includes/db/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing
   4  *
   5  * @file
   6  * @ingroup Database
   7  */
   8
   9 /**
  10  * Database load balancing object
  11  *
  12  * @todo document
  13  * @ingroup Database
  14  */
  15 class LoadBalancer {
  16         private $mServers, $mConns, $mLoads, $mGroupLoads;
  17         private $mErrorConnection;
  18         private $mReadIndex, $mAllowLagged;
  19         private $mWaitForPos, $mWaitTimeout;
  20         private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  21         private $mParentInfo, $mLagTimes;
  22         private $mLoadMonitorClass, $mLoadMonitor;
  23
  24         /**
  25          * @param $params Array with keys:
  26          *    servers           Required. Array of server info structures.
  27          *    masterWaitTimeout Replication lag wait timeout
  28          *    loadMonitor       Name of a class used to fetch server lag and load.
  29          */
  30         function __construct( $params ) {
  31                 if ( !isset( $params['servers'] ) ) {
  32                         throw new MWException( __CLASS__.': missing servers parameter' );
  33                 }
  34                 $this->mServers = $params['servers'];
  35
  36                 if ( isset( $params['waitTimeout'] ) ) {
  37                         $this->mWaitTimeout = $params['waitTimeout'];
  38                 } else {
  39                         $this->mWaitTimeout = 10;
  40                 }
  41
  42                 $this->mReadIndex = -1;
  43                 $this->mWriteIndex = -1;
  44                 $this->mConns = array(
  45                         'local' => array(),
  46                         'foreignUsed' => array(),
  47                         'foreignFree' => array() );
  48                 $this->mLoads = array();
  49                 $this->mWaitForPos = false;
  50                 $this->mLaggedSlaveMode = false;
  51                 $this->mErrorConnection = false;
  52                 $this->mAllowLagged = false;
  53
  54                 if ( isset( $params['loadMonitor'] ) ) {
  55                         $this->mLoadMonitorClass = $params['loadMonitor'];
  56                 } else {
  57                         $master = reset( $params['servers'] );
  58                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  59                                 $this->mLoadMonitorClass = 'LoadMonitor_MySQL';
  60                         } else {
  61                                 $this->mLoadMonitorClass = 'LoadMonitor_Null';
  62                         }
  63                 }
  64
  65                 foreach( $params['servers'] as $i => $server ) {
  66                         $this->mLoads[$i] = $server['load'];
  67                         if ( isset( $server['groupLoads'] ) ) {
  68                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  69                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  70                                                 $this->mGroupLoads[$group] = array();
  71                                         }
  72                                         $this->mGroupLoads[$group][$i] = $ratio;
  73                                 }
  74                         }
  75                 }
  76         }
  77
  78         /**
  79          * Get a LoadMonitor instance
  80          *
  81          * @return LoadMonitor
  82          */
  83         function getLoadMonitor() {
  84                 if ( !isset( $this->mLoadMonitor ) ) {
  85                         $class = $this->mLoadMonitorClass;
  86                         $this->mLoadMonitor = new $class( $this );
  87                 }
  88                 return $this->mLoadMonitor;
  89         }
  90
  91         /**
  92          * Get or set arbitrary data used by the parent object, usually an LBFactory
  93          * @param $x
  94          * @return Mixed
  95          */
  96         function parentInfo( $x = null ) {
  97                 return wfSetVar( $this->mParentInfo, $x );
  98         }
  99
 100         /**
 101          * Given an array of non-normalised probabilities, this function will select
 102          * an element and return the appropriate key
 103          *
 104          * @param $weights array
 105          *
 106          * @return int
 107          */
 108         function pickRandom( $weights ) {
 109                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
 110                         return false;
 111                 }
 112
 113                 $sum = array_sum( $weights );
 114                 if ( $sum == 0 ) {
 115                         # No loads on any of them
 116                         # In previous versions, this triggered an unweighted random selection,
 117                         # but this feature has been removed as of April 2006 to allow for strict
 118                         # separation of query groups.
