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         private $mServers, $mConns, $mLoads, $mGroupLoads;
  32
  33         /** @var bool|DatabaseBase Database connection that caused a problem */
  34         private $mErrorConnection;
  35         private $mReadIndex, $mAllowLagged;
  36
  37         /** @var bool|DBMasterPos False if not set */
  38         private $mWaitForPos;
  39
  40         private $mWaitTimeout;
  41         private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  42         private $mParentInfo, $mLagTimes;
  43         private $mLoadMonitorClass, $mLoadMonitor;
  44
  45         /**
  46          * @param array $params with keys:
  47          *   servers           Required. Array of server info structures.
  48          *   masterWaitTimeout Replication lag wait timeout
  49          *   loadMonitor       Name of a class used to fetch server lag and load.
  50          * @throws MWException
  51          */
  52         function __construct( $params ) {
  53                 if ( !isset( $params['servers'] ) ) {
  54                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  55                 }
  56                 $this->mServers = $params['servers'];
  57
  58                 if ( isset( $params['waitTimeout'] ) ) {
  59                         $this->mWaitTimeout = $params['waitTimeout'];
  60                 } else {
  61                         $this->mWaitTimeout = 10;
  62                 }
  63
  64                 $this->mReadIndex = -1;
  65                 $this->mWriteIndex = -1;
  66                 $this->mConns = array(
  67                         'local' => array(),
  68                         'foreignUsed' => array(),
  69                         'foreignFree' => array() );
  70                 $this->mLoads = array();
  71                 $this->mWaitForPos = false;
  72                 $this->mLaggedSlaveMode = false;
  73                 $this->mErrorConnection = false;
  74                 $this->mAllowLagged = false;
  75
  76                 if ( isset( $params['loadMonitor'] ) ) {
  77                         $this->mLoadMonitorClass = $params['loadMonitor'];
  78                 } else {
  79                         $master = reset( $params['servers'] );
  80                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  81                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  82                         } else {
  83                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
  84                         }
  85                 }
  86
  87                 foreach ( $params['servers'] as $i => $server ) {
  88                         $this->mLoads[$i] = $server['load'];
  89                         if ( isset( $server['groupLoads'] ) ) {
  90                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  91                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  92                                                 $this->mGroupLoads[$group] = array();
  93                                         }
  94                                         $this->mGroupLoads[$group][$i] = $ratio;
  95                                 }
  96                         }
  97                 }
  98         }
  99
 100         /**
 101          * Get a LoadMonitor instance
 102          *
 103          * @return LoadMonitor
 104          */
 105         function getLoadMonitor() {
 106                 if ( !isset( $this->mLoadMonitor ) ) {
 107                         $class = $this->mLoadMonitorClass;
 108                         $this->mLoadMonitor = new $class( $this );
 109                 }
 110
 111                 return $this->mLoadMonitor;
 112         }
 113
 114         /**
 115          * Get or set arbitrary data used by the parent object, usually an LBFactory
 116          * @param $x
 117          * @return mixed
 118          */
 119         function parentInfo( $x = null ) {
 120                 return wfSetVar( $this->mParentInfo, $x );
 121         }
 122
 123         /**
 124          * Given an array of non-normalised probabilities, this function will select
 125          * an element and return the appropriate key
 126          *
 127          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 128          *
 129          * @param array $weights
 130          * @return bool|int|string
 131          */
 132         function pickRandom( $weights ) {
 133                 return ArrayUtils::pickRandom( $weights );
 134         }
 135
 136         /**
 137          * @param array $loads
 138          * @param bool|string $wiki Wiki to get non-lagged for
 139          * @return bool|int|string
 140          */
 141         function getRandomNonLagged( $loads, $wiki = false ) {
 142                 # Unset excessively lagged servers
 143                 $lags = $this->getLagTimes( $wiki );
 144                 foreach ( $lags as $i => $lag ) {
 145                         if ( $i != 0 ) {
 146                                 if ( $lag === false ) {
 147                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 148                                         unset( $loads[$i] );
 149                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 150                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 151                                         unset( $loads[$i] );
 152                                 }
 153                         }
 154                 }
 155
 156                 # Find out if all the slaves with non-zero load are lagged
 157                 $sum = 0;
 158                 foreach ( $loads as $load ) {
 159                         $sum += $load;
 160                 }
 161                 if ( $sum == 0 ) {
 162                         # No appropriate DB servers except maybe the master and some slaves with zero load
 163                         # Do NOT use the master
 164                         # Instead, this function will return false, triggering read-only mode,
 165                         # and a lagged slave will be used instead.
