Current File : //www/varak.net/wiki.varak.net/includes/db/loadbalancer/LoadBalancer.php
<?php
/**
* Database load balancing.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
* http://www.gnu.org/copyleft/gpl.html
*
* @file
* @ingroup Database
*/
/**
* Database load balancing object
*
* @todo document
* @ingroup Database
*/
class LoadBalancer {
/** @var array[] Map of (server index => server config array) */
private $mServers;
/** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
private $mConns;
/** @var array Map of (server index => weight) */
private $mLoads;
/** @var array[] Map of (group => server index => weight) */
private $mGroupLoads;
/** @var bool Whether to disregard slave lag as a factor in slave selection */
private $mAllowLagged;
/** @var integer Seconds to spend waiting on slave lag to resolve */
private $mWaitTimeout;
/** @var array LBFactory information */
private $mParentInfo;
/** @var string The LoadMonitor subclass name */
private $mLoadMonitorClass;
/** @var LoadMonitor */
private $mLoadMonitor;
/** @var BagOStuff */
private $srvCache;
/** @var WANObjectCache */
private $wanCache;
/** @var TransactionProfiler */
protected $trxProfiler;
/** @var bool|DatabaseBase Database connection that caused a problem */
private $mErrorConnection;
/** @var integer The generic (not query grouped) slave index (of $mServers) */
private $mReadIndex;
/** @var bool|DBMasterPos False if not set */
private $mWaitForPos;
/** @var bool Whether the generic reader fell back to a lagged slave */
private $laggedSlaveMode = false;
/** @var bool Whether the generic reader fell back to a lagged slave */
private $slavesDownMode = false;
/** @var string The last DB selection or connection error */
private $mLastError = 'Unknown error';
/** @var string|bool Reason the LB is read-only or false if not */
private $readOnlyReason = false;
/** @var integer Total connections opened */
private $connsOpened = 0;
/** @var string|bool String if a requested DBO_TRX transaction round is active */
private $trxRoundId = false;
/** @var integer Warn when this many connection are held */
const CONN_HELD_WARN_THRESHOLD = 10;
/** @var integer Default 'max lag' when unspecified */
const MAX_LAG = 10;
/** @var integer Max time to wait for a slave to catch up (e.g. ChronologyProtector) */
const POS_WAIT_TIMEOUT = 10;
/** @var integer Seconds to cache master server read-only status */
const TTL_CACHE_READONLY = 5;
/**
* @var boolean
*/
private $disabled = false;
/**
* @param array $params Array with keys:
* - servers : Required. Array of server info structures.
* - loadMonitor : Name of a class used to fetch server lag and load.
* - readOnlyReason : Reason the master DB is read-only if so [optional]
* - srvCache : BagOStuff object [optional]
* - wanCache : WANObjectCache object [optional]
* @throws MWException
*/
public function __construct( array $params ) {
if ( !isset( $params['servers'] ) ) {
throw new MWException( __CLASS__ . ': missing servers parameter' );
}
$this->mServers = $params['servers'];
$this->mWaitTimeout = self::POS_WAIT_TIMEOUT;
$this->mReadIndex = -1;
$this->mWriteIndex = -1;
$this->mConns = [
'local' => [],
'foreignUsed' => [],
'foreignFree' => [] ];
$this->mLoads = [];
$this->mWaitForPos = false;
$this->mErrorConnection = false;
$this->mAllowLagged = false;
if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
$this->readOnlyReason = $params['readOnlyReason'];
}
if ( isset( $params['loadMonitor'] ) ) {
$this->mLoadMonitorClass = $params['loadMonitor'];
} else {
$master = reset( $params['servers'] );
if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
$this->mLoadMonitorClass = 'LoadMonitorMySQL';
} else {
$this->mLoadMonitorClass = 'LoadMonitorNull';
}
}
foreach ( $params['servers'] as $i => $server ) {
$this->mLoads[$i] = $server['load'];
if ( isset( $server['groupLoads'] ) ) {
foreach ( $server['groupLoads'] as $group => $ratio ) {
if ( !isset( $this->mGroupLoads[$group] ) ) {
$this->mGroupLoads[$group] = [];
}
$this->mGroupLoads[$group][$i] = $ratio;
}
}
}
if ( isset( $params['srvCache'] ) ) {
$this->srvCache = $params['srvCache'];
} else {
$this->srvCache = new EmptyBagOStuff();
}
if ( isset( $params['wanCache'] ) ) {
$this->wanCache = $params['wanCache'];
} else {
$this->wanCache = WANObjectCache::newEmpty();
}
if ( isset( $params['trxProfiler'] ) ) {
$this->trxProfiler = $params['trxProfiler'];
} else {
$this->trxProfiler = new TransactionProfiler();
}
}
/**
* Get a LoadMonitor instance
*
* @return LoadMonitor
*/
private function getLoadMonitor() {
if ( !isset( $this->mLoadMonitor ) ) {
$class = $this->mLoadMonitorClass;
$this->mLoadMonitor = new $class( $this );
}
return $this->mLoadMonitor;
}
/**
* Get or set arbitrary data used by the parent object, usually an LBFactory
* @param mixed $x
* @return mixed
*/
public function parentInfo( $x = null ) {
return wfSetVar( $this->mParentInfo, $x );
}
/**
* @param array $loads
* @param bool|string $wiki Wiki to get non-lagged for
* @param int $maxLag Restrict the maximum allowed lag to this many seconds
* @return bool|int|string
*/
private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) {
$lags = $this->getLagTimes( $wiki );
# Unset excessively lagged servers
foreach ( $lags as $i => $lag ) {
if ( $i != 0 ) {
$maxServerLag = $maxLag;
if ( isset( $this->mServers[$i]['max lag'] ) ) {
$maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
}
$host = $this->getServerName( $i );
if ( $lag === false ) {
wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
unset( $loads[$i] );
} elseif ( $lag > $maxServerLag ) {
wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
unset( $loads[$i] );
}
}
}
# Find out if all the slaves with non-zero load are lagged
$sum = 0;
foreach ( $loads as $load ) {
$sum += $load;
