first commit

2 files changed, 1239 insertions, 0 deletions

diff --git a/www/wiki/includes/objectcache/ObjectCache.php b/www/wiki/includes/objectcache/ObjectCache.php
new file mode 100644
index 00000000..67d23460
--- /dev/null
+++ b/www/wiki/includes/objectcache/ObjectCache.php
@@ -0,0 +1,414 @@
+<?php
+/**
+ * Functions to get cache 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 Cache
+ */
+
+use MediaWiki\Logger\LoggerFactory;
+use MediaWiki\MediaWikiServices;
+
+/**
+ * Functions to get cache objects
+ *
+ * The word "cache" has two main dictionary meanings, and both
+ * are used in this factory class. They are:
+ *
+ *   - a) Cache (the computer science definition).
+ *        A place to store copies or computations on existing data for
+ *        higher access speeds.
+ *   - b) Storage.
+ *        A place to store lightweight data that is not canonically
+ *        stored anywhere else (e.g. a "hoard" of objects).
+ *
+ * The former should always use strongly consistent stores, so callers don't
+ * have to deal with stale reads. The latter may be eventually consistent, but
+ * callers can use BagOStuff:READ_LATEST to see the latest available data.
+ *
+ * Primary entry points:
+ *
+ * - ObjectCache::getMainWANInstance()
+ *   Purpose: Memory cache.
+ *   Stored in the local data-center's main cache (keyspace different from local-cluster cache).
+ *   Delete events are broadcasted to other DCs main cache. See WANObjectCache for details.
+ *
+ * - ObjectCache::getLocalServerInstance( $fallbackType )
+ *   Purpose: Memory cache for very hot keys.
+ *   Stored only on the individual web server (typically APC or APCu for web requests,
+ *   and EmptyBagOStuff in CLI mode).
+ *   Not replicated to the other servers.
+ *
+ * - ObjectCache::getLocalClusterInstance()
+ *   Purpose: Memory storage for per-cluster coordination and tracking.
+ *   A typical use case would be a rate limit counter or cache regeneration mutex.
+ *   Stored centrally within the local data-center. Not replicated to other DCs.
+ *   Configured by $wgMainCacheType.
+ *
+ * - ObjectCache::getMainStashInstance()
+ *   Purpose: Ephemeral global storage.
+ *   Stored centrally within the primary data-center.
+ *   Changes are applied there first and replicated to other DCs (best-effort).
+ *   To retrieve the latest value (e.g. not from a replica DB), use BagOStuff::READ_LATEST.
+ *   This store may be subject to LRU style evictions.
+ *
+ * - ObjectCache::getInstance( $cacheType )
+ *   Purpose: Special cases (like tiered memory/disk caches).
+ *   Get a specific cache type by key in $wgObjectCaches.
+ *
+ * All the above cache instances (BagOStuff and WANObjectCache) have their makeKey()
+ * method scoped to the *current* wiki ID. Use makeGlobalKey() to avoid this scoping
+ * when using keys that need to be shared amongst wikis.
+ *
+ * @ingroup Cache
+ */
+class ObjectCache {
+	/** @var BagOStuff[] Map of (id => BagOStuff) */
+	public static $instances = [];
+	/** @var WANObjectCache[] Map of (id => WANObjectCache) */
+	public static $wanInstances = [];
+
+	/**
+	 * Get a cached instance of the specified type of cache object.
+	 *
+	 * @param string $id A key in $wgObjectCaches.
+	 * @return BagOStuff
+	 */
+	public static function getInstance( $id ) {
+		if ( !isset( self::$instances[$id] ) ) {
+			self::$instances[$id] = self::newFromId( $id );
+		}
+
+		return self::$instances[$id];
+	}
+
+	/**
+	 * Get a cached instance of the specified type of WAN cache object.
+	 *
+	 * @since 1.26
+	 * @param string $id A key in $wgWANObjectCaches.
+	 * @return WANObjectCache
+	 */
+	public static function getWANInstance( $id ) {
+		if ( !isset( self::$wanInstances[$id] ) ) {
+			self::$wanInstances[$id] = self::newWANCacheFromId( $id );
+		}
+
+		return self::$wanInstances[$id];
+	}
+
+	/**
+	 * Create a new cache object of the specified type.
+	 *
+	 * @param string $id A key in $wgObjectCaches.
+	 * @return BagOStuff
+	 * @throws InvalidArgumentException
+	 */
+	public static function newFromId( $id ) {
+		global $wgObjectCaches;
+
+		if ( !isset( $wgObjectCaches[$id] ) ) {
+			// Always recognize these ones
+			if ( $id === CACHE_NONE ) {
+				return new EmptyBagOStuff();
+			} elseif ( $id === 'hash' ) {
+				return new HashBagOStuff();
+			}
+
+			throw new InvalidArgumentException( "Invalid object cache type \"$id\" requested. " .
+				"It is not present in \$wgObjectCaches." );
+		}
+
+		return self::newFromParams( $wgObjectCaches[$id] );
+	}
+
+	/**
+	 * Get the default keyspace for this wiki.