 166                         return false;
 167                 }
 168
 169                 if ( count( $loads ) == 0 ) {
 170                         return false;
 171                 }
 172
 173                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 174
 175                 # Return a random representative of the remainder
 176                 return ArrayUtils::pickRandom( $loads );
 177         }
 178
 179         /**
 180          * Get the index of the reader connection, which may be a slave
 181          * This takes into account load ratios and lag times. It should
 182          * always return a consistent index during a given invocation
 183          *
 184          * Side effect: opens connections to databases
 185          * @param bool|string $group
 186          * @param bool|string $wiki
 187          * @throws MWException
 188          * @return bool|int|string
 189          */
 190         function getReaderIndex( $group = false, $wiki = false ) {
 191                 global $wgReadOnly, $wgDBtype;
 192
 193                 # @todo FIXME: For now, only go through all this for mysql databases
 194                 if ( $wgDBtype != 'mysql' ) {
 195                         return $this->getWriterIndex();
 196                 }
 197
 198                 if ( count( $this->mServers ) == 1 ) {
 199                         # Skip the load balancing if there's only one server
 200                         return 0;
 201                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 202                         # Shortcut if generic reader exists already
 203                         return $this->mReadIndex;
 204                 }
 205
 206                 $section = new ProfileSection( __METHOD__ );
 207
 208                 # Find the relevant load array
 209                 if ( $group !== false ) {
 210                         if ( isset( $this->mGroupLoads[$group] ) ) {
 211                                 $nonErrorLoads = $this->mGroupLoads[$group];
 212                         } else {
 213                                 # No loads for this group, return false and the caller can use some other group
 214                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 215
 216                                 return false;
 217                         }
 218                 } else {
 219                         $nonErrorLoads = $this->mLoads;
 220                 }
 221
 222                 if ( !count( $nonErrorLoads ) ) {
 223                         throw new MWException( "Empty server array given to LoadBalancer" );
 224                 }
 225
 226                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 227                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 228
 229                 $laggedSlaveMode = false;
 230
 231                 # No server found yet
 232                 $i = false;
 233                 # First try quickly looking through the available servers for a server that
 234                 # meets our criteria
 235                 $currentLoads = $nonErrorLoads;
 236                 while ( count( $currentLoads ) ) {
 237                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 238                                 $i = ArrayUtils::pickRandom( $currentLoads );
 239                         } else {
 240                                 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 241                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 242                                         # All slaves lagged. Switch to read-only mode
 243                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 244                                         $wgReadOnly = 'The database has been automatically locked ' .
 245                                                 'while the slave database servers catch up to the master';
 246                                         $i = ArrayUtils::pickRandom( $currentLoads );
 247                                         $laggedSlaveMode = true;
 248                                 }
 249                         }
 250
 251                         if ( $i === false ) {
 252                                 # pickRandom() returned false
 253                                 # This is permanent and means the configuration or the load monitor
 254                                 # wants us to return false.
 255                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 256
 257                                 return false;
 258                         }
 259
 260                         wfDebugLog( 'connect', __METHOD__ .
 261                                 ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 262
 263                         $conn = $this->openConnection( $i, $wiki );
 264                         if ( !$conn ) {
 265                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 266                                 unset( $nonErrorLoads[$i] );
 267                                 unset( $currentLoads[$i] );
 268                                 continue;
 269                         }
 270
 271                         // Decrement reference counter, we are finished with this connection.
 272                         // It will be incremented for the caller later.
