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 ChronologyProtector */
  30         protected $chronProt;
  31
  32         /** @var LBFactory */
  33         private static $instance;
  34
  35         /** @var string|bool Reason all LBs are read-only or false if not */
  36         protected $readOnlyReason = false;
  37
  38         const SHUTDOWN_NO_CHRONPROT = 1; // don't save ChronologyProtector positions (for async code)
  39
  40         /**
  41          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  42          * @param array $conf
  43          */
  44         public function __construct( array $conf ) {
  45                 if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
  46                         $this->readOnlyReason = $conf['readOnlyReason'];
  47                 }
  48
  49                 $this->chronProt = $this->newChronologyProtector();
  50         }
  51
  52         /**
  53          * Disables all access to the load balancer, will cause all database access
  54          * to throw a DBAccessError
  55          */
  56         public static function disableBackend() {
  57                 global $wgLBFactoryConf;
  58                 self::$instance = new LBFactoryFake( $wgLBFactoryConf );
  59         }
  60
  61         /**
  62          * Get an LBFactory instance
  63          *
  64          * @return LBFactory
  65          */
  66         public static function singleton() {
  67                 global $wgLBFactoryConf;
  68
  69                 if ( is_null( self::$instance ) ) {
  70                         $class = self::getLBFactoryClass( $wgLBFactoryConf );
  71                         $config = $wgLBFactoryConf;
  72                         if ( !isset( $config['readOnlyReason'] ) ) {
  73                                 $config['readOnlyReason'] = wfConfiguredReadOnlyReason();
  74                         }
  75                         self::$instance = new $class( $config );
  76                 }
  77
  78                 return self::$instance;
  79         }
  80
  81         /**
  82          * Returns the LBFactory class to use and the load balancer configuration.
  83          *
  84          * @param array $config (e.g. $wgLBFactoryConf)
  85          * @return string Class name
  86          */
  87         public static function getLBFactoryClass( array $config ) {
  88                 // For configuration backward compatibility after removing
  89                 // underscores from class names in MediaWiki 1.23.
  90                 $bcClasses = array(
  91                         'LBFactory_Simple' => 'LBFactorySimple',
  92                         'LBFactory_Single' => 'LBFactorySingle',
  93                         'LBFactory_Multi' => 'LBFactoryMulti',
  94                         'LBFactory_Fake' => 'LBFactoryFake',
  95                 );
  96
  97                 $class = $config['class'];
  98
  99                 if ( isset( $bcClasses[$class] ) ) {
 100                         $class = $bcClasses[$class];
 101                         wfDeprecated(
 102                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
 103                                 '1.23'
 104                         );
 105                 }
 106
 107                 return $class;
 108         }
 109
 110         /**
 111          * Shut down, close connections and destroy the cached instance.
 112          */
 113         public static function destroyInstance() {
 114                 if ( self::$instance ) {
 115                         self::$instance->shutdown();
 116                         self::$instance->forEachLBCallMethod( 'closeAll' );
 117                         self::$instance = null;
 118                 }
 119         }
 120
 121         /**
 122          * Set the instance to be the given object
 123          *
 124          * @param LBFactory $instance
 125          */
 126         public static function setInstance( $instance ) {
 127                 self::destroyInstance();
 128                 self::$instance = $instance;
 129         }
 130
 131         /**
 132          * Create a new load balancer object. The resulting object will be untracked,
 133          * not chronology-protected, and the caller is responsible for cleaning it up.
 134          *
 135          * @param bool|string $wiki Wiki ID, or false for the current wiki
 136          * @return LoadBalancer
 137          */
 138         abstract public function newMainLB( $wiki = false );
 139
 140         /**
 141          * Get a cached (tracked) load balancer object.
 142          *
 143          * @param bool|string $wiki Wiki ID, or false for the current wiki
 144          * @return LoadBalancer
 145          */
 146         abstract public function getMainLB( $wiki = false );
 147
 148         /**
 149          * Create a new load balancer for external storage. The resulting object will be
 150          * untracked, not chronology-protected, and the caller is responsible for
 151          * cleaning it up.
 152          *
 153          * @param string $cluster External storage cluster, or false for core
 154          * @param bool|string $wiki Wiki ID, or false for the current wiki
 155          * @return LoadBalancer
 156          */
 157         abstract protected function newExternalLB( $cluster, $wiki = false );
 158
 159         /**
 160          * Get a cached (tracked) load balancer for external storage
 161          *
 162          * @param string $cluster External storage cluster, or false for core
 163          * @param bool|string $wiki Wiki ID, or false for the current wiki
 164          * @return LoadBalancer
 165          */
 166         abstract public function &getExternalLB( $cluster, $wiki = false );
 167
 168         /**
 169          * Execute a function for each tracked load balancer
 170          * The callback is called with the load balancer as the first parameter,
 171          * and $params passed as the subsequent parameters.