+	 *
+	 * This is either the value of the `CachePrefix` configuration variable,
+	 * or (if the former is unset) the `DBname` configuration variable, with
+	 * `DBprefix` (if defined).
+	 *
+	 * @return string
+	 */
+	public static function getDefaultKeyspace() {
+		global $wgCachePrefix;
+
+		$keyspace = $wgCachePrefix;
+		if ( is_string( $keyspace ) && $keyspace !== '' ) {
+			return $keyspace;
+		}
+
+		return wfWikiID();
+	}
+
+	/**
+	 * Create a new cache object from parameters.
+	 *
+	 * @param array $params Must have 'factory' or 'class' property.
+	 *  - factory: Callback passed $params that returns BagOStuff.
+	 *  - class: BagOStuff subclass constructed with $params.
+	 *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
+	 *  - .. Other parameters passed to factory or class.
+	 * @return BagOStuff
+	 * @throws InvalidArgumentException
+	 */
+	public static function newFromParams( $params ) {
+		if ( isset( $params['loggroup'] ) ) {
+			$params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
+		} else {
+			$params['logger'] = LoggerFactory::getInstance( 'objectcache' );
+		}
+		if ( !isset( $params['keyspace'] ) ) {
+			$params['keyspace'] = self::getDefaultKeyspace();
+		}
+		if ( isset( $params['factory'] ) ) {
+			return call_user_func( $params['factory'], $params );
+		} elseif ( isset( $params['class'] ) ) {
+			$class = $params['class'];
+			// Automatically set the 'async' update handler
+			$params['asyncHandler'] = isset( $params['asyncHandler'] )
+				? $params['asyncHandler']
+				: 'DeferredUpdates::addCallableUpdate';
+			// Enable reportDupes by default
+			$params['reportDupes'] = isset( $params['reportDupes'] )
+				? $params['reportDupes']
+				: true;
+			// Do b/c logic for SqlBagOStuff
+			if ( is_a( $class, SqlBagOStuff::class, true ) ) {
+				if ( isset( $params['server'] ) && !isset( $params['servers'] ) ) {
+					$params['servers'] = [ $params['server'] ];
+					unset( $params['server'] );
+				}
+				// In the past it was not required to set 'dbDirectory' in $wgObjectCaches
+				if ( isset( $params['servers'] ) ) {
+					foreach ( $params['servers'] as &$server ) {
+						if ( $server['type'] === 'sqlite' && !isset( $server['dbDirectory'] ) ) {
+							$server['dbDirectory'] = MediaWikiServices::getInstance()
+								->getMainConfig()->get( 'SQLiteDataDir' );
+						}
+					}
+				}
+			}
+
+			// Do b/c logic for MemcachedBagOStuff
+			if ( is_subclass_of( $class, MemcachedBagOStuff::class ) ) {
+				if ( !isset( $params['servers'] ) ) {
+					$params['servers'] = $GLOBALS['wgMemCachedServers'];
+				}
+				if ( !isset( $params['debug'] ) ) {
+					$params['debug'] = $GLOBALS['wgMemCachedDebug'];
+				}
+				if ( !isset( $params['persistent'] ) ) {
+					$params['persistent'] = $GLOBALS['wgMemCachedPersistent'];
+				}
+				if ( !isset( $params['timeout'] ) ) {
+					$params['timeout'] = $GLOBALS['wgMemCachedTimeout'];
+				}
+			}
+			return new $class( $params );
+		} else {
+			throw new InvalidArgumentException( "The definition of cache type \""
+				. print_r( $params, true ) . "\" lacks both "
+				. "factory and class parameters." );
+		}
+	}
+
+	/**
+	 * Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
+	 *
+	 * CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
+	 * If a caching method is configured for any of the main caches ($wgMainCacheType,
+	 * $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
+	 * be an alias to the configured cache choice for that.
+	 * If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
+	 * then CACHE_ANYTHING will forward to CACHE_DB.
+	 *
+	 * @param array $params
+	 * @return BagOStuff
+	 */
+	public static function newAnything( $params ) {
+		global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
+		$candidates = [ $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType ];
+		foreach ( $candidates as $candidate ) {
+			$cache = false;
+			if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
+				$cache = self::getInstance( $candidate );
+				// CACHE_ACCEL might default to nothing if no APCu
+				// See includes/ServiceWiring.php
+				if ( !( $cache instanceof EmptyBagOStuff ) ) {
+					return $cache;
+				}
+			}
+		}
+
+		if ( MediaWikiServices::getInstance()->isServiceDisabled( 'DBLoadBalancer' ) ) {
+			// The LoadBalancer is disabled, probably because
+			// MediaWikiServices::disableStorageBackend was called.
+			$candidate = CACHE_NONE;
+		} else {
+			$candidate = CACHE_DB;
+		}
+
+		return self::getInstance( $candidate );
+	}
+
+	/**
+	 * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
+	 *
+	 * This will look for any APC or APCu style server-local cache.
+	 * A fallback cache can be specified if none is found.