 119                         return false;
 120                 }
 121                 $max = mt_getrandmax();
 122                 $rand = mt_rand( 0, $max ) / $max * $sum;
 123
 124                 $sum = 0;
 125                 foreach ( $weights as $i => $w ) {
 126                         $sum += $w;
 127                         if ( $sum >= $rand ) {
 128                                 break;
 129                         }
 130                 }
 131                 return $i;
 132         }
 133
 134         /**
 135          * @param $loads array
 136          * @param $wiki bool
 137          * @return bool|int|string
 138          */
 139         function getRandomNonLagged( $loads, $wiki = false ) {
 140                 # Unset excessively lagged servers
 141                 $lags = $this->getLagTimes( $wiki );
 142                 foreach ( $lags as $i => $lag ) {
 143                         if ( $i != 0 ) {
 144                                 if ( $lag === false ) {
 145                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 146                                         unset( $loads[$i] );
 147                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 148                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 149                                         unset( $loads[$i] );
 150                                 }
 151                         }
 152                 }
 153
 154                 # Find out if all the slaves with non-zero load are lagged
 155                 $sum = 0;
 156                 foreach ( $loads as $load ) {
 157                         $sum += $load;
 158                 }
 159                 if ( $sum == 0 ) {
 160                         # No appropriate DB servers except maybe the master and some slaves with zero load
 161                         # Do NOT use the master
 162                         # Instead, this function will return false, triggering read-only mode,
 163                         # and a lagged slave will be used instead.
 164                         return false;
 165                 }
 166
 167                 if ( count( $loads ) == 0 ) {
 168                         return false;
 169                 }
 170
 171                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 172
 173                 # Return a random representative of the remainder
 174                 return $this->pickRandom( $loads );
 175         }
 176
 177         /**
 178          * Get the index of the reader connection, which may be a slave
 179          * This takes into account load ratios and lag times. It should
 180          * always return a consistent index during a given invocation
 181          *
 182          * Side effect: opens connections to databases
 183          * @param $group bool
 184          * @param $wiki bool
 185          * @return bool|int|string
 186          */
 187         function getReaderIndex( $group = false, $wiki = false ) {
 188                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 189
 190                 # @todo FIXME: For now, only go through all this for mysql databases
 191                 if ($wgDBtype != 'mysql') {
 192                         return $this->getWriterIndex();
 193                 }
 194
 195                 if ( count( $this->mServers ) == 1 )  {
 196                         # Skip the load balancing if there's only one server
 197                         return 0;
 198                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 199                         # Shortcut if generic reader exists already
 200                         return $this->mReadIndex;
 201                 }
 202
 203                 wfProfileIn( __METHOD__ );
 204
 205                 $totalElapsed = 0;
 206
 207                 # convert from seconds to microseconds
 208                 $timeout = $wgDBClusterTimeout * 1e6;
 209
 210                 # Find the relevant load array
 211                 if ( $group !== false ) {
 212                         if ( isset( $this->mGroupLoads[$group] ) ) {
 213                                 $nonErrorLoads = $this->mGroupLoads[$group];
 214                         } else {
 215                                 # No loads for this group, return false and the caller can use some other group
 216                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 217                                 wfProfileOut( __METHOD__ );
 218                                 return false;
 219                         }
 220                 } else {
 221                         $nonErrorLoads = $this->mLoads;
 222                 }
 223
 224                 if ( !$nonErrorLoads ) {
 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                 # First try quickly looking through the available servers for a server that
 234                 # meets our criteria
 235                 do {
 236                         $totalThreadsConnected = 0;
 237                         $overloadedServers = 0;
 238                         $currentLoads = $nonErrorLoads;
 239                         while ( count( $currentLoads ) ) {
 240                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 241                                         $i = $this->pickRandom( $currentLoads );
 242                                 } else {
 243                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 244                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 245                                                 # All slaves lagged. Switch to read-only mode
 246                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 247                                                 $wgReadOnly = 'The database has been automatically locked ' .
 248                                                         'while the slave database servers catch up to the master';
 249                                                 $i = $this->pickRandom( $currentLoads );
 250                                                 $laggedSlaveMode = true;
 251                                         }
 252                                 }
 253
 254                                 if ( $i === false ) {
 255                                         # pickRandom() returned false
 256                                         # This is permanent and means the configuration or the load monitor
 257                                         # wants us to return false.
