includes/db/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing.
   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  * Database load balancing object
  26  *
  27  * @todo document
  28  * @ingroup Database
  29  */
  30 class LoadBalancer {
  31         /** @var array Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard slave lag as a factor in slave selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on slave lag to resolve */
  42         private $mWaitTimeout;
  43
  44         /** @var array LBFactory information */
  45         private $mParentInfo;
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50
  51         /** @var bool|DatabaseBase Database connection that caused a problem */
  52         private $mErrorConnection;
  53         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  54         private $mReadIndex;
  55         /** @var bool|DBMasterPos False if not set */
  56         private $mWaitForPos;
  57         /** @var bool Whether the generic reader fell back to a lagged slave */
  58         private $mLaggedSlaveMode;
  59         /** @var string The last DB selection or connection error */
  60         private $mLastError = 'Unknown error';
  61         /** @var array Process cache of LoadMonitor::getLagTimes() */
  62         private $mLagTimes;
  63
  64         /**
  65          * @param array $params Array with keys:
  66          *   servers           Required. Array of server info structures.
  67          *   loadMonitor       Name of a class used to fetch server lag and load.
  68          * @throws MWException
  69          */
  70         function __construct( $params ) {
  71                 if ( !isset( $params['servers'] ) ) {
  72                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  73                 }
  74                 $this->mServers = $params['servers'];
  75                 $this->mWaitTimeout = 10;
  76
  77                 $this->mReadIndex = -1;
  78                 $this->mWriteIndex = -1;
  79                 $this->mConns = array(
  80                         'local' => array(),
  81                         'foreignUsed' => array(),
  82                         'foreignFree' => array() );
  83                 $this->mLoads = array();
  84                 $this->mWaitForPos = false;
  85                 $this->mLaggedSlaveMode = false;
  86                 $this->mErrorConnection = false;
  87                 $this->mAllowLagged = false;
  88
  89                 if ( isset( $params['loadMonitor'] ) ) {
  90                         $this->mLoadMonitorClass = $params['loadMonitor'];
  91                 } else {
  92                         $master = reset( $params['servers'] );
  93                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  94                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  95                         } else {
  96                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
  97                         }
  98                 }
  99
 100                 foreach ( $params['servers'] as $i => $server ) {
 101                         $this->mLoads[$i] = $server['load'];
 102                         if ( isset( $server['groupLoads'] ) ) {
 103                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 104                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 105                                                 $this->mGroupLoads[$group] = array();
 106                                         }
 107                                         $this->mGroupLoads[$group][$i] = $ratio;
 108                                 }
 109                         }
 110                 }
 111         }
 112
 113         /**
 114          * Get a LoadMonitor instance
 115          *
 116          * @return LoadMonitor
 117          */
 118         function getLoadMonitor() {
 119                 if ( !isset( $this->mLoadMonitor ) ) {
 120                         $class = $this->mLoadMonitorClass;
 121                         $this->mLoadMonitor = new $class( $this );
 122                 }
 123
 124                 return $this->mLoadMonitor;
 125         }
 126
 127         /**
 128          * Get or set arbitrary data used by the parent object, usually an LBFactory
 129          * @param mixed $x
 130          * @return mixed
 131          */
 132         function parentInfo( $x = null ) {
 133                 return wfSetVar( $this->mParentInfo, $x );
 134         }
 135
 136         /**
 137          * Given an array of non-normalised probabilities, this function will select
 138          * an element and return the appropriate key
 139          *
 140          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 141          *
 142          * @param array $weights
 143          * @return bool|int|string
 144          */
 145         function pickRandom( $weights ) {
 146                 return ArrayUtils::pickRandom( $weights );
 147         }
 148
 149         /**
 150          * @param array $loads
 151          * @param bool|string $wiki Wiki to get non-lagged for
 152          * @return bool|int|string
 153          */
 154         function getRandomNonLagged( $loads, $wiki = false ) {
 155                 # Unset excessively lagged servers
 156                 $lags = $this->getLagTimes( $wiki );
 157                 foreach ( $lags as $i => $lag ) {
 158                         if ( $i != 0 ) {
 159                                 if ( $lag === false ) {
 160                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 161                                         unset( $loads[$i] );
 162                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 163                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 164                                         unset( $loads[$i] );
 165                                 }
 166                         }
 167                 }
 168
 169                 # Find out if all the slaves with non-zero load are lagged
 170                 $sum = 0;
 171                 foreach ( $loads as $load ) {
 172                         $sum += $load;
 173                 }
 174                 if ( $sum == 0 ) {
 175                         # No appropriate DB servers except maybe the master and some slaves with zero load
 176                         # Do NOT use the master
 177                         # Instead, this function will return false, triggering read-only mode,
 178                         # and a lagged slave will be used instead.
