includes/db/LBFactory.php

   1 <?php
   2 /**
   3  * Generator of database load balancing objects
   4  *
   5  * @file
   6  * @ingroup Database
   7  */
   8
   9 /**
  10  * An interface for generating database load balancers
  11  * @ingroup Database
  12  */
  13 abstract class LBFactory {
  14
  15         /**
  16          * @var LBFactory
  17          */
  18         static $instance;
  19
  20         /**
  21          * Disables all access to the load balancer, will cause all database access
  22          * to throw a DBAccessError
  23          */
  24         public static function disableBackend() {
  25                 global $wgLBFactoryConf;
  26                 self::$instance = new LBFactory_Fake( $wgLBFactoryConf );
  27         }
  28
  29         /**
  30          * Get an LBFactory instance
  31          */
  32         static function &singleton() {
  33                 if ( is_null( self::$instance ) ) {
  34                         global $wgLBFactoryConf;
  35                         $class = $wgLBFactoryConf['class'];
  36                         self::$instance = new $class( $wgLBFactoryConf );
  37                 }
  38                 return self::$instance;
  39         }
  40
  41         /**
  42          * Shut down, close connections and destroy the cached instance.
  43          *
  44          */
  45         static function destroyInstance() {
  46                 if ( self::$instance ) {
  47                         self::$instance->shutdown();
  48                         self::$instance->forEachLBCallMethod( 'closeAll' );
  49                         self::$instance = null;
  50                 }
  51         }
  52
  53         /**
  54          * Set the instance to be the given object
  55          */
  56         static function setInstance( $instance ) {
  57                 self::destroyInstance();
  58                 self::$instance = $instance;
  59         }
  60
  61         /**
  62          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  63          */
  64         abstract function __construct( $conf );
  65
  66         /**
  67          * Create a new load balancer object. The resulting object will be untracked,
  68          * not chronology-protected, and the caller is responsible for cleaning it up.
  69          *
  70          * @param $wiki String: wiki ID, or false for the current wiki
  71          * @return LoadBalancer
  72          */
  73         abstract function newMainLB( $wiki = false );
  74
  75         /**
  76          * Get a cached (tracked) load balancer object.
  77          *
  78          * @param $wiki String: wiki ID, or false for the current wiki
  79          * @return LoadBalancer
  80          */
  81         abstract function getMainLB( $wiki = false );
  82
  83         /*
  84          * Create a new load balancer for external storage. The resulting object will be
  85          * untracked, not chronology-protected, and the caller is responsible for
  86          * cleaning it up.
  87          *
  88          * @param $cluster String: external storage cluster, or false for core
  89          * @param $wiki String: wiki ID, or false for the current wiki
  90          */
  91         abstract function newExternalLB( $cluster, $wiki = false );
  92
  93         /*
  94          * Get a cached (tracked) load balancer for external storage
  95          *
  96          * @param $cluster String: external storage cluster, or false for core
  97          * @param $wiki String: wiki ID, or false for the current wiki
  98          */
  99         abstract function &getExternalLB( $cluster, $wiki = false );
 100
 101         /**
 102          * Execute a function for each tracked load balancer
 103          * The callback is called with the load balancer as the first parameter,
 104          * and $params passed as the subsequent parameters.