 273                         if ( $wiki !== false ) {
 274                                 $this->reuseConnection( $conn );
 275                         }
 276
 277                         # Return this server
 278                         break;
 279                 }
 280
 281                 # If all servers were down, quit now
 282                 if ( !count( $nonErrorLoads ) ) {
 283                         wfDebugLog( 'connect', "All servers down\n" );
 284                 }
 285
 286                 if ( $i !== false ) {
 287                         # Slave connection successful
 288                         # Wait for the session master pos for a short time
 289                         if ( $this->mWaitForPos && $i > 0 ) {
 290                                 if ( !$this->doWait( $i ) ) {
 291                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 292                                 }
 293                         }
 294                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group !== false ) {
 295                                 $this->mReadIndex = $i;
 296                         }
 297                 }
 298
 299                 return $i;
 300         }
 301
 302         /**
 303          * Wait for a specified number of microseconds, and return the period waited
 304          * @param int $t
 305          * @return int
 306          */
 307         function sleep( $t ) {
 308                 wfProfileIn( __METHOD__ );
 309                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 310                 usleep( $t );
 311                 wfProfileOut( __METHOD__ );
 312
 313                 return $t;
 314         }
 315
 316         /**
 317          * Set the master wait position
 318          * If a DB_SLAVE connection has been opened already, waits
 319          * Otherwise sets a variable telling it to wait if such a connection is opened
 320          * @param DBMasterPos $pos
 321          */
 322         public function waitFor( $pos ) {
 323                 wfProfileIn( __METHOD__ );
 324                 $this->mWaitForPos = $pos;
 325                 $i = $this->mReadIndex;
 326
 327                 if ( $i > 0 ) {
 328                         if ( !$this->doWait( $i ) ) {
 329                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 330                                 $this->mLaggedSlaveMode = true;
 331                         }
 332                 }
 333                 wfProfileOut( __METHOD__ );
 334         }
 335
 336         /**
 337          * Set the master wait position and wait for ALL slaves to catch up to it
 338          * @param DBMasterPos $pos
 339          */
 340         public function waitForAll( $pos ) {
 341                 wfProfileIn( __METHOD__ );
 342                 $this->mWaitForPos = $pos;
 343                 $serverCount = count( $this->mServers );
 344                 for ( $i = 1; $i < $serverCount; $i++ ) {
 345                         if ( $this->mLoads[$i] > 0 ) {
 346                                 $this->doWait( $i, true );
 347                         }
 348                 }
 349                 wfProfileOut( __METHOD__ );
 350         }
 351
 352         /**
 353          * Get any open connection to a given server index, local or foreign
 354          * Returns false if there is no connection open
 355          *
 356          * @param int $i
 357          * @return DatabaseBase|bool False on failure
 358          */
 359         function getAnyOpenConnection( $i ) {
 360                 foreach ( $this->mConns as $conns ) {
 361                         if ( !empty( $conns[$i] ) ) {
 362                                 return reset( $conns[$i] );
 363                         }
 364                 }
 365
 366                 return false;
 367         }
 368
 369         /**
 370          * Wait for a given slave to catch up to the master pos stored in $this
 371          * @param $index
 372          * @param $open bool
 373          * @return bool
 374          */
 375         protected function doWait( $index, $open = false ) {
 376                 # Find a connection to wait on
 377                 $conn = $this->getAnyOpenConnection( $index );
 378                 if ( !$conn ) {
 379                         if ( !$open ) {
 380                                 wfDebug( __METHOD__ . ": no connection open\n" );
 381
 382                                 return false;
 383                         } else {
 384                                 $conn = $this->openConnection( $index, '' );
 385                                 if ( !$conn ) {
 386                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 387
 388                                         return false;
 389                                 }
 390                         }
 391                 }
 392
 393                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 394                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 395
 396                 if ( $result == -1 || is_null( $result ) ) {
 397                         # Timed out waiting for slave, use master instead
 398                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 399
 400                         return false;
 401                 } else {
 402                         wfDebug( __METHOD__ . ": Done\n" );
 403
 404                         return true;
 405                 }
 406         }
 407
 408         /**
 409          * Get a connection by index
 410          * This is the main entry point for this class.
