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                 # Find a connection to wait on
 398                 $conn = $this->getAnyOpenConnection( $index );
 399                 if ( !$conn ) {
 400                         if ( !$open ) {
 401                                 wfDebug( __METHOD__ . ": no connection open\n" );
 402
 403                                 return false;
 404                         } else {
 405                                 $conn = $this->openConnection( $index, '' );
 406                                 if ( !$conn ) {
 407                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 408
 409                                         return false;
 410                                 }
 411                         }
 412                 }
 413
 414                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 415                 $timeout = $timeout ?: $this->mWaitTimeout;
 416                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 417
 418                 if ( $result == -1 || is_null( $result ) ) {
 419                         # Timed out waiting for slave, use master instead
 420                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 421
 422                         return false;
 423                 } else {
 424                         wfDebug( __METHOD__ . ": Done\n" );
 425
 426                         return true;
 427                 }
 428         }
 429
 430         /**
 431          * Get a connection by index
 432          * This is the main entry point for this class.
 433          *
 434          * @param int $i Server index
 435          * @param array $groups Query groups
 436          * @param bool|string $wiki Wiki ID
 437          *
 438          * @throws MWException
 439          * @return DatabaseBase
 440          */
 441         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 442                 wfProfileIn( __METHOD__ );
 443
 444                 if ( $i === null || $i === false ) {
 445                         wfProfileOut( __METHOD__ );
 446                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 447                                 ' with invalid server index' );
 448                 }
 449
 450                 if ( $wiki === wfWikiID() ) {
 451                         $wiki = false;
 452                 }
 453
 454                 # Query groups
 455                 if ( $i == DB_MASTER ) {
 456                         $i = $this->getWriterIndex();
 457                 } elseif ( !is_array( $groups ) ) {
 458                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 459                         if ( $groupIndex !== false ) {
 460                                 $serverName = $this->getServerName( $groupIndex );
 461                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 462                                 $i = $groupIndex;
 463                         }
 464                 } else {
 465                         foreach ( $groups as $group ) {
 466                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 467                                 if ( $groupIndex !== false ) {
 468                                         $serverName = $this->getServerName( $groupIndex );
 469                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 470                                         $i = $groupIndex;
 471                                         break;
 472                                 }
 473                         }
 474                 }
 475
 476                 # Operation-based index
 477                 if ( $i == DB_SLAVE ) {
 478                         $this->mLastError = 'Unknown error'; // reset error string
 479                         $i = $this->getReaderIndex( false, $wiki );
 480                         # Couldn't find a working server in getReaderIndex()?
 481                         if ( $i === false ) {
 482                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 483                                 wfProfileOut( __METHOD__ );
 484
 485                                 return $this->reportConnectionError();
 486                         }
 487                 }
 488
 489                 # Now we have an explicit index into the servers array
 490                 $conn = $this->openConnection( $i, $wiki );
 491                 if ( !$conn ) {
 492                         wfProfileOut( __METHOD__ );
 493
 494                         return $this->reportConnectionError();
 495                 }
 496
 497                 wfProfileOut( __METHOD__ );
 498
 499                 return $conn;
 500         }
 501
 502         /**
 503          * Mark a foreign connection as being available for reuse under a different
 504          * DB name or prefix. This mechanism is reference-counted, and must be called
 505          * the same number of times as getConnection() to work.
 506          *
 507          * @param DatabaseBase $conn
 508          * @throws MWException
 509          */
 510         public function reuseConnection( $conn ) {
 511                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 512                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 513                 if ( $serverIndex === null || $refCount === null ) {
 514                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 515
 516                         /**
 517                          * This can happen in code like:
 518                          *   foreach ( $dbs as $db ) {
 519                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 520                          *     ...
 521                          *     $lb->reuseConnection( $conn );
 522                          *   }
 523                          * When a connection to the local DB is opened in this way, reuseConnection()
 524                          * should be ignored
 525                          */
 526
 527                         return;
 528                 }
 529
 530                 $dbName = $conn->getDBname();
 531                 $prefix = $conn->tablePrefix();
 532                 if ( strval( $prefix ) !== '' ) {
 533                         $wiki = "$dbName-$prefix";
 534                 } else {
 535                         $wiki = $dbName;
 536                 }
 537                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 538                         throw new MWException( __METHOD__ . ": connection not found, has " .