}
if ( $sum == 0 ) {
# No appropriate DB servers except maybe the master and some slaves with zero load
# Do NOT use the master
# Instead, this function will return false, triggering read-only mode,
# and a lagged slave will be used instead.
return false;
}
if ( count( $loads ) == 0 ) {
return false;
}
# Return a random representative of the remainder
return ArrayUtils::pickRandom( $loads );
}
/**
* Get the index of the reader connection, which may be a slave
* This takes into account load ratios and lag times. It should
* always return a consistent index during a given invocation
*
* Side effect: opens connections to databases
* @param string|bool $group Query group, or false for the generic reader
* @param string|bool $wiki Wiki ID, or false for the current wiki
* @throws MWException
* @return bool|int|string
*/
public function getReaderIndex( $group = false, $wiki = false ) {
global $wgDBtype;
# @todo FIXME: For now, only go through all this for mysql databases
if ( $wgDBtype != 'mysql' ) {
return $this->getWriterIndex();
}
if ( count( $this->mServers ) == 1 ) {
# Skip the load balancing if there's only one server
return 0;
} elseif ( $group === false && $this->mReadIndex >= 0 ) {
# Shortcut if generic reader exists already
return $this->mReadIndex;
}
# Find the relevant load array
if ( $group !== false ) {
if ( isset( $this->mGroupLoads[$group] ) ) {
$nonErrorLoads = $this->mGroupLoads[$group];
} else {
# No loads for this group, return false and the caller can use some other group
wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
return false;
}
} else {
$nonErrorLoads = $this->mLoads;
}
if ( !count( $nonErrorLoads ) ) {
throw new MWException( "Empty server array given to LoadBalancer" );
}
# Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
$this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
$laggedSlaveMode = false;
# No server found yet
$i = false;
$conn = false;
# First try quickly looking through the available servers for a server that
# meets our criteria
$currentLoads = $nonErrorLoads;
while ( count( $currentLoads ) ) {
if ( $this->mAllowLagged || $laggedSlaveMode ) {
$i = ArrayUtils::pickRandom( $currentLoads );
} else {
$i = false;
if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
# ChronologyProtecter causes mWaitForPos to be set via sessions.
# This triggers doWait() after connect, so it's especially good to
# avoid lagged servers so as to avoid just blocking in that method.
$ago = microtime( true ) - $this->mWaitForPos->asOfTime();
# Aim for <= 1 second of waiting (being too picky can backfire)
$i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
}
if ( $i === false ) {
# Any server with less lag than it's 'max lag' param is preferable
$i = $this->getRandomNonLagged( $currentLoads, $wiki );
}
if ( $i === false && count( $currentLoads ) != 0 ) {
# All slaves lagged. Switch to read-only mode
wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
$i = ArrayUtils::pickRandom( $currentLoads );
$laggedSlaveMode = true;
}
}
if ( $i === false ) {
# pickRandom() returned false
# This is permanent and means the configuration or the load monitor
# wants us to return false.
wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
return false;
}
$serverName = $this->getServerName( $i );
wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
$conn = $this->openConnection( $i, $wiki );
if ( !$conn ) {
wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
unset( $nonErrorLoads[$i] );
unset( $currentLoads[$i] );
$i = false;
continue;
}
// Decrement reference counter, we are finished with this connection.
// It will be incremented for the caller later.
if ( $wiki !== false ) {
$this->reuseConnection( $conn );
}
# Return this server
break;
}
# If all servers were down, quit now
if ( !count( $nonErrorLoads ) ) {
wfDebugLog( 'connect', "All servers down" );
}
if ( $i !== false ) {
# Slave connection successful
# Wait for the session master pos for a short time
if ( $this->mWaitForPos && $i > 0 ) {
if ( !$this->doWait( $i ) ) {
$this->mServers[$i]['slave pos'] = $conn->getSlavePos();
}
}
if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
$this->mReadIndex = $i;
# Record if the generic reader index is in "lagged slave" mode
if ( $laggedSlaveMode ) {
$this->laggedSlaveMode = true;
}
}
$serverName = $this->getServerName( $i );
wfDebugLog( 'connect', __METHOD__ .