 258                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 259                                         wfProfileOut( __METHOD__ );
 260                                         return false;
 261                                 }
 262
 263                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 264                                 $conn = $this->openConnection( $i, $wiki );
 265
 266                                 if ( !$conn ) {
 267                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 268                                         unset( $nonErrorLoads[$i] );
 269                                         unset( $currentLoads[$i] );
 270                                         continue;
 271                                 }
 272
 273                                 // Perform post-connection backoff
 274                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 275                                         ? $this->mServers[$i]['max threads'] : false;
 276                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 277
 278                                 // Decrement reference counter, we are finished with this connection.
 279                                 // It will be incremented for the caller later.
 280                                 if ( $wiki !== false ) {
 281                                         $this->reuseConnection( $conn );
 282                                 }
 283
 284                                 if ( $backoff ) {
 285                                         # Post-connection overload, don't use this server for now
 286                                         $totalThreadsConnected += $backoff;
 287                                         $overloadedServers++;
 288                                         unset( $currentLoads[$i] );
 289                                 } else {
 290                                         # Return this server
 291                                         break 2;
 292                                 }
 293                         }
 294
 295                         # No server found yet
 296                         $i = false;
 297
 298                         # If all servers were down, quit now
 299                         if ( !count( $nonErrorLoads ) ) {
 300                                 wfDebugLog( 'connect', "All servers down\n" );
 301                                 break;
 302                         }
 303
 304                         # Some servers must have been overloaded
 305                         if ( $overloadedServers == 0 ) {
 306                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 307                         }
 308                         # Back off for a while
 309                         # Scale the sleep time by the number of connected threads, to produce a
 310                         # roughly constant global poll rate
 311                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 312                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 313                 } while ( $totalElapsed < $timeout );
 314
 315                 if ( $totalElapsed >= $timeout ) {
 316                         wfDebugLog( 'connect', "All servers busy\n" );
 317                         $this->mErrorConnection = false;
 318                         $this->mLastError = 'All servers busy';
 319                 }
 320
 321                 if ( $i !== false ) {
 322                         # Slave connection successful
 323                         # Wait for the session master pos for a short time
 324                         if ( $this->mWaitForPos && $i > 0 ) {
 325                                 if ( !$this->doWait( $i ) ) {
 326                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 327                                 }
 328                         }
 329                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 330                                 $this->mReadIndex = $i;
 331                         }
 332                 }
 333                 wfProfileOut( __METHOD__ );
 334                 return $i;
 335         }
 336
 337         /**
 338          * Wait for a specified number of microseconds, and return the period waited
 339          * @param $t int
 340          * @return int
 341          */
 342         function sleep( $t ) {
 343                 wfProfileIn( __METHOD__ );
 344                 wfDebug( __METHOD__.": waiting $t us\n" );
 345                 usleep( $t );
 346                 wfProfileOut( __METHOD__ );
 347                 return $t;
 348         }
 349
 350         /**
 351          * Set the master wait position
 352          * If a DB_SLAVE connection has been opened already, waits
 353          * Otherwise sets a variable telling it to wait if such a connection is opened
 354          * @param $pos int
 355          */
 356         public function waitFor( $pos ) {
 357                 wfProfileIn( __METHOD__ );
 358                 $this->mWaitForPos = $pos;
 359                 $i = $this->mReadIndex;
 360
 361                 if ( $i > 0 ) {
 362                         if ( !$this->doWait( $i ) ) {
 363                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 364                                 $this->mLaggedSlaveMode = true;
 365                         }
 366                 }
 367                 wfProfileOut( __METHOD__ );
 368         }
 369
 370         /**
 371          * Set the master wait position and wait for ALL slaves to catch up to it
 372          * @param $pos int
 373          */
 374         public function waitForAll( $pos ) {
 375                 wfProfileIn( __METHOD__ );
 376                 $this->mWaitForPos = $pos;
 377                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 378                         $this->doWait( $i , true );
 379                 }
 380                 wfProfileOut( __METHOD__ );
 381         }
 382
 383         /**
 384          * Get any open connection to a given server index, local or foreign
 385          * Returns false if there is no connection open
 386          *
 387          * @param $i int
 388          * @return DatabaseBase|bool False on failure
 389          */