 539                                 "the connection been freed already?" );
 540                 }
 541                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 542                 if ( $refCount <= 0 ) {
 543                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 544                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 545                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 546                 } else {
 547                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 548                 }
 549         }
 550
 551         /**
 552          * Get a database connection handle reference
 553          *
 554          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 555          *
 556          * @see LoadBalancer::getConnection() for parameter information
 557          *
 558          * @param int $db
 559          * @param mixed $groups
 560          * @param bool|string $wiki
 561          * @return DBConnRef
 562          */
 563         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 564                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 565         }
 566
 567         /**
 568          * Get a database connection handle reference without connecting yet
 569          *
 570          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 571          *
 572          * @see LoadBalancer::getConnection() for parameter information
 573          *
 574          * @param int $db
 575          * @param mixed $groups
 576          * @param bool|string $wiki
 577          * @return DBConnRef
 578          */
 579         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 580                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 581         }
 582
 583         /**
 584          * Open a connection to the server given by the specified index
 585          * Index must be an actual index into the array.
 586          * If the server is already open, returns it.
 587          *
 588          * On error, returns false, and the connection which caused the
 589          * error will be available via $this->mErrorConnection.
 590          *
 591          * @param int $i Server index
 592          * @param bool|string $wiki Wiki ID to open
 593          * @return DatabaseBase
 594          *
 595          * @access private
 596          */
 597         function openConnection( $i, $wiki = false ) {
 598                 wfProfileIn( __METHOD__ );
 599                 if ( $wiki !== false ) {
 600                         $conn = $this->openForeignConnection( $i, $wiki );
 601                         wfProfileOut( __METHOD__ );
 602
 603                         return $conn;
 604                 }
 605                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 606                         $conn = $this->mConns['local'][$i][0];
 607                 } else {
 608                         $server = $this->mServers[$i];
 609                         $server['serverIndex'] = $i;
 610                         $conn = $this->reallyOpenConnection( $server, false );
 611                         if ( $conn->isOpen() ) {
 612                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 613                                 $this->mConns['local'][$i][0] = $conn;
 614                         } else {
 615                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 616                                 $this->mErrorConnection = $conn;
 617                                 $conn = false;
 618                         }
 619                 }
 620                 wfProfileOut( __METHOD__ );
 621
 622                 return $conn;
 623         }
 624
 625         /**
 626          * Open a connection to a foreign DB, or return one if it is already open.
 627          *
 628          * Increments a reference count on the returned connection which locks the
 629          * connection to the requested wiki. This reference count can be
 630          * decremented by calling reuseConnection().
 631          *
 632          * If a connection is open to the appropriate server already, but with the wrong
 633          * database, it will be switched to the right database and returned, as long as
 634          * it has been freed first with reuseConnection().
 635          *
 636          * On error, returns false, and the connection which caused the
 637          * error will be available via $this->mErrorConnection.
 638          *
 639          * @param int $i Server index
 640          * @param string $wiki Wiki ID to open
 641          * @return DatabaseBase
 642          */
 643         function openForeignConnection( $i, $wiki ) {
 644                 wfProfileIn( __METHOD__ );
 645                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 646                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 647                         // Reuse an already-used connection
 648                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 649                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 650                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 651                         // Reuse a free connection for the same wiki
 652                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 653                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 654                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 655                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 656                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 657                         // Reuse a connection from another wiki
 658                         $conn = reset( $this->mConns['foreignFree'][$i] );
 659                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 660
 661                         if ( !$conn->selectDB( $dbName ) ) {
 662                                 $this->mLastError = "Error selecting database $dbName on server " .