 172          *
 173          * @param callable $callback
 174          * @param array $params
 175          */
 176         abstract public function forEachLB( $callback, array $params = array() );
 177
 178         /**
 179          * Prepare all tracked load balancers for shutdown
 180          * @param integer $flags Supports SHUTDOWN_* flags
 181          * STUB
 182          */
 183         public function shutdown( $flags = 0 ) {
 184         }
 185
 186         /**
 187          * Call a method of each tracked load balancer
 188          *
 189          * @param string $methodName
 190          * @param array $args
 191          */
 192         private function forEachLBCallMethod( $methodName, array $args = array() ) {
 193                 $this->forEachLB( function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 194                         call_user_func_array( array( $loadBalancer, $methodName ), $args );
 195                 }, array( $methodName, $args ) );
 196         }
 197
 198         /**
 199          * Commit on all connections. Done for two reasons:
 200          * 1. To commit changes to the masters.
 201          * 2. To release the snapshot on all connections, master and slave.
 202          */
 203         public function commitAll() {
 204                 $this->forEachLBCallMethod( 'commitAll' );
 205         }
 206
 207         /**
 208          * Commit changes on all master connections
 209          */
 210         public function commitMasterChanges() {
 211                 $start = microtime( true );
 212                 $this->forEachLBCallMethod( 'commitMasterChanges' );
 213                 $timeMs = 1000 * ( microtime( true ) - $start );
 214                 RequestContext::getMain()->getStats()->timing( "db.commit-masters", $timeMs );
 215         }
 216
 217         /**
 218          * Rollback changes on all master connections
 219          * @since 1.23
 220          */
 221         public function rollbackMasterChanges() {
 222                 $this->forEachLBCallMethod( 'rollbackMasterChanges' );
 223         }
 224
 225         /**
 226          * Determine if any master connection has pending changes
 227          * @return bool
 228          * @since 1.23
 229          */
 230         public function hasMasterChanges() {
 231                 $ret = false;
 232                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 233                         $ret = $ret || $lb->hasMasterChanges();
 234                 } );
 235
 236                 return $ret;
 237         }
 238
 239         /**
 240          * Detemine if any lagged slave connection was used
 241          * @since 1.27
 242          * @return bool
 243          */
 244         public function laggedSlaveUsed() {
 245                 $ret = false;
 246                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 247                         $ret = $ret || $lb->laggedSlaveUsed();
 248                 } );
 249
 250                 return $ret;
 251         }
 252
 253         /**
 254          * Determine if any master connection has pending/written changes from this request
 255          * @return bool
 256          * @since 1.27
 257          */
 258         public function hasOrMadeRecentMasterChanges() {
 259                 $ret = false;
 260                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 261                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges();
 262                 } );
 263                 return $ret;
 264         }
 265
 266         /**
 267          * Disable the ChronologyProtector for all load balancers
 268          *
 269          * This can be called at the start of special API entry points
 270          *
 271          * @since 1.27
 272          */
 273         public function disableChronologyProtection() {
 274                 $this->chronProt->setEnabled( false );
 275         }
 276
 277         /**
 278          * @return ChronologyProtector
 279          */
 280         protected function newChronologyProtector() {
 281                 $request = RequestContext::getMain()->getRequest();
 282                 $chronProt = new ChronologyProtector(
 283                         ObjectCache::getMainStashInstance(),
 284                         array(
 285                                 'ip' => $request->getIP(),
 286                                 'agent' => $request->getHeader( 'User-Agent' )
 287                         )
 288                 );
 289                 if ( PHP_SAPI === 'cli' ) {
 290                         $chronProt->setEnabled( false );
 291                 } elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
 292                         // Request opted out of using position wait logic. This is useful for requests
 293                         // done by the job queue or background ETL that do not have a meaningful session.
 294                         $chronProt->setWaitEnabled( false );
 295                 }
 296
 297                 return $chronProt;
 298         }
 299
 300         /**
 301          * @param ChronologyProtector $cp
 302          */
 303         protected function shutdownChronologyProtector( ChronologyProtector $cp ) {
 304                 // Get all the master positions needed
 305                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
 306                         $cp->shutdownLB( $lb );
 307                 } );
 308                 // Write them to the stash
 309                 $unsavedPositions = $cp->shutdown();
 310                 // If the positions failed to write to the stash, at least wait on local datacenter
 311                 // slaves to catch up before responding. Even if there are several DCs, this increases
 312                 // the chance that the user will see their own changes immediately afterwards. As long
 313                 // as the sticky DC cookie applies (same domain), this is not even an issue.
 314                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
 315                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 316                         if ( isset( $unsavedPositions[$masterName] ) ) {
 317                                 $lb->waitForAll( $unsavedPositions[$masterName] );
 318                         }
 319                 } );
 320         }
 321 }
 322
 323 /**
 324  * Exception class for attempted DB access
 325  */
 326 class DBAccessError extends MWException {
 327         public function __construct() {
 328                 parent::__construct( "Mediawiki tried to access the database via wfGetDB(). " .
 329                         "This is not allowed." );
 330         }
 331 }