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, $mLastIndex, $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->mLastIndex = -1;
  54                 $this->mLoads = array();
  55                 $this->mWaitForPos = false;
  56                 $this->mLaggedSlaveMode = false;
  57                 $this->mErrorConnection = false;
  58                 $this->mAllowLag = false;
  59                 $this->mLoadMonitorClass = isset( $params['loadMonitor'] )
  60                         ? $params['loadMonitor'] : 'LoadMonitor_MySQL';
  61
  62                 foreach( $params['servers'] as $i => $server ) {
  63                         $this->mLoads[$i] = $server['load'];
  64                         if ( isset( $server['groupLoads'] ) ) {
  65                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  66                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  67                                                 $this->mGroupLoads[$group] = array();
  68                                         }
  69                                         $this->mGroupLoads[$group][$i] = $ratio;
  70                                 }
  71                         }
  72                 }
  73         }
  74
  75         static function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
  76         {
  77                 return new LoadBalancer( $servers, $failFunction, $waitTimeout );
  78         }
  79
  80         /**
  81          * Get a LoadMonitor instance
  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          */
  94         function parentInfo( $x = null ) {
  95                 return wfSetVar( $this->mParentInfo, $x );
  96         }
  97
  98         /**
  99          * Given an array of non-normalised probabilities, this function will select
 100          * an element and return the appropriate key
 101          */
 102         function pickRandom( $weights )
 103         {
 104                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
 105                         return false;
 106                 }
 107
 108                 $sum = array_sum( $weights );
 109                 if ( $sum == 0 ) {
 110                         # No loads on any of them
 111                         # In previous versions, this triggered an unweighted random selection,
 112                         # but this feature has been removed as of April 2006 to allow for strict
 113                         # separation of query groups.
 114                         return false;
 115                 }
 116                 $max = mt_getrandmax();
 117                 $rand = mt_rand(0, $max) / $max * $sum;
 118
 119                 $sum = 0;
 120                 foreach ( $weights as $i => $w ) {
 121                         $sum += $w;
 122                         if ( $sum >= $rand ) {
 123                                 break;
 124                         }
 125                 }
 126                 return $i;
 127         }
 128
 129         function getRandomNonLagged( $loads, $wiki = false ) {
 130                 # Unset excessively lagged servers
 131                 $lags = $this->getLagTimes( $wiki );
 132                 foreach ( $lags as $i => $lag ) {
 133                         if ( $i != 0 && isset( $this->mServers[$i]['max lag'] ) ) {
 134                                 if ( $lag === false ) {
 135                                         wfDebug( "Server #$i is not replicating\n" );
 136                                         unset( $loads[$i] );
 137                                 } elseif ( $lag > $this->mServers[$i]['max lag'] ) {
 138                                         wfDebug( "Server #$i is excessively lagged ($lag seconds)\n" );
 139                                         unset( $loads[$i] );
 140                                 }
 141                         }
 142                 }
 143
 144                 # Find out if all the slaves with non-zero load are lagged
 145                 $sum = 0;
 146                 foreach ( $loads as $load ) {
 147                         $sum += $load;
 148                 }
 149                 if ( $sum == 0 ) {
 150                         # No appropriate DB servers except maybe the master and some slaves with zero load
 151                         # Do NOT use the master
 152                         # Instead, this function will return false, triggering read-only mode,
 153                         # and a lagged slave will be used instead.
