includes/db/LBFactory.php

   1 <?php
   2 /**
   3  * Generator of database load balancing objects.
   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 generating database load balancers
  26  * @ingroup Database
  27  */
  28 abstract class LBFactory {
  29
  30         /**
  31          * @var LBFactory
  32          */
  33         static $instance;
  34
  35         /**
  36          * Disables all access to the load balancer, will cause all database access
  37          * to throw a DBAccessError
  38          */
  39         public static function disableBackend() {
  40                 global $wgLBFactoryConf;
  41                 self::$instance = new LBFactory_Fake( $wgLBFactoryConf );
  42         }
  43
  44         /**
  45          * Get an LBFactory instance
  46          *
  47          * @return LBFactory
  48          */
  49         static function &singleton() {
  50                 if ( is_null( self::$instance ) ) {
  51                         global $wgLBFactoryConf;
  52                         $class = $wgLBFactoryConf['class'];
  53                         self::$instance = new $class( $wgLBFactoryConf );
  54                 }
  55                 return self::$instance;
  56         }
  57
  58         /**
  59          * Shut down, close connections and destroy the cached instance.
  60          */
  61         static function destroyInstance() {
  62                 if ( self::$instance ) {
  63                         self::$instance->shutdown();
  64                         self::$instance->forEachLBCallMethod( 'closeAll' );
  65                         self::$instance = null;
  66                 }
  67         }
  68
  69         /**
  70          * Set the instance to be the given object
  71          *
  72          * @param $instance LBFactory
  73          */
  74         static function setInstance( $instance ) {
  75                 self::destroyInstance();
  76                 self::$instance = $instance;
  77         }
  78
  79         /**
  80          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  81          * @param $conf
  82          */
  83         abstract function __construct( $conf );
  84
  85         /**
  86          * Create a new load balancer object. The resulting object will be untracked,
  87          * not chronology-protected, and the caller is responsible for cleaning it up.
  88          *
  89          * @param $wiki String: wiki ID, or false for the current wiki
  90          * @return LoadBalancer
  91          */
  92         abstract function newMainLB( $wiki = false );
  93
  94         /**
  95          * Get a cached (tracked) load balancer object.
  96          *
  97          * @param $wiki String: wiki ID, or false for the current wiki
  98          * @return LoadBalancer
  99          */
 100         abstract function getMainLB( $wiki = false );
 101
 102         /**
 103          * Create a new load balancer for external storage. The resulting object will be
 104          * untracked, not chronology-protected, and the caller is responsible for
 105          * cleaning it up.
 106          *
 107          * @param $cluster String: external storage cluster, or false for core
 108          * @param $wiki String: wiki ID, or false for the current wiki
 109          *
 110          * @return LoadBalancer
 111          */
 112         abstract function newExternalLB( $cluster, $wiki = false );
 113
 114         /**
 115          * Get a cached (tracked) load balancer for external storage
 116          *
 117          * @param $cluster String: external storage cluster, or false for core
 118          * @param $wiki String: wiki ID, or false for the current wiki
 119          *
 120          * @return LoadBalancer
 121          */
 122         abstract function &getExternalLB( $cluster, $wiki = false );
 123
 124         /**
 125          * Execute a function for each tracked load balancer
 126          * The callback is called with the load balancer as the first parameter,
 127          * and $params passed as the subsequent parameters.