 179                         return false;
 180                 }
 181
 182                 if ( count( $loads ) == 0 ) {
 183                         return false;
 184                 }
 185
 186                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 187
 188                 # Return a random representative of the remainder
 189                 return ArrayUtils::pickRandom( $loads );
 190         }
 191
 192         /**
 193          * Get the index of the reader connection, which may be a slave
 194          * This takes into account load ratios and lag times. It should
 195          * always return a consistent index during a given invocation
 196          *
 197          * Side effect: opens connections to databases
 198          * @param bool|string $group
 199          * @param bool|string $wiki
 200          * @throws MWException
 201          * @return bool|int|string
 202          */
 203         function getReaderIndex( $group = false, $wiki = false ) {
 204                 global $wgReadOnly, $wgDBtype;
 205
 206                 # @todo FIXME: For now, only go through all this for mysql databases
 207                 if ( $wgDBtype != 'mysql' ) {
 208                         return $this->getWriterIndex();
 209                 }
 210
 211                 if ( count( $this->mServers ) == 1 ) {
 212                         # Skip the load balancing if there's only one server
 213                         return 0;
 214                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 215                         # Shortcut if generic reader exists already
 216                         return $this->mReadIndex;
 217                 }
 218
 219                 $section = new ProfileSection( __METHOD__ );
 220
 221                 # Find the relevant load array
 222                 if ( $group !== false ) {
 223                         if ( isset( $this->mGroupLoads[$group] ) ) {
 224                                 $nonErrorLoads = $this->mGroupLoads[$group];
 225                         } else {
 226                                 # No loads for this group, return false and the caller can use some other group
 227                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 228
 229                                 return false;
 230                         }
 231                 } else {
 232                         $nonErrorLoads = $this->mLoads;
 233                 }
 234
 235                 if ( !count( $nonErrorLoads ) ) {
 236                         throw new MWException( "Empty server array given to LoadBalancer" );
 237                 }
 238
 239                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 240                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 241
 242                 $laggedSlaveMode = false;
 243
 244                 # No server found yet
 245                 $i = false;
 246                 # First try quickly looking through the available servers for a server that
 247                 # meets our criteria
 248                 $currentLoads = $nonErrorLoads;
 249                 while ( count( $currentLoads ) ) {
 250                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 251                                 $i = ArrayUtils::pickRandom( $currentLoads );
 252                         } else {
 253                                 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 254                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 255                                         # All slaves lagged. Switch to read-only mode
 256                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 257                                         $wgReadOnly = 'The database has been automatically locked ' .
 258                                                 'while the slave database servers catch up to the master';
 259                                         $i = ArrayUtils::pickRandom( $currentLoads );
 260                                         $laggedSlaveMode = true;
 261                                 }
 262                         }
 263
 264                         if ( $i === false ) {
 265                                 # pickRandom() returned false
 266                                 # This is permanent and means the configuration or the load monitor
 267                                 # wants us to return false.
 268                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 269
 270                                 return false;
 271                         }
 272
 273                         wfDebugLog( 'connect', __METHOD__ .
 274                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 275
 276                         $conn = $this->openConnection( $i, $wiki );
 277                         if ( !$conn ) {
 278                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 279                                 unset( $nonErrorLoads[$i] );
 280                                 unset( $currentLoads[$i] );
 281                                 $i = false;
 282                                 continue;
 283                         }
 284
 285                         // Decrement reference counter, we are finished with this connection.
 286                         // It will be incremented for the caller later.