+	 *
+	 *     // Direct calls
+	 *     ObjectCache::getLocalServerInstance( $fallbackType );
+	 *
+	 *     // From $wgObjectCaches via newFromParams()
+	 *     ObjectCache::getLocalServerInstance( [ 'fallback' => $fallbackType ] );
+	 *
+	 * @param int|string|array $fallback Fallback cache or parameter map with 'fallback'
+	 * @return BagOStuff
+	 * @throws InvalidArgumentException
+	 * @since 1.27
+	 */
+	public static function getLocalServerInstance( $fallback = CACHE_NONE ) {
+		$cache = MediaWikiServices::getInstance()->getLocalServerObjectCache();
+		if ( $cache instanceof EmptyBagOStuff ) {
+			if ( is_array( $fallback ) ) {
+				$fallback = isset( $fallback['fallback'] ) ? $fallback['fallback'] : CACHE_NONE;
+			}
+			$cache = self::getInstance( $fallback );
+		}
+
+		return $cache;
+	}
+
+	/**
+	 * Create a new cache object of the specified type.
+	 *
+	 * @since 1.26
+	 * @param string $id A key in $wgWANObjectCaches.
+	 * @return WANObjectCache
+	 * @throws UnexpectedValueException
+	 */
+	public static function newWANCacheFromId( $id ) {
+		global $wgWANObjectCaches, $wgObjectCaches;
+
+		if ( !isset( $wgWANObjectCaches[$id] ) ) {
+			throw new UnexpectedValueException(
+				"Cache type \"$id\" requested is not present in \$wgWANObjectCaches." );
+		}
+
+		$params = $wgWANObjectCaches[$id];
+		if ( !isset( $wgObjectCaches[$params['cacheId']] ) ) {
+			throw new UnexpectedValueException(
+				"Cache type \"{$params['cacheId']}\" is not present in \$wgObjectCaches." );
+		}
+		$params['store'] = $wgObjectCaches[$params['cacheId']];
+
+		return self::newWANCacheFromParams( $params );
+	}
+
+	/**
+	 * Create a new cache object of the specified type.
+	 *
+	 * @since 1.28
+	 * @param array $params
+	 * @return WANObjectCache
+	 * @throws UnexpectedValueException
+	 */
+	public static function newWANCacheFromParams( array $params ) {
+		global $wgCommandLineMode;
+
+		$services = MediaWikiServices::getInstance();
+
+		$erGroup = $services->getEventRelayerGroup();
+		foreach ( $params['channels'] as $action => $channel ) {
+			$params['relayers'][$action] = $erGroup->getRelayer( $channel );
+			$params['channels'][$action] = $channel;
+		}
+		$params['cache'] = self::newFromParams( $params['store'] );
+		if ( isset( $params['loggroup'] ) ) {
+			$params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
+		} else {
+			$params['logger'] = LoggerFactory::getInstance( 'objectcache' );
+		}
+		if ( !$wgCommandLineMode ) {
+			// Send the statsd data post-send on HTTP requests; avoid in CLI mode (T181385)
+			$params['stats'] = $services->getStatsdDataFactory();
+			// Let pre-emptive refreshes happen post-send on HTTP requests
+			$params['asyncHandler'] = [ DeferredUpdates::class, 'addCallableUpdate' ];
+		}
+		$class = $params['class'];
+
+		return new $class( $params );
+	}
+
+	/**
+	 * Get the main cluster-local cache object.
+	 *
+	 * @since 1.27
+	 * @return BagOStuff
+	 */
+	public static function getLocalClusterInstance() {
+		global $wgMainCacheType;
+
+		return self::getInstance( $wgMainCacheType );
+	}
+
+	/**
+	 * Get the main WAN cache object.
+	 *
+	 * @since 1.26
+	 * @return WANObjectCache
+	 * @deprecated Since 1.28 Use MediaWikiServices::getMainWANObjectCache()
+	 */
+	public static function getMainWANInstance() {
+		return MediaWikiServices::getInstance()->getMainWANObjectCache();
+	}
+
+	/**
+	 * Get the cache object for the main stash.
+	 *
+	 * Stash objects are BagOStuff instances suitable for storing light
+	 * weight data that is not canonically stored elsewhere (such as RDBMS).
+	 * Stashes should be configured to propagate changes to all data-centers.
+	 *
+	 * Callers should be prepared for:
+	 *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
+	 *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
+	 * In general, this means avoiding updates on idempotent HTTP requests and
+	 * avoiding an assumption of perfect serializability (or accepting anomalies).
+	 * Reads may be eventually consistent or data might rollback as nodes flap.
+	 * Callers can use BagOStuff:READ_LATEST to see the latest available data.
+	 *
+	 * @return BagOStuff
+	 * @since 1.26
+	 * @deprecated Since 1.28 Use MediaWikiServices::getMainObjectStash
+	 */
+	public static function getMainStashInstance() {
+		return MediaWikiServices::getInstance()->getMainObjectStash();
+	}
+
+	/**
+	 * Clear all the cached instances.