 128          * @param $callback string|array
 129          * @param array $params
 130          */
 131         abstract function forEachLB( $callback, $params = array() );
 132
 133         /**
 134          * Prepare all tracked load balancers for shutdown
 135          * STUB
 136          */
 137         function shutdown() {}
 138
 139         /**
 140          * Call a method of each tracked load balancer
 141          * @param $methodName string
 142          * @param $args array
 143          */
 144         function forEachLBCallMethod( $methodName, $args = array() ) {
 145                 $this->forEachLB( array( $this, 'callMethod' ), array( $methodName, $args ) );
 146         }
 147
 148         /**
 149          * Private helper for forEachLBCallMethod
 150          * @param $loadBalancer
 151          * @param $methodName string
 152          * @param $args
 153          */
 154         function callMethod( $loadBalancer, $methodName, $args ) {
 155                 call_user_func_array( array( $loadBalancer, $methodName ), $args );
 156         }
 157
 158         /**
 159          * Commit changes on all master connections
 160          */
 161         function commitMasterChanges() {
 162                 $this->forEachLBCallMethod( 'commitMasterChanges' );
 163         }
 164 }
 165
 166 /**
 167  * A simple single-master LBFactory that gets its configuration from the b/c globals
 168  */
 169 class LBFactory_Simple extends LBFactory {
 170
 171         /**
 172          * @var LoadBalancer
 173          */
 174         var $mainLB;
 175         var $extLBs = array();
 176
 177         # Chronology protector
 178         var $chronProt;
 179
 180         function __construct( $conf ) {
 181                 $this->chronProt = new ChronologyProtector;
 182         }
 183
 184         /**
 185          * @param $wiki
 186          * @return LoadBalancer
 187          */
 188         function newMainLB( $wiki = false ) {
 189                 global $wgDBservers, $wgMasterWaitTimeout;
 190                 if ( $wgDBservers ) {
 191                         $servers = $wgDBservers;
 192                 } else {
 193                         global $wgDBserver, $wgDBuser, $wgDBpassword, $wgDBname, $wgDBtype, $wgDebugDumpSql;
 194                         $servers = array(array(
 195                                 'host' => $wgDBserver,
 196                                 'user' => $wgDBuser,
 197                                 'password' => $wgDBpassword,
 198                                 'dbname' => $wgDBname,
 199                                 'type' => $wgDBtype,
 200                                 'load' => 1,
 201                                 'flags' => ($wgDebugDumpSql ? DBO_DEBUG : 0) | DBO_DEFAULT
 202                         ));
 203                 }
 204
 205                 return new LoadBalancer( array(
 206                         'servers' => $servers,
 207                         'masterWaitTimeout' => $wgMasterWaitTimeout
 208                 ));
 209         }
 210
 211         /**
 212          * @param $wiki
 213          * @return LoadBalancer
 214          */
 215         function getMainLB( $wiki = false ) {
 216                 if ( !isset( $this->mainLB ) ) {
 217                         $this->mainLB = $this->newMainLB( $wiki );
 218                         $this->mainLB->parentInfo( array( 'id' => 'main' ) );
 219                         $this->chronProt->initLB( $this->mainLB );
 220                 }
 221                 return $this->mainLB;
 222         }
 223
 224         /**
 225          * @throws MWException
 226          * @param $cluster
 227          * @param $wiki
 228          * @return LoadBalancer
 229          */
 230         function newExternalLB( $cluster, $wiki = false ) {
 231                 global $wgExternalServers;
 232                 if ( !isset( $wgExternalServers[$cluster] ) ) {
 233                         throw new MWException( __METHOD__.": Unknown cluster \"$cluster\"" );
 234                 }
 235                 return new LoadBalancer( array(
 236                         'servers' => $wgExternalServers[$cluster]
 237                 ));
 238         }
 239
 240         /**
 241          * @param $cluster
 242          * @param $wiki
 243          * @return array
 244          */
 245         function &getExternalLB( $cluster, $wiki = false ) {
 246                 if ( !isset( $this->extLBs[$cluster] ) ) {
 247                         $this->extLBs[$cluster] = $this->newExternalLB( $cluster, $wiki );
 248                         $this->extLBs[$cluster]->parentInfo( array( 'id' => "ext-$cluster" ) );
 249                 }
 250                 return $this->extLBs[$cluster];
 251         }
 252
 253         /**
 254          * Execute a function for each tracked load balancer
 255          * The callback is called with the load balancer as the first parameter,
 256          * and $params passed as the subsequent parameters.
 257          * @param $callback
 258          * @param $params array
 259          */
 260         function forEachLB( $callback, $params = array() ) {
 261                 if ( isset( $this->mainLB ) ) {
 262                         call_user_func_array( $callback, array_merge( array( $this->mainLB ), $params ) );
 263                 }
 264                 foreach ( $this->extLBs as $lb ) {
 265                         call_user_func_array( $callback, array_merge( array( $lb ), $params ) );
 266                 }
 267         }
 268
 269         function shutdown() {
 270                 if ( $this->mainLB ) {
 271                         $this->chronProt->shutdownLB( $this->mainLB );
 272                 }
 273                 $this->chronProt->shutdown();
 274                 $this->commitMasterChanges();
 275         }
 276 }
 277
 278 /**
 279  * LBFactory class that throws an error on any attempt to use it.
