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                 wfProfileIn( __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                                 wfProfileOut( __METHOD__ );
 216
 217                                 return false;
 218                         }
 219                 } else {
 220                         $nonErrorLoads = $this->mLoads;
 221                 }
 222
 223                 if ( !count( $nonErrorLoads ) ) {
 224                         wfProfileOut( __METHOD__ );
 225                         throw new MWException( "Empty server array given to LoadBalancer" );
 226                 }
 227
 228                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 229                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 230
 231                 $laggedSlaveMode = false;
 232
 233                 # No server found yet
 234                 $i = false;
 235                 # First try quickly looking through the available servers for a server that
 236                 # meets our criteria
 237                 $currentLoads = $nonErrorLoads;
 238                 while ( count( $currentLoads ) ) {
 239                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 240                                 $i = ArrayUtils::pickRandom( $currentLoads );
 241                         } else {
 242                                 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 243                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 244                                         # All slaves lagged. Switch to read-only mode
 245                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 246                                         $wgReadOnly = 'The database has been automatically locked ' .
 247                                                 'while the slave database servers catch up to the master';
 248                                         $i = ArrayUtils::pickRandom( $currentLoads );
 249                                         $laggedSlaveMode = true;
 250                                 }
 251                         }
 252
 253                         if ( $i === false ) {
 254                                 # pickRandom() returned false
 255                                 # This is permanent and means the configuration or the load monitor
 256                                 # wants us to return false.
 257                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 258                                 wfProfileOut( __METHOD__ );
 259
 260                                 return false;
 261                         }
 262
 263                         wfDebugLog( 'connect', __METHOD__ .
 264                                 ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 265
 266                         $conn = $this->openConnection( $i, $wiki );
 267                         if ( !$conn ) {
 268                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 269                                 unset( $nonErrorLoads[$i] );
 270                                 unset( $currentLoads[$i] );
 271                                 continue;
 272                         }
 273
 274                         // Decrement reference counter, we are finished with this connection.
 275                         // It will be incremented for the caller later.
 276                         if ( $wiki !== false ) {
 277                                 $this->reuseConnection( $conn );
 278                         }
 279
 280                         # Return this server
 281                         break;
 282                 }
 283
 284                 # If all servers were down, quit now
 285                 if ( !count( $nonErrorLoads ) ) {
 286                         wfDebugLog( 'connect', "All servers down\n" );
 287                 }
 288
 289                 if ( $i !== false ) {
 290                         # Slave connection successful
 291                         # Wait for the session master pos for a short time
 292                         if ( $this->mWaitForPos && $i > 0 ) {
 293                                 if ( !$this->doWait( $i ) ) {
 294                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 295                                 }
 296                         }
 297                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
 298                                 $this->mReadIndex = $i;
 299                         }
 300                 }
 301                 wfProfileOut( __METHOD__ );
 302
 303                 return $i;
 304         }
 305
 306         /**
 307          * Wait for a specified number of microseconds, and return the period waited
 308          * @param int $t
 309          * @return int
 310          */
 311         function sleep( $t ) {
 312                 wfProfileIn( __METHOD__ );
 313                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 314                 usleep( $t );
 315                 wfProfileOut( __METHOD__ );
 316
 317                 return $t;
 318         }
 319
 320         /**
 321          * Set the master wait position
 322          * If a DB_SLAVE connection has been opened already, waits
 323          * Otherwise sets a variable telling it to wait if such a connection is opened
 324          * @param DBMasterPos $pos
 325          */
 326         public function waitFor( $pos ) {
 327                 wfProfileIn( __METHOD__ );
 328                 $this->mWaitForPos = $pos;
 329                 $i = $this->mReadIndex;
 330
 331                 if ( $i > 0 ) {
 332                         if ( !$this->doWait( $i ) ) {
 333                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 334                                 $this->mLaggedSlaveMode = true;