+	 */
+	public static function clear() {
+		self::$instances = [];
+		self::$wanInstances = [];
+	}
+}
diff --git a/www/wiki/includes/objectcache/SqlBagOStuff.php b/www/wiki/includes/objectcache/SqlBagOStuff.php
new file mode 100644
index 00000000..8ff14ed7
--- /dev/null
+++ b/www/wiki/includes/objectcache/SqlBagOStuff.php
@@ -0,0 +1,825 @@
+<?php
+/**
+ * Object caching using a SQL database.
+ *
+ * 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 Cache
+ */
+
+use MediaWiki\MediaWikiServices;
+use Wikimedia\Rdbms\Database;
+use Wikimedia\Rdbms\IDatabase;
+use Wikimedia\Rdbms\DBError;
+use Wikimedia\Rdbms\DBQueryError;
+use Wikimedia\Rdbms\DBConnectionError;
+use Wikimedia\Rdbms\LoadBalancer;
+use Wikimedia\Rdbms\TransactionProfiler;
+use Wikimedia\WaitConditionLoop;
+
+/**
+ * Class to store objects in the database
+ *
+ * @ingroup Cache
+ */
+class SqlBagOStuff extends BagOStuff {
+	/** @var array[] (server index => server config) */
+	protected $serverInfos;
+	/** @var string[] (server index => tag/host name) */
+	protected $serverTags;
+	/** @var int */
+	protected $numServers;
+	/** @var int */
+	protected $lastExpireAll = 0;
+	/** @var int */
+	protected $purgePeriod = 100;
+	/** @var int */
+	protected $shards = 1;
+	/** @var string */
+	protected $tableName = 'objectcache';
+	/** @var bool */
+	protected $replicaOnly = false;
+	/** @var int */
+	protected $syncTimeout = 3;
+
+	/** @var LoadBalancer|null */
+	protected $separateMainLB;
+	/** @var array */
+	protected $conns;
+	/** @var array UNIX timestamps */
+	protected $connFailureTimes = [];
+	/** @var array Exceptions */
+	protected $connFailureErrors = [];
+
+	/**
+	 * Constructor. Parameters are:
+	 *   - server:      A server info structure in the format required by each
+	 *                  element in $wgDBServers.
+	 *
+	 *   - servers:     An array of server info structures describing a set of database servers
+	 *                  to distribute keys to. If this is specified, the "server" option will be
+	 *                  ignored. If string keys are used, then they will be used for consistent
+	 *                  hashing *instead* of the host name (from the server config). This is useful
+	 *                  when a cluster is replicated to another site (with different host names)
+	 *                  but each server has a corresponding replica in the other cluster.
+	 *
+	 *   - purgePeriod: The average number of object cache requests in between
+	 *                  garbage collection operations, where expired entries
+	 *                  are removed from the database. Or in other words, the
+	 *                  reciprocal of the probability of purging on any given
+	 *                  request. If this is set to zero, purging will never be
+	 *                  done.
+	 *
+	 *   - tableName:   The table name to use, default is "objectcache".
+	 *
+	 *   - shards:      The number of tables to use for data storage on each server.
+	 *                  If this is more than 1, table names will be formed in the style
+	 *                  objectcacheNNN where NNN is the shard index, between 0 and
+	 *                  shards-1. The number of digits will be the minimum number
+	 *                  required to hold the largest shard index. Data will be
+	 *                  distributed across all tables by key hash. This is for
+	 *                  MySQL bugs 61735 and 61736.
+	 *   - slaveOnly:   Whether to only use replica DBs and avoid triggering
+	 *                  garbage collection logic of expired items. This only
+	 *                  makes sense if the primary DB is used and only if get()
+	 *                  calls will be used. This is used by ReplicatedBagOStuff.
+	 *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
+	 *
+	 * @param array $params
+	 */
+	public function __construct( $params ) {
+		parent::__construct( $params );
+
+		$this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
+		$this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
+
+		if ( isset( $params['servers'] ) ) {
+			$this->serverInfos = [];
+			$this->serverTags = [];
+			$this->numServers = count( $params['servers'] );
+			$index = 0;
+			foreach ( $params['servers'] as $tag => $info ) {
+				$this->serverInfos[$index] = $info;
+				if ( is_string( $tag ) ) {
+					$this->serverTags[$index] = $tag;
+				} else {
+					$this->serverTags[$index] = isset( $info['host'] ) ? $info['host'] : "#$index";
+				}
+				++$index;
+			}
+		} elseif ( isset( $params['server'] ) ) {
+			$this->serverInfos = [ $params['server'] ];
+			$this->numServers = count( $this->serverInfos );
+		} else {
+			// Default to using the main wiki's database servers
+			$this->serverInfos = false;
+			$this->numServers = 1;
+			$this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
+		}
+		if ( isset( $params['purgePeriod'] ) ) {
+			$this->purgePeriod = intval( $params['purgePeriod'] );
+		}
+		if ( isset( $params['tableName'] ) ) {
+			$this->tableName = $params['tableName'];