 105          */
 106         abstract function forEachLB( $callback, $params = array() );
 107
 108         /**
 109          * Prepare all tracked load balancers for shutdown
 110          * STUB
 111          */
 112         function shutdown() {}
 113
 114         /**
 115          * Call a method of each tracked load balancer
 116          */
 117         function forEachLBCallMethod( $methodName, $args = array() ) {
 118                 $this->forEachLB( array( $this, 'callMethod' ), array( $methodName, $args ) );
 119         }
 120
 121         /**
 122          * Private helper for forEachLBCallMethod
 123          */
 124         function callMethod( $loadBalancer, $methodName, $args ) {
 125                 call_user_func_array( array( $loadBalancer, $methodName ), $args );
 126         }
 127
 128         /**
 129          * Commit changes on all master connections
 130          */
 131         function commitMasterChanges() {
 132                 $this->forEachLBCallMethod( 'commitMasterChanges' );
 133         }
 134 }
 135
 136 /**
 137  * A simple single-master LBFactory that gets its configuration from the b/c globals
 138  */
 139 class LBFactory_Simple extends LBFactory {
 140
 141         /**
 142          * @var LoadBalancer
 143          */
 144         var $mainLB;
 145         var $extLBs = array();
 146
 147         # Chronology protector
 148         var $chronProt;
 149
 150         function __construct( $conf ) {
 151                 $this->chronProt = new ChronologyProtector;
 152         }
 153
 154         function newMainLB( $wiki = false ) {
 155                 global $wgDBservers, $wgMasterWaitTimeout;
 156                 if ( $wgDBservers ) {
 157                         $servers = $wgDBservers;
 158                 } else {
 159                         global $wgDBserver, $wgDBuser, $wgDBpassword, $wgDBname, $wgDBtype, $wgDebugDumpSql;
 160                         $servers = array(array(
 161                                 'host' => $wgDBserver,
 162                                 'user' => $wgDBuser,
 163                                 'password' => $wgDBpassword,
 164                                 'dbname' => $wgDBname,
 165                                 'type' => $wgDBtype,
 166                                 'load' => 1,
 167                                 'flags' => ($wgDebugDumpSql ? DBO_DEBUG : 0) | DBO_DEFAULT
 168                         ));
 169                 }
 170
 171                 return new LoadBalancer( array(
 172                         'servers' => $servers,
 173                         'masterWaitTimeout' => $wgMasterWaitTimeout
 174                 ));
 175         }
 176
 177         function getMainLB( $wiki = false ) {
 178                 if ( !isset( $this->mainLB ) ) {
 179                         $this->mainLB = $this->newMainLB( $wiki );
 180                         $this->mainLB->parentInfo( array( 'id' => 'main' ) );
 181                         $this->chronProt->initLB( $this->mainLB );
 182                 }
 183                 return $this->mainLB;
 184         }
 185
 186         function newExternalLB( $cluster, $wiki = false ) {
 187                 global $wgExternalServers;
 188                 if ( !isset( $wgExternalServers[$cluster] ) ) {
 189                         throw new MWException( __METHOD__.": Unknown cluster \"$cluster\"" );
 190                 }
 191                 return new LoadBalancer( array(
 192                         'servers' => $wgExternalServers[$cluster]
 193                 ));
 194         }
 195
 196         function &getExternalLB( $cluster, $wiki = false ) {
 197                 if ( !isset( $this->extLBs[$cluster] ) ) {
 198                         $this->extLBs[$cluster] = $this->newExternalLB( $cluster, $wiki );
 199                         $this->extLBs[$cluster]->parentInfo( array( 'id' => "ext-$cluster" ) );
 200                 }
 201                 return $this->extLBs[$cluster];
 202         }
 203
 204         /**
 205          * Execute a function for each tracked load balancer
 206          * The callback is called with the load balancer as the first parameter,
 207          * and $params passed as the subsequent parameters.
 208          */
 209         function forEachLB( $callback, $params = array() ) {
 210                 if ( isset( $this->mainLB ) ) {
 211                         call_user_func_array( $callback, array_merge( array( $this->mainLB ), $params ) );
 212                 }
 213                 foreach ( $this->extLBs as $lb ) {
 214                         call_user_func_array( $callback, array_merge( array( $lb ), $params ) );
 215                 }
 216         }
 217
 218         function shutdown() {
 219                 if ( $this->mainLB ) {
 220                         $this->chronProt->shutdownLB( $this->mainLB );
 221                 }
 222                 $this->chronProt->shutdown();
 223                 $this->commitMasterChanges();
 224         }
 225 }
 226
 227 /**
 228  * LBFactory class that throws an error on any attempt to use it.
