Current File : /www/varak.net/wiki.varak.net/includes/db/loadbalancer/LBFactory.php
<?php
/**
* Generator of database load balancing objects.
*
* 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
*/
use MediaWiki\MediaWikiServices;
use MediaWiki\Services\DestructibleService;
use Psr\Log\LoggerInterface;
use MediaWiki\Logger\LoggerFactory;
/**
* An interface for generating database load balancers
* @ingroup Database
*/
abstract class LBFactory implements DestructibleService {
/** @var ChronologyProtector */
protected $chronProt;
/** @var TransactionProfiler */
protected $trxProfiler;
/** @var LoggerInterface */
protected $trxLogger;
/** @var BagOStuff */
protected $srvCache;
/** @var WANObjectCache */
protected $wanCache;
/** @var mixed */
protected $ticket;
/** @var string|bool String if a requested DBO_TRX transaction round is active */
protected $trxRoundId = false;
/** @var string|bool Reason all LBs are read-only or false if not */
protected $readOnlyReason = false;
/** @var callable[] */
protected $replicationWaitCallbacks = [];
const SHUTDOWN_NO_CHRONPROT = 1; // don't save ChronologyProtector positions (for async code)
/**
* Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
* @param array $conf
* @TODO: inject objects via dependency framework
*/
public function __construct( array $conf ) {
if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
$this->readOnlyReason = $conf['readOnlyReason'];
}
$this->chronProt = $this->newChronologyProtector();
$this->trxProfiler = Profiler::instance()->getTransactionProfiler();
// Use APC/memcached style caching, but avoids loops with CACHE_DB (T141804)
$cache = ObjectCache::getLocalServerInstance();
if ( $cache->getQoS( $cache::ATTR_EMULATION ) > $cache::QOS_EMULATION_SQL ) {
$this->srvCache = $cache;
} else {
$this->srvCache = new EmptyBagOStuff();
}
$wCache = ObjectCache::getMainWANInstance();
if ( $wCache->getQoS( $wCache::ATTR_EMULATION ) > $wCache::QOS_EMULATION_SQL ) {
$this->wanCache = $wCache;
} else {
$this->wanCache = WANObjectCache::newEmpty();
}
$this->trxLogger = LoggerFactory::getInstance( 'DBTransaction' );
$this->ticket = mt_rand();
}
/**
* Disables all load balancers. All connections are closed, and any attempt to
* open a new connection will result in a DBAccessError.
* @see LoadBalancer::disable()
*/
public function destroy() {
$this->shutdown();
$this->forEachLBCallMethod( 'disable' );
}
/**
* Disables all access to the load balancer, will cause all database access
* to throw a DBAccessError
*/
public static function disableBackend() {
MediaWikiServices::disableStorageBackend();
}
/**
* Get an LBFactory instance
*
* @deprecated since 1.27, use MediaWikiServices::getDBLoadBalancerFactory() instead.
*
* @return LBFactory
*/
public static function singleton() {
return MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
}
/**
* Returns the LBFactory class to use and the load balancer configuration.
*
* @todo instead of this, use a ServiceContainer for managing the different implementations.
*
* @param array $config (e.g. $wgLBFactoryConf)
* @return string Class name
*/
public static function getLBFactoryClass( array $config ) {
// For configuration backward compatibility after removing
// underscores from class names in MediaWiki 1.23.
$bcClasses = [
'LBFactory_Simple' => 'LBFactorySimple',
'LBFactory_Single' => 'LBFactorySingle',
'LBFactory_Multi' => 'LBFactoryMulti',
'LBFactory_Fake' => 'LBFactoryFake',
];
$class = $config['class'];
if ( isset( $bcClasses[$class] ) ) {
$class = $bcClasses[$class];
wfDeprecated(
'$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
'1.23'
);
}
return $class;
}
/**
* Shut down, close connections and destroy the cached instance.
*
* @deprecated since 1.27, use LBFactory::destroy()
*/
public static function destroyInstance() {
self::singleton()->destroy();
}
/**
* Create a new load balancer object. The resulting object will be untracked,
* not chronology-protected, and the caller is responsible for cleaning it up.