+		}
+		if ( isset( $params['shards'] ) ) {
+			$this->shards = intval( $params['shards'] );
+		}
+		if ( isset( $params['syncTimeout'] ) ) {
+			$this->syncTimeout = $params['syncTimeout'];
+		}
+		$this->replicaOnly = !empty( $params['slaveOnly'] );
+	}
+
+	/**
+	 * Get a connection to the specified database
+	 *
+	 * @param int $serverIndex
+	 * @return Database
+	 * @throws MWException
+	 */
+	protected function getDB( $serverIndex ) {
+		if ( !isset( $this->conns[$serverIndex] ) ) {
+			if ( $serverIndex >= $this->numServers ) {
+				throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
+			}
+
+			# Don't keep timing out trying to connect for each call if the DB is down
+			if ( isset( $this->connFailureErrors[$serverIndex] )
+				&& ( time() - $this->connFailureTimes[$serverIndex] ) < 60
+			) {
+				throw $this->connFailureErrors[$serverIndex];
+			}
+
+			if ( $this->serverInfos ) {
+				// Use custom database defined by server connection info
+				$info = $this->serverInfos[$serverIndex];
+				$type = isset( $info['type'] ) ? $info['type'] : 'mysql';
+				$host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
+				$this->logger->debug( __CLASS__ . ": connecting to $host" );
+				// Use a blank trx profiler to ignore expections as this is a cache
+				$info['trxProfiler'] = new TransactionProfiler();
+				$db = Database::factory( $type, $info );
+				$db->clearFlag( DBO_TRX ); // auto-commit mode
+			} else {
+				// Use the main LB database
+				$lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
+				$index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
+				if ( $lb->getServerType( $lb->getWriterIndex() ) !== 'sqlite' ) {
+					// Keep a separate connection to avoid contention and deadlocks
+					$db = $lb->getConnection( $index, [], false, $lb::CONN_TRX_AUTOCOMMIT );
+					// @TODO: Use a blank trx profiler to ignore expections as this is a cache
+				} else {
+					// However, SQLite has the opposite behavior due to DB-level locking.
+					// Stock sqlite MediaWiki installs use a separate sqlite cache DB instead.
+					$db = $lb->getConnection( $index );
+				}
+			}
+
+			$this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
+			$this->conns[$serverIndex] = $db;
+		}
+
+		return $this->conns[$serverIndex];
+	}
+
+	/**
+	 * Get the server index and table name for a given key
+	 * @param string $key
+	 * @return array Server index and table name
+	 */
+	protected function getTableByKey( $key ) {
+		if ( $this->shards > 1 ) {
+			$hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
+			$tableIndex = $hash % $this->shards;
+		} else {
+			$tableIndex = 0;
+		}
+		if ( $this->numServers > 1 ) {
+			$sortedServers = $this->serverTags;
+			ArrayUtils::consistentHashSort( $sortedServers, $key );
+			reset( $sortedServers );
+			$serverIndex = key( $sortedServers );
+		} else {
+			$serverIndex = 0;
+		}
+		return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
+	}
+
+	/**
+	 * Get the table name for a given shard index
+	 * @param int $index
+	 * @return string
+	 */
+	protected function getTableNameByShard( $index ) {
+		if ( $this->shards > 1 ) {
+			$decimals = strlen( $this->shards - 1 );
+			return $this->tableName .
+				sprintf( "%0{$decimals}d", $index );
+		} else {
+			return $this->tableName;
+		}
+	}
+
+	protected function doGet( $key, $flags = 0 ) {
+		$casToken = null;
+
+		return $this->getWithToken( $key, $casToken, $flags );
+	}
+
+	protected function getWithToken( $key, &$casToken, $flags = 0 ) {
+		$values = $this->getMulti( [ $key ] );
+		if ( array_key_exists( $key, $values ) ) {
+			$casToken = $values[$key];
+			return $values[$key];
+		}
+		return false;
+	}
+
+	public function getMulti( array $keys, $flags = 0 ) {
+		$values = []; // array of (key => value)
+
+		$keysByTable = [];
+		foreach ( $keys as $key ) {
+			list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
+			$keysByTable[$serverIndex][$tableName][] = $key;
+		}
+
+		$this->garbageCollect(); // expire old entries if any
+
+		$dataRows = [];
+		foreach ( $keysByTable as $serverIndex => $serverKeys ) {
+			try {
+				$db = $this->getDB( $serverIndex );
+				foreach ( $serverKeys as $tableName => $tableKeys ) {
+					$res = $db->select( $tableName,
+						[ 'keyname', 'value', 'exptime' ],
+						[ 'keyname' => $tableKeys ],
+						__METHOD__,
+						// Approximate write-on-the-fly BagOStuff API via blocking.
+						// This approximation fails if a ROLLBACK happens (which is rare).
+						// We do not want to flush the TRX as that can break callers.
+						$db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
+					);
+					if ( $res === false ) {
+						continue;
+					}
+					foreach ( $res as $row ) {
+						$row->serverIndex = $serverIndex;
+						$row->tableName = $tableName;
+						$dataRows[$row->keyname] = $row;
+					}
+				}
+			} catch ( DBError $e ) {
+				$this->handleReadError( $e, $serverIndex );
+			}
+		}
+
+		foreach ( $keys as $key ) {
+			if ( isset( $dataRows[$key] ) ) { // HIT?
