includes/db/loadbalancer/LoadMonitorMySQL.php

   1 <?php
   2 /**
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  16  * http://www.gnu.org/copyleft/gpl.html
  17  *
  18  * @file
  19  * @ingroup Database
  20  */
  21
  22 use Psr\Log\LoggerInterface;
  23
  24 /**
  25  * Basic MySQL load monitor with no external dependencies
  26  * Uses memcached to cache the replication lag for a short time
  27  *
  28  * @ingroup Database
  29  */
  30 class LoadMonitorMySQL implements LoadMonitor {
  31         /** @var LoadBalancer */
  32         public $parent;
  33         /** @var BagOStuff */
  34         protected $srvCache;
  35         /** @var BagOStuff */
  36         protected $mainCache;
  37         /** @var LoggerInterface */
  38         protected $replLogger;
  39
  40         public function __construct( LoadBalancer $parent ) {
  41                 $this->parent = $parent;
  42                 $this->srvCache = ObjectCache::getLocalServerInstance( 'hash' );
  43                 $this->mainCache = ObjectCache::getLocalClusterInstance();
  44                 $this->replLogger = new \Psr\Log\NullLogger();
  45         }
  46
  47         public function setLogger( LoggerInterface $logger ) {
  48                 $this->replLogger = $logger;
  49         }
  50
  51         public function scaleLoads( &$loads, $group = false, $wiki = false ) {
  52         }
  53
  54         public function getLagTimes( $serverIndexes, $wiki ) {
  55                 if ( count( $serverIndexes ) == 1 && reset( $serverIndexes ) == 0 ) {
  56                         # Single server only, just return zero without caching
  57                         return [ 0 => 0 ];
  58                 }
  59
  60                 $key = $this->getLagTimeCacheKey();
  61                 # Randomize TTLs to reduce stampedes (4.0 - 5.0 sec)
  62                 $ttl = mt_rand( 4e6, 5e6 ) / 1e6;
  63                 # Keep keys around longer as fallbacks
  64                 $staleTTL = 60;
  65
  66                 # (a) Check the local APC cache
  67                 $value = $this->srvCache->get( $key );
  68                 if ( $value && $value['timestamp'] > ( microtime( true ) - $ttl ) ) {
  69                         $this->replLogger->debug( __METHOD__ . ": got lag times ($key) from local cache" );
  70                         return $value['lagTimes']; // cache hit
  71                 }
  72                 $staleValue = $value ?: false;
  73
  74                 # (b) Check the shared cache and backfill APC
  75                 $value = $this->mainCache->get( $key );
  76                 if ( $value && $value['timestamp'] > ( microtime( true ) - $ttl ) ) {
  77                         $this->srvCache->set( $key, $value, $staleTTL );
  78                         $this->replLogger->debug( __METHOD__ . ": got lag times ($key) from main cache" );
  79
  80                         return $value['lagTimes']; // cache hit
  81                 }
  82                 $staleValue = $value ?: $staleValue;
  83
  84                 # (c) Cache key missing or expired; regenerate and backfill
  85                 if ( $this->mainCache->lock( $key, 0, 10 ) ) {
  86                         # Let this process alone update the cache value
  87                         $cache = $this->mainCache;
  88                         /** @noinspection PhpUnusedLocalVariableInspection */
  89                         $unlocker = new ScopedCallback( function () use ( $cache, $key ) {
  90                                 $cache->unlock( $key );
  91                         } );
  92                 } elseif ( $staleValue ) {
  93                         # Could not acquire lock but an old cache exists, so use it
  94                         return $staleValue['lagTimes'];
  95                 }
  96
  97                 $lagTimes = [];
  98                 foreach ( $serverIndexes as $i ) {
  99                         if ( $i == $this->parent->getWriterIndex() ) {
 100                                 $lagTimes[$i] = 0; // master always has no lag
 101                                 continue;
 102                         }
 103
 104                         $conn = $this->parent->getAnyOpenConnection( $i );
 105                         if ( $conn ) {
 106                                 $close = false; // already open
 107                         } else {
 108                                 $conn = $this->parent->openConnection( $i, $wiki );
 109                                 $close = true; // new connection
 110                         }
 111
 112                         if ( !$conn ) {
 113                                 $lagTimes[$i] = false;
 114                                 $host = $this->parent->getServerName( $i );
 115                                 $this->replLogger->error( __METHOD__ . ": host $host (#$i) is unreachable" );
 116                                 continue;
 117                         }
 118
 119                         $lagTimes[$i] = $conn->getLag();
 120                         if ( $lagTimes[$i] === false ) {
 121                                 $host = $this->parent->getServerName( $i );
 122                                 $this->replLogger->error( __METHOD__ . ": host $host (#$i) is not replicating?" );
 123                         }
 124
 125                         if ( $close ) {
 126                                 # Close the connection to avoid sleeper connections piling up.
 127                                 # Note that the caller will pick one of these DBs and reconnect,
 128                                 # which is slightly inefficient, but this only matters for the lag
 129                                 # time cache miss cache, which is far less common that cache hits.
 130                                 $this->parent->closeConnection( $conn );
 131                         }
 132                 }
 133
 134                 # Add a timestamp key so we know when it was cached
 135                 $value = [ 'lagTimes' => $lagTimes, 'timestamp' => microtime( true ) ];
 136                 $this->mainCache->set( $key, $value, $staleTTL );
 137                 $this->srvCache->set( $key, $value, $staleTTL );
 138                 $this->replLogger->info( __METHOD__ . ": re-calculated lag times ($key)" );
 139
 140                 return $value['lagTimes'];
 141         }
 142
 143         public function clearCaches() {
 144                 $key = $this->getLagTimeCacheKey();
 145                 $this->srvCache->delete( $key );
 146                 $this->mainCache->delete( $key );
 147         }
 148
 149         private function getLagTimeCacheKey() {
 150                 $writerIndex = $this->parent->getWriterIndex();
 151                 // Lag is per-server, not per-DB, so key on the master DB name
 152                 return $this->srvCache->makeGlobalKey(
 153                         'lag-times', $this->parent->getServerName( $writerIndex )
 154                 );
 155         }
 156 }