 335                         }
 336                 }
 337                 wfProfileOut( __METHOD__ );
 338         }
 339
 340         /**
 341          * Set the master wait position and wait for ALL slaves to catch up to it
 342          * @param DBMasterPos $pos
 343          */
 344         public function waitForAll( $pos ) {
 345                 wfProfileIn( __METHOD__ );
 346                 $this->mWaitForPos = $pos;
 347                 $serverCount = count( $this->mServers );
 348                 for ( $i = 1; $i < $serverCount; $i++ ) {
 349                         if ( $this->mLoads[$i] > 0 ) {
 350                                 $this->doWait( $i, true );
 351                         }
 352                 }
 353                 wfProfileOut( __METHOD__ );
 354         }
 355
 356         /**
 357          * Get any open connection to a given server index, local or foreign
 358          * Returns false if there is no connection open
 359          *
 360          * @param int $i
 361          * @return DatabaseBase|bool False on failure
 362          */
 363         function getAnyOpenConnection( $i ) {
 364                 foreach ( $this->mConns as $conns ) {
 365                         if ( !empty( $conns[$i] ) ) {
 366                                 return reset( $conns[$i] );
 367                         }
 368                 }
 369
 370                 return false;
 371         }
 372
 373         /**
 374          * Wait for a given slave to catch up to the master pos stored in $this
 375          * @param $index
 376          * @param $open bool
 377          * @return bool
 378          */
 379         protected function doWait( $index, $open = false ) {
 380                 # Find a connection to wait on
 381                 $conn = $this->getAnyOpenConnection( $index );
 382                 if ( !$conn ) {
 383                         if ( !$open ) {
 384                                 wfDebug( __METHOD__ . ": no connection open\n" );
 385
 386                                 return false;
 387                         } else {
 388                                 $conn = $this->openConnection( $index, '' );
 389                                 if ( !$conn ) {
 390                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 391
 392                                         return false;
 393                                 }
 394                         }
 395                 }
 396
 397                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 398                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 399
 400                 if ( $result == -1 || is_null( $result ) ) {
 401                         # Timed out waiting for slave, use master instead
 402                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 403
 404                         return false;
 405                 } else {
 406                         wfDebug( __METHOD__ . ": Done\n" );
 407
 408                         return true;
 409                 }
 410         }
 411
 412         /**
 413          * Get a connection by index
 414          * This is the main entry point for this class.
 415          *
 416          * @param $i Integer: server index
 417          * @param array $groups query groups
 418          * @param bool|string $wiki Wiki ID
 419          *
 420          * @throws MWException
 421          * @return DatabaseBase
 422          */
 423         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 424                 wfProfileIn( __METHOD__ );
 425
 426                 if ( $i == DB_LAST ) {
 427                         wfProfileOut( __METHOD__ );
 428                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 429                                 ' with deprecated server index DB_LAST' );
 430                 } elseif ( $i === null || $i === false ) {
 431                         wfProfileOut( __METHOD__ );
 432                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 433                                 ' with invalid server index' );
 434                 }
 435
 436                 if ( $wiki === wfWikiID() ) {
 437                         $wiki = false;
 438                 }
 439
 440                 # Query groups
 441                 if ( $i == DB_MASTER ) {
 442                         $i = $this->getWriterIndex();
 443                 } elseif ( !is_array( $groups ) ) {
 444                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 445                         if ( $groupIndex !== false ) {
 446                                 $serverName = $this->getServerName( $groupIndex );
 447                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 448                                 $i = $groupIndex;
 449                         }
 450                 } else {
 451                         foreach ( $groups as $group ) {
 452                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 453                                 if ( $groupIndex !== false ) {
 454                                         $serverName = $this->getServerName( $groupIndex );
 455                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 456                                         $i = $groupIndex;
 457                                         break;
 458                                 }
 459                         }
 460                 }
 461
 462                 # Operation-based index
 463                 if ( $i == DB_SLAVE ) {
 464                         $this->mLastError = 'Unknown error'; // reset error string
 465                         $i = $this->getReaderIndex( false, $wiki );
 466                         # Couldn't find a working server in getReaderIndex()?
