ignored): {$error}\n");
         $this->ignoreErrors($ignore);
     } else {
         $sql1line = str_replace("\n", "\\n", $sql);
         wfLogDBError("{$fname}\t{$this->mServer}\t{$errno}\t{$error}\t{$sql1line}\n");
         wfDebug("SQL ERROR: " . $error . "\n");
         throw new DBQueryError($this, $error, $errno, $sql, $fname);
     }
 }

 /**
  * @param string $server
  * @param string $user
  * @param string $password
  * @param string $dbName
  * @throws Exception|DBConnectionError
  * @return bool
  */
 function open($server, $user, $password, $dbName)
 {
     global $wgAllDBsAreLocalhost, $wgSQLMode;
     # Close/unset connection handle
     $this->close();
     # Debugging hack -- fake cluster
     $realServer = $wgAllDBsAreLocalhost ? 'localhost' : $server;
     $this->mServer = $server;
     $this->mUser = $user;
     $this->mPassword = $password;
     $this->mDBname = $dbName;
     $this->installErrorHandler();
     try {
         $this->mConn = $this->mysqlConnect($realServer);
     } catch (Exception $ex) {
         $this->restoreErrorHandler();
         throw $ex;
     }
     $error = $this->restoreErrorHandler();
     # Always log connection errors
     if (!$this->mConn) {
         if (!$error) {
             $error = $this->lastError();
         }
         wfLogDBError("Error connecting to {db_server}: {error}", $this->getLogContext(array('method' => __METHOD__, 'error' => $error)));
         wfDebug("DB connection error\n" . "Server: {$server}, User: {$user}, Password: " . substr($password, 0, 3) . "..., error: " . $error . "\n");
         $this->reportConnectionError($error);
     }
     if ($dbName != '') {
         MediaWiki\suppressWarnings();
         $success = $this->selectDB($dbName);
         MediaWiki\restoreWarnings();
         if (!$success) {
             wfLogDBError("Error selecting database {db_name} on server {db_server}", $this->getLogContext(array('method' => __METHOD__)));
             wfDebug("Error selecting database {$dbName} on server {$this->mServer} " . "from client host " . wfHostname() . "\n");
             $this->reportConnectionError("Error selecting database {$dbName}");
         }
     }
     // Tell the server what we're communicating with
     if (!$this->connectInitCharset()) {
         $this->reportConnectionError("Error setting character set");
     }
     // Abstract over any insane MySQL defaults
     $set = array('group_concat_max_len = 262144');
     // Set SQL mode, default is turning them all off, can be overridden or skipped with null
     if (is_string($wgSQLMode)) {
         $set[] = 'sql_mode = ' . $this->addQuotes($wgSQLMode);
     }
     // Set any custom settings defined by site config
     // (e.g. https://dev.mysql.com/doc/refman/4.1/en/innodb-parameters.html)
     foreach ($this->mSessionVars 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) {
             wfLogDBError('Error setting MySQL variables on server {db_server} (check $wgSQLMode)', $this->getLogContext(array('method' => __METHOD__)));
             $this->reportConnectionError('Error setting MySQL variables on server {db_server} (check $wgSQLMode)');
         }
     }
     $this->mOpened = true;
     return true;
 }