": using server $serverName for group '$group'\n" );
}
return $i;
}
/**
* Set the master wait position
* If a DB_SLAVE connection has been opened already, waits
* Otherwise sets a variable telling it to wait if such a connection is opened
* @param DBMasterPos $pos
*/
public function waitFor( $pos ) {
$this->mWaitForPos = $pos;
$i = $this->mReadIndex;
if ( $i > 0 ) {
if ( !$this->doWait( $i ) ) {
$this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
$this->laggedSlaveMode = true;
}
}
}
/**
* Set the master wait position and wait for a "generic" slave to catch up to it
*
* This can be used a faster proxy for waitForAll()
*
* @param DBMasterPos $pos
* @param int $timeout Max seconds to wait; default is mWaitTimeout
* @return bool Success (able to connect and no timeouts reached)
* @since 1.26
*/
public function waitForOne( $pos, $timeout = null ) {
$this->mWaitForPos = $pos;
$i = $this->mReadIndex;
if ( $i <= 0 ) {
// Pick a generic slave if there isn't one yet
$readLoads = $this->mLoads;
unset( $readLoads[$this->getWriterIndex()] ); // slaves only
$readLoads = array_filter( $readLoads ); // with non-zero load
$i = ArrayUtils::pickRandom( $readLoads );
}
if ( $i > 0 ) {
$ok = $this->doWait( $i, true, $timeout );
} else {
$ok = true; // no applicable loads
}
return $ok;
}
/**
* Set the master wait position and wait for ALL slaves to catch up to it
* @param DBMasterPos $pos
* @param int $timeout Max seconds to wait; default is mWaitTimeout
* @return bool Success (able to connect and no timeouts reached)
*/
public function waitForAll( $pos, $timeout = null ) {
$this->mWaitForPos = $pos;
$serverCount = count( $this->mServers );
$ok = true;
for ( $i = 1; $i < $serverCount; $i++ ) {
if ( $this->mLoads[$i] > 0 ) {
$ok = $this->doWait( $i, true, $timeout ) && $ok;
}
}
return $ok;
}
/**
* Get any open connection to a given server index, local or foreign
* Returns false if there is no connection open
*
* @param int $i
* @return DatabaseBase|bool False on failure
*/
public function getAnyOpenConnection( $i ) {
foreach ( $this->mConns as $conns ) {
if ( !empty( $conns[$i] ) ) {
return reset( $conns[$i] );
}
}
return false;
}
/**
* Wait for a given slave to catch up to the master pos stored in $this
* @param int $index Server index
* @param bool $open Check the server even if a new connection has to be made
* @param int $timeout Max seconds to wait; default is mWaitTimeout
* @return bool
*/
protected function doWait( $index, $open = false, $timeout = null ) {
$close = false; // close the connection afterwards
// Check if we already know that the DB has reached this point
$server = $this->getServerName( $index );
$key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
/** @var DBMasterPos $knownReachedPos */
$knownReachedPos = $this->srvCache->get( $key );
if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
wfDebugLog( 'replication', __METHOD__ .
": slave $server known to be caught up (pos >= $knownReachedPos).\n" );
return true;
}
// Find a connection to wait on, creating one if needed and allowed
$conn = $this->getAnyOpenConnection( $index );
if ( !$conn ) {
if ( !$open ) {
wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
return false;
} else {
$conn = $this->openConnection( $index, '' );
if ( !$conn ) {
wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
return false;
}
// Avoid connection spam in waitForAll() when connections
// are made just for the sake of doing this lag check.
$close = true;
}
}
wfDebugLog( 'replication', __METHOD__ . ": Waiting for slave $server to catch up...\n" );
$timeout = $timeout ?: $this->mWaitTimeout;
$result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
if ( $result == -1 || is_null( $result ) ) {
// Timed out waiting for slave, use master instead
$msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
wfDebugLog( 'replication', "$msg\n" );
wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
$ok = false;
} else {
wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
$ok = true;
// Remember that the DB reached this point
$this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
}
if ( $close ) {
$this->closeConnection( $conn );
}
return $ok;
}
/**
* Get a connection by index
* This is the main entry point for this class.
*
* @param int $i Server index
* @param array|string|bool $groups Query group(s), or false for the generic reader
* @param string|bool $wiki Wiki ID, or false for the current wiki
*
* @throws MWException
* @return DatabaseBase
*/
public function getConnection( $i, $groups = [], $wiki = false ) {
if ( $i === null || $i === false ) {
throw new MWException( 'Attempt to call ' . __METHOD__ .
' with invalid server index' );
}
if ( $wiki === wfWikiID() ) {
$wiki = false;
}
$groups = ( $groups === false || $groups === [] )
? [ false ] // check one "group": the generic pool
: (array)$groups;
$masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
$oldConnsOpened = $this->connsOpened; // connections open now
if ( $i == DB_MASTER ) {
$i = $this->getWriterIndex();
} else {
# Try to find an available server in any the query groups (in order)
foreach ( $groups as $group ) {
$groupIndex = $this->getReaderIndex( $group, $wiki );
if ( $groupIndex !== false ) {
$i = $groupIndex;
break;
}
}
}
# Operation-based index
if ( $i == DB_SLAVE ) {
$this->mLastError = 'Unknown error'; // reset error string
# Try the general server pool if $groups are unavailable.
$i = in_array( false, $groups, true )
? false // don't bother with this if that is what was tried above
: $this->getReaderIndex( false, $wiki );
# Couldn't find a working server in getReaderIndex()?
if ( $i === false ) {
$this->mLastError = 'No working slave server: ' . $this->mLastError;
return $this->reportConnectionError();
}
}
# Now we have an explicit index into the servers array
$conn = $this->openConnection( $i, $wiki );
if ( !$conn ) {
return $this->reportConnectionError();
}
# Profile any new connections that happen
if ( $this->connsOpened > $oldConnsOpened ) {
$host = $conn->getServer();
$dbname = $conn->getDBname();
$trxProf = Profiler::instance()->getTransactionProfiler();
$trxProf->recordConnection( $host, $dbname, $masterOnly );
}
if ( $masterOnly ) {
# Make master-requested DB handles inherit any read-only mode setting
$conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
}
return $conn;
}
/**
* Mark a foreign connection as being available for reuse under a different
* DB name or prefix. This mechanism is reference-counted, and must be called
* the same number of times as getConnection() to work.