 287                         if ( $wiki !== false ) {
 288                                 $this->reuseConnection( $conn );
 289                         }
 290
 291                         # Return this server
 292                         break;
 293                 }
 294
 295                 # If all servers were down, quit now
 296                 if ( !count( $nonErrorLoads ) ) {
 297                         wfDebugLog( 'connect', "All servers down" );
 298                 }
 299
 300                 if ( $i !== false ) {
 301                         # Slave connection successful
 302                         # Wait for the session master pos for a short time
 303                         if ( $this->mWaitForPos && $i > 0 ) {
 304                                 if ( !$this->doWait( $i ) ) {
 305                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 306                                 }
 307                         }
 308                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group !== false ) {
 309                                 $this->mReadIndex = $i;
 310                         }
 311                 }
 312
 313                 return $i;
 314         }
 315
 316         /**
 317          * Wait for a specified number of microseconds, and return the period waited
 318          * @param int $t
 319          * @return int
 320          */
 321         function sleep( $t ) {
 322                 wfProfileIn( __METHOD__ );
 323                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 324                 usleep( $t );
 325                 wfProfileOut( __METHOD__ );
 326
 327                 return $t;
 328         }
 329
 330         /**
 331          * Set the master wait position
 332          * If a DB_SLAVE connection has been opened already, waits
 333          * Otherwise sets a variable telling it to wait if such a connection is opened
 334          * @param DBMasterPos $pos
 335          */
 336         public function waitFor( $pos ) {
 337                 wfProfileIn( __METHOD__ );
 338                 $this->mWaitForPos = $pos;
 339                 $i = $this->mReadIndex;
 340
 341                 if ( $i > 0 ) {
 342                         if ( !$this->doWait( $i ) ) {
 343                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 344                                 $this->mLaggedSlaveMode = true;
 345                         }
 346                 }
 347                 wfProfileOut( __METHOD__ );
 348         }
 349
 350         /**
 351          * Set the master wait position and wait for ALL slaves to catch up to it
 352          * @param DBMasterPos $pos
 353          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 354          * @return bool Success (able to connect and no timeouts reached)
 355          */
 356         public function waitForAll( $pos, $timeout = null ) {
 357                 wfProfileIn( __METHOD__ );
 358                 $this->mWaitForPos = $pos;
 359                 $serverCount = count( $this->mServers );
 360
 361                 $ok = true;
 362                 for ( $i = 1; $i < $serverCount; $i++ ) {
 363                         if ( $this->mLoads[$i] > 0 ) {
 364                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 365                         }
 366                 }
 367                 wfProfileOut( __METHOD__ );
 368
 369                 return $ok;
 370         }
 371
 372         /**
 373          * Get any open connection to a given server index, local or foreign
 374          * Returns false if there is no connection open
 375          *
 376          * @param int $i
 377          * @return DatabaseBase|bool False on failure
 378          */
 379         function getAnyOpenConnection( $i ) {
 380                 foreach ( $this->mConns as $conns ) {
 381                         if ( !empty( $conns[$i] ) ) {
 382                                 return reset( $conns[$i] );
 383                         }
 384                 }
 385
 386                 return false;
 387         }
 388
 389         /**
 390          * Wait for a given slave to catch up to the master pos stored in $this
 391          * @param int $index Server index
 392          * @param bool $open Check the server even if a new connection has to be made
 393          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 394          * @return bool
 395          */
 396         protected function doWait( $index, $open = false, $timeout = null ) {
 397                 $close = false; // close the connection afterwards
 398
 399                 # Find a connection to wait on, creating one if needed and allowed
 400                 $conn = $this->getAnyOpenConnection( $index );
 401                 if ( !$conn ) {
 402                         if ( !$open ) {
 403                                 wfDebug( __METHOD__ . ": no connection open\n" );
 404
 405                                 return false;
 406                         } else {
 407                                 $conn = $this->openConnection( $index, '' );
 408                                 if ( !$conn ) {
 409                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 410
 411                                         return false;
 412                                 }
 413                                 // Avoid connection spam in waitForAll() when connections
 414                                 // are made just for the sake of doing this lag check.
 415                                 $close = true;
 416                         }
 417                 }
 418
 419                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 420                 $timeout = $timeout ?: $this->mWaitTimeout;
 421                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 422
 423                 if ( $result == -1 || is_null( $result ) ) {
 424                         # Timed out waiting for slave, use master instead
 425                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 426                         $ok = false;
 427                 } else {
 428                         wfDebug( __METHOD__ . ": Done\n" );
 429                         $ok = true;
 430                 }
 431
 432                 if ( $close ) {
 433                         $this->closeConnection( $conn );
 434                 }
 435
 436                 return $ok;
 437         }
 438
 439         /**
 440          * Get a connection by index
 441          * This is the main entry point for this class.
 442          *
 443          * @param int $i Server index
 444          * @param array $groups Query groups
 445          * @param bool|string $wiki Wiki ID
 446          *
 447          * @throws MWException
 448          * @return DatabaseBase
 449          */
 450         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 451                 wfProfileIn( __METHOD__ );
 452
 453                 if ( $i === null || $i === false ) {
 454                         wfProfileOut( __METHOD__ );
 455                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 456                                 ' with invalid server index' );
 457                 }
 458
 459                 if ( $wiki === wfWikiID() ) {
 460                         $wiki = false;
 461                 }
 462
 463                 # Query groups
 464                 if ( $i == DB_MASTER ) {
 465                         $i = $this->getWriterIndex();
 466                 } elseif ( !is_array( $groups ) ) {
 467                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 468                         if ( $groupIndex !== false ) {
 469                                 $serverName = $this->getServerName( $groupIndex );
 470                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 471                                 $i = $groupIndex;
 472                         }
 473                 } else {
 474                         foreach ( $groups as $group ) {
 475                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 476                                 if ( $groupIndex !== false ) {
 477                                         $serverName = $this->getServerName( $groupIndex );
 478                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 479                                         $i = $groupIndex;
 480                                         break;
 481                                 }
 482                         }
 483                 }
 484
 485                 # Operation-based index
 486                 if ( $i == DB_SLAVE ) {
 487                         $this->mLastError = 'Unknown error'; // reset error string
 488                         $i = $this->getReaderIndex( false, $wiki );
 489                         # Couldn't find a working server in getReaderIndex()?