 663                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 664                                 $this->mErrorConnection = $conn;
 665                                 $conn = false;
 666                         } else {
 667                                 $conn->tablePrefix( $prefix );
 668                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 669                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 670                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 671                         }
 672                 } else {
 673                         // Open a new connection
 674                         $server = $this->mServers[$i];
 675                         $server['serverIndex'] = $i;
 676                         $server['foreignPoolRefCount'] = 0;
 677                         $server['foreign'] = true;
 678                         $conn = $this->reallyOpenConnection( $server, $dbName );
 679                         if ( !$conn->isOpen() ) {
 680                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 681                                 $this->mErrorConnection = $conn;
 682                                 $conn = false;
 683                         } else {
 684                                 $conn->tablePrefix( $prefix );
 685                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 686                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 687                         }
 688                 }
 689
 690                 // Increment reference count
 691                 if ( $conn ) {
 692                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 693                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 694                 }
 695                 wfProfileOut( __METHOD__ );
 696
 697                 return $conn;
 698         }
 699
 700         /**
 701          * Test if the specified index represents an open connection
 702          *
 703          * @param int $index Server index
 704          * @access private
 705          * @return bool
 706          */
 707         function isOpen( $index ) {
 708                 if ( !is_integer( $index ) ) {
 709                         return false;
 710                 }
 711
 712                 return (bool)$this->getAnyOpenConnection( $index );
 713         }
 714
 715         /**
 716          * Really opens a connection. Uncached.
 717          * Returns a Database object whether or not the connection was successful.
 718          * @access private
 719          *
 720          * @param array $server
 721          * @param bool $dbNameOverride
 722          * @throws MWException
 723          * @return DatabaseBase
 724          */
 725         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 726                 if ( !is_array( $server ) ) {
 727                         throw new MWException( 'You must update your load-balancing configuration. ' .
 728                                 'See DefaultSettings.php entry for $wgDBservers.' );
 729                 }
 730
 731                 if ( $dbNameOverride !== false ) {
 732                         $server['dbname'] = $dbNameOverride;
 733                 }
 734
 735                 # Create object
 736                 try {
 737                         $db = DatabaseBase::factory( $server['type'], $server );
 738                 } catch ( DBConnectionError $e ) {
 739                         // FIXME: This is probably the ugliest thing I have ever done to
 740                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 741                         $db = $e->db;
 742                 }
 743
 744                 $db->setLBInfo( $server );
 745                 if ( isset( $server['fakeSlaveLag'] ) ) {
 746                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 747                 }
 748                 if ( isset( $server['fakeMaster'] ) ) {
 749                         $db->setFakeMaster( true );
 750                 }
 751
 752                 return $db;
 753         }
 754
 755         /**
 756          * @throws DBConnectionError
 757          * @return bool
 758          */
 759         private function reportConnectionError() {
 760                 $conn = $this->mErrorConnection; // The connection which caused the error
 761
 762                 if ( !is_object( $conn ) ) {
 763                         // No last connection, probably due to all servers being too busy
 764                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}" );
 765
 766                         // If all servers were busy, mLastError will contain something sensible
 767                         throw new DBConnectionError( null, $this->mLastError );
 768                 } else {
 769                         $server = $conn->getProperty( 'mServer' );
 770                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})" );
 771                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 772                 }
 773
 774                 return false; /* not reached */
 775         }
 776
 777         /**
 778          * @return int
 779          */
 780         function getWriterIndex() {
 781                 return 0;
 782         }
 783
 784         /**
 785          * Returns true if the specified index is a valid server index
 786          *
 787          * @param string $i
 788          * @return bool
 789          */
 790         function haveIndex( $i ) {
 791                 return array_key_exists( $i, $this->mServers );
 792         }
 793
 794         /**
 795          * Returns true if the specified index is valid and has non-zero load
 796          *
 797          * @param string $i
 798          * @return bool
 799          */
 800         function isNonZeroLoad( $i ) {
 801                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 802         }
 803
 804         /**
 805          * Get the number of defined servers (not the number of open connections)
 806          *
 807          * @return int
 808          */
 809         function getServerCount() {
 810                 return count( $this->mServers );
 811         }
 812
 813         /**
 814          * Get the host name or IP address of the server with the specified index
 815          * Prefer a readable name if available.
 816          * @param string $i
 817          * @return string
 818          */
 819         function getServerName( $i ) {
 820                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 821                         return $this->mServers[$i]['hostName'];
 822                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 823                         return $this->mServers[$i]['host'];
 824                 } else {
 825                         return '';
 826                 }
 827         }
 828
 829         /**
 830          * Return the server info structure for a given index, or false if the index is invalid.
