includes/LBFactory.php

   1 <?php
   2
   3 /**
   4  * An interface for generating database load balancers
   5  */
   6 abstract class LBFactory {
   7         static $instance;
   8
   9         /**
  10          * Get an LBFactory instance
  11          */
  12         static function &singleton() {
  13                 if ( is_null( self::$instance ) ) {
  14                         global $wgLBFactoryConf;
  15                         $class = $wgLBFactoryConf['class'];
  16                         self::$instance = new $class( $wgLBFactoryConf );
  17                 }
  18                 return self::$instance;
  19         }
  20
  21         /**
  22          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  23          */
  24         abstract function __construct( $conf );
  25
  26         /**
  27          * Get a load balancer object.
  28          *
  29          * @param string $wiki Wiki ID, or false for the current wiki
  30          * @return LoadBalancer
  31          */
  32         abstract function getMainLB( $wiki = false );
  33
  34         /*
  35          * Get a load balancer for external storage
  36          *
  37          * @param string $cluster External storage cluster, or false for core
  38          * @param string $wiki Wiki ID, or false for the current wiki
  39          */
  40         abstract function &getExternalLB( $cluster, $wiki = false );
  41
  42         /**
  43          * Execute a function for each tracked load balancer
  44          * The callback is called with the load balancer as the first parameter,
  45          * and $params passed as the subsequent parameters.
  46          */
  47         abstract function forEachLB( $callback, $params = array() );
  48
  49         /**
  50          * Prepare all load balancers for shutdown
  51          * STUB
  52          */
  53         function shutdown() {}
  54
  55         /**
  56          * Call a method of each load balancer
  57          */
  58         function forEachLBCallMethod( $methodName, $args = array() ) {
  59                 $this->forEachLB( array( $this, 'callMethod' ), array( $methodName, $args ) );
  60         }
  61
  62         /**
  63          * Private helper for forEachLBCallMethod
  64          */
  65         function callMethod( $loadBalancer, $methodName, $args ) {
  66                 call_user_func_array( array( $loadBalancer, $methodName ), $args );
  67         }
  68
  69         /**
  70          * Commit changes on all master connections
  71          */
  72         function commitMasterChanges() {
  73                 $this->forEachLBCallMethod( 'commitMasterChanges' );
  74         }
  75 }
  76
  77 /**
  78  * A simple single-master LBFactory that gets its configuration from the b/c globals
  79  */
  80 class LBFactory_Simple extends LBFactory {
  81         var $mainLB;
  82         var $extLBs = array();
  83
  84         # Chronology protector
  85         var $chronProt;
  86
  87         function __construct( $conf ) {
  88                 $this->chronProt = new ChronologyProtector;
  89         }
  90
  91         function getMainLB( $wiki = false ) {
  92                 if ( !isset( $this->mainLB ) ) {
  93                         global $wgDBservers, $wgMasterWaitTimeout;
  94                         if ( !$wgDBservers ) {
  95                                 global $wgDBserver, $wgDBuser, $wgDBpassword, $wgDBname, $wgDBtype, $wgDebugDumpSql;
  96                                 $wgDBservers = array(array(
  97                                         'host' => $wgDBserver,
  98                                         'user' => $wgDBuser,
  99                                         'password' => $wgDBpassword,
 100                                         'dbname' => $wgDBname,
 101                                         'type' => $wgDBtype,
 102                                         'load' => 1,
 103                                         'flags' => ($wgDebugDumpSql ? DBO_DEBUG : 0) | DBO_DEFAULT
 104                                 ));
 105                         }
 106
 107                         $this->mainLB = new LoadBalancer( $wgDBservers, false, $wgMasterWaitTimeout, true );
 108                         $this->mainLB->parentInfo( array( 'id' => 'main' ) );
 109                         $this->chronProt->initLB( $this->mainLB );
 110                 }
 111                 return $this->mainLB;
 112         }
 113
 114         function &getExternalLB( $cluster, $wiki = false ) {
 115                 global $wgExternalServers;
 116                 if ( !isset( $this->extLBs[$cluster] ) ) {
 117                         if ( !isset( $wgExternalServers[$cluster] ) ) {
 118                                 throw new MWException( __METHOD__.": Unknown cluster \"$cluster\"" );
 119                         }
 120                         $this->extLBs[$cluster] = new LoadBalancer( $wgExternalServers[$cluster] );
 121                         $this->extLBs[$cluster]->parentInfo( array( 'id' => "ext-$cluster" ) );
 122                 }
 123                 return $this->extLBs[$cluster];
 124         }
 125
 126         /**
 127          * Execute a function for each tracked load balancer
 128          * The callback is called with the load balancer as the first parameter,
 129          * and $params passed as the subsequent parameters.
