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diff --git a/www/wiki/includes/libs/rdbms/loadmonitor/LoadMonitorMySQL.php b/www/wiki/includes/libs/rdbms/loadmonitor/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
+ */
+
+namespace Wikimedia\Rdbms;
+
+use BagOStuff;
+use WANObjectCache;
+
+/**
+ * Basic MySQL load monitor with no external dependencies
+ * Uses memcached to cache the replication lag for a short time
+ *
+ * @ingroup Database
+ */
+class LoadMonitorMySQL extends LoadMonitor {
+	/** @var float What buffer pool use ratio counts as "warm" (e.g. 0.5 for 50% usage) */
+	private $warmCacheRatio;
+
+	public function __construct(
+		ILoadBalancer $lb, BagOStuff $srvCache, WANObjectCache $wCache, array $options = []
+	) {
+		parent::__construct( $lb, $srvCache, $wCache, $options );
+
+		$this->warmCacheRatio = isset( $options['warmCacheRatio'] )
+			? $options['warmCacheRatio']
+			: 0.0;
+	}
+
+	protected function getWeightScale( $index, IDatabase $conn = null ) {
+		if ( !$conn ) {
+			return parent::getWeightScale( $index, $conn );
+		}
+
+		$weight = 1.0;
+		if ( $this->warmCacheRatio > 0 ) {
+			$res = $conn->query( 'SHOW STATUS', __METHOD__ );
+			$s = $res ? $conn->fetchObject( $res ) : false;
+			if ( $s === false ) {
+				$host = $this->parent->getServerName( $index );
+				$this->replLogger->error( __METHOD__ . ": could not get status for $host" );
+			} else {
+				// https://dev.mysql.com/doc/refman/5.7/en/server-status-variables.html
+				if ( $s->Innodb_buffer_pool_pages_total > 0 ) {
+					$ratio = $s->Innodb_buffer_pool_pages_data / $s->Innodb_buffer_pool_pages_total;
+				} else {
+					$ratio = 1.0;
+				}
+				// Stop caring once $ratio >= $this->warmCacheRatio
+				$weight *= min( $ratio / $this->warmCacheRatio, 1.0 );
+			}
+		}
+
+		return $weight;
+	}
+}