 467                         if ( $i === false ) {
 468                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 469                                 wfProfileOut( __METHOD__ );
 470
 471                                 return $this->reportConnectionError();
 472                         }
 473                 }
 474
 475                 # Now we have an explicit index into the servers array
 476                 $conn = $this->openConnection( $i, $wiki );
 477                 if ( !$conn ) {
 478                         wfProfileOut( __METHOD__ );
 479
 480                         return $this->reportConnectionError();
 481                 }
 482
 483                 wfProfileOut( __METHOD__ );
 484
 485                 return $conn;
 486         }
 487
 488         /**
 489          * Mark a foreign connection as being available for reuse under a different
 490          * DB name or prefix. This mechanism is reference-counted, and must be called
 491          * the same number of times as getConnection() to work.
 492          *
 493          * @param DatabaseBase $conn
 494          * @throws MWException
 495          */
 496         public function reuseConnection( $conn ) {
 497                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 498                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 499                 $dbName = $conn->getDBname();
 500                 $prefix = $conn->tablePrefix();
 501                 if ( strval( $prefix ) !== '' ) {
 502                         $wiki = "$dbName-$prefix";
 503                 } else {
 504                         $wiki = $dbName;
 505                 }
 506                 if ( $serverIndex === null || $refCount === null ) {
 507                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 508
 509                         /**
 510                          * This can happen in code like:
 511                          *   foreach ( $dbs as $db ) {
 512                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 513                          *     ...
 514                          *     $lb->reuseConnection( $conn );
 515                          *   }
 516                          * When a connection to the local DB is opened in this way, reuseConnection()
 517                          * should be ignored
 518                          */
 519
 520                         return;
 521                 }
 522                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 523                         throw new MWException( __METHOD__ . ": connection not found, has " .
 524                                 "the connection been freed already?" );
 525                 }
 526                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 527                 if ( $refCount <= 0 ) {
 528                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 529                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 530                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 531                 } else {
 532                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 533                 }
 534         }
 535
 536         /**
 537          * Get a database connection handle reference
 538          *
 539          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 540          *
 541          * @see LoadBalancer::getConnection() for parameter information
 542          *
 543          * @param integer $db
 544          * @param mixed $groups
 545          * @param bool|string $wiki
 546          * @return DBConnRef
 547          */
 548         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 549                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 550         }
 551
 552         /**
 553          * Get a database connection handle reference without connecting yet
 554          *
 555          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 556          *
 557          * @see LoadBalancer::getConnection() for parameter information
 558          *
 559          * @param integer $db
 560          * @param mixed $groups
 561          * @param bool|string $wiki
 562          * @return DBConnRef
 563          */
 564         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 565                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 566         }
 567
 568         /**
 569          * Open a connection to the server given by the specified index
 570          * Index must be an actual index into the array.
 571          * If the server is already open, returns it.
 572          *
 573          * On error, returns false, and the connection which caused the
 574          * error will be available via $this->mErrorConnection.
 575          *
 576          * @param $i Integer server index
 577          * @param bool|string $wiki wiki ID to open
 578          * @return DatabaseBase
 579          *
 580          * @access private
 581          */
 582         function openConnection( $i, $wiki = false ) {
 583                 wfProfileIn( __METHOD__ );
 584                 if ( $wiki !== false ) {
 585                         $conn = $this->openForeignConnection( $i, $wiki );
 586                         wfProfileOut( __METHOD__ );
 587
 588                         return $conn;
 589                 }
 590                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 591                         $conn = $this->mConns['local'][$i][0];
 592                 } else {
 593                         $server = $this->mServers[$i];
 594                         $server['serverIndex'] = $i;
 595                         $conn = $this->reallyOpenConnection( $server, false );
 596                         if ( $conn->isOpen() ) {
 597                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 598                                 $this->mConns['local'][$i][0] = $conn;
 599                         } else {
 600                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 601                                 $this->mErrorConnection = $conn;
 602                                 $conn = false;
 603                         }
 604                 }
 605                 wfProfileOut( __METHOD__ );
 606
 607                 return $conn;
 608         }
 609
 610         /**
 611          * Open a connection to a foreign DB, or return one if it is already open.
 612          *
 613          * Increments a reference count on the returned connection which locks the
 614          * connection to the requested wiki. This reference count can be
 615          * decremented by calling reuseConnection().
