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: , 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 ]; } }