+				$row = $dataRows[$key];
+				$this->debug( "get: retrieved data; expiry time is " . $row->exptime );
+				$db = null;
+				try {
+					$db = $this->getDB( $row->serverIndex );
+					if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
+						$this->debug( "get: key has expired" );
+					} else { // HIT
+						$values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
+					}
+				} catch ( DBQueryError $e ) {
+					$this->handleWriteError( $e, $db, $row->serverIndex );
+				}
+			} else { // MISS
+				$this->debug( 'get: no matching rows' );
+			}
+		}
+
+		return $values;
+	}
+
+	public function setMulti( array $data, $expiry = 0 ) {
+		$keysByTable = [];
+		foreach ( $data as $key => $value ) {
+			list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
+			$keysByTable[$serverIndex][$tableName][] = $key;
+		}
+
+		$this->garbageCollect(); // expire old entries if any
+
+		$result = true;
+		$exptime = (int)$expiry;
+		foreach ( $keysByTable as $serverIndex => $serverKeys ) {
+			$db = null;
+			try {
+				$db = $this->getDB( $serverIndex );
+			} catch ( DBError $e ) {
+				$this->handleWriteError( $e, $db, $serverIndex );
+				$result = false;
+				continue;
+			}
+
+			if ( $exptime < 0 ) {
+				$exptime = 0;
+			}
+
+			if ( $exptime == 0 ) {
+				$encExpiry = $this->getMaxDateTime( $db );
+			} else {
+				$exptime = $this->convertExpiry( $exptime );
+				$encExpiry = $db->timestamp( $exptime );
+			}
+			foreach ( $serverKeys as $tableName => $tableKeys ) {
+				$rows = [];
+				foreach ( $tableKeys as $key ) {
+					$rows[] = [
+						'keyname' => $key,
+						'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
+						'exptime' => $encExpiry,
+					];
+				}
+
+				try {
+					$db->replace(
+						$tableName,
+						[ 'keyname' ],
+						$rows,
+						__METHOD__
+					);
+				} catch ( DBError $e ) {
+					$this->handleWriteError( $e, $db, $serverIndex );
+					$result = false;
+				}
+
+			}
+
+		}
+
+		return $result;
+	}
+
+	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
+		$ok = $this->setMulti( [ $key => $value ], $exptime );
+		if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
+			$ok = $this->waitForReplication() && $ok;
+		}
+
+		return $ok;
+	}
+
+	protected function cas( $casToken, $key, $value, $exptime = 0 ) {
+		list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
+		$db = null;
+		try {
+			$db = $this->getDB( $serverIndex );
+			$exptime = intval( $exptime );
+
+			if ( $exptime < 0 ) {
+				$exptime = 0;
+			}
+
+			if ( $exptime == 0 ) {
+				$encExpiry = $this->getMaxDateTime( $db );
+			} else {
+				$exptime = $this->convertExpiry( $exptime );
+				$encExpiry = $db->timestamp( $exptime );
+			}
+			// (T26425) use a replace if the db supports it instead of
+			// delete/insert to avoid clashes with conflicting keynames
+			$db->update(
+				$tableName,
+				[
+					'keyname' => $key,
+					'value' => $db->encodeBlob( $this->serialize( $value ) ),
+					'exptime' => $encExpiry
+				],
+				[
+					'keyname' => $key,
+					'value' => $db->encodeBlob( $this->serialize( $casToken ) )
+				],
+				__METHOD__
+			);
+		} catch ( DBQueryError $e ) {
+			$this->handleWriteError( $e, $db, $serverIndex );
+
+			return false;
+		}
+
+		return (bool)$db->affectedRows();
+	}
+
+	public function delete( $key ) {
+		list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
+		$db = null;
+		try {
+			$db = $this->getDB( $serverIndex );
+			$db->delete(
+				$tableName,
+				[ 'keyname' => $key ],
+				__METHOD__ );
+		} catch ( DBError $e ) {
+			$this->handleWriteError( $e, $db, $serverIndex );
+			return false;
+		}
+
+		return true;
+	}
+
+	public function incr( $key, $step = 1 ) {
+		list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
+		$db = null;
+		try {
+			$db = $this->getDB( $serverIndex );
+			$step = intval( $step );
+			$row = $db->selectRow(
+				$tableName,
+				[ 'value', 'exptime' ],
+				[ 'keyname' => $key ],
+				__METHOD__,
+				[ 'FOR UPDATE' ] );
+			if ( $row === false ) {
+				// Missing
+
+				return null;
+			}
+			$db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
+			if ( $this->isExpired( $db, $row->exptime ) ) {
+				// Expired, do not reinsert
+
+				return null;
+			}
+
+			$oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
+			$newValue = $oldValue + $step;
+			$db->insert( $tableName,
+				[
+					'keyname' => $key,
+					'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
+					'exptime' => $row->exptime
+				], __METHOD__, 'IGNORE' );
+
+			if ( $db->affectedRows() == 0 ) {
+				// Race condition. See T30611
+				$newValue = null;
+			}
+		} catch ( DBError $e ) {
+			$this->handleWriteError( $e, $db, $serverIndex );
+			return null;
+		}
+
+		return $newValue;
+	}
+
+	public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
+		$ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts );
+		if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
+			$ok = $this->waitForReplication() && $ok;
+		}
+
+		return $ok;
+	}
+
+	public function changeTTL( $key, $expiry = 0 ) {
+		list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
+		$db = null;
+		try {
+			$db = $this->getDB( $serverIndex );
+			$db->update(
+				$tableName,
+				[ 'exptime' => $db->timestamp( $this->convertExpiry( $expiry ) ) ],
+				[ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
+				__METHOD__
+			);
+			if ( $db->affectedRows() == 0 ) {
+				return false;
+			}
+		} catch ( DBError $e ) {
+			$this->handleWriteError( $e, $db, $serverIndex );
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * @param IDatabase $db
+	 * @param string $exptime
+	 * @return bool
+	 */
+	protected function isExpired( $db, $exptime ) {
+		return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
+	}
+
+	/**
+	 * @param IDatabase $db
+	 * @return string
+	 */
+	protected function getMaxDateTime( $db ) {
+		if ( time() > 0x7fffffff ) {
+			return $db->timestamp( 1 << 62 );
+		} else {
+			return $db->timestamp( 0x7fffffff );
+		}
+	}
+
+	protected function garbageCollect() {
+		if ( !$this->purgePeriod || $this->replicaOnly ) {
+			// Disabled
+			return;
+		}
+		// Only purge on one in every $this->purgePeriod requests.