 616          *
 617          * If a connection is open to the appropriate server already, but with the wrong
 618          * database, it will be switched to the right database and returned, as long as
 619          * it has been freed first with reuseConnection().
 620          *
 621          * On error, returns false, and the connection which caused the
 622          * error will be available via $this->mErrorConnection.
 623          *
 624          * @param $i Integer: server index
 625          * @param string $wiki wiki ID to open
 626          * @return DatabaseBase
 627          */
 628         function openForeignConnection( $i, $wiki ) {
 629                 wfProfileIn( __METHOD__ );
 630                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 631                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 632                         // Reuse an already-used connection
 633                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 634                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 635                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 636                         // Reuse a free connection for the same wiki
 637                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 638                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 639                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 640                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 641                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 642                         // Reuse a connection from another wiki
 643                         $conn = reset( $this->mConns['foreignFree'][$i] );
 644                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 645
 646                         if ( !$conn->selectDB( $dbName ) ) {
 647                                 $this->mLastError = "Error selecting database $dbName on server " .
 648                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 649                                 $this->mErrorConnection = $conn;
 650                                 $conn = false;
 651                         } else {
 652                                 $conn->tablePrefix( $prefix );
 653                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 654                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 655                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 656                         }
 657                 } else {
 658                         // Open a new connection
 659                         $server = $this->mServers[$i];
 660                         $server['serverIndex'] = $i;
 661                         $server['foreignPoolRefCount'] = 0;
 662                         $server['foreign'] = true;
 663                         $conn = $this->reallyOpenConnection( $server, $dbName );
 664                         if ( !$conn->isOpen() ) {
 665                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 666                                 $this->mErrorConnection = $conn;
 667                                 $conn = false;
 668                         } else {
 669                                 $conn->tablePrefix( $prefix );
 670                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 671                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 672                         }
 673                 }
 674
 675                 // Increment reference count
 676                 if ( $conn ) {
 677                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 678                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 679                 }
 680                 wfProfileOut( __METHOD__ );
 681
 682                 return $conn;
 683         }
 684
 685         /**
 686          * Test if the specified index represents an open connection
 687          *
 688          * @param $index Integer: server index
 689          * @access private
 690          * @return bool
 691          */
 692         function isOpen( $index ) {
 693                 if ( !is_integer( $index ) ) {
 694                         return false;
 695                 }
 696
 697                 return (bool)$this->getAnyOpenConnection( $index );
 698         }
 699
 700         /**
 701          * Really opens a connection. Uncached.
 702          * Returns a Database object whether or not the connection was successful.
 703          * @access private
 704          *
 705          * @param $server
 706          * @param $dbNameOverride bool
 707          * @throws MWException
 708          * @return DatabaseBase
 709          */
 710         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 711                 if ( !is_array( $server ) ) {
 712                         throw new MWException( 'You must update your load-balancing configuration. ' .
 713                                 'See DefaultSettings.php entry for $wgDBservers.' );
 714                 }
 715
 716                 if ( $dbNameOverride !== false ) {
 717                         $server['dbname'] = $dbNameOverride;
 718                 }
 719
 720                 # Create object
 721                 try {
 722                         $db = DatabaseBase::factory( $server['type'], $server );
 723                 } catch ( DBConnectionError $e ) {
 724                         // FIXME: This is probably the ugliest thing I have ever done to
 725                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 726                         $db = $e->db;
 727                 }
 728
 729                 $db->setLBInfo( $server );
 730                 if ( isset( $server['fakeSlaveLag'] ) ) {
 731                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 732                 }
 733                 if ( isset( $server['fakeMaster'] ) ) {
 734                         $db->setFakeMaster( true );
 735                 }
 736
 737                 return $db;
 738         }
 739
 740         /**
 741          * @throws DBConnectionError
 742          * @return bool
 743          */
 744         private function reportConnectionError() {
 745                 $conn = $this->mErrorConnection; // The connection which caused the error
 746
 747                 if ( !is_object( $conn ) ) {
 748                         // No last connection, probably due to all servers being too busy
 749                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 750
 751                         // If all servers were busy, mLastError will contain something sensible
 752                         throw new DBConnectionError( null, $this->mLastError );
 753                 } else {
 754                         $server = $conn->getProperty( 'mServer' );
 755                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 756                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 757                 }
 758
 759                 return false; /* not reached */
 760         }
 761
 762         /**
 763          * @return int
 764          */
 765         function getWriterIndex() {
 766                 return 0;
 767         }
 768
 769         /**
 770          * Returns true if the specified index is a valid server index
 771          *
 772          * @param string $i
 773          * @return bool
 774          */
 775         function haveIndex( $i ) {
 776                 return array_key_exists( $i, $this->mServers );
 777         }
 778
 779         /**
 780          * Returns true if the specified index is valid and has non-zero load
 781          *
 782          * @param string $i
 783          * @return bool
 784          */
 785         function isNonZeroLoad( $i ) {
 786                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 787         }
 788
 789         /**
 790          * Get the number of defined servers (not the number of open connections)
 791          *
 792          * @return int
 793          */
 794         function getServerCount() {
 795                 return count( $this->mServers );
 796         }
 797
 798         /**
 799          * Get the host name or IP address of the server with the specified index
 800          * Prefer a readable name if available.