 390         function getAnyOpenConnection( $i ) {
 391                 foreach ( $this->mConns as $conns ) {
 392                         if ( !empty( $conns[$i] ) ) {
 393                                 return reset( $conns[$i] );
 394                         }
 395                 }
 396                 return false;
 397         }
 398
 399         /**
 400          * Wait for a given slave to catch up to the master pos stored in $this
 401          * @param $index
 402          * @param $open bool
 403          * @return bool
 404          */
 405         function doWait( $index, $open = false ) {
 406                 # Find a connection to wait on
 407                 $conn = $this->getAnyOpenConnection( $index );
 408                 if ( !$conn ) {
 409                         if ( !$open ) {
 410                                 wfDebug( __METHOD__ . ": no connection open\n" );
 411                                 return false;
 412                         } else {
 413                                 $conn = $this->openConnection( $index );
 414                                 if ( !$conn ) {
 415                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 416                                         return false;
 417                                 }
 418                         }
 419                 }
 420
 421                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 422                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 423
 424                 if ( $result == -1 || is_null( $result ) ) {
 425                         # Timed out waiting for slave, use master instead
 426                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 427                         return false;
 428                 } else {
 429                         wfDebug( __METHOD__.": Done\n" );
 430                         return true;
 431                 }
 432         }
 433
 434         /**
 435          * Get a connection by index
 436          * This is the main entry point for this class.
 437          *
 438          * @param $i Integer: server index
 439          * @param $groups Array: query groups
 440          * @param $wiki String: wiki ID
 441          *
 442          * @return DatabaseBase
 443          */
 444         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 445                 wfProfileIn( __METHOD__ );
 446
 447                 if ( $i == DB_LAST ) {
 448                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 449                 } elseif ( $i === null || $i === false ) {
 450                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 451                 }
 452
 453                 if ( $wiki === wfWikiID() ) {
 454                         $wiki = false;
 455                 }
 456
 457                 # Query groups
 458                 if ( $i == DB_MASTER ) {
 459                         $i = $this->getWriterIndex();
 460                 } elseif ( !is_array( $groups ) ) {
 461                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 462                         if ( $groupIndex !== false ) {
 463                                 $serverName = $this->getServerName( $groupIndex );
 464                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 465                                 $i = $groupIndex;
 466                         }
 467                 } else {
 468                         foreach ( $groups as $group ) {
 469                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 470                                 if ( $groupIndex !== false ) {
 471                                         $serverName = $this->getServerName( $groupIndex );
 472                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 473                                         $i = $groupIndex;
 474                                         break;
 475                                 }
 476                         }
 477                 }
 478
 479                 # Operation-based index
 480                 if ( $i == DB_SLAVE ) {
 481                         $i = $this->getReaderIndex( false, $wiki );
 482                         # Couldn't find a working server in getReaderIndex()?
 483                         if ( $i === false ) {
 484                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 485                                 $this->reportConnectionError( $this->mErrorConnection );
 486                                 wfProfileOut( __METHOD__ );
 487                                 return false;
 488                         }
 489                 }
 490
 491                 # Now we have an explicit index into the servers array
 492                 $conn = $this->openConnection( $i, $wiki );
 493                 if ( !$conn ) {
 494                         $this->reportConnectionError( $this->mErrorConnection );
 495                 }
 496
 497                 wfProfileOut( __METHOD__ );
 498                 return $conn;
 499         }
 500
 501         /**
 502          * Mark a foreign connection as being available for reuse under a different
 503          * DB name or prefix. This mechanism is reference-counted, and must be called
 504          * the same number of times as getConnection() to work.
 505          *
 506          * @param DatabaseBase $conn
 507          */
 508         public function reuseConnection( $conn ) {
 509                 $serverIndex = $conn->getLBInfo('serverIndex');
 510                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 511                 $dbName = $conn->getDBname();
 512                 $prefix = $conn->tablePrefix();
 513                 if ( strval( $prefix ) !== '' ) {
 514                         $wiki = "$dbName-$prefix";
 515                 } else {
 516                         $wiki = $dbName;
 517                 }
 518                 if ( $serverIndex === null || $refCount === null ) {
 519                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 520                         /**
 521                          * This can happen in code like:
 522                          *   foreach ( $dbs as $db ) {
 523                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 524                          *     ...