*
* @param DatabaseBase $conn
* @throws MWException
*/
public function reuseConnection( $conn ) {
$serverIndex = $conn->getLBInfo( 'serverIndex' );
$refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
if ( $serverIndex === null || $refCount === null ) {
wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
/**
* This can happen in code like:
* foreach ( $dbs as $db ) {
* $conn = $lb->getConnection( DB_SLAVE, [], $db );
* ...
* $lb->reuseConnection( $conn );
* }
* When a connection to the local DB is opened in this way, reuseConnection()
* should be ignored
*/
return;
}
$dbName = $conn->getDBname();
$prefix = $conn->tablePrefix();
if ( strval( $prefix ) !== '' ) {
$wiki = "$dbName-$prefix";
} else {
$wiki = $dbName;
}
if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
throw new MWException( __METHOD__ . ": connection not found, has " .
"the connection been freed already?" );
}
$conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
if ( $refCount <= 0 ) {
$this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
} else {
wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
}
}
/**
* Get a database connection handle reference
*
* The handle's methods wrap simply wrap those of a DatabaseBase handle
*
* @see LoadBalancer::getConnection() for parameter information
*
* @param int $db
* @param array|string|bool $groups Query group(s), or false for the generic reader
* @param string|bool $wiki Wiki ID, or false for the current wiki
* @return DBConnRef
*/
public function getConnectionRef( $db, $groups = [], $wiki = false ) {
return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
}
/**
* Get a database connection handle reference without connecting yet
*
* The handle's methods wrap simply wrap those of a DatabaseBase handle
*
* @see LoadBalancer::getConnection() for parameter information
*
* @param int $db
* @param array|string|bool $groups Query group(s), or false for the generic reader
* @param string|bool $wiki Wiki ID, or false for the current wiki
* @return DBConnRef
*/
public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
return new DBConnRef( $this, [ $db, $groups, $wiki ] );
}
/**
* Open a connection to the server given by the specified index
* Index must be an actual index into the array.
* If the server is already open, returns it.
*
* On error, returns false, and the connection which caused the
* error will be available via $this->mErrorConnection.
*
* @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
*
* @param int $i Server index
* @param string|bool $wiki Wiki ID, or false for the current wiki
* @return DatabaseBase|bool Returns false on errors
*/
public function openConnection( $i, $wiki = false ) {
if ( $wiki !== false ) {
$conn = $this->openForeignConnection( $i, $wiki );
} elseif ( isset( $this->mConns['local'][$i][0] ) ) {
$conn = $this->mConns['local'][$i][0];
} else {
$server = $this->mServers[$i];
$server['serverIndex'] = $i;
$conn = $this->reallyOpenConnection( $server, false );
$serverName = $this->getServerName( $i );
if ( $conn->isOpen() ) {
wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
$this->mConns['local'][$i][0] = $conn;
} else {
wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
$this->mErrorConnection = $conn;
$conn = false;
}
}
if ( $conn && !$conn->isOpen() ) {
// Connection was made but later unrecoverably lost for some reason.
// Do not return a handle that will just throw exceptions on use,
// but let the calling code (e.g. getReaderIndex) try another server.
// See DatabaseMyslBase::ping() for how this can happen.
$this->mErrorConnection = $conn;
$conn = false;
}
return $conn;
}
/**
* Open a connection to a foreign DB, or return one if it is already open.
*
* Increments a reference count on the returned connection which locks the
* connection to the requested wiki. This reference count can be
* decremented by calling reuseConnection().
*
* If a connection is open to the appropriate server already, but with the wrong
* database, it will be switched to the right database and returned, as long as
* it has been freed first with reuseConnection().
*
* On error, returns false, and the connection which caused the
* error will be available via $this->mErrorConnection.
*
* @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
*
* @param int $i Server index
* @param string $wiki Wiki ID to open
* @return DatabaseBase
*/
private function openForeignConnection( $i, $wiki ) {
list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
// Reuse an already-used connection
$conn = $this->mConns['foreignUsed'][$i][$wiki];
wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
} elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
// Reuse a free connection for the same wiki
$conn = $this->mConns['foreignFree'][$i][$wiki];
unset( $this->mConns['foreignFree'][$i][$wiki] );
$this->mConns['foreignUsed'][$i][$wiki] = $conn;
wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
} elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
// Reuse a connection from another wiki
$conn = reset( $this->mConns['foreignFree'][$i] );
$oldWiki = key( $this->mConns['foreignFree'][$i] );
// The empty string as a DB name means "don't care".
// DatabaseMysqlBase::open() already handle this on connection.
if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
$this->mLastError = "Error selecting database $dbName on server " .