 411          *
 412          * @param $i Integer: server index
 413          * @param array $groups query groups
 414          * @param bool|string $wiki Wiki ID
 415          *
 416          * @throws MWException
 417          * @return DatabaseBase
 418          */
 419         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 420                 wfProfileIn( __METHOD__ );
 421
 422                 if ( $i == DB_LAST ) {
 423                         wfProfileOut( __METHOD__ );
 424                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 425                                 ' with deprecated server index DB_LAST' );
 426                 } elseif ( $i === null || $i === false ) {
 427                         wfProfileOut( __METHOD__ );
 428                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 429                                 ' with invalid server index' );
 430                 }
 431
 432                 if ( $wiki === wfWikiID() ) {
 433                         $wiki = false;
 434                 }
 435
 436                 # Query groups
 437                 if ( $i == DB_MASTER ) {
 438                         $i = $this->getWriterIndex();
 439                 } elseif ( !is_array( $groups ) ) {
 440                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 441                         if ( $groupIndex !== false ) {
 442                                 $serverName = $this->getServerName( $groupIndex );
 443                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 444                                 $i = $groupIndex;
 445                         }
 446                 } else {
 447                         foreach ( $groups as $group ) {
 448                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 449                                 if ( $groupIndex !== false ) {
 450                                         $serverName = $this->getServerName( $groupIndex );
 451                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 452                                         $i = $groupIndex;
 453                                         break;
 454                                 }
 455                         }
 456                 }
 457
 458                 # Operation-based index
 459                 if ( $i == DB_SLAVE ) {
 460                         $this->mLastError = 'Unknown error'; // reset error string
 461                         $i = $this->getReaderIndex( false, $wiki );
 462                         # Couldn't find a working server in getReaderIndex()?
 463                         if ( $i === false ) {
 464                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 465                                 wfProfileOut( __METHOD__ );
 466
 467                                 return $this->reportConnectionError();
 468                         }
 469                 }
 470
 471                 # Now we have an explicit index into the servers array
 472                 $conn = $this->openConnection( $i, $wiki );
 473                 if ( !$conn ) {
 474                         wfProfileOut( __METHOD__ );
 475
 476                         return $this->reportConnectionError();
 477                 }
 478
 479                 wfProfileOut( __METHOD__ );
 480
 481                 return $conn;
 482         }
 483
 484         /**
 485          * Mark a foreign connection as being available for reuse under a different
 486          * DB name or prefix. This mechanism is reference-counted, and must be called
 487          * the same number of times as getConnection() to work.
 488          *
 489          * @param DatabaseBase $conn
 490          * @throws MWException
 491          */
 492         public function reuseConnection( $conn ) {
 493                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 494                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 495                 $dbName = $conn->getDBname();
 496                 $prefix = $conn->tablePrefix();
 497                 if ( strval( $prefix ) !== '' ) {
 498                         $wiki = "$dbName-$prefix";
 499                 } else {
 500                         $wiki = $dbName;
 501                 }
 502                 if ( $serverIndex === null || $refCount === null ) {
 503                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 504
 505                         /**
 506                          * This can happen in code like:
 507                          *   foreach ( $dbs as $db ) {
 508                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 509                          *     ...
 510                          *     $lb->reuseConnection( $conn );
 511                          *   }
 512                          * When a connection to the local DB is opened in this way, reuseConnection()
 513                          * should be ignored
 514                          */
 515
 516                         return;
 517                 }
 518                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 519                         throw new MWException( __METHOD__ . ": connection not found, has " .
 520                                 "the connection been freed already?" );
 521                 }
 522                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 523                 if ( $refCount <= 0 ) {
 524                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 525                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 526                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 527                 } else {
 528                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 529                 }
 530         }
 531
 532         /**
 533          * Get a database connection handle reference
 534          *
 535          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 536          *
 537          * @see LoadBalancer::getConnection() for parameter information
 538          *
 539          * @param integer $db
 540          * @param mixed $groups
 541          * @param bool|string $wiki
 542          * @return DBConnRef
 543          */
 544         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 545                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 546         }
 547
 548         /**
 549          * Get a database connection handle reference without connecting yet
 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 integer $db
 556          * @param mixed $groups
 557          * @param bool|string $wiki
 558          * @return DBConnRef
 559          */
 560         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 561                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 562         }
 563
 564         /**
 565          * Open a connection to the server given by the specified index
 566          * Index must be an actual index into the array.
 567          * If the server is already open, returns it.
 568          *
 569          * On error, returns false, and the connection which caused the
 570          * error will be available via $this->mErrorConnection.