 801          * @param string $i
 802          * @return string
 803          */
 804         function getServerName( $i ) {
 805                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 806                         return $this->mServers[$i]['hostName'];
 807                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 808                         return $this->mServers[$i]['host'];
 809                 } else {
 810                         return '';
 811                 }
 812         }
 813
 814         /**
 815          * Return the server info structure for a given index, or false if the index is invalid.
 816          * @param $i
 817          * @return bool
 818          */
 819         function getServerInfo( $i ) {
 820                 if ( isset( $this->mServers[$i] ) ) {
 821                         return $this->mServers[$i];
 822                 } else {
 823                         return false;
 824                 }
 825         }
 826
 827         /**
 828          * Sets the server info structure for the given index. Entry at index $i
 829          * is created if it doesn't exist
 830          * @param $i
 831          * @param $serverInfo
 832          */
 833         function setServerInfo( $i, $serverInfo ) {
 834                 $this->mServers[$i] = $serverInfo;
 835         }
 836
 837         /**
 838          * Get the current master position for chronology control purposes
 839          * @return mixed
 840          */
 841         function getMasterPos() {
 842                 # If this entire request was served from a slave without opening a connection to the
 843                 # master (however unlikely that may be), then we can fetch the position from the slave.
 844                 $masterConn = $this->getAnyOpenConnection( 0 );
 845                 if ( !$masterConn ) {
 846                         $serverCount = count( $this->mServers );
 847                         for ( $i = 1; $i < $serverCount; $i++ ) {
 848                                 $conn = $this->getAnyOpenConnection( $i );
 849                                 if ( $conn ) {
 850                                         wfDebug( "Master pos fetched from slave\n" );
 851
 852                                         return $conn->getSlavePos();
 853                                 }
 854                         }
 855                 } else {
 856                         wfDebug( "Master pos fetched from master\n" );
 857
 858                         return $masterConn->getMasterPos();
 859                 }
 860
 861                 return false;
 862         }
 863
 864         /**
 865          * Close all open connections
 866          */
 867         function closeAll() {
 868                 foreach ( $this->mConns as $conns2 ) {
 869                         foreach ( $conns2 as $conns3 ) {
 870                                 /** @var DatabaseBase $conn */
 871                                 foreach ( $conns3 as $conn ) {
 872                                         $conn->close();
 873                                 }
 874                         }
 875                 }
 876                 $this->mConns = array(
 877                         'local' => array(),
 878                         'foreignFree' => array(),
 879                         'foreignUsed' => array(),
 880                 );
 881         }
 882
 883         /**
 884          * Deprecated function, typo in function name
 885          *
 886          * @deprecated in 1.18
 887          * @param DatabaseBase $conn
 888          */
 889         function closeConnecton( $conn ) {
 890                 wfDeprecated( __METHOD__, '1.18' );
 891                 $this->closeConnection( $conn );
 892         }
 893
 894         /**
 895          * Close a connection
 896          * Using this function makes sure the LoadBalancer knows the connection is closed.