 831          * @param int $i
 832          * @return array|bool
 833          */
 834         function getServerInfo( $i ) {
 835                 if ( isset( $this->mServers[$i] ) ) {
 836                         return $this->mServers[$i];
 837                 } else {
 838                         return false;
 839                 }
 840         }
 841
 842         /**
 843          * Sets the server info structure for the given index. Entry at index $i
 844          * is created if it doesn't exist
 845          * @param int $i
 846          * @param array $serverInfo
 847          */
 848         function setServerInfo( $i, $serverInfo ) {
 849                 $this->mServers[$i] = $serverInfo;
 850         }
 851
 852         /**
 853          * Get the current master position for chronology control purposes
 854          * @return mixed
 855          */
 856         function getMasterPos() {
 857                 # If this entire request was served from a slave without opening a connection to the
 858                 # master (however unlikely that may be), then we can fetch the position from the slave.
 859                 $masterConn = $this->getAnyOpenConnection( 0 );
 860                 if ( !$masterConn ) {
 861                         $serverCount = count( $this->mServers );
 862                         for ( $i = 1; $i < $serverCount; $i++ ) {
 863                                 $conn = $this->getAnyOpenConnection( $i );
 864                                 if ( $conn ) {
 865                                         wfDebug( "Master pos fetched from slave\n" );
 866
 867                                         return $conn->getSlavePos();
 868                                 }
 869                         }
 870                 } else {
 871                         wfDebug( "Master pos fetched from master\n" );
 872
 873                         return $masterConn->getMasterPos();
 874                 }
 875
 876                 return false;
 877         }
 878
 879         /**
 880          * Close all open connections
 881          */
 882         function closeAll() {
 883                 foreach ( $this->mConns as $conns2 ) {
 884                         foreach ( $conns2 as $conns3 ) {
 885                                 /** @var DatabaseBase $conn */
 886                                 foreach ( $conns3 as $conn ) {
 887                                         $conn->close();
 888                                 }
 889                         }
 890                 }
 891                 $this->mConns = array(
 892                         'local' => array(),
 893                         'foreignFree' => array(),
 894                         'foreignUsed' => array(),
 895                 );
 896         }
 897
 898         /**
 899          * Close a connection
 900          * Using this function makes sure the LoadBalancer knows the connection is closed.
 901          * If you use $conn->close() directly, the load balancer won't update its state.
 902          * @param DatabaseBase $conn
 903          */
 904         function closeConnection( $conn ) {
 905                 $done = false;
 906                 foreach ( $this->mConns as $i1 => $conns2 ) {
 907                         foreach ( $conns2 as $i2 => $conns3 ) {
 908                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 909                                         if ( $conn === $candidateConn ) {
 910                                                 $conn->close();
 911                                                 unset( $this->mConns[$i1][$i2][$i3] );
 912                                                 $done = true;
 913                                                 break;
 914                                         }
 915                                 }
 916                         }
 917                 }
 918                 if ( !$done ) {
 919                         $conn->close();
 920                 }
 921         }
 922
 923         /**
 924          * Commit transactions on all open connections
 925          */
 926         function commitAll() {
 927                 foreach ( $this->mConns as $conns2 ) {
 928                         foreach ( $conns2 as $conns3 ) {
 929                                 /** @var DatabaseBase[] $conns3 */
 930                                 foreach ( $conns3 as $conn ) {
 931                                         if ( $conn->trxLevel() ) {
 932                                                 $conn->commit( __METHOD__, 'flush' );
 933                                         }
 934                                 }
 935                         }
 936                 }
 937         }
 938
 939         /**
 940          *  Issue COMMIT only on master, only if queries were done on connection
 941          */
 942         function commitMasterChanges() {
 943                 // Always 0, but who knows.. :)
 944                 $masterIndex = $this->getWriterIndex();
 945                 foreach ( $this->mConns as $conns2 ) {
 946                         if ( empty( $conns2[$masterIndex] ) ) {
 947                                 continue;
 948                         }
 949                         /** @var DatabaseBase $conn */
 950                         foreach ( $conns2[$masterIndex] as $conn ) {
 951                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 952                                         $conn->commit( __METHOD__, 'flush' );
 953                                 }
 954                         }
 955                 }
 956         }
 957
 958         /**
 959          * Issue ROLLBACK only on master, only if queries were done on connection
 960          * @since 1.23
 961          */
 962         function rollbackMasterChanges() {
 963                 // Always 0, but who knows.. :)
 964                 $masterIndex = $this->getWriterIndex();
 965                 foreach ( $this->mConns as $conns2 ) {
 966                         if ( empty( $conns2[$masterIndex] ) ) {
 967                                 continue;
 968                         }
 969                         /** @var DatabaseBase $conn */
 970                         foreach ( $conns2[$masterIndex] as $conn ) {
 971                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 972                                         $conn->rollback( __METHOD__, 'flush' );
 973                                 }
 974                         }
 975                 }
 976         }
 977
 978         /**
 979          * @return bool Whether a master connection is already open
 980          * @since 1.24
 981          */
 982         function hasMasterConnection() {
 983                 return $this->isOpen( $this->getWriterIndex() );
 984         }
 985
 986         /**
 987          * Determine if there are any pending changes that need to be rolled back
 988          * or committed.
