includes/db/LoadMonitor.php

   1 <?php
   2 /**
   3  * Database load monitoring.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23
  24 /**
  25  * An interface for database load monitoring
  26  *
  27  * @ingroup Database
  28  */
  29 interface LoadMonitor {
  30         /**
  31          * Construct a new LoadMonitor with a given LoadBalancer parent
  32          *
  33          * @param LoadBalancer $parent
  34          */
  35         function __construct( $parent );
  36
  37         /**
  38          * Perform pre-connection load ratio adjustment.
  39          * @param array $loads
  40          * @param string|bool $group the selected query group. Default: false
  41          * @param string|bool $wiki Default: false
  42          */
  43         function scaleLoads( &$loads, $group = false, $wiki = false );
  44
  45         /**
  46          * Perform post-connection backoff.
  47          *
  48          * If the connection is in overload, this should return a backoff factor
  49          * which will be used to control polling time. The number of threads
  50          * connected is a good measure.
  51          *
  52          * If there is no overload, zero can be returned.
  53          *
  54          * A threshold thread count is given, the concrete class may compare this
  55          * to the running thread count. The threshold may be false, which indicates
  56          * that the sysadmin has not configured this feature.
  57          *
  58          * @param $conn DatabaseBase
  59          * @param $threshold Float
  60          */
  61         function postConnectionBackoff( $conn, $threshold );
  62
  63         /**
  64          * Return an estimate of replication lag for each server
  65          *
  66          * @param $serverIndexes
  67          * @param $wiki
  68          *
  69          * @return array
  70          */
  71         function getLagTimes( $serverIndexes, $wiki );
  72 }
  73
  74 /**
  75  * @todo FIXME: Should be  LoadMonitorNull per naming conventions.
  76  * PHP CodeSniffer Squiz.Classes.ValidClassName.NotCamelCaps
  77  */
  78 class LoadMonitor_Null implements LoadMonitor {
  79         function __construct( $parent ) {
  80         }
  81
  82         function scaleLoads( &$loads, $group = false, $wiki = false ) {
  83         }
  84
  85         function postConnectionBackoff( $conn, $threshold ) {
  86         }
  87
  88         /**
  89          * @param $serverIndexes
  90          * @param $wiki
  91          * @return array
  92          */
  93         function getLagTimes( $serverIndexes, $wiki ) {
  94                 return array_fill_keys( $serverIndexes, 0 );
  95         }
  96 }
  97
  98 /**
  99  * Basic MySQL load monitor with no external dependencies
 100  * Uses memcached to cache the replication lag for a short time
 101  *
 102  * @ingroup Database
 103  * @todo FIXME: Should be  LoadMonitorMySQL per naming conventions.
 104  * PHP CodeSniffer Squiz.Classes.ValidClassName.NotCamelCaps
 105  */
 106 class LoadMonitor_MySQL implements LoadMonitor {
 107         /**
 108          * @var LoadBalancer
 109          */
 110         public $parent;
 111
 112         /**
 113          * @param LoadBalancer $parent
 114          */
 115         function __construct( $parent ) {
 116                 $this->parent = $parent;
 117         }
 118
 119         /**
 120          * @param $loads
 121          * @param $group bool
 122          * @param $wiki bool
 123          */
 124         function scaleLoads( &$loads, $group = false, $wiki = false ) {
 125         }
 126
 127         /**
 128          * @param $serverIndexes
 129          * @param $wiki
 130          * @return array
 131          */
 132         function getLagTimes( $serverIndexes, $wiki ) {
 133                 if ( count( $serverIndexes ) == 1 && reset( $serverIndexes ) == 0 ) {
 134                         // Single server only, just return zero without caching
 135                         return array( 0 => 0 );
 136                 }
 137
 138                 wfProfileIn( __METHOD__ );
 139                 $expiry = 5;
 140                 $requestRate = 10;
 141
 142                 global $wgMemc;
 143                 if ( empty( $wgMemc ) ) {
 144                         $wgMemc = wfGetMainCache();
 145                 }
 146
 147                 $masterName = $this->parent->getServerName( 0 );
 148                 $memcKey = wfMemcKey( 'lag_times', $masterName );
 149                 $times = $wgMemc->get( $memcKey );
 150                 if ( is_array( $times ) ) {
 151                         # Randomly recache with probability rising over $expiry
 152                         $elapsed = time() - $times['timestamp'];
 153                         $chance = max( 0, ( $expiry - $elapsed ) * $requestRate );
 154                         if ( mt_rand( 0, $chance ) != 0 ) {
 155                                 unset( $times['timestamp'] ); // hide from caller
 156                                 wfProfileOut( __METHOD__ );
 157
 158                                 return $times;
 159                         }
 160                         wfIncrStats( 'lag_cache_miss_expired' );
 161                 } else {
 162                         wfIncrStats( 'lag_cache_miss_absent' );
 163                 }
 164
 165                 # Cache key missing or expired
 166                 if ( $wgMemc->add( "$memcKey:lock", 1, 10 ) ) {
 167                         # Let this process alone update the cache value
 168                         $unlocker = new ScopedCallback( function () use ( $wgMemc, $memcKey ) {
 169                                 $wgMemc->delete( $memcKey );
 170                         } );
 171                 } elseif ( is_array( $times ) ) {
 172                         # Could not acquire lock but an old cache exists, so use it
 173                         unset( $times['timestamp'] ); // hide from caller
 174                         wfProfileOut( __METHOD__ );
 175
 176                         return $times;
 177                 }
 178
 179                 $times = array();
 180                 foreach ( $serverIndexes as $i ) {
 181                         if ( $i == 0 ) { # Master
 182                                 $times[$i] = 0;
 183                         } elseif ( false !== ( $conn = $this->parent->getAnyOpenConnection( $i ) ) ) {
 184                                 $times[$i] = $conn->getLag();
 185                         } elseif ( false !== ( $conn = $this->parent->openConnection( $i, $wiki ) ) ) {
 186                                 $times[$i] = $conn->getLag();
 187                         }
 188                 }
 189
 190                 # Add a timestamp key so we know when it was cached
 191                 $times['timestamp'] = time();
 192                 $wgMemc->set( $memcKey, $times, $expiry + 10 );
 193                 unset( $times['timestamp'] ); // hide from caller
 194
 195                 wfProfileOut( __METHOD__ );
 196
 197                 return $times;
 198         }
 199
 200         /**
 201          * @param $conn DatabaseBase
 202          * @param $threshold
 203          * @return int
 204          */
 205         function postConnectionBackoff( $conn, $threshold ) {
 206                 if ( !$threshold ) {
 207                         return 0;
 208                 }
 209                 $status = $conn->getMysqlStatus( "Thread%" );
 210                 if ( $status['Threads_running'] > $threshold ) {
 211                         $server = $conn->getProperty( 'mServer' );
 212                         wfLogDBError( "LB backoff from $server - Threads_running = {$status['Threads_running']}\n" );
 213
 214                         return $status['Threads_connected'];
 215                 } else {
 216                         return 0;
 217                 }
 218         }
 219 }