includes/db/LoadBalancer.php

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