includes/db/loadbalancer/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         /** @var LBFactory */
  30         private static $instance;
  31
  32         /** @var string|bool Reason all LBs are read-only or false if not */
  33         protected $readOnlyReason = false;
  34
  35         const SHUTDOWN_NO_CHRONPROT = 1; // don't save ChronologyProtector positions (for async code)
  36
  37         /**
  38          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  39          * @param array $conf
  40          */
  41         public function __construct( array $conf ) {
  42                 if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
  43                         $this->readOnlyReason = $conf['readOnlyReason'];
  44                 }
  45         }
  46
  47         /**
  48          * Disables all access to the load balancer, will cause all database access
  49          * to throw a DBAccessError
  50          */
  51         public static function disableBackend() {
  52                 global $wgLBFactoryConf;
  53                 self::$instance = new LBFactoryFake( $wgLBFactoryConf );
  54         }
  55
  56         /**
  57          * Get an LBFactory instance
  58          *
  59          * @return LBFactory
  60          */
  61         public static function singleton() {
  62                 global $wgLBFactoryConf;
  63
  64                 if ( is_null( self::$instance ) ) {
  65                         $class = self::getLBFactoryClass( $wgLBFactoryConf );
  66                         $config = $wgLBFactoryConf;
  67                         if ( !isset( $config['readOnlyReason'] ) ) {
  68                                 $config['readOnlyReason'] = wfConfiguredReadOnlyReason();
  69                         }
  70                         self::$instance = new $class( $config );
  71                 }
  72
  73                 return self::$instance;
  74         }
  75
  76         /**
  77          * Returns the LBFactory class to use and the load balancer configuration.
  78          *
  79          * @param array $config (e.g. $wgLBFactoryConf)
  80          * @return string Class name
  81          */
  82         public static function getLBFactoryClass( array $config ) {
  83                 // For configuration backward compatibility after removing
  84                 // underscores from class names in MediaWiki 1.23.
  85                 $bcClasses = array(
  86                         'LBFactory_Simple' => 'LBFactorySimple',
  87                         'LBFactory_Single' => 'LBFactorySingle',
  88                         'LBFactory_Multi' => 'LBFactoryMulti',
  89                         'LBFactory_Fake' => 'LBFactoryFake',
  90                 );
  91
  92                 $class = $config['class'];
  93
  94                 if ( isset( $bcClasses[$class] ) ) {
  95                         $class = $bcClasses[$class];
  96                         wfDeprecated(
  97                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
  98                                 '1.23'
  99                         );
 100                 }
 101
 102                 return $class;
 103         }
 104
 105         /**
 106          * Shut down, close connections and destroy the cached instance.
 107          */
 108         public static function destroyInstance() {
 109                 if ( self::$instance ) {
 110                         self::$instance->shutdown();
 111                         self::$instance->forEachLBCallMethod( 'closeAll' );
 112                         self::$instance = null;
 113                 }
 114         }
 115
 116         /**
 117          * Set the instance to be the given object
 118          *
 119          * @param LBFactory $instance
 120          */
 121         public static function setInstance( $instance ) {
 122                 self::destroyInstance();
 123                 self::$instance = $instance;
 124         }
 125
 126         /**
 127          * Create a new load balancer object. The resulting object will be untracked,
 128          * not chronology-protected, and the caller is responsible for cleaning it up.
 129          *
 130          * @param bool|string $wiki Wiki ID, or false for the current wiki
 131          * @return LoadBalancer
 132          */
 133         abstract public function newMainLB( $wiki = false );
 134
 135         /**
 136          * Get a cached (tracked) load balancer object.
 137          *
 138          * @param bool|string $wiki Wiki ID, or false for the current wiki
 139          * @return LoadBalancer
 140          */
 141         abstract public function getMainLB( $wiki = false );
 142
 143         /**
 144          * Create a new load balancer for external storage. The resulting object will be
 145          * untracked, not chronology-protected, and the caller is responsible for
 146          * cleaning it up.
 147          *
 148          * @param string $cluster External storage cluster, or false for core
 149          * @param bool|string $wiki Wiki ID, or false for the current wiki
 150          * @return LoadBalancer
 151          */
 152         abstract protected function newExternalLB( $cluster, $wiki = false );
 153
 154         /**
 155          * Get a cached (tracked) load balancer for external storage
 156          *
 157          * @param string $cluster External storage cluster, or false for core
 158          * @param bool|string $wiki Wiki ID, or false for the current wiki
 159          * @return LoadBalancer
 160          */
 161         abstract public function &getExternalLB( $cluster, $wiki = false );
 162
 163         /**
 164          * Execute a function for each tracked load balancer
 165          * The callback is called with the load balancer as the first parameter,
 166          * and $params passed as the subsequent parameters.