 989          * @since 1.23
 990          * @return bool
 991          */
 992         function hasMasterChanges() {
 993                 // Always 0, but who knows.. :)
 994                 $masterIndex = $this->getWriterIndex();
 995                 foreach ( $this->mConns as $conns2 ) {
 996                         if ( empty( $conns2[$masterIndex] ) ) {
 997                                 continue;
 998                         }
 999                         /** @var DatabaseBase $conn */
1000                         foreach ( $conns2[$masterIndex] as $conn ) {
1001                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1002                                         return true;
1003                                 }
1004                         }
1005                 }
1006                 return false;
1007         }
1008
1009         /**
1010          * @param mixed $value
1011          * @return mixed
1012          */
1013         function waitTimeout( $value = null ) {
1014                 return wfSetVar( $this->mWaitTimeout, $value );
1015         }
1016
1017         /**
1018          * @return bool
1019          */
1020         function getLaggedSlaveMode() {
1021                 return $this->mLaggedSlaveMode;
1022         }
1023
1024         /**
1025          * Disables/enables lag checks
1026          * @param null|bool $mode
1027          * @return bool
1028          */
1029         function allowLagged( $mode = null ) {
1030                 if ( $mode === null ) {
1031                         return $this->mAllowLagged;
1032                 }
1033                 $this->mAllowLagged = $mode;
1034
1035                 return $this->mAllowLagged;
1036         }
1037
1038         /**
1039          * @return bool
1040          */
1041         function pingAll() {
1042                 $success = true;
1043                 foreach ( $this->mConns as $conns2 ) {
1044                         foreach ( $conns2 as $conns3 ) {
1045                                 /** @var DatabaseBase[] $conns3 */
1046                                 foreach ( $conns3 as $conn ) {
1047                                         if ( !$conn->ping() ) {
1048                                                 $success = false;
1049                                         }
1050                                 }
1051                         }
1052                 }
1053
1054                 return $success;
1055         }
1056
1057         /**
1058          * Call a function with each open connection object
1059          * @param callable $callback
1060          * @param array $params
1061          */
1062         function forEachOpenConnection( $callback, $params = array() ) {
1063                 foreach ( $this->mConns as $conns2 ) {
1064                         foreach ( $conns2 as $conns3 ) {
1065                                 foreach ( $conns3 as $conn ) {
1066                                         $mergedParams = array_merge( array( $conn ), $params );
1067                                         call_user_func_array( $callback, $mergedParams );
1068                                 }
1069                         }
1070                 }
1071         }
1072
1073         /**
1074          * Get the hostname and lag time of the most-lagged slave.
1075          * This is useful for maintenance scripts that need to throttle their updates.
1076          * May attempt to open connections to slaves on the default DB. If there is
1077          * no lag, the maximum lag will be reported as -1.
