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         /** @var TransactionProfiler */
  32         protected $trxProfiler;
  33
  34         /** @var LBFactory */
  35         private static $instance;
  36
  37         /** @var string|bool Reason all LBs are read-only or false if not */
  38         protected $readOnlyReason = false;
  39
  40         const SHUTDOWN_NO_CHRONPROT = 1; // don't save ChronologyProtector positions (for async code)
  41
  42         /**
  43          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  44          * @param array $conf
  45          */
  46         public function __construct( array $conf ) {
  47                 if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
  48                         $this->readOnlyReason = $conf['readOnlyReason'];
  49                 }
  50
  51                 $this->chronProt = $this->newChronologyProtector();
  52                 $this->trxProfiler = Profiler::instance()->getTransactionProfiler();
  53         }
  54
  55         /**
  56          * Disables all access to the load balancer, will cause all database access
  57          * to throw a DBAccessError
  58          */
  59         public static function disableBackend() {
  60                 global $wgLBFactoryConf;
  61                 self::$instance = new LBFactoryFake( $wgLBFactoryConf );
  62         }
  63
  64         /**
  65          * Get an LBFactory instance
  66          *
  67          * @return LBFactory
  68          */
  69         public static function singleton() {
  70                 global $wgLBFactoryConf;
  71
  72                 if ( is_null( self::$instance ) ) {
  73                         $class = self::getLBFactoryClass( $wgLBFactoryConf );
  74                         $config = $wgLBFactoryConf;
  75                         if ( !isset( $config['readOnlyReason'] ) ) {
  76                                 $config['readOnlyReason'] = wfConfiguredReadOnlyReason();
  77                         }
  78                         self::$instance = new $class( $config );
  79                 }
  80
  81                 return self::$instance;
  82         }
  83
  84         /**
  85          * Returns the LBFactory class to use and the load balancer configuration.
  86          *
  87          * @param array $config (e.g. $wgLBFactoryConf)
  88          * @return string Class name
  89          */
  90         public static function getLBFactoryClass( array $config ) {
  91                 // For configuration backward compatibility after removing
  92                 // underscores from class names in MediaWiki 1.23.
  93                 $bcClasses = array(
  94                         'LBFactory_Simple' => 'LBFactorySimple',
  95                         'LBFactory_Single' => 'LBFactorySingle',
  96                         'LBFactory_Multi' => 'LBFactoryMulti',
  97                         'LBFactory_Fake' => 'LBFactoryFake',
  98                 );
  99
 100                 $class = $config['class'];
 101
 102                 if ( isset( $bcClasses[$class] ) ) {
 103                         $class = $bcClasses[$class];
 104                         wfDeprecated(
 105                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
 106                                 '1.23'
 107                         );
 108                 }
 109
 110                 return $class;
 111         }
 112
 113         /**
 114          * Shut down, close connections and destroy the cached instance.
 115          */
 116         public static function destroyInstance() {
 117                 if ( self::$instance ) {
 118                         self::$instance->shutdown();
 119                         self::$instance->forEachLBCallMethod( 'closeAll' );
 120                         self::$instance = null;
 121                 }
 122         }
 123
 124         /**
 125          * Set the instance to be the given object
 126          *
 127          * @param LBFactory $instance
 128          */
 129         public static function setInstance( $instance ) {
 130                 self::destroyInstance();
 131                 self::$instance = $instance;
 132         }
 133
 134         /**
 135          * Create a new load balancer object. The resulting object will be untracked,
 136          * not chronology-protected, and the caller is responsible for cleaning it up.
 137          *
 138          * @param bool|string $wiki Wiki ID, or false for the current wiki
 139          * @return LoadBalancer
 140          */
 141         abstract public function newMainLB( $wiki = false );
 142
 143         /**
 144          * Get a cached (tracked) load balancer object.
 145          *
 146          * @param bool|string $wiki Wiki ID, or false for the current wiki
 147          * @return LoadBalancer
 148          */
 149         abstract public function getMainLB( $wiki = false );
 150
 151         /**
 152          * Create a new load balancer for external storage. The resulting object will be
 153          * untracked, not chronology-protected, and the caller is responsible for
 154          * cleaning it up.
 155          *
 156          * @param string $cluster External storage cluster, or false for core
 157          * @param bool|string $wiki Wiki ID, or false for the current wiki
 158          * @return LoadBalancer
 159          */
 160         abstract protected function newExternalLB( $cluster, $wiki = false );
 161
 162         /**
 163          * Get a cached (tracked) load balancer for external storage
 164          *
 165          * @param string $cluster External storage cluster, or false for core
 166          * @param bool|string $wiki Wiki ID, or false for the current wiki
 167          * @return LoadBalancer
 168          */
 169         abstract public function &getExternalLB( $cluster, $wiki = false );
 170
 171         /**
 172          * Execute a function for each tracked load balancer
 173          * The callback is called with the load balancer as the first parameter,
 174          * and $params passed as the subsequent parameters.