 525                          *     $lb->reuseConnection( $conn );
 526                          *   }
 527                          * When a connection to the local DB is opened in this way, reuseConnection()
 528                          * should be ignored
 529                          */
 530                         return;
 531                 }
 532                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 533                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 534                 }
 535                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 536                 if ( $refCount <= 0 ) {
 537                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 538                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 539                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 540                 } else {
 541                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 542                 }
 543         }
 544
 545         /**
 546          * Open a connection to the server given by the specified index
 547          * Index must be an actual index into the array.
 548          * If the server is already open, returns it.
 549          *
 550          * On error, returns false, and the connection which caused the
 551          * error will be available via $this->mErrorConnection.
 552          *
 553          * @param $i Integer server index
 554          * @param $wiki String wiki ID to open
 555          * @return DatabaseBase
 556          *
 557          * @access private
 558          */
 559         function openConnection( $i, $wiki = false ) {
 560                 wfProfileIn( __METHOD__ );
 561                 if ( $wiki !== false ) {
 562                         $conn = $this->openForeignConnection( $i, $wiki );
 563                         wfProfileOut( __METHOD__);
 564                         return $conn;
 565                 }
 566                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 567                         $conn = $this->mConns['local'][$i][0];
 568                 } else {
 569                         $server = $this->mServers[$i];
 570                         $server['serverIndex'] = $i;
 571                         $conn = $this->reallyOpenConnection( $server, false );
 572                         if ( $conn->isOpen() ) {
 573                                 $this->mConns['local'][$i][0] = $conn;
 574                         } else {
 575                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 576                                 $this->mErrorConnection = $conn;
 577                                 $conn = false;
 578                         }
 579                 }
 580                 wfProfileOut( __METHOD__ );
 581                 return $conn;
 582         }
 583
 584         /**
 585          * Open a connection to a foreign DB, or return one if it is already open.
 586          *
 587          * Increments a reference count on the returned connection which locks the
 588          * connection to the requested wiki. This reference count can be
 589          * decremented by calling reuseConnection().
 590          *
 591          * If a connection is open to the appropriate server already, but with the wrong
 592          * database, it will be switched to the right database and returned, as long as
 593          * it has been freed first with reuseConnection().
 594          *
 595          * On error, returns false, and the connection which caused the
 596          * error will be available via $this->mErrorConnection.
 597          *
 598          * @param $i Integer: server index
 599          * @param $wiki String: wiki ID to open
 600          * @return DatabaseBase
 601          */
 602         function openForeignConnection( $i, $wiki ) {
 603                 wfProfileIn(__METHOD__);
 604                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 605                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 606                         // Reuse an already-used connection
 607                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 608                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 609                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 610                         // Reuse a free connection for the same wiki
 611                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 612                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 613                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 614                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 615                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 616                         // Reuse a connection from another wiki
 617                         $conn = reset( $this->mConns['foreignFree'][$i] );
 618                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 619
 620                         if ( !$conn->selectDB( $dbName ) ) {
 621                                 $this->mLastError = "Error selecting database $dbName on server " .
 622                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 623                                 $this->mErrorConnection = $conn;
 624                                 $conn = false;
 625                         } else {
 626                                 $conn->tablePrefix( $prefix );
 627                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 628                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 629                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 630                         }
 631                 } else {
 632                         // Open a new connection
 633                         $server = $this->mServers[$i];
 634                         $server['serverIndex'] = $i;
 635                         $server['foreignPoolRefCount'] = 0;
 636                         $conn = $this->reallyOpenConnection( $server, $dbName );
 637                         if ( !$conn->isOpen() ) {
 638                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 639                                 $this->mErrorConnection = $conn;
 640                                 $conn = false;
 641                         } else {
 642                                 $conn->tablePrefix( $prefix );
 643                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 644                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 645                         }
 646                 }
 647
 648                 // Increment reference count
 649                 if ( $conn ) {
 650                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 651                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 652                 }
 653                 wfProfileOut(__METHOD__);
 654                 return $conn;
 655         }
 656
 657         /**
 658          * Test if the specified index represents an open connection
 659          *
 660          * @param $index Integer: server index
 661          * @access private
 662          * @return bool
 663          */
 664         function isOpen( $index ) {
 665                 if( !is_integer( $index ) ) {
 666                         return false;
 667                 }
 668                 return (bool)$this->getAnyOpenConnection( $index );
 669         }
 670
 671         /**
 672          * Really opens a connection. Uncached.