 490                         if ( $i === false ) {
 491                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 492                                 wfProfileOut( __METHOD__ );
 493
 494                                 return $this->reportConnectionError();
 495                         }
 496                 }
 497
 498                 # Now we have an explicit index into the servers array
 499                 $conn = $this->openConnection( $i, $wiki );
 500                 if ( !$conn ) {
 501                         wfProfileOut( __METHOD__ );
 502
 503                         return $this->reportConnectionError();
 504                 }
 505
 506                 wfProfileOut( __METHOD__ );
 507
 508                 return $conn;
 509         }
 510
 511         /**
 512          * Mark a foreign connection as being available for reuse under a different
 513          * DB name or prefix. This mechanism is reference-counted, and must be called
 514          * the same number of times as getConnection() to work.
 515          *
 516          * @param DatabaseBase $conn
 517          * @throws MWException
 518          */
 519         public function reuseConnection( $conn ) {
 520                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 521                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 522                 if ( $serverIndex === null || $refCount === null ) {
 523                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 524
 525                         /**
 526                          * This can happen in code like:
 527                          *   foreach ( $dbs as $db ) {
 528                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 529                          *     ...
 530                          *     $lb->reuseConnection( $conn );
 531                          *   }
 532                          * When a connection to the local DB is opened in this way, reuseConnection()
 533                          * should be ignored
 534                          */
 535
 536                         return;
 537                 }
 538
 539                 $dbName = $conn->getDBname();
 540                 $prefix = $conn->tablePrefix();
 541                 if ( strval( $prefix ) !== '' ) {
 542                         $wiki = "$dbName-$prefix";
 543                 } else {
 544                         $wiki = $dbName;
 545                 }
 546                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 547                         throw new MWException( __METHOD__ . ": connection not found, has " .
 548                                 "the connection been freed already?" );
 549                 }
 550                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 551                 if ( $refCount <= 0 ) {
 552                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 553                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 554                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 555                 } else {
 556                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 557                 }
 558         }
 559
 560         /**
 561          * Get a database connection handle reference
 562          *
 563          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 564          *
 565          * @see LoadBalancer::getConnection() for parameter information
 566          *
 567          * @param int $db
 568          * @param mixed $groups
 569          * @param bool|string $wiki
 570          * @return DBConnRef
 571          */
 572         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 573                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 574         }
 575
 576         /**
 577          * Get a database connection handle reference without connecting yet
 578          *
 579          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 580          *
 581          * @see LoadBalancer::getConnection() for parameter information
 582          *
 583          * @param int $db
 584          * @param mixed $groups
 585          * @param bool|string $wiki
 586          * @return DBConnRef
 587          */
 588         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 589                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 590         }
 591
 592         /**
 593          * Open a connection to the server given by the specified index
 594          * Index must be an actual index into the array.
 595          * If the server is already open, returns it.
 596          *
 597          * On error, returns false, and the connection which caused the
 598          * error will be available via $this->mErrorConnection.
 599          *
 600          * @param int $i Server index
 601          * @param bool|string $wiki Wiki ID to open
 602          * @return DatabaseBase
 603          *
 604          * @access private
 605          */
 606         function openConnection( $i, $wiki = false ) {
 607                 wfProfileIn( __METHOD__ );
 608                 if ( $wiki !== false ) {
 609                         $conn = $this->openForeignConnection( $i, $wiki );
 610                         wfProfileOut( __METHOD__ );
 611
 612                         return $conn;
 613                 }
 614                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 615                         $conn = $this->mConns['local'][$i][0];
 616                 } else {
 617                         $server = $this->mServers[$i];
 618                         $server['serverIndex'] = $i;
 619                         $conn = $this->reallyOpenConnection( $server, false );
 620                         if ( $conn->isOpen() ) {
 621                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 622                                 $this->mConns['local'][$i][0] = $conn;
 623                         } else {
 624                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 625                                 $this->mErrorConnection = $conn;
 626                                 $conn = false;
 627                         }
 628                 }
 629                 wfProfileOut( __METHOD__ );
 630
 631                 return $conn;
 632         }
 633
 634         /**
 635          * Open a connection to a foreign DB, or return one if it is already open.