$conn->getServer() . " from client host " . wfHostname() . "\n";
$this->mErrorConnection = $conn;
$conn = false;
} else {
$conn->tablePrefix( $prefix );
unset( $this->mConns['foreignFree'][$i][$oldWiki] );
$this->mConns['foreignUsed'][$i][$wiki] = $conn;
wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
}
} else {
// Open a new connection
$server = $this->mServers[$i];
$server['serverIndex'] = $i;
$server['foreignPoolRefCount'] = 0;
$server['foreign'] = true;
$conn = $this->reallyOpenConnection( $server, $dbName );
if ( !$conn->isOpen() ) {
wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
$this->mErrorConnection = $conn;
$conn = false;
} else {
$conn->tablePrefix( $prefix );
$this->mConns['foreignUsed'][$i][$wiki] = $conn;
wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
}
}
// Increment reference count
if ( $conn ) {
$refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
$conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
}
return $conn;
}
/**
* Test if the specified index represents an open connection
*
* @param int $index Server index
* @access private
* @return bool
*/
private function isOpen( $index ) {
if ( !is_integer( $index ) ) {
return false;
}
return (bool)$this->getAnyOpenConnection( $index );
}
/**
* Really opens a connection. Uncached.
* Returns a Database object whether or not the connection was successful.
* @access private
*
* @param array $server
* @param bool $dbNameOverride
* @throws MWException
* @return DatabaseBase
*/
protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
if ( $this->disabled ) {
throw new DBAccessError();
}
if ( !is_array( $server ) ) {
throw new MWException( 'You must update your load-balancing configuration. ' .
'See DefaultSettings.php entry for $wgDBservers.' );
}
if ( $dbNameOverride !== false ) {
$server['dbname'] = $dbNameOverride;
}
// Let the handle know what the cluster master is (e.g. "db1052")
$masterName = $this->getServerName( 0 );
$server['clusterMasterHost'] = $masterName;
// Log when many connection are made on requests
if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
"{$this->connsOpened}+ connections made (master=$masterName)\n" .
wfBacktrace( true ) );
}
# Create object
try {
$db = DatabaseBase::factory( $server['type'], $server );
} catch ( DBConnectionError $e ) {
// FIXME: This is probably the ugliest thing I have ever done to
// PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
$db = $e->db;
}
$db->setLBInfo( $server );
$db->setLazyMasterHandle(
$this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
);
$db->setTransactionProfiler( $this->trxProfiler );
if ( $this->trxRoundId !== false ) {
$this->applyTransactionRoundFlags( $db );
}
return $db;
}
/**
* @throws DBConnectionError
* @return bool
*/
private function reportConnectionError() {
$conn = $this->mErrorConnection; // The connection which caused the error
$context = [
'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
);
// throws DBConnectionError
$conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
}
return false; /* not reached */
}
/**
* @return int
* @since 1.26
*/
public function getWriterIndex() {
return 0;
}
/**
* Returns true if the specified index is a valid server index
*
* @param string $i
* @return bool
*/
public function haveIndex( $i ) {
return array_key_exists( $i, $this->mServers );
}
/**
* Returns true if the specified index is valid and has non-zero load
*
* @param string $i
* @return bool
*/
public function isNonZeroLoad( $i ) {
return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
}
/**
* Get the number of defined servers (not the number of open connections)
*
* @return int
*/
public function getServerCount() {
return count( $this->mServers );
}
/**
* Get the host name or IP address of the server with the specified index
* Prefer a readable name if available.
* @param string $i
* @return string
*/
public function getServerName( $i ) {
if ( isset( $this->mServers[$i]['hostName'] ) ) {
$name = $this->mServers[$i]['hostName'];
} elseif ( isset( $this->mServers[$i]['host'] ) ) {
$name = $this->mServers[$i]['host'];
} else {
$name = '';
}
return ( $name != '' ) ? $name : 'localhost';
}
/**
* Return the server info structure for a given index, or false if the index is invalid.
* @param int $i
* @return array|bool
*/
public function getServerInfo( $i ) {
if ( isset( $this->mServers[$i] ) ) {
return $this->mServers[$i];
} else {
return false;
}
}
/**
* Sets the server info structure for the given index. Entry at index $i
* is created if it doesn't exist
* @param int $i
* @param array $serverInfo
*/
public function setServerInfo( $i, array $serverInfo ) {
$this->mServers[$i] = $serverInfo;
}
/**
* Get the current master position for chronology control purposes
* @return mixed
*/
public function getMasterPos() {
# If this entire request was served from a slave without opening a connection to the
# master (however unlikely that may be), then we can fetch the position from the slave.
$masterConn = $this->getAnyOpenConnection( 0 );
if ( !$masterConn ) {
$serverCount = count( $this->mServers );
for ( $i = 1; $i < $serverCount; $i++ ) {
$conn = $this->getAnyOpenConnection( $i );
if ( $conn ) {
return $conn->getSlavePos();
}
}
} else {
return $masterConn->getMasterPos();
}
return false;
}
/**
* Disable this load balancer. All connections are closed, and any attempt to
* open a new connection will result in a DBAccessError.
*
* @since 1.27
*/
public function disable() {
$this->closeAll();
$this->disabled = true;
}
/**
* Close all open connections
*/
public function closeAll() {
$this->forEachOpenConnection( function ( DatabaseBase $conn ) {
$conn->close();
} );
$this->mConns = [
'local' => [],
'foreignFree' => [],
'foreignUsed' => [],
];
$this->connsOpened = 0;
}
/**
* Close a connection
* Using this function makes sure the LoadBalancer knows the connection is closed.