 571          *
 572          * @param $i Integer server index
 573          * @param bool|string $wiki wiki ID to open
 574          * @return DatabaseBase
 575          *
 576          * @access private
 577          */
 578         function openConnection( $i, $wiki = false ) {
 579                 wfProfileIn( __METHOD__ );
 580                 if ( $wiki !== false ) {
 581                         $conn = $this->openForeignConnection( $i, $wiki );
 582                         wfProfileOut( __METHOD__ );
 583
 584                         return $conn;
 585                 }
 586                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 587                         $conn = $this->mConns['local'][$i][0];
 588                 } else {
 589                         $server = $this->mServers[$i];
 590                         $server['serverIndex'] = $i;
 591                         $conn = $this->reallyOpenConnection( $server, false );
 592                         if ( $conn->isOpen() ) {
 593                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 594                                 $this->mConns['local'][$i][0] = $conn;
 595                         } else {
 596                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 597                                 $this->mErrorConnection = $conn;
 598                                 $conn = false;
 599                         }
 600                 }
 601                 wfProfileOut( __METHOD__ );
 602
 603                 return $conn;
 604         }
 605
 606         /**
 607          * Open a connection to a foreign DB, or return one if it is already open.
 608          *
 609          * Increments a reference count on the returned connection which locks the
 610          * connection to the requested wiki. This reference count can be
 611          * decremented by calling reuseConnection().
 612          *
 613          * If a connection is open to the appropriate server already, but with the wrong
 614          * database, it will be switched to the right database and returned, as long as
 615          * it has been freed first with reuseConnection().
 616          *
 617          * On error, returns false, and the connection which caused the
 618          * error will be available via $this->mErrorConnection.
 619          *
 620          * @param $i Integer: server index
 621          * @param string $wiki wiki ID to open
 622          * @return DatabaseBase
 623          */
 624         function openForeignConnection( $i, $wiki ) {
 625                 wfProfileIn( __METHOD__ );
 626                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 627                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 628                         // Reuse an already-used connection
 629                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 630                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 631                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 632                         // Reuse a free connection for the same wiki
 633                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 634                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 635                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 636                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 637                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 638                         // Reuse a connection from another wiki
 639                         $conn = reset( $this->mConns['foreignFree'][$i] );
 640                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 641
 642                         if ( !$conn->selectDB( $dbName ) ) {
 643                                 $this->mLastError = "Error selecting database $dbName on server " .
 644                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 645                                 $this->mErrorConnection = $conn;
 646                                 $conn = false;
 647                         } else {
 648                                 $conn->tablePrefix( $prefix );
 649                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 650                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 651                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 652                         }
 653                 } else {
 654                         // Open a new connection
 655                         $server = $this->mServers[$i];
 656                         $server['serverIndex'] = $i;
 657                         $server['foreignPoolRefCount'] = 0;
 658                         $server['foreign'] = true;
 659                         $conn = $this->reallyOpenConnection( $server, $dbName );
 660                         if ( !$conn->isOpen() ) {
 661                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 662                                 $this->mErrorConnection = $conn;
 663                                 $conn = false;
 664                         } else {
 665                                 $conn->tablePrefix( $prefix );
 666                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 667                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 668                         }
 669                 }
 670
 671                 // Increment reference count
 672                 if ( $conn ) {
 673                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 674                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 675                 }
 676                 wfProfileOut( __METHOD__ );
 677
 678                 return $conn;
 679         }
 680
 681         /**
 682          * Test if the specified index represents an open connection
 683          *
 684          * @param $index Integer: server index
 685          * @access private
 686          * @return bool
 687          */
 688         function isOpen( $index ) {
 689                 if ( !is_integer( $index ) ) {
 690                         return false;
 691                 }
 692
 693                 return (bool)$this->getAnyOpenConnection( $index );
 694         }
 695
 696         /**
 697          * Really opens a connection. Uncached.
 698          * Returns a Database object whether or not the connection was successful.
 699          * @access private
 700          *
 701          * @param $server
 702          * @param $dbNameOverride bool
 703          * @throws MWException
 704          * @return DatabaseBase
 705          */
 706         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 707                 if ( !is_array( $server ) ) {
 708                         throw new MWException( 'You must update your load-balancing configuration. ' .