 636          *
 637          * Increments a reference count on the returned connection which locks the
 638          * connection to the requested wiki. This reference count can be
 639          * decremented by calling reuseConnection().
 640          *
 641          * If a connection is open to the appropriate server already, but with the wrong
 642          * database, it will be switched to the right database and returned, as long as
 643          * it has been freed first with reuseConnection().
 644          *
 645          * On error, returns false, and the connection which caused the
 646          * error will be available via $this->mErrorConnection.
 647          *
 648          * @param int $i Server index
 649          * @param string $wiki Wiki ID to open
 650          * @return DatabaseBase
 651          */
 652         function openForeignConnection( $i, $wiki ) {
 653                 wfProfileIn( __METHOD__ );
 654                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 655                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 656                         // Reuse an already-used connection
 657                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 658                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 659                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 660                         // Reuse a free connection for the same wiki
 661                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 662                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 663                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 664                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 665                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 666                         // Reuse a connection from another wiki
 667                         $conn = reset( $this->mConns['foreignFree'][$i] );
 668                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 669
 670                         if ( !$conn->selectDB( $dbName ) ) {
 671                                 $this->mLastError = "Error selecting database $dbName on server " .
 672                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 673                                 $this->mErrorConnection = $conn;
 674                                 $conn = false;
 675                         } else {
 676                                 $conn->tablePrefix( $prefix );
 677                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 678                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 679                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 680                         }
 681                 } else {
 682                         // Open a new connection
 683                         $server = $this->mServers[$i];
 684                         $server['serverIndex'] = $i;
 685                         $server['foreignPoolRefCount'] = 0;
 686                         $server['foreign'] = true;
 687                         $conn = $this->reallyOpenConnection( $server, $dbName );
 688                         if ( !$conn->isOpen() ) {
 689                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 690                                 $this->mErrorConnection = $conn;
 691                                 $conn = false;
 692                         } else {
 693                                 $conn->tablePrefix( $prefix );
 694                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 695                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 696                         }
 697                 }
 698
 699                 // Increment reference count
 700                 if ( $conn ) {
 701                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 702                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 703                 }
 704                 wfProfileOut( __METHOD__ );
 705
 706                 return $conn;
 707         }
 708
 709         /**
 710          * Test if the specified index represents an open connection
 711          *
 712          * @param int $index Server index
 713          * @access private
 714          * @return bool
 715          */
 716         function isOpen( $index ) {
 717                 if ( !is_integer( $index ) ) {
 718                         return false;
 719                 }
 720
 721                 return (bool)$this->getAnyOpenConnection( $index );
 722         }
 723
 724         /**
 725          * Really opens a connection. Uncached.
 726          * Returns a Database object whether or not the connection was successful.
 727          * @access private
 728          *
 729          * @param array $server
 730          * @param bool $dbNameOverride
 731          * @throws MWException
 732          * @return DatabaseBase
 733          */
 734         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 735                 if ( !is_array( $server ) ) {
 736                         throw new MWException( 'You must update your load-balancing configuration. ' .
 737                                 'See DefaultSettings.php entry for $wgDBservers.' );
 738                 }
 739
 740                 if ( $dbNameOverride !== false ) {
 741                         $server['dbname'] = $dbNameOverride;
 742                 }
 743
 744                 # Create object
 745                 try {
 746                         $db = DatabaseBase::factory( $server['type'], $server );
 747                 } catch ( DBConnectionError $e ) {
 748                         // FIXME: This is probably the ugliest thing I have ever done to
 749                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 750                         $db = $e->db;
 751                 }
 752
 753                 $db->setLBInfo( $server );
 754                 if ( isset( $server['fakeSlaveLag'] ) ) {
 755                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 756                 }
 757                 if ( isset( $server['fakeMaster'] ) ) {
 758                         $db->setFakeMaster( true );
 759                 }
 760
 761                 return $db;
 762         }
 763
 764         /**
 765          * @throws DBConnectionError
 766          * @return bool
 767          */
 768         private function reportConnectionError() {
 769                 $conn = $this->mErrorConnection; // The connection which caused the error
 770
 771                 if ( !is_object( $conn ) ) {
 772                         // No last connection, probably due to all servers being too busy
 773                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}" );
 774
 775                         // If all servers were busy, mLastError will contain something sensible
 776                         throw new DBConnectionError( null, $this->mLastError );
 777                 } else {
 778                         $server = $conn->getProperty( 'mServer' );
 779                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})" );
 780                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 781                 }
 782
 783                 return false; /* not reached */
 784         }
 785
 786         /**
 787          * @return int
 788          */
 789         function getWriterIndex() {
 790                 return 0;
 791         }
 792
 793         /**
 794          * Returns true if the specified index is a valid server index
 795          *
 796          * @param string $i
 797          * @return bool
 798          */
 799         function haveIndex( $i ) {
 800                 return array_key_exists( $i, $this->mServers );
 801         }
 802
 803         /**
 804          * Returns true if the specified index is valid and has non-zero load
 805          *
 806          * @param string $i
 807          * @return bool
 808          */
 809         function isNonZeroLoad( $i ) {
 810                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 811         }
 812
 813         /**
 814          * Get the number of defined servers (not the number of open connections)
 815          *
 816          * @return int
 817          */
 818         function getServerCount() {
 819                 return count( $this->mServers );
 820         }
 821
 822         /**
 823          * Get the host name or IP address of the server with the specified index
 824          * Prefer a readable name if available.
