Merge commit 'fa89acd'

# Conflicts:
#	.gitignore
#	extensions/ArchInterWiki.sql

1 files changed, 124 insertions, 0 deletions

diff --git a/includes/db/LoadMonitorMySQL.php b/includes/db/LoadMonitorMySQL.php
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+<?php
+/**
+ * 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
+ */
+
+/**
+ * Basic MySQL load monitor with no external dependencies
+ * Uses memcached to cache the replication lag for a short time
+ *
+ * @ingroup Database
+ */
+class LoadMonitorMySQL implements LoadMonitor {
+	/** @var LoadBalancer */
+	public $parent;
+	/** @var BagOStuff */
+	protected $srvCache;
+	/** @var BagOStuff */
+	protected $mainCache;
+
+	public function __construct( $parent ) {
+		$this->parent = $parent;
+
+		$this->srvCache = ObjectCache::newAccelerator( 'hash' );
+		$this->mainCache = wfGetMainCache();
+	}
+
+	public function scaleLoads( &$loads, $group = false, $wiki = false ) {
+	}
+
+	public function getLagTimes( $serverIndexes, $wiki ) {
+		if ( count( $serverIndexes ) == 1 && reset( $serverIndexes ) == 0 ) {
+			# Single server only, just return zero without caching
+			return array( 0 => 0 );
+		}
+
+		$key = $this->getLagTimeCacheKey();
+		# Randomize TTLs to reduce stampedes (4.0 - 5.0 sec)
+		$ttl = mt_rand( 4e6, 5e6 ) / 1e6;
+		# Keep keys around longer as fallbacks
+		$staleTTL = 60;
+
+		# (a) Check the local APC cache
+		$value = $this->srvCache->get( $key );
+		if ( $value && $value['timestamp'] > ( microtime( true ) - $ttl ) ) {
+			wfDebugLog( 'replication',  __FUNCTION__ . ": got lag times ($key) from local cache" );
+			return $value['lagTimes']; // cache hit
+		}
+		$staleValue = $value ?: false;
+
+		# (b) Check the shared cache and backfill APC
+		$value = $this->mainCache->get( $key );
+		if ( $value && $value['timestamp'] > ( microtime( true ) - $ttl ) ) {
+			$this->srvCache->set( $key, $value, $staleTTL );
+			wfDebugLog( 'replication',  __FUNCTION__ . ": got lag times ($key) from main cache" );
+
+			return $value['lagTimes']; // cache hit
+		}
+		$staleValue = $value ?: $staleValue;
+
+		# (c) Cache key missing or expired; regenerate and backfill
+		if ( $this->mainCache->lock( $key, 0, 10 ) ) {
+			# Let this process alone update the cache value
+			$cache = $this->mainCache;
+			/** @noinspection PhpUnusedLocalVariableInspection */
+			$unlocker = new ScopedCallback( function () use ( $cache, $key ) {
+				$cache->unlock( $key );
+			} );
+		} elseif ( $staleValue ) {
+			# Could not acquire lock but an old cache exists, so use it
+			return $staleValue['lagTimes'];
+		}
+
+		$lagTimes = array();
+		foreach ( $serverIndexes as $i ) {
+			if ( $i == 0 ) { # Master
+				$lagTimes[$i] = 0;
+			} elseif ( false !== ( $conn = $this->parent->getAnyOpenConnection( $i ) ) ) {
+				$lagTimes[$i] = $conn->getLag();
+			} elseif ( false !== ( $conn = $this->parent->openConnection( $i, $wiki ) ) ) {
+				$lagTimes[$i] = $conn->getLag();
+				# Close the connection to avoid sleeper connections piling up.
+				# Note that the caller will pick one of these DBs and reconnect,
+				# which is slightly inefficient, but this only matters for the lag
+				# time cache miss cache, which is far less common that cache hits.
+				$this->parent->closeConnection( $conn );
+			}
+		}
+
+		# Add a timestamp key so we know when it was cached
+		$value = array( 'lagTimes' => $lagTimes, 'timestamp' => microtime( true ) );
+		$this->mainCache->set( $key, $value, $staleTTL );
+		$this->srvCache->set( $key, $value, $staleTTL );
+		wfDebugLog( 'replication',  __FUNCTION__ . ": re-calculated lag times ($key)" );
+
+		return $value['lagTimes'];
+	}
+
+	public function clearCaches() {
+		$key = $this->getLagTimeCacheKey();
+		$this->srvCache->delete( $key );
+		$this->mainCache->delete( $key );
+	}
+
+	private function getLagTimeCacheKey() {
+		# Lag is per-server, not per-DB, so key on the master DB name
+		return wfGlobalCacheKey( 'lag-times', $this->parent->getServerName( 0 ) );
+	}
+}