 709                                 'See DefaultSettings.php entry for $wgDBservers.' );
 710                 }
 711
 712                 if ( $dbNameOverride !== false ) {
 713                         $server['dbname'] = $dbNameOverride;
 714                 }
 715
 716                 # Create object
 717                 try {
 718                         $db = DatabaseBase::factory( $server['type'], $server );
 719                 } catch ( DBConnectionError $e ) {
 720                         // FIXME: This is probably the ugliest thing I have ever done to
 721                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 722                         $db = $e->db;
 723                 }
 724
 725                 $db->setLBInfo( $server );
 726                 if ( isset( $server['fakeSlaveLag'] ) ) {
 727                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 728                 }
 729                 if ( isset( $server['fakeMaster'] ) ) {
 730                         $db->setFakeMaster( true );
 731                 }
 732
 733                 return $db;
 734         }
 735
 736         /**
 737          * @throws DBConnectionError
 738          * @return bool
 739          */
 740         private function reportConnectionError() {
 741                 $conn = $this->mErrorConnection; // The connection which caused the error
 742
 743                 if ( !is_object( $conn ) ) {
 744                         // No last connection, probably due to all servers being too busy
 745                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 746
 747                         // If all servers were busy, mLastError will contain something sensible
 748                         throw new DBConnectionError( null, $this->mLastError );
 749                 } else {
 750                         $server = $conn->getProperty( 'mServer' );
 751                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 752                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 753                 }
 754
 755                 return false; /* not reached */
 756         }
 757
 758         /**
 759          * @return int
 760          */
 761         function getWriterIndex() {
 762                 return 0;
 763         }
 764
 765         /**
 766          * Returns true if the specified index is a valid server index
 767          *
 768          * @param string $i
 769          * @return bool
 770          */
 771         function haveIndex( $i ) {
 772                 return array_key_exists( $i, $this->mServers );
 773         }
 774
 775         /**
 776          * Returns true if the specified index is valid and has non-zero load
 777          *
 778          * @param string $i
 779          * @return bool
 780          */
 781         function isNonZeroLoad( $i ) {
 782                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 783         }
 784
 785         /**
 786          * Get the number of defined servers (not the number of open connections)
 787          *
 788          * @return int
 789          */
 790         function getServerCount() {
 791                 return count( $this->mServers );
 792         }
 793
 794         /**
 795          * Get the host name or IP address of the server with the specified index
 796          * Prefer a readable name if available.
 797          * @param string $i
 798          * @return string
 799          */
 800         function getServerName( $i ) {
 801                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 802                         return $this->mServers[$i]['hostName'];
 803                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 804                         return $this->mServers[$i]['host'];
 805                 } else {
 806                         return '';
 807                 }
 808         }
 809
 810         /**
 811          * Return the server info structure for a given index, or false if the index is invalid.
 812          * @param $i
 813          * @return bool
 814          */
 815         function getServerInfo( $i ) {
 816                 if ( isset( $this->mServers[$i] ) ) {
 817                         return $this->mServers[$i];
 818                 } else {
 819                         return false;
 820                 }
 821         }
 822
 823         /**
 824          * Sets the server info structure for the given index. Entry at index $i
 825          * is created if it doesn't exist
 826          * @param $i
 827          * @param $serverInfo
 828          */
 829         function setServerInfo( $i, $serverInfo ) {
 830                 $this->mServers[$i] = $serverInfo;
 831         }
 832
 833         /**
 834          * Get the current master position for chronology control purposes
 835          * @return mixed
 836          */
 837         function getMasterPos() {
 838                 # If this entire request was served from a slave without opening a connection to the
 839                 # master (however unlikely that may be), then we can fetch the position from the slave.
 840                 $masterConn = $this->getAnyOpenConnection( 0 );
 841                 if ( !$masterConn ) {
 842                         $serverCount = count( $this->mServers );
 843                         for ( $i = 1; $i < $serverCount; $i++ ) {
 844                                 $conn = $this->getAnyOpenConnection( $i );
 845                                 if ( $conn ) {
 846                                         wfDebug( "Master pos fetched from slave\n" );
 847
 848                                         return $conn->getSlavePos();
 849                                 }
 850                         }
 851                 } else {
 852                         wfDebug( "Master pos fetched from master\n" );
 853
 854                         return $masterConn->getMasterPos();
 855                 }
 856
 857                 return false;
 858         }
 859
 860         /**
 861          * Close all open connections
 862          */
 863         function closeAll() {
 864                 foreach ( $this->mConns as $conns2 ) {
 865                         foreach ( $conns2 as $conns3 ) {
 866                                 /** @var DatabaseBase $conn */
 867                                 foreach ( $conns3 as $conn ) {
 868                                         $conn->close();
 869                                 }
 870                         }
 871                 }
 872                 $this->mConns = array(
 873                         'local' => array(),
 874                         'foreignFree' => array(),
 875                         'foreignUsed' => array(),
 876                 );
 877         }
 878
 879         /**
 880          * Deprecated function, typo in function name
 881          *
 882          * @deprecated in 1.18
 883          * @param DatabaseBase $conn
 884          */
 885         function closeConnecton( $conn ) {
 886                 wfDeprecated( __METHOD__, '1.18' );
 887                 $this->closeConnection( $conn );
 888         }
 889
 890         /**
 891          * Close a connection
 892          * Using this function makes sure the LoadBalancer knows the connection is closed.
