LoadMonitorMySQL.php

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<?php
namespace Wikimedia\Rdbms;
 
use BagOStuff;
use WANObjectCache;
 
class LoadMonitorMySQL extends LoadMonitor {
    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;
    }
}