 130          */
 131         function forEachLB( $callback, $params = array() ) {
 132                 if ( isset( $this->mainLB ) ) {
 133                         call_user_func_array( $callback, array_merge( array( $this->mainLB ), $params ) );
 134                 }
 135                 foreach ( $this->extLBs as $lb ) {
 136                         call_user_func_array( $callback, array_merge( array( $lb ), $params ) );
 137                 }
 138         }
 139
 140         function shutdown() {
 141                 if ( $this->mainLB ) {
 142                         $this->chronProt->shutdownLB( $this->mainLB );
 143                 }
 144                 $this->chronProt->shutdown();
 145                 $this->commitMasterChanges();
 146         }
 147 }
 148
 149 /**
 150  * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
 151  * Kind of like Hawking's [[Chronology Protection Agency]].
 152  */
 153 class ChronologyProtector {
 154         var $startupPos;
 155         var $shutdownPos = array();
 156
 157         /**
 158          * Initialise a LoadBalancer to give it appropriate chronology protection.
 159          *
 160          * @param LoadBalancer $lb
 161          */
 162         function initLB( $lb ) {
 163                 if ( $this->startupPos === null ) {
 164                         if ( !empty( $_SESSION[__CLASS__] ) ) {
 165                                 $this->startupPos = $_SESSION[__CLASS__];
 166                         }
 167                 }
 168                 if ( !$this->startupPos ) {
 169                         return;
 170                 }
 171                 $masterName = $lb->getServerName( 0 );
 172
 173                 if ( $lb->getServerCount() > 1 && !empty( $this->startupPos[$masterName] ) ) {
 174                         $info = $lb->parentInfo();
 175                         $pos = $this->startupPos[$masterName];
 176                         wfDebug( __METHOD__.": LB " . $info['id'] . " waiting for master pos $pos\n" );
 177                         $lb->waitFor( $this->startupPos[$masterName] );
 178                 }
 179         }
 180
 181         /**
 182          * Notify the ChronologyProtector that the LoadBalancer is about to shut
 183          * down. Saves replication positions.
 184          *
 185          * @param LoadBalancer $lb
 186          */
 187         function shutdownLB( $lb ) {
 188                 if ( session_id() != '' && $lb->getServerCount() > 1 ) {
 189                         $masterName = $lb->getServerName( 0 );
 190                         if ( !isset( $this->shutdownPos[$masterName] ) ) {
 191                                 $pos = $lb->getMasterPos();
 192                                 $info = $lb->parentInfo();
 193                                 wfDebug( __METHOD__.": LB " . $info['id'] . " has master pos $pos\n" );
 194                                 $this->shutdownPos[$masterName] = $pos;
 195                         }
 196                 }
 197         }
 198
 199         /**
 200          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
 201          * May commit chronology data to persistent storage.
 202          */
 203         function shutdown() {
 204                 if ( session_id() != '' && count( $this->shutdownPos ) ) {
 205                         wfDebug( __METHOD__.": saving master pos for " .
 206                                 count( $this->shutdownPos ) . " master(s)\n" );
 207                         $_SESSION[__CLASS__] = $this->shutdownPos;
 208                 }
 209         }
 210 }
 211