 825          * @param string $i
 826          * @return string
 827          */
 828         function getServerName( $i ) {
 829                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 830                         return $this->mServers[$i]['hostName'];
 831                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 832                         return $this->mServers[$i]['host'];
 833                 } else {
 834                         return '';
 835                 }
 836         }
 837
 838         /**
 839          * Return the server info structure for a given index, or false if the index is invalid.
 840          * @param int $i
 841          * @return array|bool
 842          */
 843         function getServerInfo( $i ) {
 844                 if ( isset( $this->mServers[$i] ) ) {
 845                         return $this->mServers[$i];
 846                 } else {
 847                         return false;
 848                 }
 849         }
 850
 851         /**
 852          * Sets the server info structure for the given index. Entry at index $i
 853          * is created if it doesn't exist
 854          * @param int $i
 855          * @param array $serverInfo
 856          */
 857         function setServerInfo( $i, $serverInfo ) {
 858                 $this->mServers[$i] = $serverInfo;
 859         }
 860
 861         /**
 862          * Get the current master position for chronology control purposes
 863          * @return mixed
 864          */
 865         function getMasterPos() {
 866                 # If this entire request was served from a slave without opening a connection to the
 867                 # master (however unlikely that may be), then we can fetch the position from the slave.
 868                 $masterConn = $this->getAnyOpenConnection( 0 );
 869                 if ( !$masterConn ) {
 870                         $serverCount = count( $this->mServers );
 871                         for ( $i = 1; $i < $serverCount; $i++ ) {
 872                                 $conn = $this->getAnyOpenConnection( $i );
 873                                 if ( $conn ) {
 874                                         wfDebug( "Master pos fetched from slave\n" );
 875
 876                                         return $conn->getSlavePos();
 877                                 }
 878                         }
 879                 } else {
 880                         wfDebug( "Master pos fetched from master\n" );
 881
 882                         return $masterConn->getMasterPos();
 883                 }
 884
 885                 return false;
 886         }
 887
 888         /**
 889          * Close all open connections
 890          */
 891         function closeAll() {
 892                 foreach ( $this->mConns as $conns2 ) {
 893                         foreach ( $conns2 as $conns3 ) {
 894                                 /** @var DatabaseBase $conn */
 895                                 foreach ( $conns3 as $conn ) {
 896                                         $conn->close();
 897                                 }
 898                         }
 899                 }
 900                 $this->mConns = array(
 901                         'local' => array(),
 902                         'foreignFree' => array(),
 903                         'foreignUsed' => array(),
 904                 );
 905         }
 906
 907         /**
 908          * Close a connection
 909          * Using this function makes sure the LoadBalancer knows the connection is closed.
 910          * If you use $conn->close() directly, the load balancer won't update its state.