 229  * This will typically be done via wfGetDB().
 230  * Call LBFactory::disableBackend() to start using this, and
 231  * LBFactory::enableBackend() to return to normal behavior
 232  */
 233 class LBFactory_Fake extends LBFactory {
 234         function __construct( $conf ) {}
 235
 236         function newMainLB( $wiki = false) {
 237                 throw new DBAccessError;
 238         }
 239         function getMainLB( $wiki = false ) {
 240                 throw new DBAccessError;
 241         }
 242         function newExternalLB( $cluster, $wiki = false ) {
 243                 throw new DBAccessError;
 244         }
 245         function &getExternalLB( $cluster, $wiki = false ) {
 246                 throw new DBAccessError;
 247         }
 248         function forEachLB( $callback, $params = array() ) {}
 249 }
 250
 251 /**
 252  * Exception class for attempted DB access
 253  */
 254 class DBAccessError extends MWException {
 255         function __construct() {
 256                 parent::__construct( "Mediawiki tried to access the database via wfGetDB(). This is not allowed." );
 257         }
 258 }
 259
 260 /**
 261  * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
 262  * Kind of like Hawking's [[Chronology Protection Agency]].
 263  */
 264 class ChronologyProtector {
 265         var $startupPos;
 266         var $shutdownPos = array();
 267
 268         /**
 269          * Initialise a LoadBalancer to give it appropriate chronology protection.
 270          *
 271          * @param $lb LoadBalancer
 272          */
 273         function initLB( $lb ) {
 274                 if ( $this->startupPos === null ) {
 275                         if ( !empty( $_SESSION[__CLASS__] ) ) {
 276                                 $this->startupPos = $_SESSION[__CLASS__];
 277                         }
 278                 }
 279                 if ( !$this->startupPos ) {
 280                         return;
 281                 }
 282                 $masterName = $lb->getServerName( 0 );
 283
 284                 if ( $lb->getServerCount() > 1 && !empty( $this->startupPos[$masterName] ) ) {
 285                         $info = $lb->parentInfo();
 286                         $pos = $this->startupPos[$masterName];
 287                         wfDebug( __METHOD__.": LB " . $info['id'] . " waiting for master pos $pos\n" );
 288                         $lb->waitFor( $this->startupPos[$masterName] );
 289                 }
 290         }
 291
 292         /**
 293          * Notify the ChronologyProtector that the LoadBalancer is about to shut
 294          * down. Saves replication positions.
 295          *
 296          * @param $lb LoadBalancer
 297          */
 298         function shutdownLB( $lb ) {
 299                 // Don't start a session, don't bother with non-replicated setups
 300                 if ( strval( session_id() ) == '' || $lb->getServerCount() <= 1 ) {
 301                         return;
 302                 }
 303                 $masterName = $lb->getServerName( 0 );
 304                 if ( isset( $this->shutdownPos[$masterName] ) ) {
 305                         // Already done
 306                         return;
 307                 }
 308                 // Only save the position if writes have been done on the connection
 309                 $db = $lb->getAnyOpenConnection( 0 );
 310                 $info = $lb->parentInfo();
 311                 if ( !$db || !$db->doneWrites() ) {
 312                         wfDebug( __METHOD__.": LB {$info['id']}, no writes done\n" );
 313                         return;
 314                 }
 315                 $pos = $db->getMasterPos();
 316                 wfDebug( __METHOD__.": LB {$info['id']} has master pos $pos\n" );
 317                 $this->shutdownPos[$masterName] = $pos;
 318         }
 319
 320         /**
 321          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
 322          * May commit chronology data to persistent storage.
 323          */
 324         function shutdown() {
 325                 if ( session_id() != '' && count( $this->shutdownPos ) ) {
 326                         wfDebug( __METHOD__.": saving master pos for " .
 327                                 count( $this->shutdownPos ) . " master(s)\n" );
 328                         $_SESSION[__CLASS__] = $this->shutdownPos;
 329                 }
 330         }
 331 }