*
* @param bool|string $wiki Wiki ID, or false for the current wiki
* @return LoadBalancer
*/
abstract public function newMainLB( $wiki = false );
/**
* Get a cached (tracked) load balancer object.
*
* @param bool|string $wiki Wiki ID, or false for the current wiki
* @return LoadBalancer
*/
abstract public function getMainLB( $wiki = false );
/**
* Create a new load balancer for external storage. The resulting object will be
* untracked, not chronology-protected, and the caller is responsible for
* cleaning it up.
*
* @param string $cluster External storage cluster, or false for core
* @param bool|string $wiki Wiki ID, or false for the current wiki
* @return LoadBalancer
*/
abstract protected function newExternalLB( $cluster, $wiki = false );
/**
* Get a cached (tracked) load balancer for external storage
*
* @param string $cluster External storage cluster, or false for core
* @param bool|string $wiki Wiki ID, or false for the current wiki
* @return LoadBalancer
*/
abstract public function &getExternalLB( $cluster, $wiki = false );
/**
* Execute a function for each tracked load balancer
* The callback is called with the load balancer as the first parameter,
* and $params passed as the subsequent parameters.
*
* @param callable $callback
* @param array $params
*/
abstract public function forEachLB( $callback, array $params = [] );
/**
* Prepare all tracked load balancers for shutdown
* @param integer $flags Supports SHUTDOWN_* flags
*/
public function shutdown( $flags = 0 ) {
if ( !( $flags & self::SHUTDOWN_NO_CHRONPROT ) ) {
$this->shutdownChronologyProtector( $this->chronProt );
}
$this->commitMasterChanges( __METHOD__ ); // sanity
}
/**
* Call a method of each tracked load balancer
*
* @param string $methodName
* @param array $args
*/
private function forEachLBCallMethod( $methodName, array $args = [] ) {
$this->forEachLB(
function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
call_user_func_array( [ $loadBalancer, $methodName ], $args );
},
[ $methodName, $args ]
);
}
/**
* 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 DBTransactionError
* @since 1.28
*/
public function beginMasterChanges( $fname = __METHOD__ ) {
if ( $this->trxRoundId !== false ) {
throw new DBTransactionError(
null,
"Transaction round '{$this->trxRoundId}' already started."
);
}
$this->trxRoundId = $fname;
// Set DBO_TRX flags on all appropriate DBs
$this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
}
/**
* Commit on all connections. Done for two reasons:
* 1. To commit changes to the masters.
* 2. To release the snapshot on all connections, master and slave.
* @param string $fname Caller name
* @param array $options Options map:
* - maxWriteDuration: abort if more than this much time was spent in write queries
*/
public function commitAll( $fname = __METHOD__, array $options = [] ) {
$this->commitMasterChanges( $fname, $options );
$this->forEachLBCallMethod( 'commitAll', [ $fname ] );
}
/**
* Commit changes on all master connections
* @param string $fname Caller name
* @param array $options Options map:
* - maxWriteDuration: abort if more than this much time was spent in write queries
* @throws Exception
*/
public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
// Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
$this->forEachLBCallMethod( 'finalizeMasterChanges' );
$this->trxRoundId = false;
// Perform pre-commit checks, aborting on failure
$this->forEachLBCallMethod( 'approveMasterChanges', [ $options ] );
// Log the DBs and methods involved in multi-DB transactions
$this->logIfMultiDbTransaction();
// Actually perform the commit on all master DB connections and revert DBO_TRX
$this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
// Run all post-commit callbacks
/** @var Exception $e */
$e = null; // first callback exception
$this->forEachLB( function ( LoadBalancer $lb ) use ( &$e ) {
$ex = $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_COMMIT );
$e = $e ?: $ex;
} );
// Commit any dangling DBO_TRX transactions from callbacks on one DB to another DB
$this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