 911          * @param DatabaseBase $conn
 912          */
 913         function closeConnection( $conn ) {
 914                 $done = false;
 915                 foreach ( $this->mConns as $i1 => $conns2 ) {
 916                         foreach ( $conns2 as $i2 => $conns3 ) {
 917                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 918                                         if ( $conn === $candidateConn ) {
 919                                                 $conn->close();
 920                                                 unset( $this->mConns[$i1][$i2][$i3] );
 921                                                 $done = true;
 922                                                 break;
 923                                         }
 924                                 }
 925                         }
 926                 }
 927                 if ( !$done ) {
 928                         $conn->close();
 929                 }
 930         }
 931
 932         /**
 933          * Commit transactions on all open connections
 934          */
 935         function commitAll() {
 936                 foreach ( $this->mConns as $conns2 ) {
 937                         foreach ( $conns2 as $conns3 ) {
 938                                 /** @var DatabaseBase[] $conns3 */
 939                                 foreach ( $conns3 as $conn ) {
 940                                         if ( $conn->trxLevel() ) {
 941                                                 $conn->commit( __METHOD__, 'flush' );
 942                                         }
 943                                 }
 944                         }
 945                 }
 946         }
 947
 948         /**
 949          *  Issue COMMIT only on master, only if queries were done on connection
 950          */
 951         function commitMasterChanges() {
 952                 // Always 0, but who knows.. :)
 953                 $masterIndex = $this->getWriterIndex();
 954                 foreach ( $this->mConns as $conns2 ) {
 955                         if ( empty( $conns2[$masterIndex] ) ) {
 956                                 continue;
 957                         }
 958                         /** @var DatabaseBase $conn */
 959                         foreach ( $conns2[$masterIndex] as $conn ) {
 960                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 961                                         $conn->commit( __METHOD__, 'flush' );
 962                                 }
 963                         }
 964                 }
 965         }
 966
 967         /**
 968          * Issue ROLLBACK only on master, only if queries were done on connection
 969          * @since 1.23
 970          */
 971         function rollbackMasterChanges() {
 972                 // Always 0, but who knows.. :)
 973                 $masterIndex = $this->getWriterIndex();
 974                 foreach ( $this->mConns as $conns2 ) {
 975                         if ( empty( $conns2[$masterIndex] ) ) {
 976                                 continue;
 977                         }
 978                         /** @var DatabaseBase $conn */
 979                         foreach ( $conns2[$masterIndex] as $conn ) {
 980                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 981                                         $conn->rollback( __METHOD__, 'flush' );
 982                                 }
 983                         }
 984                 }
 985         }
 986
 987         /**
 988          * @return bool Whether a master connection is already open
 989          * @since 1.24
 990          */
 991         function hasMasterConnection() {
 992                 return $this->isOpen( $this->getWriterIndex() );
 993         }
 994
 995         /**
 996          * Determine if there are any pending changes that need to be rolled back
 997          * or committed.
 998          * @since 1.23
 999          * @return bool
1000          */
1001         function hasMasterChanges() {
1002                 // Always 0, but who knows.. :)
1003                 $masterIndex = $this->getWriterIndex();
1004                 foreach ( $this->mConns as $conns2 ) {
1005                         if ( empty( $conns2[$masterIndex] ) ) {
1006                                 continue;
1007                         }
1008                         /** @var DatabaseBase $conn */
1009                         foreach ( $conns2[$masterIndex] as $conn ) {
1010                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1011                                         return true;
1012                                 }
1013                         }
1014                 }
1015                 return false;
1016         }
1017
1018         /**
1019          * @param mixed $value
1020          * @return mixed
1021          */
1022         function waitTimeout( $value = null ) {
1023                 return wfSetVar( $this->mWaitTimeout, $value );
1024         }
1025
1026         /**
1027          * @return bool
1028          */
1029         function getLaggedSlaveMode() {
1030                 return $this->mLaggedSlaveMode;
1031         }
1032
1033         /**
1034          * Disables/enables lag checks
1035          * @param null|bool $mode
1036          * @return bool
1037          */
1038         function allowLagged( $mode = null ) {
1039                 if ( $mode === null ) {
1040                         return $this->mAllowLagged;
1041                 }
1042                 $this->mAllowLagged = $mode;
1043
1044                 return $this->mAllowLagged;
1045         }
1046
1047         /**
1048          * @return bool
1049          */
1050         function pingAll() {
1051                 $success = true;
1052                 foreach ( $this->mConns as $conns2 ) {
1053                         foreach ( $conns2 as $conns3 ) {
1054                                 /** @var DatabaseBase[] $conns3 */
1055                                 foreach ( $conns3 as $conn ) {
1056                                         if ( !$conn->ping() ) {
1057                                                 $success = false;
1058                                         }
1059                                 }
1060                         }
1061                 }
1062
1063                 return $success;
1064         }
1065
1066         /**
1067          * Call a function with each open connection object
1068          * @param callable $callback
1069          * @param array $params
1070          */
1071         function forEachOpenConnection( $callback, $params = array() ) {
1072                 foreach ( $this->mConns as $conns2 ) {
1073                         foreach ( $conns2 as $conns3 ) {
1074                                 foreach ( $conns3 as $conn ) {
1075                                         $mergedParams = array_merge( array( $conn ), $params );
1076                                         call_user_func_array( $callback, $mergedParams );
1077                                 }
1078                         }
1079                 }
1080         }
1081
1082         /**
1083          * Get the hostname and lag time of the most-lagged slave.
1084          * This is useful for maintenance scripts that need to throttle their updates.
1085          * May attempt to open connections to slaves on the default DB. If there is
1086          * no lag, the maximum lag will be reported as -1.