 673          * Returns a Database object whether or not the connection was successful.
 674          * @access private
 675          *
 676          * @param $server
 677          * @param $dbNameOverride bool
 678          * @return DatabaseBase
 679          */
 680         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 681                 if( !is_array( $server ) ) {
 682                         throw new MWException( 'You must update your load-balancing configuration. ' .
 683                                 'See DefaultSettings.php entry for $wgDBservers.' );
 684                 }
 685
 686                 $host = $server['host'];
 687                 $dbname = $server['dbname'];
 688
 689                 if ( $dbNameOverride !== false ) {
 690                         $server['dbname'] = $dbname = $dbNameOverride;
 691                 }
 692
 693                 # Create object
 694                 wfDebug( "Connecting to $host $dbname...\n" );
 695                 try {
 696                         $db = DatabaseBase::factory( $server['type'], $server );
 697                 } catch ( DBConnectionError $e ) {
 698                         // FIXME: This is probably the ugliest thing I have ever done to
 699                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 700                         $db = $e->db;
 701                 }
 702
 703                 if ( $db->isOpen() ) {
 704                         wfDebug( "Connected to $host $dbname.\n" );
 705                 } else {
 706                         wfDebug( "Connection failed to $host $dbname.\n" );
 707                 }
 708                 $db->setLBInfo( $server );
 709                 if ( isset( $server['fakeSlaveLag'] ) ) {
 710                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 711                 }
 712                 if ( isset( $server['fakeMaster'] ) ) {
 713                         $db->setFakeMaster( true );
 714                 }
 715                 return $db;
 716         }
 717
 718         /**
 719          * @param $conn
 720          * @throws DBConnectionError
 721          */
 722         function reportConnectionError( &$conn ) {
 723                 wfProfileIn( __METHOD__ );
 724
 725                 if ( !is_object( $conn ) ) {
 726                         // No last connection, probably due to all servers being too busy
 727                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 728                         $conn = new Database;
 729                         // If all servers were busy, mLastError will contain something sensible
 730                         throw new DBConnectionError( $conn, $this->mLastError );
 731                 } else {
 732                         $server = $conn->getProperty( 'mServer' );
 733                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 734                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 735                 }
 736                 wfProfileOut( __METHOD__ );
 737         }
 738
 739         /**
 740          * @return int
 741          */
 742         function getWriterIndex() {
 743                 return 0;
 744         }
 745
 746         /**
 747          * Returns true if the specified index is a valid server index
 748          *
 749          * @param $i
 750          * @return bool
 751          */
 752         function haveIndex( $i ) {
 753                 return array_key_exists( $i, $this->mServers );
 754         }
 755
 756         /**
 757          * Returns true if the specified index is valid and has non-zero load
 758          *
 759          * @param $i
 760          * @return bool
 761          */
 762         function isNonZeroLoad( $i ) {
 763                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 764         }
 765
 766         /**
 767          * Get the number of defined servers (not the number of open connections)
 768          *
 769          * @return int
 770          */
 771         function getServerCount() {
 772                 return count( $this->mServers );
 773         }
 774
 775         /**
 776          * Get the host name or IP address of the server with the specified index
 777          * Prefer a readable name if available.
 778          * @param $i
 779          * @return string
 780          */
 781         function getServerName( $i ) {
 782                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 783                         return $this->mServers[$i]['hostName'];
 784                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 785                         return $this->mServers[$i]['host'];
 786                 } else {
 787                         return '';
 788                 }
 789         }
 790
 791         /**
 792          * Return the server info structure for a given index, or false if the index is invalid.
 793          * @param $i
 794          * @return bool
 795          */
 796         function getServerInfo( $i ) {
 797                 if ( isset( $this->mServers[$i] ) ) {
 798                         return $this->mServers[$i];
 799                 } else {
 800                         return false;
 801                 }
 802         }
 803
 804         /**
 805          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 806          * @param $i
 807          * @param $serverInfo
 808          */
 809         function setServerInfo( $i, $serverInfo ) {
 810                 $this->mServers[$i] = $serverInfo;
 811         }
 812
 813         /**
 814          * Get the current master position for chronology control purposes
 815          * @return mixed
 816          */
 817         function getMasterPos() {
 818                 # If this entire request was served from a slave without opening a connection to the
 819                 # master (however unlikely that may be), then we can fetch the position from the slave.
