--- /dev/null
+<?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 float|null Minimum UNIX timestamp of 1+ expected startup positions */
+ protected $waitForPosTime;
+ /** @var int Max seconds to wait on positions to appear */
+ protected $waitForPosTimeout = self::POS_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_WAIT_TIMEOUT = 5;
+
+ /**
+ * @param BagOStuff $store
+ * @param array $client Map of (ip: <IP>, agent: <user-agent>)
+ * @param float $posTime UNIX timestamp
+ * @since 1.27
+ */
+ public function __construct( BagOStuff $store, array $client, $posTime = null ) {
+ $this->store = $store;
+ $this->clientId = md5( $client['ip'] . "\n" . $client['agent'] );
+ $this->key = $store->makeGlobalKey( __CLASS__, $this->clientId, 'v1' );
+ $this->waitForPosTime = $posTime;
+ $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];
+ $this->logger->info( __METHOD__ . ": LB for '$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();
+ $this->logger->info( __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
+ $this->shutdownPositions[$masterName] = $pos;
+ } else {
+ $this->logger->info( __METHOD__ . ": DB '$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
+ * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
+ */
+ public function shutdown( callable $workCallback = null, $mode = 'sync' ) {
+ if ( !$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->info( __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,
+ self::mergePositions( $store->get( $this->key ), $this->shutdownPositions ),
+ self::POSITION_TTL,
+ ( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
+ );
+ $store->unlock( $this->key );
+ } else {
+ $ok = false;
+ }
+
+ if ( !$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 with a certain min
+ // timestamp, then block until they appear, or until a timeout is reached.
+ if ( $this->waitForPosTime > 0.0 ) {
+ $data = null;
+ $loop = new WaitConditionLoop(
+ function () use ( &$data ) {
+ $data = $this->store->get( $this->key );
+
+ return ( self::minPosTime( $data ) >= $this->waitForPosTime )
+ ? WaitConditionLoop::CONDITION_REACHED
+ : WaitConditionLoop::CONDITION_CONTINUE;
+ },
+ $this->waitForPosTimeout
+ );
+ $result = $loop->invoke();
+ $waitedMs = $loop->getLastWaitTime() * 1e3;
+
+ if ( $result == $loop::CONDITION_REACHED ) {
+ $msg = "expected and found pos time {$this->waitForPosTime} ({$waitedMs}ms)";
+ $this->logger->debug( $msg );
+ } else {
+ $msg = "expected but missed pos time {$this->waitForPosTime} ({$waitedMs}ms)";
+ $this->logger->info( $msg );
+ }
+ } else {
+ $data = $this->store->get( $this->key );
+ }
+
+ $this->startupPositions = $data ? $data['positions'] : [];
+ $this->logger->info( __METHOD__ . ": key is {$this->key} (read)\n" );
+ } else {
+ $this->startupPositions = [];
+ $this->logger->info( __METHOD__ . ": key is {$this->key} (unread)\n" );
+ }
+ }
+
+ /**
+ * @param array|bool $data
+ * @return float|null
+ */
+ private static function minPosTime( $data ) {
+ if ( !isset( $data['positions'] ) ) {
+ return null;
+ }
+
+ $min = null;
+ foreach ( $data['positions'] as $pos ) {
+ if ( $pos instanceof DBMasterPos ) {
+ $min = $min ? min( $pos->asOfTime(), $min ) : $pos->asOfTime();
+ }
+ }
+
+ return $min;
+ }
+
+ /**
+ * @param array|bool $curValue
+ * @param DBMasterPos[] $shutdownPositions
+ * @return array
+ */
+ private static function mergePositions( $curValue, array $shutdownPositions ) {
+ /** @var DBMasterPos[] $curPositions */
+ if ( $curValue === false ) {
+ $curPositions = $shutdownPositions;
+ } else {
+ $curPositions = $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;
+ }
+ }
+ }
+
+ return [ 'positions' => $curPositions ];
+ }
+}
scripts.mit.edu / autoinstallsdev / mediawiki.git / blobdiff