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Diffstat (limited to 'www/wiki/includes/libs/rdbms/ChronologyProtector.php')
| -rw-r--r-- | www/wiki/includes/libs/rdbms/ChronologyProtector.php | 336 |
1 files changed, 336 insertions, 0 deletions
diff --git a/www/wiki/includes/libs/rdbms/ChronologyProtector.php b/www/wiki/includes/libs/rdbms/ChronologyProtector.php new file mode 100644 index 00000000..e1152865 --- /dev/null +++ b/www/wiki/includes/libs/rdbms/ChronologyProtector.php @@ -0,0 +1,336 @@ +<?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 + */ + +namespace Wikimedia\Rdbms; + +use Psr\Log\LoggerAwareInterface; +use Psr\Log\LoggerInterface; +use Psr\Log\NullLogger; +use Wikimedia\WaitConditionLoop; +use BagOStuff; + +/** + * Class for ensuring a consistent ordering of events as seen by the user, despite replication. + * Kind of like Hawking's [[Chronology Protection Agency]]. + */ +class ChronologyProtector implements LoggerAwareInterface { + /** @var BagOStuff */ + protected $store; + /** @var LoggerInterface */ + protected $logger; + + /** @var string Storage key name */ + protected $key; + /** @var string Hash of client parameters */ + protected $clientId; + /** @var int|null Expected minimum index of the last write to the position store */ + protected $waitForPosIndex; + /** @var int Max seconds to wait on positions to appear */ + protected $waitForPosStoreTimeout = self::POS_STORE_WAIT_TIMEOUT; + /** @var bool Whether to no-op all method calls */ + protected $enabled = true; + /** @var bool Whether to check and wait on positions */ + protected $wait = true; + + /** @var bool Whether the client data was loaded */ + protected $initialized = false; + /** @var DBMasterPos[] Map of (DB master name => position) */ + protected $startupPositions = []; + /** @var DBMasterPos[] Map of (DB master name => position) */ + protected $shutdownPositions = []; + /** @var float[] Map of (DB master name => 1) */ + protected $shutdownTouchDBs = []; + + /** @var int Seconds to store positions */ + const POSITION_TTL = 60; + /** @var int Max time to wait for positions to appear */ + const POS_STORE_WAIT_TIMEOUT = 5; + + /** + * @param BagOStuff $store + * @param array[] $client Map of (ip: <IP>, agent: <user-agent>) + * @param int|null $posIndex Write counter index [optional] + * @since 1.27 + */ + public function __construct( BagOStuff $store, array $client, $posIndex = null ) { + $this->store = $store; + $this->clientId = md5( $client['ip'] . "\n" . $client['agent'] ); + $this->key = $store->makeGlobalKey( __CLASS__, $this->clientId, 'v2' ); + $this->waitForPosIndex = $posIndex; + $this->logger = new NullLogger(); + } + + public function setLogger( LoggerInterface $logger ) { + $this->logger = $logger; + } + + /** + * @param bool $enabled Whether to no-op all method calls + * @since 1.27 + */ + public function setEnabled( $enabled ) { + $this->enabled = $enabled; + } + + /** + * @param bool $enabled Whether to check and wait on positions + * @since 1.27 + */ + public function setWaitEnabled( $enabled ) { + $this->wait = $enabled; + } + + /** + * Initialise a ILoadBalancer to give it appropriate chronology protection. + * + * If the stash has a previous master position recorded, this will try to + * make sure that the next query to a replica DB of that master will see changes up + * to that position by delaying execution. The delay may timeout and allow stale + * data if no non-lagged replica DBs are available. + * + * @param ILoadBalancer $lb + * @return void + */ + public function initLB( ILoadBalancer $lb ) { + if ( !$this->enabled || $lb->getServerCount() <= 1 ) { + return; // non-replicated setup or disabled + } + + $this->initPositions(); + + $masterName = $lb->getServerName( $lb->getWriterIndex() ); + if ( + isset( $this->startupPositions[$masterName] ) && + $this->startupPositions[$masterName] instanceof DBMasterPos + ) { + $pos = $this->startupPositions[$masterName]; + $this->logger->debug( __METHOD__ . ": LB for '$masterName' set to pos $pos\n" ); + $lb->waitFor( $pos ); + } + } + + /** + * Notify the ChronologyProtector that the ILoadBalancer is about to shut + * down. Saves replication positions. + * + * @param ILoadBalancer $lb + * @return void + */ + public function shutdownLB( ILoadBalancer $lb ) { + if ( !$this->enabled ) { + return; // not enabled + } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) { + // Only save the position if writes have been done on the connection + return; + } + + $masterName = $lb->getServerName( $lb->getWriterIndex() ); + if ( $lb->getServerCount() > 1 ) { + $pos = $lb->getMasterPos(); + if ( $pos ) { + $this->logger->debug( __METHOD__ . ": LB for '$masterName' has pos $pos\n" ); + $this->shutdownPositions[$masterName] = $pos; + } + } else { + $this->logger->debug( __METHOD__ . ": DB '$masterName' touched\n" ); + } + $this->shutdownTouchDBs[$masterName] = 1; + } + + /** + * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now. + * May commit chronology data to persistent storage. + * + * @param callable|null $workCallback Work to do instead of waiting on syncing positions + * @param string $mode One of (sync, async); whether to wait on remote datacenters + * @param int|null &$cpIndex DB position key write counter; incremented on update + * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure + */ + public function shutdown( callable $workCallback = null, $mode = 'sync', &$cpIndex = null ) { + if ( !