 893          * If you use $conn->close() directly, the load balancer won't update its state.
 894          * @param DatabaseBase $conn
 895          */
 896         function closeConnection( $conn ) {
 897                 $done = false;
 898                 foreach ( $this->mConns as $i1 => $conns2 ) {
 899                         foreach ( $conns2 as $i2 => $conns3 ) {
 900                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 901                                         if ( $conn === $candidateConn ) {
 902                                                 $conn->close();
 903                                                 unset( $this->mConns[$i1][$i2][$i3] );
 904                                                 $done = true;
 905                                                 break;
 906                                         }
 907                                 }
 908                         }
 909                 }
 910                 if ( !$done ) {
 911                         $conn->close();
 912                 }
 913         }
 914
 915         /**
 916          * Commit transactions on all open connections
 917          */
 918         function commitAll() {
 919                 foreach ( $this->mConns as $conns2 ) {
 920                         foreach ( $conns2 as $conns3 ) {
 921                                 /** @var DatabaseBase[] $conns3 */
 922                                 foreach ( $conns3 as $conn ) {
 923                                         if ( $conn->trxLevel() ) {
 924                                                 $conn->commit( __METHOD__, 'flush' );
 925                                         }
 926                                 }
 927                         }
 928                 }
 929         }
 930
 931         /**
 932          *  Issue COMMIT only on master, only if queries were done on connection
 933          */
 934         function commitMasterChanges() {
 935                 // Always 0, but who knows.. :)
 936                 $masterIndex = $this->getWriterIndex();
 937                 foreach ( $this->mConns as $conns2 ) {
 938                         if ( empty( $conns2[$masterIndex] ) ) {
 939                                 continue;
 940                         }
 941                         /** @var DatabaseBase $conn */
 942                         foreach ( $conns2[$masterIndex] as $conn ) {
 943                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 944                                         $conn->commit( __METHOD__, 'flush' );
 945                                 }
 946                         }
 947                 }
 948         }
 949
 950         /**
 951          * @param $value null
 952          * @return Mixed
 953          */
 954         function waitTimeout( $value = null ) {
 955                 return wfSetVar( $this->mWaitTimeout, $value );
 956         }
 957
 958         /**
 959          * @return bool
 960          */
 961         function getLaggedSlaveMode() {
 962                 return $this->mLaggedSlaveMode;
 963         }
 964
 965         /**
 966          * Disables/enables lag checks
 967          * @param null|bool $mode
 968          * @return bool
 969          */
 970         function allowLagged( $mode = null ) {
 971                 if ( $mode === null ) {
 972                         return $this->mAllowLagged;
 973                 }
 974                 $this->mAllowLagged = $mode;
 975
 976                 return $this->mAllowLagged;
 977         }
 978
 979         /**
 980          * @return bool
 981          */
 982         function pingAll() {
 983                 $success = true;
 984                 foreach ( $this->mConns as $conns2 ) {
 985                         foreach ( $conns2 as $conns3 ) {
 986                                 /** @var DatabaseBase[] $conns3 */
 987                                 foreach ( $conns3 as $conn ) {
 988                                         if ( !$conn->ping() ) {
 989                                                 $success = false;
 990                                         }
 991                                 }
 992                         }
 993                 }
 994
 995                 return $success;
 996         }
 997
 998         /**
 999          * Call a function with each open connection object
1000          * @param callable $callback
1001          * @param array $params
1002          */
1003         function forEachOpenConnection( $callback, $params = array() ) {
1004                 foreach ( $this->mConns as $conns2 ) {
1005                         foreach ( $conns2 as $conns3 ) {
1006                                 foreach ( $conns3 as $conn ) {
1007                                         $mergedParams = array_merge( array( $conn ), $params );
1008                                         call_user_func_array( $callback, $mergedParams );
1009                                 }
1010                         }
1011                 }
1012         }
1013
1014         /**
1015          * Get the hostname and lag time of the most-lagged slave.
