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