 154                         return false;
 155                 }
 156
 157                 if ( count( $loads ) == 0 ) {
 158                         return false;
 159                 }
 160
 161                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 162
 163                 # Return a random representative of the remainder
 164                 return $this->pickRandom( $loads );
 165         }
 166
 167         /**
 168          * Get the index of the reader connection, which may be a slave
 169          * This takes into account load ratios and lag times. It should
 170          * always return a consistent index during a given invocation
 171          *
 172          * Side effect: opens connections to databases
 173          */
 174         function getReaderIndex( $group = false, $wiki = false ) {
 175                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 176
 177                 # FIXME: For now, only go through all this for mysql databases
 178                 if ($wgDBtype != 'mysql') {
 179                         return $this->getWriterIndex();
 180                 }
 181
 182                 if ( count( $this->mServers ) == 1 )  {
 183                         # Skip the load balancing if there's only one server
 184                         return 0;
 185                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 186                         # Shortcut if generic reader exists already
 187                         return $this->mReadIndex;
 188                 }
 189
 190                 wfProfileIn( __METHOD__ );
 191
 192                 $totalElapsed = 0;
 193
 194                 # convert from seconds to microseconds
 195                 $timeout = $wgDBClusterTimeout * 1e6;
 196
 197                 # Find the relevant load array
 198                 if ( $group !== false ) {
 199                         if ( isset( $this->mGroupLoads[$group] ) ) {
 200                                 $nonErrorLoads = $this->mGroupLoads[$group];
 201                         } else {
 202                                 # No loads for this group, return false and the caller can use some other group
 203                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 204                                 wfProfileOut( __METHOD__ );
 205                                 return false;
 206                         }
 207                 } else {
 208                         $nonErrorLoads = $this->mLoads;
 209                 }
 210
 211                 if ( !$nonErrorLoads ) {
 212                         throw new MWException( "Empty server array given to LoadBalancer" );
 213                 }
 214
 215                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 216                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 217
 218                 $i = false;
 219                 $found = false;
 220                 $laggedSlaveMode = false;
 221
 222                 # First try quickly looking through the available servers for a server that
 223                 # meets our criteria
 224                 do {
 225                         $totalThreadsConnected = 0;
 226                         $overloadedServers = 0;
 227                         $currentLoads = $nonErrorLoads;
 228                         while ( count( $currentLoads ) ) {
 229                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 230                                         $i = $this->pickRandom( $currentLoads );
 231                                 } else {
 232                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 233                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 234                                                 # All slaves lagged. Switch to read-only mode
 235                                                 $wgReadOnly = wfMsgNoDBForContent( 'readonly_lag' );
 236                                                 $i = $this->pickRandom( $currentLoads );
 237                                                 $laggedSlaveMode = true;
 238                                         }
 239                                 }
 240
 241                                 if ( $i === false ) {
 242                                         # pickRandom() returned false
 243                                         # This is permanent and means the configuration or the load monitor
 244                                         # wants us to return false.
 245                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 246                                         wfProfileOut( __METHOD__ );
 247                                         return false;
 248                                 }
 249
 250                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 251                                 $conn = $this->openConnection( $i, $wiki );
 252
 253                                 if ( !$conn ) {
 254                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 255                                         unset( $nonErrorLoads[$i] );
 256                                         unset( $currentLoads[$i] );
 257                                         continue;
 258                                 }
 259
 260                                 // Perform post-connection backoff
 261                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 262                                         ? $this->mServers[$i]['max threads'] : false;
 263                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 264
 265                                 // Decrement reference counter, we are finished with this connection.
 266                                 // It will be incremented for the caller later.