 175          *
 176          * @param callable $callback
 177          * @param array $params
 178          */
 179         abstract public function forEachLB( $callback, array $params = array() );
 180
 181         /**
 182          * Prepare all tracked load balancers for shutdown
 183          * @param integer $flags Supports SHUTDOWN_* flags
 184          * STUB
 185          */
 186         public function shutdown( $flags = 0 ) {
 187         }
 188
 189         /**
 190          * Call a method of each tracked load balancer
 191          *
 192          * @param string $methodName
 193          * @param array $args
 194          */
 195         private function forEachLBCallMethod( $methodName, array $args = array() ) {
 196                 $this->forEachLB(
 197                         function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 198                                 call_user_func_array( array( $loadBalancer, $methodName ), $args );
 199                         },
 200                         array( $methodName, $args )
 201                 );
 202         }
 203
 204         /**
 205          * Commit on all connections. Done for two reasons:
 206          * 1. To commit changes to the masters.
 207          * 2. To release the snapshot on all connections, master and slave.
 208          * @param string $fname Caller name
 209          */
 210         public function commitAll( $fname = __METHOD__ ) {
 211                 $start = microtime( true );
 212                 $this->forEachLBCallMethod( 'commitAll', array( $fname ) );
 213                 $timeMs = 1000 * ( microtime( true ) - $start );
 214
 215                 RequestContext::getMain()->getStats()->timing( "db.commit-all", $timeMs );
 216         }
 217
 218         /**
 219          * Commit changes on all master connections
 220          * @param string $fname Caller name
 221          */
 222         public function commitMasterChanges( $fname = __METHOD__ ) {
 223                 $start = microtime( true );
 224                 $this->forEachLBCallMethod( 'commitMasterChanges', array( $fname ) );
 225                 $timeMs = 1000 * ( microtime( true ) - $start );
 226
 227                 RequestContext::getMain()->getStats()->timing( "db.commit-masters", $timeMs );
 228         }
 229
 230         /**
 231          * Rollback changes on all master connections
 232          * @param string $fname Caller name
 233          * @since 1.23
 234          */
 235         public function rollbackMasterChanges( $fname = __METHOD__ ) {
 236                 $this->forEachLBCallMethod( 'rollbackMasterChanges', array( $fname ) );
 237         }
 238
 239         /**
 240          * Determine if any master connection has pending changes
 241          * @return bool
 242          * @since 1.23
 243          */
 244         public function hasMasterChanges() {
 245                 $ret = false;
 246                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 247                         $ret = $ret || $lb->hasMasterChanges();
 248                 } );
 249
 250                 return $ret;
 251         }
 252
 253         /**
 254          * Detemine if any lagged slave connection was used
 255          * @since 1.27
 256          * @return bool
 257          */
 258         public function laggedSlaveUsed() {
 259                 $ret = false;
 260                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 261                         $ret = $ret || $lb->laggedSlaveUsed();
 262                 } );
 263
 264                 return $ret;
 265         }
 266
 267         /**
 268          * Determine if any master connection has pending/written changes from this request
 269          * @return bool
 270          * @since 1.27
 271          */
 272         public function hasOrMadeRecentMasterChanges() {
 273                 $ret = false;
 274                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 275                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges();
 276                 } );
 277                 return $ret;
 278         }
 279
 280         /**
 281          * Disable the ChronologyProtector for all load balancers
 282          *
 283          * This can be called at the start of special API entry points
 284          *
 285          * @since 1.27
 286          */
 287         public function disableChronologyProtection() {
 288                 $this->chronProt->setEnabled( false );
 289         }
 290
 291         /**
 292          * @return ChronologyProtector
 293          */
 294         protected function newChronologyProtector() {
 295                 $request = RequestContext::getMain()->getRequest();
 296                 $chronProt = new ChronologyProtector(
 297                         ObjectCache::getMainStashInstance(),
 298                         array(
 299                                 'ip' => $request->getIP(),
 300                                 'agent' => $request->getHeader( 'User-Agent' )
 301                         )
 302                 );
 303                 if ( PHP_SAPI === 'cli' ) {
 304                         $chronProt->setEnabled( false );
 305                 } elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
 306                         // Request opted out of using position wait logic. This is useful for requests
 307                         // done by the job queue or background ETL that do not have a meaningful session.
 308                         $chronProt->setWaitEnabled( false );
 309                 }
 310
 311                 return $chronProt;
 312         }
 313
 314         /**
 315          * @param ChronologyProtector $cp
 316          */
 317         protected function shutdownChronologyProtector( ChronologyProtector $cp ) {
 318                 // Get all the master positions needed
 319                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
 320                         $cp->shutdownLB( $lb );
 321                 } );
 322                 // Write them to the stash
 323                 $unsavedPositions = $cp->shutdown();
 324                 // If the positions failed to write to the stash, at least wait on local datacenter
 325                 // slaves to catch up before responding. Even if there are several DCs, this increases
 326                 // the chance that the user will see their own changes immediately afterwards. As long
 327                 // as the sticky DC cookie applies (same domain), this is not even an issue.
 328                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
 329                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 330                         if ( isset( $unsavedPositions[$masterName] ) ) {
 331                                 $lb->waitForAll( $unsavedPositions[$masterName] );
 332                         }
 333                 } );
 334         }
 335 }
 336
 337 /**
 338  * Exception class for attempted DB access
 339  */
 340 class DBAccessError extends MWException {
 341         public function __construct() {
 342                 parent::__construct( "Mediawiki tried to access the database via wfGetDB(). " .
 343                         "This is not allowed." );
 344         }
 345 }