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