 897          * If you use $conn->close() directly, the load balancer won't update its state.
 898          * @param DatabaseBase $conn
 899          */
 900         function closeConnection( $conn ) {
 901                 $done = false;
 902                 foreach ( $this->mConns as $i1 => $conns2 ) {
 903                         foreach ( $conns2 as $i2 => $conns3 ) {
 904                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 905                                         if ( $conn === $candidateConn ) {
 906                                                 $conn->close();
 907                                                 unset( $this->mConns[$i1][$i2][$i3] );
 908                                                 $done = true;
 909                                                 break;
 910                                         }
 911                                 }
 912                         }
 913                 }
 914                 if ( !$done ) {
 915                         $conn->close();
 916                 }
 917         }
 918
 919         /**
 920          * Commit transactions on all open connections
 921          */
 922         function commitAll() {
 923                 foreach ( $this->mConns as $conns2 ) {
 924                         foreach ( $conns2 as $conns3 ) {
 925                                 /** @var DatabaseBase[] $conns3 */
 926                                 foreach ( $conns3 as $conn ) {
 927                                         if ( $conn->trxLevel() ) {
 928                                                 $conn->commit( __METHOD__, 'flush' );
 929                                         }
 930                                 }
 931                         }
 932                 }
 933         }
 934
 935         /**
 936          *  Issue COMMIT only on master, only if queries were done on connection
 937          */
 938         function commitMasterChanges() {
 939                 // Always 0, but who knows.. :)
 940                 $masterIndex = $this->getWriterIndex();
 941                 foreach ( $this->mConns as $conns2 ) {
 942                         if ( empty( $conns2[$masterIndex] ) ) {
 943                                 continue;
 944                         }
 945                         /** @var DatabaseBase $conn */
 946                         foreach ( $conns2[$masterIndex] as $conn ) {
 947                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 948                                         $conn->commit( __METHOD__, 'flush' );
 949                                 }
 950                         }
 951                 }
 952         }
 953
 954         /**
 955          * @param $value null
 956          * @return Mixed
 957          */
 958         function waitTimeout( $value = null ) {
 959                 return wfSetVar( $this->mWaitTimeout, $value );
 960         }
 961
 962         /**
 963          * @return bool
 964          */
 965         function getLaggedSlaveMode() {
 966                 return $this->mLaggedSlaveMode;
 967         }
 968
 969         /**
 970          * Disables/enables lag checks
 971          * @param null|bool $mode
 972          * @return bool
 973          */
 974         function allowLagged( $mode = null ) {
 975                 if ( $mode === null ) {
 976                         return $this->mAllowLagged;
 977                 }
 978                 $this->mAllowLagged = $mode;
 979
 980                 return $this->mAllowLagged;
 981         }
 982
 983         /**
 984          * @return bool
 985          */
 986         function pingAll() {
 987                 $success = true;
 988                 foreach ( $this->mConns as $conns2 ) {
 989                         foreach ( $conns2 as $conns3 ) {
 990                                 /** @var DatabaseBase[] $conns3 */
 991                                 foreach ( $conns3 as $conn ) {
 992                                         if ( !$conn->ping() ) {
 993                                                 $success = false;
 994                                         }
 995                                 }
 996                         }
 997                 }
 998
 999                 return $success;
1000         }
1001
1002         /**
1003          * Call a function with each open connection object
1004          * @param callable $callback
1005          * @param array $params
1006          */
1007         function forEachOpenConnection( $callback, $params = array() ) {
1008                 foreach ( $this->mConns as $conns2 ) {
1009                         foreach ( $conns2 as $conns3 ) {
1010                                 foreach ( $conns3 as $conn ) {
1011                                         $mergedParams = array_merge( array( $conn ), $params );
1012                                         call_user_func_array( $callback, $mergedParams );
1013                                 }
1014                         }
1015                 }
1016         }
1017
1018         /**
1019          * Get the hostname and lag time of the most-lagged slave.
1020          * This is useful for maintenance scripts that need to throttle their updates.