$this->enabled ) { + return []; + } + + $store = $this->store; + // Some callers might want to know if a user recently touched a DB. + // These writes do not need to block on all datacenters receiving them. + foreach ( $this->shutdownTouchDBs as $dbName => $unused ) { + $store->set( + $this->getTouchedKey( $this->store, $dbName ), + microtime( true ), + $store::TTL_DAY + ); + } + + if ( !count( $this->shutdownPositions ) ) { + return []; // nothing to save + } + + $this->logger->debug( __METHOD__ . ": saving master pos for " . + implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n" + ); + + // CP-protected writes should overwhemingly go to the master datacenter, so get DC-local + // lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This + // makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT. + if ( $store->lock( $this->key, 3 ) ) { + if ( $workCallback ) { + // Let the store run the work before blocking on a replication sync barrier. By the + // time it's done with the work, the barrier should be fast if replication caught up. + $store->addBusyCallback( $workCallback ); + } + $ok = $store->set( + $this->key, + $this->mergePositions( + $store->get( $this->key ), + $this->shutdownPositions, + $cpIndex + ), + self::POSITION_TTL, + ( $mode === 'sync' ) ? $store::WRITE_SYNC : 0 + ); + $store->unlock( $this->key ); + } else { + $ok = false; + $cpIndex = null; // nothing saved + } + + if ( !$ok ) { + $bouncedPositions = $this->shutdownPositions; + // Raced out too many times or stash is down + $this->logger->warning( __METHOD__ . ": failed to save master pos for " . + implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n" + ); + } elseif ( $mode === 'sync' && + $store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE + ) { + // Positions may not be in all datacenters, force LBFactory to play it safe + $this->logger->info( __METHOD__ . ": store may not support synchronous writes." ); + $bouncedPositions = $this->shutdownPositions; + } else { + $bouncedPositions = []; + } + + return $bouncedPositions; + } + + /** + * @param string $dbName DB master name (e.g. "db1052") + * @return float|bool UNIX timestamp when client last touched the DB; false if not on record + * @since 1.28 + */ + public function getTouched( $dbName ) { + return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) ); + } + + /** + * @param BagOStuff $store + * @param string $dbName + * @return string + */ + private function getTouchedKey( BagOStuff $store, $dbName ) { + return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName ); + } + + /** + * Load in previous master positions for the client + */ + protected function initPositions() { + if ( $this->initialized ) { + return; + } + + $this->initialized = true; + if ( $this->wait ) { + // If there is an expectation to see master positions from a certain write + // index or higher, then block until it appears, or until a timeout is reached. + // Since the write index restarts each time the key is created, it is possible that + // a lagged store has a matching key write index. However, in that case, it should + // already be expired and thus treated as non-existing, maintaining correctness. + if ( $this->waitForPosIndex > 0 ) { + $data = null; + $loop = new WaitConditionLoop( + function () use ( &$data ) { + $data = $this->store->get( $this->key ); + if ( !is_array( $data ) ) { + return WaitConditionLoop::CONDITION_CONTINUE; // not found yet + } elseif ( !isset( $data['writeIndex'] ) ) { + return WaitConditionLoop::CONDITION_REACHED; // b/c + } + + return ( $data['writeIndex'] >= $this->waitForPosIndex ) + ? WaitConditionLoop::CONDITION_REACHED + : WaitConditionLoop::CONDITION_CONTINUE; + }, + $this->waitForPosStoreTimeout + ); + $result = $loop->invoke(); + $waitedMs = $loop->getLastWaitTime() * 1e3; + + if ( $result == $loop::CONDITION_REACHED ) { + $msg = "expected and found pos index {$this->waitForPosIndex} ({$waitedMs}ms)"; + $this->logger->debug( $msg ); + } else { + $msg = "expected but missed pos index {$this->waitForPosIndex} ({$waitedMs}ms)"; + $this->logger->info( $msg ); + } + } else { + $data = $this->store->get( $this->key ); + } + + $this->startupPositions = $data ? $data['positions'] : []; + $this->logger->debug( __METHOD__ . ": key is {$this->key} (read)\n" ); + } else { + $this->startupPositions = []; + $this->logger->debug( __METHOD__ . ": key is {$this->key} (unread)\n" ); + } + } + + /** + * @param array|bool $curValue + * @param DBMasterPos[] $shutdownPositions + * @param int|null &$cpIndex + * @return array + */ + protected function mergePositions( $curValue, array $shutdownPositions, &$cpIndex = null ) { + /** @var DBMasterPos[] $curPositions */ + $curPositions = isset( $curValue['positions'] ) ? $curValue['positions'] : []; + // Use the newest positions for each DB master + foreach ( $shutdownPositions as $db => $pos ) { + if ( + !isset( $curPositions[$db] ) || + !( $curPositions[$db] instanceof DBMasterPos ) || + $pos->asOfTime() > $curPositions[$db]->asOfTime() + ) { + $curPositions[$db] = $pos; + } + } + + $cpIndex = isset( $curValue['writeIndex'] ) ? $curValue['writeIndex'] : 0; + + return [ + 'positions' => $curPositions, + 'writeIndex' => ++$cpIndex + ]; + } +} |