// Throw any last post-commit callback error
if ( $e instanceof Exception ) {
throw $e;
}
}
/**
* Rollback changes on all master connections
* @param string $fname Caller name
* @since 1.23
*/
public function rollbackMasterChanges( $fname = __METHOD__ ) {
$this->trxRoundId = false;
$this->forEachLBCallMethod( 'suppressTransactionEndCallbacks' );
$this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
// Run all post-rollback callbacks
$this->forEachLB( function ( LoadBalancer $lb ) {
$lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_ROLLBACK );
} );
}
/**
* Log query info if multi DB transactions are going to be committed now
*/
private function logIfMultiDbTransaction() {
$callersByDB = [];
$this->forEachLB( function ( LoadBalancer $lb ) use ( &$callersByDB ) {
$masterName = $lb->getServerName( $lb->getWriterIndex() );
$callers = $lb->pendingMasterChangeCallers();
if ( $callers ) {
$callersByDB[$masterName] = $callers;
}
} );
if ( count( $callersByDB ) >= 2 ) {
$dbs = implode( ', ', array_keys( $callersByDB ) );
$msg = "Multi-DB transaction [{$dbs}]:\n";
foreach ( $callersByDB as $db => $callers ) {
$msg .= "$db: " . implode( '; ', $callers ) . "\n";
}
$this->trxLogger->info( $msg );
}
}
/**
* Determine if any master connection has pending changes
* @return bool
* @since 1.23
*/
public function hasMasterChanges() {
$ret = false;
$this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
$ret = $ret || $lb->hasMasterChanges();
} );
return $ret;
}
/**
* Detemine if any lagged slave connection was used
* @since 1.27
* @return bool
*/
public function laggedSlaveUsed() {
$ret = false;
$this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
$ret = $ret || $lb->laggedSlaveUsed();
} );
return $ret;
}
/**
* Determine if any master connection has pending/written changes from this request
* @return bool
* @since 1.27
*/
public function hasOrMadeRecentMasterChanges() {
$ret = false;
$this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
$ret = $ret || $lb->hasOrMadeRecentMasterChanges();
} );
return $ret;
}
/**
* Waits for the slave DBs to catch up to the current master position
*
* Use this when updating very large numbers of rows, as in maintenance scripts,
* to avoid causing too much lag. Of course, this is a no-op if there are no slaves.
*
* By default this waits on all DB clusters actually used in this request.
* This makes sense when lag being waiting on is caused by the code that does this check.
* In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
* that were not changed since the last wait check. To forcefully wait on a specific cluster
* for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
* use the "cluster" parameter.
*
* Never call this function after a large DB write that is *still* in a transaction.
* It only makes sense to call this after the possible lag inducing changes were committed.
*
* @param array $opts Optional fields that include:
* - wiki : wait on the load balancer DBs that handles the given wiki
* - cluster : wait on the given external load balancer DBs
* - timeout : Max wait time. Default: ~60 seconds
* - ifWritesSince: Only wait if writes were done since this UNIX timestamp
* @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
* @since 1.27
*/
public function waitForReplication( array $opts = [] ) {
$opts += [
'wiki' => false,
'cluster' => false,
'timeout' => 60,
'ifWritesSince' => null
];
foreach ( $this->replicationWaitCallbacks as $callback ) {
$callback();
}
// Figure out which clusters need to be checked
/** @var LoadBalancer[] $lbs */
$lbs = [];
if ( $opts['cluster'] !== false ) {
$lbs[] = $this->getExternalLB( $opts['cluster'] );
} elseif ( $opts['wiki'] !== false ) {
$lbs[] = $this->getMainLB( $opts['wiki'] );
} else {
$this->forEachLB( function ( LoadBalancer $lb ) use ( &$lbs ) {
$lbs[] = $lb;
} );
if ( !$lbs ) {
return; // nothing actually used
}
}
// Get all the master positions of applicable DBs right now.
// This can be faster since waiting on one cluster reduces the
// time needed to wait on the next clusters.