1016          * This is useful for maintenance scripts that need to throttle their updates.
1017          * May attempt to open connections to slaves on the default DB. If there is
1018          * no lag, the maximum lag will be reported as -1.
1019          *
1020          * @param bool|string $wiki Wiki ID, or false for the default database
1021          * @return array ( host, max lag, index of max lagged host )
1022          */
1023         function getMaxLag( $wiki = false ) {
1024                 $maxLag = -1;
1025                 $host = '';
1026                 $maxIndex = 0;
1027                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1028                         foreach ( $this->mServers as $i => $conn ) {
1029                                 $conn = false;
1030                                 if ( $wiki === false ) {
1031                                         $conn = $this->getAnyOpenConnection( $i );
1032                                 }
1033                                 if ( !$conn ) {
1034                                         $conn = $this->openConnection( $i, $wiki );
1035                                 }
1036                                 if ( !$conn ) {
1037                                         continue;
1038                                 }
1039                                 $lag = $conn->getLag();
1040                                 if ( $lag > $maxLag ) {
1041                                         $maxLag = $lag;
1042                                         $host = $this->mServers[$i]['host'];
1043                                         $maxIndex = $i;
1044                                 }
1045                         }
1046                 }
1047
1048                 return array( $host, $maxLag, $maxIndex );
1049         }
1050
1051         /**
1052          * Get lag time for each server
1053          * Results are cached for a short time in memcached, and indefinitely in the process cache
1054          *
1055          * @param string|bool $wiki
1056          * @return array
1057          */
1058         function getLagTimes( $wiki = false ) {
1059                 # Try process cache
1060                 if ( isset( $this->mLagTimes ) ) {
1061                         return $this->mLagTimes;
1062                 }
1063                 if ( $this->getServerCount() == 1 ) {
1064                         # No replication
1065                         $this->mLagTimes = array( 0 => 0 );
1066                 } else {
1067                         # Send the request to the load monitor
1068                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1069                                 array_keys( $this->mServers ), $wiki );
1070                 }
1071
1072                 return $this->mLagTimes;
1073         }
1074
1075         /**
1076          * Get the lag in seconds for a given connection, or zero if this load
1077          * balancer does not have replication enabled.
1078          *
1079          * This should be used in preference to Database::getLag() in cases where
1080          * replication may not be in use, since there is no way to determine if
1081          * replication is in use at the connection level without running
1082          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1083          * function instead of Database::getLag() avoids a fatal error in this
1084          * case on many installations.
1085          *
1086          * @param DatabaseBase $conn
1087          * @return int
1088          */
1089         function safeGetLag( $conn ) {
1090                 if ( $this->getServerCount() == 1 ) {
1091                         return 0;
1092                 } else {
1093                         return $conn->getLag();
1094                 }
1095         }
1096
1097         /**
1098          * Clear the cache for getLagTimes
1099          */
1100         function clearLagTimeCache() {
1101                 $this->mLagTimes = null;
1102         }
1103 }
1104
1105 /**
1106  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1107  * as well handling deferring the actual network connection until the handle is used
1108  *
1109  * @ingroup Database
1110  * @since 1.22
1111  */
1112 class DBConnRef implements IDatabase {
1113         /** @var LoadBalancer */
1114         protected $lb;
1115
1116         /** @var DatabaseBase|null */
1117         protected $conn;
1118
1119         /** @var array|null */
1120         protected $params;
1121
1122         /**
1123          * @param LoadBalancer $lb
1124          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1125          */
1126         public function __construct( LoadBalancer $lb, $conn ) {
1127                 $this->lb = $lb;
1128                 if ( $conn instanceof DatabaseBase ) {
1129                         $this->conn = $conn;
1130                 } else {
1131                         $this->params = $conn;
1132                 }
1133         }
1134
1135         public function __call( $name, $arguments ) {
1136                 if ( $this->conn === null ) {
1137                         list( $db, $groups, $wiki ) = $this->params;
1138                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1139                 }
1140
1141                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1142         }
1143
1144         function __destruct() {
1145                 if ( $this->conn !== null ) {
1146                         $this->lb->reuseConnection( $this->conn );
1147                 }
1148         }
1149 }