 820                 $masterConn = $this->getAnyOpenConnection( 0 );
 821                 if ( !$masterConn ) {
 822                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 823                                 $conn = $this->getAnyOpenConnection( $i );
 824                                 if ( $conn ) {
 825                                         wfDebug( "Master pos fetched from slave\n" );
 826                                         return $conn->getSlavePos();
 827                                 }
 828                         }
 829                 } else {
 830                         wfDebug( "Master pos fetched from master\n" );
 831                         return $masterConn->getMasterPos();
 832                 }
 833                 return false;
 834         }
 835
 836         /**
 837          * Close all open connections
 838          */
 839         function closeAll() {
 840                 foreach ( $this->mConns as $conns2 ) {
 841                         foreach  ( $conns2 as $conns3 ) {
 842                                 foreach ( $conns3 as $conn ) {
 843                                         $conn->close();
 844                                 }
 845                         }
 846                 }
 847                 $this->mConns = array(
 848                         'local' => array(),
 849                         'foreignFree' => array(),
 850                         'foreignUsed' => array(),
 851                 );
 852         }
 853
 854         /**
 855          * Deprecated function, typo in function name
 856          *
 857          * @deprecated in 1.18
 858          * @param $conn
 859          */
 860         function closeConnecton( $conn ) {
 861                 wfDeprecated( __METHOD__, '1.18' );
 862                 $this->closeConnection( $conn );
 863         }
 864
 865         /**
 866          * Close a connection
 867          * Using this function makes sure the LoadBalancer knows the connection is closed.
 868          * If you use $conn->close() directly, the load balancer won't update its state.
 869          * @param $conn DatabaseBase
 870          */
 871         function closeConnection( $conn ) {
 872                 $done = false;
 873                 foreach ( $this->mConns as $i1 => $conns2 ) {
 874                         foreach ( $conns2 as $i2 => $conns3 ) {
 875                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 876                                         if ( $conn === $candidateConn ) {
 877                                                 $conn->close();
 878                                                 unset( $this->mConns[$i1][$i2][$i3] );
 879                                                 $done = true;
 880                                                 break;
 881                                         }
 882                                 }
 883                         }
 884                 }
 885                 if ( !$done ) {
 886                         $conn->close();
 887                 }
 888         }
 889
 890         /**
 891          * Commit transactions on all open connections
 892          */
 893         function commitAll() {
 894                 foreach ( $this->mConns as $conns2 ) {
 895                         foreach ( $conns2 as $conns3 ) {
 896                                 foreach ( $conns3 as $conn ) {
 897                                         $conn->commit( __METHOD__ );
 898                                 }
 899                         }
 900                 }
 901         }
 902
 903         /**
 904          *  Issue COMMIT only on master, only if queries were done on connection
 905          */
 906         function commitMasterChanges() {
 907                 // Always 0, but who knows.. :)
 908                 $masterIndex = $this->getWriterIndex();
 909                 foreach ( $this->mConns as $conns2 ) {
 910                         if ( empty( $conns2[$masterIndex] ) ) {
 911                                 continue;
 912                         }
 913                         foreach ( $conns2[$masterIndex] as $conn ) {
 914                                 if ( $conn->doneWrites() ) {
 915                                         $conn->commit( __METHOD__ );
 916                                 }
 917                         }
 918                 }
 919         }
 920
 921         /**
 922          * @param $value null
 923          * @return Mixed
 924          */
 925         function waitTimeout( $value = null ) {
 926                 return wfSetVar( $this->mWaitTimeout, $value );
 927         }
 928
 929         /**
 930          * @return bool
 931          */
 932         function getLaggedSlaveMode() {
 933                 return $this->mLaggedSlaveMode;
 934         }
 935
 936         /**
 937          * Disables/enables lag checks
 938          * @param $mode null
 939          * @return bool
 940          */
 941         function allowLagged( $mode = null ) {
 942                 if ( $mode === null) {
 943                         return $this->mAllowLagged;
 944                 }
 945                 $this->mAllowLagged = $mode;
 946         }
 947
 948         /**
 949          * @return bool
 950          */
 951         function pingAll() {
 952                 $success = true;
 953                 foreach ( $this->mConns as $conns2 ) {
 954                         foreach ( $conns2 as $conns3 ) {
 955                                 foreach ( $conns3 as $conn ) {
 956                                         if ( !$conn->ping() ) {
 957                                                 $success = false;
 958                                         }
 959                                 }
 960                         }
 961                 }
 962                 return $success;
 963         }
 964
 965         /**
 966          * Call a function with each open connection object
 967          * @param $callback
 968          * @param array $params
 969          */
 970         function forEachOpenConnection( $callback, $params = array() ) {
 971                 foreach ( $this->mConns as $conns2 ) {
 972                         foreach ( $conns2 as $conns3 ) {
 973                                 foreach ( $conns3 as $conn ) {
 974                                         $mergedParams = array_merge( array( $conn ), $params );
 975                                         call_user_func_array( $callback, $mergedParams );
 976                                 }
 977                         }
 978                 }
 979         }
 980
 981         /**
 982          * Get the hostname and lag time of the most-lagged slave.