* If you use $conn->close() directly, the load balancer won't update its state.
* @param DatabaseBase $conn
*/
public function closeConnection( $conn ) {
$done = false;
foreach ( $this->mConns as $i1 => $conns2 ) {
foreach ( $conns2 as $i2 => $conns3 ) {
foreach ( $conns3 as $i3 => $candidateConn ) {
if ( $conn === $candidateConn ) {
$conn->close();
unset( $this->mConns[$i1][$i2][$i3] );
--$this->connsOpened;
$done = true;
break;
}
}
}
}
if ( !$done ) {
$conn->close();
}
}
/**
* Commit transactions on all open connections
* @param string $fname Caller name
* @throws DBExpectedError
*/
public function commitAll( $fname = __METHOD__ ) {
$failures = [];
$restore = ( $this->trxRoundId !== false );
$this->trxRoundId = false;
$this->forEachOpenConnection(
function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
try {
$conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
} catch ( DBError $e ) {
MWExceptionHandler::logException( $e );
$failures[] = "{$conn->getServer()}: {$e->getMessage()}";
}
if ( $restore && $conn->getLBInfo( 'master' ) ) {
$this->undoTransactionRoundFlags( $conn );
}
}
);
if ( $failures ) {
throw new DBExpectedError(
null,
"Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
);
}
}
/**
* Perform all pre-commit callbacks that remain part of the atomic transactions
* and disable any post-commit callbacks until runMasterPostTrxCallbacks()
* @since 1.28
*/
public function finalizeMasterChanges() {
$this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
// Any error should cause all DB transactions to be rolled back together
$conn->setTrxEndCallbackSuppression( false );
$conn->runOnTransactionPreCommitCallbacks();
// Defer post-commit callbacks until COMMIT finishes for all DBs
$conn->setTrxEndCallbackSuppression( true );
} );
}
/**
* Perform all pre-commit checks for things like replication safety
* @param array $options Includes:
* - maxWriteDuration : max write query duration time in seconds
* @throws DBTransactionError
* @since 1.28
*/
public function approveMasterChanges( array $options ) {
$limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
$this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
// If atomic sections or explicit transactions are still open, some caller must have
// caught an exception but failed to properly rollback any changes. Detect that and
// throw and error (causing rollback).
if ( $conn->explicitTrxActive() ) {
throw new DBTransactionError(
$conn,
"Explicit transaction still active. A caller may have caught an error."
);
}
// Assert that the time to replicate the transaction will be sane.
// If this fails, then all DB transactions will be rollback back together.
$time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
if ( $limit > 0 && $time > $limit ) {
throw new DBTransactionError(
$conn,
wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
);
}
// If a connection sits idle while slow queries execute on another, that connection
// may end up dropped before the commit round is reached. Ping servers to detect this.
if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
throw new DBTransactionError(
$conn,
"A connection to the {$conn->getDBname()} database was lost before commit."
);
}
} );
}
/**
* Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
*
* The DBO_TRX setting will be reverted to the default in each of these methods:
* - commitMasterChanges()
* - rollbackMasterChanges()
* - commitAll()
* This allows for custom transaction rounds from any outer transaction scope.
*
* @param string $fname
* @throws DBExpectedError
* @since 1.28
*/
public function beginMasterChanges( $fname = __METHOD__ ) {
if ( $this->trxRoundId !== false ) {
throw new DBTransactionError(
null,
"$fname: Transaction round '{$this->trxRoundId}' already started."
);
}
$this->trxRoundId = $fname;
$failures = [];
$this->forEachOpenMasterConnection(
function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
$conn->setTrxEndCallbackSuppression( true );
try {
$conn->clearSnapshot( $fname );
} catch ( DBError $e ) {
MWExceptionHandler::logException( $e );
$failures[] = "{$conn->getServer()}: {$e->getMessage()}";
}
$conn->setTrxEndCallbackSuppression( false );
$this->applyTransactionRoundFlags( $conn );
}
);
if ( $failures ) {
throw new DBExpectedError(
null,
"$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
);
}
}
/**
* Issue COMMIT on all master connections where writes where done
* @param string $fname Caller name
* @throws DBExpectedError
*/
public function commitMasterChanges( $fname = __METHOD__ ) {
$failures = [];
$restore = ( $this->trxRoundId !== false );
$this->trxRoundId = false;
$this->forEachOpenMasterConnection(
function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
try {
if ( $conn->writesOrCallbacksPending() ) {
$conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
} elseif ( $restore ) {
$conn->clearSnapshot( $fname );
}
} catch ( DBError $e ) {
MWExceptionHandler::logException( $e );
$failures[] = "{$conn->getServer()}: {$e->getMessage()}";
}
if ( $restore ) {
$this->undoTransactionRoundFlags( $conn );
}
}
);
if ( $failures ) {
throw new DBExpectedError(
null,
"$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
);
}
}
/**
* Issue all pending post-COMMIT/ROLLBACK callbacks
* @param integer $type IDatabase::TRIGGER_* constant
* @return Exception|null The first exception or null if there were none
* @since 1.28
*/
public function runMasterPostTrxCallbacks( $type ) {
$e = null; // first exception
$this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
$conn->clearSnapshot( __METHOD__ ); // clear no-op transactions
$conn->setTrxEndCallbackSuppression( false );
try {
$conn->runOnTransactionIdleCallbacks( $type );
} catch ( Exception $ex ) {
$e = $e ?: $ex;
}
try {
$conn->runTransactionListenerCallbacks( $type );
} catch ( Exception $ex ) {
$e = $e ?: $ex;
}
} );
return $e;
}
/**
* Issue ROLLBACK only on master, only if queries were done on connection
* @param string $fname Caller name
* @throws DBExpectedError
* @since 1.23
*/
public function rollbackMasterChanges( $fname = __METHOD__ ) {
$restore = ( $this->trxRoundId !== false );
$this->trxRoundId = false;
$this->forEachOpenMasterConnection(
function ( DatabaseBase $conn ) use ( $fname, $restore ) {
if ( $conn->writesOrCallbacksPending() ) {
$conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
}
if ( $restore ) {
$this->undoTransactionRoundFlags( $conn );
}
}
);
}
/**
* Suppress all pending post-COMMIT/ROLLBACK callbacks
* @return Exception|null The first exception or null if there were none
* @since 1.28
*/
public function suppressTransactionEndCallbacks() {
$this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
$conn->setTrxEndCallbackSuppression( true );
} );
}
/**
* @param DatabaseBase $conn
*/
private function applyTransactionRoundFlags( DatabaseBase $conn ) {
if ( $conn->getFlag( DBO_DEFAULT ) ) {
// DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
// Force DBO_TRX even in CLI mode since a commit round is expected soon.
$conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
// If config has explicitly requested DBO_TRX be either on or off by not
// setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
// for things like blob stores (ExternalStore) which want auto-commit mode.
}
}
/**
* @param DatabaseBase $conn
*/
private function undoTransactionRoundFlags( DatabaseBase $conn ) {
if ( $conn->getFlag( DBO_DEFAULT ) ) {
$conn->restoreFlags( $conn::RESTORE_PRIOR );
}
}
/**
* @return bool Whether a master connection is already open
* @since 1.24
*/
public function hasMasterConnection() {
return $this->isOpen( $this->getWriterIndex() );
}
/**
* Determine if there are pending changes in a transaction by this thread
* @since 1.23
* @return bool
*/
public function hasMasterChanges() {
$masterIndex = $this->getWriterIndex();
foreach ( $this->mConns as $conns2 ) {
if ( empty( $conns2[$masterIndex] ) ) {
continue;
}
/** @var DatabaseBase $conn */
foreach ( $conns2[$masterIndex] as $conn ) {
if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
return true;
}
}
}
return false;
}
/**
* Get the timestamp of the latest write query done by this thread
* @since 1.25
* @return float|bool UNIX timestamp or false
*/
public function lastMasterChangeTimestamp() {
$lastTime = false;
$masterIndex = $this->getWriterIndex();
foreach ( $this->mConns as $conns2 ) {
if ( empty( $conns2[$masterIndex] ) ) {
continue;
}
/** @var DatabaseBase $conn */
foreach ( $conns2[$masterIndex] as $conn ) {
$lastTime = max( $lastTime, $conn->lastDoneWrites() );
}
}
return $lastTime;
}
/**
* Check if this load balancer object had any recent or still
* pending writes issued against it by this PHP thread
*
* @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
* @return bool
* @since 1.25
*/
public function hasOrMadeRecentMasterChanges( $age = null ) {
$age = ( $age === null ) ? $this->mWaitTimeout : $age;
return ( $this->hasMasterChanges()
|| $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
}
/**
* Get the list of callers that have pending master changes
*
* @return array
* @since 1.27
*/
public function pendingMasterChangeCallers() {
$fnames = [];
$masterIndex = $this->getWriterIndex();
foreach ( $this->mConns as $conns2 ) {
if ( empty( $conns2[$masterIndex] ) ) {
continue;
}
/** @var DatabaseBase $conn */
foreach ( $conns2[$masterIndex] as $conn ) {
$fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
}
}
return $fnames;
}
/**
* @param mixed $value
* @return mixed
*/
public function waitTimeout( $value = null ) {
return wfSetVar( $this->mWaitTimeout, $value );
}
/**
* @note This method will trigger a DB connection if not yet done
*
* @param string|bool $wiki Wiki ID, or false for the current wiki
* @return bool Whether the generic connection for reads is highly "lagged"
*/
public function getLaggedSlaveMode( $wiki = false ) {
// No-op if there is only one DB (also avoids recursion)
if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
try {
// See if laggedSlaveMode gets set
$conn = $this->getConnection( DB_SLAVE, false, $wiki );
$this->reuseConnection( $conn );
} catch ( DBConnectionError $e ) {
// Avoid expensive re-connect attempts and failures
$this->slavesDownMode = true;
$this->laggedSlaveMode = true;
}
}
return $this->laggedSlaveMode;
}
/**
* @note This method will never cause a new DB connection
* @return bool Whether any generic connection used for reads was highly "lagged"
* @since 1.27
*/
public function laggedSlaveUsed() {
return $this->laggedSlaveMode;
}
/**
* @note This method may trigger a DB connection if not yet done
* @param string|bool $wiki Wiki ID, or false for the current wiki
* @param DatabaseBase|null DB master connection; used to avoid loops [optional]
* @return string|bool Reason the master is read-only or false if it is not
* @since 1.27
*/
public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
if ( $this->readOnlyReason !== false ) {
return $this->readOnlyReason;
} elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
if ( $this->slavesDownMode ) {
return 'The database has been automatically locked ' .