1021          * May attempt to open connections to slaves on the default DB. If there is
1022          * no lag, the maximum lag will be reported as -1.
1023          *
1024          * @param bool|string $wiki Wiki ID, or false for the default database
1025          * @return array ( host, max lag, index of max lagged host )
1026          */
1027         function getMaxLag( $wiki = false ) {
1028                 $maxLag = -1;
1029                 $host = '';
1030                 $maxIndex = 0;
1031                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1032                         foreach ( $this->mServers as $i => $conn ) {
1033                                 $conn = false;
1034                                 if ( $wiki === false ) {
1035                                         $conn = $this->getAnyOpenConnection( $i );
1036                                 }
1037                                 if ( !$conn ) {
1038                                         $conn = $this->openConnection( $i, $wiki );
1039                                 }
1040                                 if ( !$conn ) {
1041                                         continue;
1042                                 }
1043                                 $lag = $conn->getLag();
1044                                 if ( $lag > $maxLag ) {
1045                                         $maxLag = $lag;
1046                                         $host = $this->mServers[$i]['host'];
1047                                         $maxIndex = $i;
1048                                 }
1049                         }
1050                 }
1051
1052                 return array( $host, $maxLag, $maxIndex );
1053         }
1054
1055         /**
1056          * Get lag time for each server
1057          * Results are cached for a short time in memcached, and indefinitely in the process cache
1058          *
1059          * @param string|bool $wiki
1060          * @return array
1061          */
1062         function getLagTimes( $wiki = false ) {
1063                 # Try process cache
1064                 if ( isset( $this->mLagTimes ) ) {
1065                         return $this->mLagTimes;
1066                 }
1067                 if ( $this->getServerCount() == 1 ) {
1068                         # No replication
1069                         $this->mLagTimes = array( 0 => 0 );
1070                 } else {
1071                         # Send the request to the load monitor
1072                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1073                                 array_keys( $this->mServers ), $wiki );
1074                 }
1075
1076                 return $this->mLagTimes;
1077         }
1078
1079         /**
1080          * Get the lag in seconds for a given connection, or zero if this load
1081          * balancer does not have replication enabled.
1082          *
1083          * This should be used in preference to Database::getLag() in cases where
1084          * replication may not be in use, since there is no way to determine if
1085          * replication is in use at the connection level without running
1086          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1087          * function instead of Database::getLag() avoids a fatal error in this
1088          * case on many installations.
1089          *
1090          * @param DatabaseBase $conn
1091          * @return int
1092          */
1093         function safeGetLag( $conn ) {
1094                 if ( $this->getServerCount() == 1 ) {
1095                         return 0;
1096                 } else {
1097                         return $conn->getLag();
1098                 }
1099         }
1100
1101         /**
1102          * Clear the cache for getLagTimes
1103          */
1104         function clearLagTimeCache() {
1105                 $this->mLagTimes = null;
1106         }
1107 }
1108
1109 /**
1110  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1111  * as well handling deferring the actual network connection until the handle is used
1112  *
1113  * @ingroup Database
1114  * @since 1.22
1115  */
1116 class DBConnRef implements IDatabase {
1117         /** @var LoadBalancer */
1118         protected $lb;
1119
1120         /** @var DatabaseBase|null */
1121         protected $conn;
1122
1123         /** @var array|null */
1124         protected $params;
1125
1126         /**
1127          * @param LoadBalancer $lb
1128          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1129          */
1130         public function __construct( LoadBalancer $lb, $conn ) {
1131                 $this->lb = $lb;
1132                 if ( $conn instanceof DatabaseBase ) {
1133                         $this->conn = $conn;
1134                 } else {
1135                         $this->params = $conn;
1136                 }
1137         }
1138
1139         public function __call( $name, $arguments ) {
1140                 if ( $this->conn === null ) {
1141                         list( $db, $groups, $wiki ) = $this->params;
1142                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1143                 }
1144
1145                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1146         }
1147
1148         function __destruct() {
1149                 if ( $this->conn !== null ) {
1150                         $this->lb->reuseConnection( $this->conn );
1151                 }
1152         }
1153 }