1078          *
1079          * @param bool|string $wiki Wiki ID, or false for the default database
1080          * @return array ( host, max lag, index of max lagged host )
1081          */
1082         function getMaxLag( $wiki = false ) {
1083                 $maxLag = -1;
1084                 $host = '';
1085                 $maxIndex = 0;
1086
1087                 if ( $this->getServerCount() <= 1 ) { // no replication = no lag
1088                         return array( $host, $maxLag, $maxIndex );
1089                 }
1090
1091                 // Try to get the max lag info from the server cache
1092                 $key = 'loadbalancer:maxlag:cluster:' . $this->mServers[0]['host'];
1093                 $cache = ObjectCache::newAccelerator( array(), 'hash' );
1094                 $maxLagInfo = $cache->get( $key ); // (host, lag, index)
1095
1096                 // Fallback to connecting to each slave and getting the lag
1097                 if ( !$maxLagInfo ) {
1098                         foreach ( $this->mServers as $i => $conn ) {
1099                                 if ( $i == $this->getWriterIndex() ) {
1100                                         continue; // nothing to check
1101                                 }
1102                                 $conn = false;
1103                                 if ( $wiki === false ) {
1104                                         $conn = $this->getAnyOpenConnection( $i );
1105                                 }
1106                                 if ( !$conn ) {
1107                                         $conn = $this->openConnection( $i, $wiki );
1108                                 }
1109                                 if ( !$conn ) {
1110                                         continue;
1111                                 }
1112                                 $lag = $conn->getLag();
1113                                 if ( $lag > $maxLag ) {
1114                                         $maxLag = $lag;
1115                                         $host = $this->mServers[$i]['host'];
1116                                         $maxIndex = $i;
1117                                 }
1118                         }
1119                         $maxLagInfo = array( $host, $maxLag, $maxIndex );
1120                         $cache->set( $key, $maxLagInfo, 5 );
1121                 }
1122
1123                 return $maxLagInfo;
1124         }
1125
1126         /**
1127          * Get lag time for each server
1128          * Results are cached for a short time in memcached, and indefinitely in the process cache
1129          *
1130          * @param string|bool $wiki
1131          * @return array
1132          */
1133         function getLagTimes( $wiki = false ) {
1134                 # Try process cache
1135                 if ( isset( $this->mLagTimes ) ) {
1136                         return $this->mLagTimes;
1137                 }
1138                 if ( $this->getServerCount() == 1 ) {
1139                         # No replication
1140                         $this->mLagTimes = array( 0 => 0 );
1141                 } else {
1142                         # Send the request to the load monitor
1143                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1144                                 array_keys( $this->mServers ), $wiki );
1145                 }
1146
1147                 return $this->mLagTimes;
1148         }
1149
1150         /**
1151          * Get the lag in seconds for a given connection, or zero if this load
1152          * balancer does not have replication enabled.
1153          *
1154          * This should be used in preference to Database::getLag() in cases where
1155          * replication may not be in use, since there is no way to determine if
1156          * replication is in use at the connection level without running
1157          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1158          * function instead of Database::getLag() avoids a fatal error in this
1159          * case on many installations.
1160          *
1161          * @param DatabaseBase $conn
1162          * @return int
1163          */
1164         function safeGetLag( $conn ) {
1165                 if ( $this->getServerCount() == 1 ) {
1166                         return 0;
1167                 } else {
1168                         return $conn->getLag();
1169                 }
1170         }
1171
1172         /**
1173          * Clear the cache for getLagTimes
1174          */
1175         function clearLagTimeCache() {
1176                 $this->mLagTimes = null;
1177         }
1178 }
1179
1180 /**
1181  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1182  * as well handling deferring the actual network connection until the handle is used
1183  *
1184  * @ingroup Database
1185  * @since 1.22
1186  */
1187 class DBConnRef implements IDatabase {
1188         /** @var LoadBalancer */
1189         protected $lb;
1190
1191         /** @var DatabaseBase|null */
1192         protected $conn;
1193
1194         /** @var array|null */
1195         protected $params;
1196
1197         /**
1198          * @param LoadBalancer $lb
1199          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1200          */
1201         public function __construct( LoadBalancer $lb, $conn ) {
1202                 $this->lb = $lb;
1203                 if ( $conn instanceof DatabaseBase ) {
1204                         $this->conn = $conn;
1205                 } else {
1206                         $this->params = $conn;
1207                 }
1208         }
1209
1210         public function __call( $name, $arguments ) {
1211                 if ( $this->conn === null ) {
1212                         list( $db, $groups, $wiki ) = $this->params;
1213                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1214                 }
1215
1216                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1217         }
1218
1219         function __destruct() {
1220                 if ( $this->conn !== null ) {
1221                         $this->lb->reuseConnection( $this->conn );
1222                 }
1223         }
1224 }