$masterPositions = array_fill( 0, count( $lbs ), false );
foreach ( $lbs as $i => $lb ) {
if ( $lb->getServerCount() <= 1 ) {
// Bug 27975 - Don't try to wait for slaves if there are none
// Prevents permission error when getting master position
continue;
} elseif ( $opts['ifWritesSince']
&& $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
) {
continue; // no writes since the last wait
}
$masterPositions[$i] = $lb->getMasterPos();
}
$failed = [];
foreach ( $lbs as $i => $lb ) {
if ( $masterPositions[$i] ) {
// The DBMS may not support getMasterPos() or the whole
// load balancer might be fake (e.g. $wgAllDBsAreLocalhost).
if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
$failed[] = $lb->getServerName( $lb->getWriterIndex() );
}
}
}
if ( $failed ) {
throw new DBReplicationWaitError(
"Could not wait for slaves to catch up to " .
implode( ', ', $failed )
);
}
}
/**
* Add a callback to be run in every call to waitForReplication() before waiting
*
* Callbacks must clear any transactions that they start
*
* @param string $name Callback name
* @param callable|null $callback Use null to unset a callback
* @since 1.28
*/
public function setWaitForReplicationListener( $name, callable $callback = null ) {
if ( $callback ) {
$this->replicationWaitCallbacks[$name] = $callback;
} else {
unset( $this->replicationWaitCallbacks[$name] );
}
}
/**
* Get a token asserting that no transaction writes are active
*
* @param string $fname Caller name (e.g. __METHOD__)
* @return mixed A value to pass to commitAndWaitForReplication()
* @since 1.28
*/
public function getEmptyTransactionTicket( $fname ) {
if ( $this->hasMasterChanges() ) {
$this->trxLogger->error( __METHOD__ . ": $fname does not have outer scope." );
return null;
}
return $this->ticket;
}
/**
* Convenience method for safely running commitMasterChanges()/waitForReplication()
*
* This will commit and wait unless $ticket indicates it is unsafe to do so
*
* @param string $fname Caller name (e.g. __METHOD__)
* @param mixed $ticket Result of getOuterTransactionScopeTicket()
* @param array $opts Options to waitForReplication()
* @throws DBReplicationWaitError
* @since 1.28
*/
public function commitAndWaitForReplication( $fname, $ticket, array $opts = [] ) {
if ( $ticket !== $this->ticket ) {
$logger = LoggerFactory::getInstance( 'DBPerformance' );
$logger->error( __METHOD__ . ": cannot commit; $fname does not have outer scope." );
return;
}
$this->commitMasterChanges( $fname );
$this->waitForReplication( $opts );
}
/**
* Disable the ChronologyProtector for all load balancers
*
* This can be called at the start of special API entry points
*
* @since 1.27
*/
public function disableChronologyProtection() {
$this->chronProt->setEnabled( false );
}
/**
* @return ChronologyProtector
*/
protected function newChronologyProtector() {
$request = RequestContext::getMain()->getRequest();
$chronProt = new ChronologyProtector(
ObjectCache::getMainStashInstance(),
[
'ip' => $request->getIP(),
'agent' => $request->getHeader( 'User-Agent' )
]
);
if ( PHP_SAPI === 'cli' ) {
$chronProt->setEnabled( false );
} elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
// Request opted out of using position wait logic. This is useful for requests
// done by the job queue or background ETL that do not have a meaningful session.
$chronProt->setWaitEnabled( false );
}
return $chronProt;
}
/**
* @param ChronologyProtector $cp
*/
protected function shutdownChronologyProtector( ChronologyProtector $cp ) {
// Get all the master positions needed
$this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
$cp->shutdownLB( $lb );
} );
// Write them to the stash
$unsavedPositions = $cp->shutdown();
// If the positions failed to write to the stash, at least wait on local datacenter
// slaves to catch up before responding. Even if there are several DCs, this increases
// the chance that the user will see their own changes immediately afterwards. As long
// as the sticky DC cookie applies (same domain), this is not even an issue.
$this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
$masterName = $lb->getServerName( $lb->getWriterIndex() );
if ( isset( $unsavedPositions[$masterName] ) ) {
$lb->waitForAll( $unsavedPositions[$masterName] );
}
} );
}
/**
* @param LoadBalancer $lb
*/
protected function initLoadBalancer( LoadBalancer $lb ) {
if ( $this->trxRoundId !== false ) {
$lb->beginMasterChanges( $this->trxRoundId ); // set DBO_TRX
}
}
/**
* Close all open database connections on all open load balancers.
* @since 1.28
*/
public function closeAll() {
$this->forEachLBCallMethod( 'closeAll', [] );
}
}
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