 167          *
 168          * @param callable $callback
 169          * @param array $params
 170          */
 171         abstract public function forEachLB( $callback, array $params = array() );
 172
 173         /**
 174          * Prepare all tracked load balancers for shutdown
 175          * @param integer $flags Supports SHUTDOWN_* flags
 176          * STUB
 177          */
 178         public function shutdown( $flags = 0 ) {
 179         }
 180
 181         /**
 182          * Call a method of each tracked load balancer
 183          *
 184          * @param string $methodName
 185          * @param array $args
 186          */
 187         private function forEachLBCallMethod( $methodName, array $args = array() ) {
 188                 $this->forEachLB( function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 189                         call_user_func_array( array( $loadBalancer, $methodName ), $args );
 190                 }, array( $methodName, $args ) );
 191         }
 192
 193         /**
 194          * Commit on all connections. Done for two reasons:
 195          * 1. To commit changes to the masters.
 196          * 2. To release the snapshot on all connections, master and slave.
 197          */
 198         public function commitAll() {
 199                 $this->forEachLBCallMethod( 'commitAll' );
 200         }
 201
 202         /**
 203          * Commit changes on all master connections
 204          */
 205         public function commitMasterChanges() {
 206                 $start = microtime( true );
 207                 $this->forEachLBCallMethod( 'commitMasterChanges' );
 208                 $timeMs = 1000 * ( microtime( true ) - $start );
 209                 RequestContext::getMain()->getStats()->timing( "db.commit-masters", $timeMs );
 210         }
 211
 212         /**
 213          * Rollback changes on all master connections
 214          * @since 1.23
 215          */
 216         public function rollbackMasterChanges() {
 217                 $this->forEachLBCallMethod( 'rollbackMasterChanges' );
 218         }
 219
 220         /**
 221          * Determine if any master connection has pending changes
 222          * @return bool
 223          * @since 1.23
 224          */
 225         public function hasMasterChanges() {
 226                 $ret = false;
 227                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 228                         $ret = $ret || $lb->hasMasterChanges();
 229                 } );
 230
 231                 return $ret;
 232         }
 233
 234         /**
 235          * Detemine if any lagged slave connection was used
 236          * @since 1.27
 237          * @return bool
 238          */
 239         public function laggedSlaveUsed() {
 240                 $ret = false;
 241                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 242                         $ret = $ret || $lb->laggedSlaveUsed();
 243                 } );
 244
 245                 return $ret;
 246         }
 247
 248         /**
 249          * Determine if any master connection has pending/written changes from this request
 250          * @return bool
 251          * @since 1.27
 252          */
 253         public function hasOrMadeRecentMasterChanges() {
 254                 $ret = false;
 255                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 256                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges();
 257                 } );
 258                 return $ret;
 259         }
 260
 261         /**
 262          * @return ChronologyProtector
 263          */
 264         protected function newChronologyProtector() {
 265                 $request = RequestContext::getMain()->getRequest();
 266                 $chronProt = new ChronologyProtector(
 267                         ObjectCache::getMainStashInstance(),
 268                         array(
 269                                 'ip' => $request->getIP(),
 270                                 'agent' => $request->getHeader( 'User-Agent' )
 271                         )
 272                 );
 273                 if ( PHP_SAPI === 'cli' ) {
 274                         $chronProt->setEnabled( false );
 275                 } elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
 276                         // Request opted out of using position wait logic. This is useful for requests
 277                         // done by the job queue or background ETL that do not have a meaningful session.
 278                         $chronProt->setWaitEnabled( false );
 279                 }
 280
 281                 return $chronProt;
 282         }
 283
 284         /**
 285          * @param ChronologyProtector $cp
 286          */
 287         protected function shutdownChronologyProtector( ChronologyProtector $cp ) {
 288                 // Get all the master positions needed
 289                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
 290                         $cp->shutdownLB( $lb );
 291                 } );
 292                 // Write them to the stash
 293                 $unsavedPositions = $cp->shutdown();
 294                 // If the positions failed to write to the stash, at least wait on local datacenter
 295                 // slaves to catch up before responding. Even if there are several DCs, this increases
 296                 // the chance that the user will see their own changes immediately afterwards. As long
 297                 // as the sticky DC cookie applies (same domain), this is not even an issue.
 298                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
 299                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 300                         if ( isset( $unsavedPositions[$masterName] ) ) {
 301                                 $lb->waitForAll( $unsavedPositions[$masterName] );
 302                         }
 303                 } );
 304         }
 305 }
 306
 307 /**
 308  * Exception class for attempted DB access
 309  */
 310 class DBAccessError extends MWException {
 311         public function __construct() {
 312                 parent::__construct( "Mediawiki tried to access the database via wfGetDB(). " .
 313                         "This is not allowed." );
 314         }
 315 }