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         static $instance;
  15
  16         /**
  17          * Disables all access to the load balancer, will cause all database access
  18          * to throw a DBAccessError
  19          */
  20         public static function disableBackend() {
  21                 global $wgLBFactoryConf;
  22                 self::$instance = new LBFactory_Fake( $wgLBFactoryConf );
  23         }
  24
  25         /**
  26          * Resets the singleton for use if it's been disabled. Does nothing otherwise
  27          */
  28         public static function enableBackend() {
  29                 if( self::$instance instanceof LBFactory_Fake )
  30                         self::$instance = null;
  31         }
  32
  33         /**
  34          * Get an LBFactory instance
  35          */
  36         static function &singleton() {
  37                 if ( is_null( self::$instance ) ) {
  38                         global $wgLBFactoryConf;
  39                         $class = $wgLBFactoryConf['class'];
  40                         self::$instance = new $class( $wgLBFactoryConf );
  41                 }
  42                 return self::$instance;
  43         }
  44
  45         /**
  46          * Shut down, close connections and destroy the cached instance.
  47          *
  48          */
  49         static function destroyInstance() {
  50                 if ( self::$instance ) {
  51                         self::$instance->shutdown();
  52                         self::$instance->forEachLBCallMethod( 'closeAll' );
  53                         self::$instance = null;
  54                 }
  55         }
  56
  57         /**
  58          * Set the instance to be the given object
  59          */
  60         static function setInstance( $instance ) {
  61                 self::destroyInstance();
  62                 self::$instance = $instance;
  63         }
  64
  65         /**
  66          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  67          */
  68         abstract function __construct( $conf );
  69
  70         /**
  71          * Create a new load balancer object. The resulting object will be untracked,
  72          * not chronology-protected, and the caller is responsible for cleaning it up.
  73          *
  74          * @param $wiki String: wiki ID, or false for the current wiki
  75          * @return LoadBalancer
  76          */
  77         abstract function newMainLB( $wiki = false );
  78
  79         /**
  80          * Get a cached (tracked) load balancer object.
  81          *
  82          * @param $wiki String: wiki ID, or false for the current wiki
  83          * @return LoadBalancer
  84          */
  85         abstract function getMainLB( $wiki = false );
  86
  87         /*
  88          * Create a new load balancer for external storage. The resulting object will be
  89          * untracked, not chronology-protected, and the caller is responsible for
  90          * cleaning it up.
  91          *
  92          * @param $cluster String: external storage cluster, or false for core
  93          * @param $wiki String: wiki ID, or false for the current wiki
  94          */
  95         abstract function newExternalLB( $cluster, $wiki = false );
  96
  97         /*
  98          * Get a cached (tracked) load balancer for external storage
  99          *
 100          * @param $cluster String: external storage cluster, or false for core
 101          * @param $wiki String: wiki ID, or false for the current wiki
 102          */
 103         abstract function &getExternalLB( $cluster, $wiki = false );
 104
 105         /**
 106          * Execute a function for each tracked load balancer
 107          * The callback is called with the load balancer as the first parameter,
 108          * and $params passed as the subsequent parameters.
 109          */
 110         abstract function forEachLB( $callback, $params = array() );
 111
 112         /**
 113          * Prepare all tracked load balancers for shutdown
 114          * STUB
 115          */
 116         function shutdown() {}
 117
 118         /**
 119          * Call a method of each tracked load balancer
 120          */
 121         function forEachLBCallMethod( $methodName, $args = array() ) {
 122                 $this->forEachLB( array( $this, 'callMethod' ), array( $methodName, $args ) );
 123         }
 124
 125         /**
 126          * Private helper for forEachLBCallMethod
 127          */
 128         function callMethod( $loadBalancer, $methodName, $args ) {
 129                 call_user_func_array( array( $loadBalancer, $methodName ), $args );
 130         }
 131
 132         /**
 133          * Commit changes on all master connections
 134          */
 135         function commitMasterChanges() {
 136                 $this->forEachLBCallMethod( 'commitMasterChanges' );
 137         }
 138 }
 139
 140 /**
 141  * A simple single-master LBFactory that gets its configuration from the b/c globals
 142  */
 143 class LBFactory_Simple extends LBFactory {
 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 }