+		if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
+			return;
+		}
+		$now = time();
+		// Avoid repeating the delete within a few seconds
+		if ( $now > ( $this->lastExpireAll + 1 ) ) {
+			$this->lastExpireAll = $now;
+			$this->expireAll();
+		}
+	}
+
+	public function expireAll() {
+		$this->deleteObjectsExpiringBefore( wfTimestampNow() );
+	}
+
+	/**
+	 * Delete objects from the database which expire before a certain date.
+	 * @param string $timestamp
+	 * @param bool|callable $progressCallback
+	 * @return bool
+	 */
+	public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
+		for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
+			$db = null;
+			try {
+				$db = $this->getDB( $serverIndex );
+				$dbTimestamp = $db->timestamp( $timestamp );
+				$totalSeconds = false;
+				$baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
+				for ( $i = 0; $i < $this->shards; $i++ ) {
+					$maxExpTime = false;
+					while ( true ) {
+						$conds = $baseConds;
+						if ( $maxExpTime !== false ) {
+							$conds[] = 'exptime >= ' . $db->addQuotes( $maxExpTime );
+						}
+						$rows = $db->select(
+							$this->getTableNameByShard( $i ),
+							[ 'keyname', 'exptime' ],
+							$conds,
+							__METHOD__,
+							[ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ] );
+						if ( $rows === false || !$rows->numRows() ) {
+							break;
+						}
+						$keys = [];
+						$row = $rows->current();
+						$minExpTime = $row->exptime;
+						if ( $totalSeconds === false ) {
+							$totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
+								- wfTimestamp( TS_UNIX, $minExpTime );
+						}
+						foreach ( $rows as $row ) {
+							$keys[] = $row->keyname;
+							$maxExpTime = $row->exptime;
+						}
+
+						$db->delete(
+							$this->getTableNameByShard( $i ),
+							[
+								'exptime >= ' . $db->addQuotes( $minExpTime ),
+								'exptime < ' . $db->addQuotes( $dbTimestamp ),
+								'keyname' => $keys
+							],
+							__METHOD__ );
+
+						if ( $progressCallback ) {
+							if ( intval( $totalSeconds ) === 0 ) {
+								$percent = 0;
+							} else {
+								$remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
+									- wfTimestamp( TS_UNIX, $maxExpTime );
+								if ( $remainingSeconds > $totalSeconds ) {
+									$totalSeconds = $remainingSeconds;
+								}
+								$processedSeconds = $totalSeconds - $remainingSeconds;
+								$percent = ( $i + $processedSeconds / $totalSeconds )
+									/ $this->shards * 100;
+							}
+							$percent = ( $percent / $this->numServers )
+								+ ( $serverIndex / $this->numServers * 100 );
+							call_user_func( $progressCallback, $percent );
+						}
+					}
+				}
+			} catch ( DBError $e ) {
+				$this->handleWriteError( $e, $db, $serverIndex );
+				return false;
+			}
+		}
+		return true;
+	}
+
+	/**
+	 * Delete content of shard tables in every server.
+	 * Return true if the operation is successful, false otherwise.
+	 * @return bool
+	 */
+	public function deleteAll() {
+		for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
+			$db = null;
+			try {
+				$db = $this->getDB( $serverIndex );
+				for ( $i = 0; $i < $this->shards; $i++ ) {
+					$db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
+				}
+			} catch ( DBError $e ) {
+				$this->handleWriteError( $e, $db, $serverIndex );
+				return false;
+			}
+		}
+		return true;
+	}
+
+	/**
+	 * Serialize an object and, if possible, compress the representation.
+	 * On typical message and page data, this can provide a 3X decrease
+	 * in storage requirements.