1087          *
1088          * @param bool|string $wiki Wiki ID, or false for the default database
1089          * @return array ( host, max lag, index of max lagged host )
1090          */
1091         function getMaxLag( $wiki = false ) {
1092                 $maxLag = -1;
1093                 $host = '';
1094                 $maxIndex = 0;
1095
1096                 if ( $this->getServerCount() <= 1 ) { // no replication = no lag
1097                         return array( $host, $maxLag, $maxIndex );
1098                 }
1099
1100                 // Try to get the max lag info from the server cache
1101                 $key = 'loadbalancer:maxlag:cluster:' . $this->mServers[0]['host'];
1102                 $cache = ObjectCache::newAccelerator( array(), 'hash' );
1103                 $maxLagInfo = $cache->get( $key ); // (host, lag, index)
1104
1105                 // Fallback to connecting to each slave and getting the lag
1106                 if ( !$maxLagInfo ) {
1107                         foreach ( $this->mServers as $i => $conn ) {
1108                                 if ( $i == $this->getWriterIndex() ) {
1109                                         continue; // nothing to check
1110                                 }
1111                                 $conn = false;
1112                                 if ( $wiki === false ) {
1113                                         $conn = $this->getAnyOpenConnection( $i );
1114                                 }
1115                                 if ( !$conn ) {
1116                                         $conn = $this->openConnection( $i, $wiki );
1117                                 }
1118                                 if ( !$conn ) {
1119                                         continue;
1120                                 }
1121                                 $lag = $conn->getLag();
1122                                 if ( $lag > $maxLag ) {
1123                                         $maxLag = $lag;
1124                                         $host = $this->mServers[$i]['host'];
1125                                         $maxIndex = $i;
1126                                 }
1127                         }
1128                         $maxLagInfo = array( $host, $maxLag, $maxIndex );
1129                         $cache->set( $key, $maxLagInfo, 5 );
1130                 }
1131
1132                 return $maxLagInfo;
1133         }
1134
1135         /**
1136          * Get lag time for each server
1137          * Results are cached for a short time in memcached, and indefinitely in the process cache
1138          *
1139          * @param string|bool $wiki
1140          * @return array Map of (server index => seconds)
1141          */
1142         function getLagTimes( $wiki = false ) {
1143                 # Try process cache
1144                 if ( isset( $this->mLagTimes ) ) {
1145                         return $this->mLagTimes;
1146                 }
1147                 if ( $this->getServerCount() == 1 ) {
1148                         # No replication
1149                         $this->mLagTimes = array( 0 => 0 );
1150                 } else {
1151                         # Send the request to the load monitor
1152                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1153                                 array_keys( $this->mServers ), $wiki );
1154                 }
1155
1156                 return $this->mLagTimes;
1157         }
1158
1159         /**
1160          * Get the lag in seconds for a given connection, or zero if this load
1161          * balancer does not have replication enabled.
1162          *
1163          * This should be used in preference to Database::getLag() in cases where
1164          * replication may not be in use, since there is no way to determine if
1165          * replication is in use at the connection level without running
1166          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1167          * function instead of Database::getLag() avoids a fatal error in this
1168          * case on many installations.
1169          *
1170          * @param DatabaseBase $conn
1171          * @return int
1172          */
1173         function safeGetLag( $conn ) {
1174                 if ( $this->getServerCount() == 1 ) {
1175                         return 0;
1176                 } else {
1177                         return $conn->getLag();
1178                 }
1179         }
1180
1181         /**
1182          * Clear the cache for getLagTimes
1183          */
1184         function clearLagTimeCache() {
1185                 $this->mLagTimes = null;
1186         }
1187 }
1188
1189 /**
1190  * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1191  * as well handling deferring the actual network connection until the handle is used
1192  *
1193  * @ingroup Database
1194  * @since 1.22
1195  */
1196 class DBConnRef implements IDatabase {
1197         /** @var LoadBalancer */
1198         protected $lb;
1199
1200         /** @var DatabaseBase|null */
1201         protected $conn;
1202
1203         /** @var array|null */
1204         protected $params;
1205
1206         /**
1207          * @param LoadBalancer $lb
1208          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1209          */
1210         public function __construct( LoadBalancer $lb, $conn ) {
1211                 $this->lb = $lb;
1212                 if ( $conn instanceof DatabaseBase ) {
1213                         $this->conn = $conn;
1214                 } else {
1215                         $this->params = $conn;
1216                 }
1217         }
1218
1219         public function __call( $name, $arguments ) {
1220                 if ( $this->conn === null ) {
1221                         list( $db, $groups, $wiki ) = $this->params;
1222                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1223                 }
1224
1225                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1226         }
1227
1228         function __destruct() {
1229                 if ( $this->conn !== null ) {
1230                         $this->lb->reuseConnection( $this->conn );
1231                 }
1232         }
1233 }