'until the slave database servers become available';
} else {
return 'The database has been automatically locked ' .
'while the slave database servers catch up to the master.';
}
} elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
return 'The database master is running in read-only mode.';
}
return false;
}
/**
* @param string $wiki Wiki ID, or false for the current wiki
* @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
* @return bool
*/
private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
$cache = $this->wanCache;
$masterServer = $this->getServerName( $this->getWriterIndex() );
return (bool)$cache->getWithSetCallback(
$cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
self::TTL_CACHE_READONLY,
function () use ( $wiki, $conn ) {
$this->trxProfiler->setSilenced( true );
try {
$dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
$readOnly = (int)$dbw->serverIsReadOnly();
} catch ( DBError $e ) {
$readOnly = 0;
}
$this->trxProfiler->setSilenced( false );
return $readOnly;
},
[ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
);
}
/**
* Disables/enables lag checks
* @param null|bool $mode
* @return bool
*/
public function allowLagged( $mode = null ) {
if ( $mode === null ) {
return $this->mAllowLagged;
}
$this->mAllowLagged = $mode;
return $this->mAllowLagged;
}
/**
* @return bool
*/
public function pingAll() {
$success = true;
$this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
if ( !$conn->ping() ) {
$success = false;
}
} );
return $success;
}
/**
* Call a function with each open connection object
* @param callable $callback
* @param array $params
*/
public function forEachOpenConnection( $callback, array $params = [] ) {
foreach ( $this->mConns as $connsByServer ) {
foreach ( $connsByServer as $serverConns ) {
foreach ( $serverConns as $conn ) {
$mergedParams = array_merge( [ $conn ], $params );
call_user_func_array( $callback, $mergedParams );
}
}
}
}
/**
* Call a function with each open connection object to a master
* @param callable $callback
* @param array $params
* @since 1.28
*/
public function forEachOpenMasterConnection( $callback, array $params = [] ) {
$masterIndex = $this->getWriterIndex();
foreach ( $this->mConns as $connsByServer ) {
if ( isset( $connsByServer[$masterIndex] ) ) {
/** @var DatabaseBase $conn */
foreach ( $connsByServer[$masterIndex] as $conn ) {
$mergedParams = array_merge( [ $conn ], $params );
call_user_func_array( $callback, $mergedParams );
}
}
}
}
/**
* Get the hostname and lag time of the most-lagged slave
*
* This is useful for maintenance scripts that need to throttle their updates.
* May attempt to open connections to slaves on the default DB. If there is
* no lag, the maximum lag will be reported as -1.
*
* @param bool|string $wiki Wiki ID, or false for the default database
* @return array ( host, max lag, index of max lagged host )
*/
public function getMaxLag( $wiki = false ) {
$maxLag = -1;
$host = '';
$maxIndex = 0;
if ( $this->getServerCount() <= 1 ) {
return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
}
$lagTimes = $this->getLagTimes( $wiki );
foreach ( $lagTimes as $i => $lag ) {
if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
$maxLag = $lag;
$host = $this->mServers[$i]['host'];
$maxIndex = $i;
}
}
return [ $host, $maxLag, $maxIndex ];
}
/**
* Get an estimate of replication lag (in seconds) for each server
*
* Results are cached for a short time in memcached/process cache
*
* Values may be "false" if replication is too broken to estimate
*
* @param string|bool $wiki
* @return int[] Map of (server index => float|int|bool)
*/
public function getLagTimes( $wiki = false ) {
if ( $this->getServerCount() <= 1 ) {
return [ 0 => 0 ]; // no replication = no lag
}
# Send the request to the load monitor
return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
}
/**
* Get the lag in seconds for a given connection, or zero if this load
* balancer does not have replication enabled.
*
* This should be used in preference to Database::getLag() in cases where
* replication may not be in use, since there is no way to determine if
* replication is in use at the connection level without running
* potentially restricted queries such as SHOW SLAVE STATUS. Using this
* function instead of Database::getLag() avoids a fatal error in this
* case on many installations.
*
* @param IDatabase $conn
* @return int|bool Returns false on error
*/
public function safeGetLag( IDatabase $conn ) {
if ( $this->getServerCount() == 1 ) {
return 0;
} else {
return $conn->getLag();
}
}
/**
* Wait for a slave DB to reach a specified master position
*
* This will connect to the master to get an accurate position if $pos is not given
*
* @param IDatabase $conn Slave DB
* @param DBMasterPos|bool $pos Master position; default: current position
* @param integer $timeout Timeout in seconds
* @return bool Success
* @since 1.27
*/
public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
return true; // server is not a slave DB
}
$pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
if ( !( $pos instanceof DBMasterPos ) ) {
return false; // something is misconfigured
}
$result = $conn->masterPosWait( $pos, $timeout );
if ( $result == -1 || is_null( $result ) ) {
$msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
wfDebugLog( 'replication', "$msg\n" );
wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
$ok = false;
} else {
wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
$ok = true;
}
return $ok;
}
/**
* Clear the cache for slag lag delay times
*
* This is only used for testing
*/
public function clearLagTimeCache() {
$this->getLoadMonitor()->clearCaches();
}
}
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