 280  * This will typically be done via wfGetDB().
 281  * Call LBFactory::disableBackend() to start using this, and
 282  * LBFactory::enableBackend() to return to normal behavior
 283  */
 284 class LBFactory_Fake extends LBFactory {
 285         function __construct( $conf ) {}
 286
 287         function newMainLB( $wiki = false) {
 288                 throw new DBAccessError;
 289         }
 290         function getMainLB( $wiki = false ) {
 291                 throw new DBAccessError;
 292         }
 293         function newExternalLB( $cluster, $wiki = false ) {
 294                 throw new DBAccessError;
 295         }
 296         function &getExternalLB( $cluster, $wiki = false ) {
 297                 throw new DBAccessError;
 298         }
 299         function forEachLB( $callback, $params = array() ) {}
 300 }
 301
 302 /**
 303  * Exception class for attempted DB access
 304  */
 305 class DBAccessError extends MWException {
 306         function __construct() {
 307                 parent::__construct( "Mediawiki tried to access the database via wfGetDB(). This is not allowed." );
 308         }
 309 }
 310
 311 /**
 312  * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
 313  * Kind of like Hawking's [[Chronology Protection Agency]].
 314  */
 315 class ChronologyProtector {
 316         var $startupPos;
 317         var $shutdownPos = array();
 318
 319         /**
 320          * Initialise a LoadBalancer to give it appropriate chronology protection.
 321          *
 322          * @param $lb LoadBalancer
 323          */
 324         function initLB( $lb ) {
 325                 if ( $this->startupPos === null ) {
 326                         if ( !empty( $_SESSION[__CLASS__] ) ) {
 327                                 $this->startupPos = $_SESSION[__CLASS__];
 328                         }
 329                 }
 330                 if ( !$this->startupPos ) {
 331                         return;
 332                 }
 333                 $masterName = $lb->getServerName( 0 );
 334
 335                 if ( $lb->getServerCount() > 1 && !empty( $this->startupPos[$masterName] ) ) {
 336                         $info = $lb->parentInfo();
 337                         $pos = $this->startupPos[$masterName];
 338                         wfDebug( __METHOD__.": LB " . $info['id'] . " waiting for master pos $pos\n" );
 339                         $lb->waitFor( $this->startupPos[$masterName] );
 340                 }
 341         }
 342
 343         /**
 344          * Notify the ChronologyProtector that the LoadBalancer is about to shut
 345          * down. Saves replication positions.
 346          *
 347          * @param $lb LoadBalancer
 348          */
 349         function shutdownLB( $lb ) {
 350                 // Don't start a session, don't bother with non-replicated setups
 351                 if ( strval( session_id() ) == '' || $lb->getServerCount() <= 1 ) {
 352                         return;
 353                 }
 354                 $masterName = $lb->getServerName( 0 );
 355                 if ( isset( $this->shutdownPos[$masterName] ) ) {
 356                         // Already done
 357                         return;
 358                 }
 359                 // Only save the position if writes have been done on the connection
 360                 $db = $lb->getAnyOpenConnection( 0 );
 361                 $info = $lb->parentInfo();
 362                 if ( !$db || !$db->doneWrites() ) {
 363                         wfDebug( __METHOD__.": LB {$info['id']}, no writes done\n" );
 364                         return;
 365                 }
 366                 $pos = $db->getMasterPos();
 367                 wfDebug( __METHOD__.": LB {$info['id']} has master pos $pos\n" );
 368                 $this->shutdownPos[$masterName] = $pos;
 369         }
 370
 371         /**
 372          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
 373          * May commit chronology data to persistent storage.
 374          */
 375         function shutdown() {
 376                 if ( session_id() != '' && count( $this->shutdownPos ) ) {
 377                         wfDebug( __METHOD__.": saving master pos for " .
 378                                 count( $this->shutdownPos ) . " master(s)\n" );
 379                         $_SESSION[__CLASS__] = $this->shutdownPos;
 380                 }
 381         }
 382 }