 267                                 if ( $wiki !== false ) {
 268                                         $this->reuseConnection( $conn );
 269                                 }
 270
 271                                 if ( $backoff ) {
 272                                         # Post-connection overload, don't use this server for now
 273                                         $totalThreadsConnected += $backoff;
 274                                         $overloadedServers++;
 275                                         unset( $currentLoads[$i] );
 276                                 } else {
 277                                         # Return this server
 278                                         break 2;
 279                                 }
 280                         }
 281
 282                         # No server found yet
 283                         $i = false;
 284
 285                         # If all servers were down, quit now
 286                         if ( !count( $nonErrorLoads ) ) {
 287                                 wfDebugLog( 'connect', "All servers down\n" );
 288                                 break;
 289                         }
 290
 291                         # Some servers must have been overloaded
 292                         if ( $overloadedServers == 0 ) {
 293                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 294                         }
 295                         # Back off for a while
 296                         # Scale the sleep time by the number of connected threads, to produce a
 297                         # roughly constant global poll rate
 298                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 299                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 300                 } while ( $totalElapsed < $timeout );
 301
 302                 if ( $totalElapsed >= $timeout ) {
 303                         wfDebugLog( 'connect', "All servers busy\n" );
 304                         $this->mErrorConnection = false;
 305                         $this->mLastError = 'All servers busy';
 306                 }
 307
 308                 if ( $i !== false ) {
 309                         # Slave connection successful
 310                         # Wait for the session master pos for a short time
 311                         if ( $this->mWaitForPos && $i > 0 ) {
 312                                 if ( !$this->doWait( $i ) ) {
 313                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 314                                 }
 315                         }
 316                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 317                                 $this->mReadIndex = $i;
 318                         }
 319                 }
 320                 wfProfileOut( __METHOD__ );
 321                 return $i;
 322         }
 323
 324         /**
 325          * Wait for a specified number of microseconds, and return the period waited
 326          */
 327         function sleep( $t ) {
 328                 wfProfileIn( __METHOD__ );
 329                 wfDebug( __METHOD__.": waiting $t us\n" );
 330                 usleep( $t );
 331                 wfProfileOut( __METHOD__ );
 332                 return $t;
 333         }
 334
 335         /**
 336          * Get a random server to use in a query group
 337          * @deprecated use getReaderIndex
 338          */
 339         function getGroupIndex( $group ) {
 340                 return $this->getReaderIndex( $group );
 341         }
 342
 343         /**
 344          * Set the master wait position
 345          * If a DB_SLAVE connection has been opened already, waits
 346          * Otherwise sets a variable telling it to wait if such a connection is opened
 347          */
 348         public function waitFor( $pos ) {
 349                 wfProfileIn( __METHOD__ );
 350                 $this->mWaitForPos = $pos;
 351                 $i = $this->mReadIndex;
 352
 353                 if ( $i > 0 ) {
 354                         if ( !$this->doWait( $i ) ) {
 355                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 356                                 $this->mLaggedSlaveMode = true;
 357                         }
 358                 }
 359                 wfProfileOut( __METHOD__ );
 360         }
 361
 362         /**
 363          * Get any open connection to a given server index, local or foreign
 364          * Returns false if there is no connection open
 365          */
 366         function getAnyOpenConnection( $i ) {
 367                 foreach ( $this->mConns as $type => $conns ) {
 368                         if ( !empty( $conns[$i] ) ) {
 369                                 return reset( $conns[$i] );
 370                         }
 371                 }
 372                 return false;
 373         }
 374
 375         /**
 376          * Wait for a given slave to catch up to the master pos stored in $this
 377          */
 378         function doWait( $index ) {
 379                 # Find a connection to wait on
 380                 $conn = $this->getAnyOpenConnection( $index );
 381                 if ( !$conn ) {
 382                         wfDebug( __METHOD__ . ": no connection open\n" );
 383                         return false;
 384                 }
 385
 386                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 387                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 388
 389                 if ( $result == -1 || is_null( $result ) ) {
 390                         # Timed out waiting for slave, use master instead
 391                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 392                         return false;
 393                 } else {
 394                         wfDebug( __METHOD__.": Done\n" );
 395                         return true;
 396                 }
 397         }
 398
 399         /**
 400          * Get a connection by index
 401          * This is the main entry point for this class.