+	 *
+	 * @param mixed &$data
+	 * @return string
+	 */
+	protected function serialize( &$data ) {
+		$serial = serialize( $data );
+
+		if ( function_exists( 'gzdeflate' ) ) {
+			return gzdeflate( $serial );
+		} else {
+			return $serial;
+		}
+	}
+
+	/**
+	 * Unserialize and, if necessary, decompress an object.
+	 * @param string $serial
+	 * @return mixed
+	 */
+	protected function unserialize( $serial ) {
+		if ( function_exists( 'gzinflate' ) ) {
+			Wikimedia\suppressWarnings();
+			$decomp = gzinflate( $serial );
+			Wikimedia\restoreWarnings();
+
+			if ( false !== $decomp ) {
+				$serial = $decomp;
+			}
+		}
+
+		$ret = unserialize( $serial );
+
+		return $ret;
+	}
+
+	/**
+	 * Handle a DBError which occurred during a read operation.
+	 *
+	 * @param DBError $exception
+	 * @param int $serverIndex
+	 */
+	protected function handleReadError( DBError $exception, $serverIndex ) {
+		if ( $exception instanceof DBConnectionError ) {
+			$this->markServerDown( $exception, $serverIndex );
+		}
+		$this->logger->error( "DBError: {$exception->getMessage()}" );
+		if ( $exception instanceof DBConnectionError ) {
+			$this->setLastError( BagOStuff::ERR_UNREACHABLE );
+			$this->logger->debug( __METHOD__ . ": ignoring connection error" );
+		} else {
+			$this->setLastError( BagOStuff::ERR_UNEXPECTED );
+			$this->logger->debug( __METHOD__ . ": ignoring query error" );
+		}
+	}
+
+	/**
+	 * Handle a DBQueryError which occurred during a write operation.
+	 *
+	 * @param DBError $exception
+	 * @param IDatabase|null $db DB handle or null if connection failed
+	 * @param int $serverIndex
+	 * @throws Exception
+	 */
+	protected function handleWriteError( DBError $exception, IDatabase $db = null, $serverIndex ) {
+		if ( !$db ) {
+			$this->markServerDown( $exception, $serverIndex );
+		} elseif ( $db->wasReadOnlyError() ) {
+			if ( $db->trxLevel() && $this->usesMainDB() ) {
+				// Errors like deadlocks and connection drops already cause rollback.
+				// For consistency, we have no choice but to throw an error and trigger
+				// complete rollback if the main DB is also being used as the cache DB.
+				throw $exception;
+			}
+		}
+
+		$this->logger->error( "DBError: {$exception->getMessage()}" );
+		if ( $exception instanceof DBConnectionError ) {
+			$this->setLastError( BagOStuff::ERR_UNREACHABLE );
+			$this->logger->debug( __METHOD__ . ": ignoring connection error" );
+		} else {
+			$this->setLastError( BagOStuff::ERR_UNEXPECTED );
+			$this->logger->debug( __METHOD__ . ": ignoring query error" );
+		}
+	}
+
+	/**
+	 * Mark a server down due to a DBConnectionError exception
+	 *
+	 * @param DBError $exception
+	 * @param int $serverIndex
+	 */
+	protected function markServerDown( DBError $exception, $serverIndex ) {
+		unset( $this->conns[$serverIndex] ); // bug T103435
+
+		if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
+			if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
+				unset( $this->connFailureTimes[$serverIndex] );
+				unset( $this->connFailureErrors[$serverIndex] );
+			} else {
+				$this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
+				return;
+			}
+		}
+		$now = time();
+		$this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
+		$this->connFailureTimes[$serverIndex] = $now;
+		$this->connFailureErrors[$serverIndex] = $exception;
+	}
+
+	/**
+	 * Create shard tables. For use from eval.php.
+	 */
+	public function createTables() {
+		for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
+			$db = $this->getDB( $serverIndex );
+			if ( $db->getType() !== 'mysql' ) {
+				throw new MWException( __METHOD__ . ' is not supported on this DB server' );
+			}
+
+			for ( $i = 0; $i < $this->shards; $i++ ) {
+				$db->query(
+					'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
+					' LIKE ' . $db->tableName( 'objectcache' ),
+					__METHOD__ );
+			}
+		}
+	}
+
+	/**
+	 * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
+	 */
+	protected function usesMainDB() {
+		return !$this->serverInfos;
+	}
+
+	protected function waitForReplication() {
+		if ( !$this->usesMainDB() ) {
+			// Custom DB server list; probably doesn't use replication
+			return true;
+		}
+
+		$lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
+		if ( $lb->getServerCount() <= 1 ) {
+			return true; // no replica DBs
+		}
+
+		// Main LB is used; wait for any replica DBs to catch up
+		$masterPos = $lb->getMasterPos();
+		if ( !$masterPos ) {
+			return true; // not applicable
+		}
+
+		$loop = new WaitConditionLoop(
+			function () use ( $lb, $masterPos ) {
+				return $lb->waitForAll( $masterPos, 1 );
+			},
+			$this->syncTimeout,
+			$this->busyCallbacks
+		);
+
+		return ( $loop->invoke() === $loop::CONDITION_REACHED );
+	}
+}