 983          * This is useful for maintenance scripts that need to throttle their updates.
 984          * May attempt to open connections to slaves on the default DB. If there is
 985          * no lag, the maximum lag will be reported as -1.
 986          *
 987          * @param $wiki string Wiki ID, or false for the default database
 988          *
 989          * @return array ( host, max lag, index of max lagged host )
 990          */
 991         function getMaxLag( $wiki = false ) {
 992                 $maxLag = -1;
 993                 $host = '';
 994                 $maxIndex = 0;
 995                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
 996                         foreach ( $this->mServers as $i => $conn ) {
 997                                 $conn = false;
 998                                 if ( $wiki === false ) {
 999                                         $conn = $this->getAnyOpenConnection( $i );
1000                                 }
1001                                 if ( !$conn ) {
1002                                         $conn = $this->openConnection( $i, $wiki );
1003                                 }
1004                                 if ( !$conn ) {
1005                                         continue;
1006                                 }
1007                                 $lag = $conn->getLag();
1008                                 if ( $lag > $maxLag ) {
1009                                         $maxLag = $lag;
1010                                         $host = $this->mServers[$i]['host'];
1011                                         $maxIndex = $i;
1012                                 }
1013                         }
1014                 }
1015                 return array( $host, $maxLag, $maxIndex );
1016         }
1017
1018         /**
1019          * Get lag time for each server
1020          * Results are cached for a short time in memcached, and indefinitely in the process cache
1021          *
1022          * @param $wiki
1023          *
1024          * @return array
1025          */
1026         function getLagTimes( $wiki = false ) {
1027                 # Try process cache
1028                 if ( isset( $this->mLagTimes ) ) {
1029                         return $this->mLagTimes;
1030                 }
1031                 if ( $this->getServerCount() == 1 ) {
1032                         # No replication
1033                         $this->mLagTimes = array( 0 => 0 );
1034                 } else {
1035                         # Send the request to the load monitor
1036                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1037                                 array_keys( $this->mServers ), $wiki );
1038                 }
1039                 return $this->mLagTimes;
1040         }
1041
1042         /**
1043          * Get the lag in seconds for a given connection, or zero if this load
1044          * balancer does not have replication enabled.
1045          *
1046          * This should be used in preference to Database::getLag() in cases where
1047          * replication may not be in use, since there is no way to determine if
1048          * replication is in use at the connection level without running
1049          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1050          * function instead of Database::getLag() avoids a fatal error in this
1051          * case on many installations.
1052          *
1053          * @param $conn DatabaseBase
1054          *
1055          * @return int
1056          */
1057         function safeGetLag( $conn ) {
1058                 if ( $this->getServerCount() == 1 ) {
1059                         return 0;
1060                 } else {
1061                         return $conn->getLag();
1062                 }
1063         }
1064
1065         /**
1066          * Clear the cache for getLagTimes
1067          */
1068         function clearLagTimeCache() {
1069                 $this->mLagTimes = null;
1070         }
1071 }