 402          */
 403         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 404                 global $wgDBtype;
 405                 wfProfileIn( __METHOD__ );
 406
 407                 if ( $wiki === wfWikiID() ) {
 408                         $wiki = false;
 409                 }
 410
 411                 # Query groups
 412                 if ( $i == DB_MASTER ) {
 413                         $i = $this->getWriterIndex();
 414                 } elseif ( !is_array( $groups ) ) {
 415                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 416                         if ( $groupIndex !== false ) {
 417                                 $serverName = $this->getServerName( $groupIndex );
 418                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 419                                 $i = $groupIndex;
 420                         }
 421                 } else {
 422                         foreach ( $groups as $group ) {
 423                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 424                                 if ( $groupIndex !== false ) {
 425                                         $serverName = $this->getServerName( $groupIndex );
 426                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 427                                         $i = $groupIndex;
 428                                         break;
 429                                 }
 430                         }
 431                 }
 432
 433                 # Operation-based index
 434                 if ( $i == DB_SLAVE ) {
 435                         $i = $this->getReaderIndex( false, $wiki );
 436                 } elseif ( $i == DB_LAST ) {
 437                         # Just use $this->mLastIndex, which should already be set
 438                         $i = $this->mLastIndex;
 439                         if ( $i === -1 ) {
 440                                 # Oh dear, not set, best to use the writer for safety
 441                                 wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
 442                                 $i = $this->getWriterIndex();
 443                         }
 444                 }
 445                 # Couldn't find a working server in getReaderIndex()?
 446                 if ( $i === false ) {
 447                         $this->reportConnectionError( $this->mErrorConnection );
 448                 }
 449
 450                 # Now we have an explicit index into the servers array
 451                 $conn = $this->openConnection( $i, $wiki );
 452                 if ( !$conn ) {
 453                         $this->reportConnectionError( $this->mErrorConnection );
 454                 }
 455
 456                 wfProfileOut( __METHOD__ );
 457                 return $conn;
 458         }
 459
 460         /**
 461          * Mark a foreign connection as being available for reuse under a different
 462          * DB name or prefix. This mechanism is reference-counted, and must be called
 463          * the same number of times as getConnection() to work.
 464          */
 465         public function reuseConnection( $conn ) {
 466                 $serverIndex = $conn->getLBInfo('serverIndex');
 467                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 468                 $dbName = $conn->getDBname();
 469                 $prefix = $conn->tablePrefix();
 470                 if ( strval( $prefix ) !== '' ) {
 471                         $wiki = "$dbName-$prefix";
 472                 } else {
 473                         $wiki = $dbName;
 474                 }
 475                 if ( $serverIndex === null || $refCount === null ) {
 476                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 477                         /**
 478                          * This can happen in code like:
 479                          *   foreach ( $dbs as $db ) {
 480                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 481                          *     ...
 482                          *     $lb->reuseConnection( $conn );
 483                          *   }
 484                          * When a connection to the local DB is opened in this way, reuseConnection()
 485                          * should be ignored
 486                          */
 487                         return;
 488                 }
 489                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 490                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 491                 }
 492                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 493                 if ( $refCount <= 0 ) {
 494                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 495                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 496                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 497                 } else {
 498                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 499                 }
 500         }
 501
 502         /**
 503          * Open a connection to the server given by the specified index
 504          * Index must be an actual index into the array.
 505          * If the server is already open, returns it.
 506          *
 507          * On error, returns false, and the connection which caused the
 508          * error will be available via $this->mErrorConnection.
 509          *
 510          * @param integer $i Server index
 511          * @param string $wiki Wiki ID to open
 512          * @return Database
 513          *
 514          * @access private
 515          */
 516         function openConnection( $i, $wiki = false ) {
 517                 wfProfileIn( __METHOD__ );
 518                 if ( $wiki !== false ) {
 519                         $conn = $this->openForeignConnection( $i, $wiki );
 520                         wfProfileOut( __METHOD__);
 521                         return $conn;
 522                 }
 523                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 524                         $conn = $this->mConns['local'][$i][0];
 525                 } else {
 526                         $server = $this->mServers[$i];
 527                         $server['serverIndex'] = $i;
 528                         $conn = $this->reallyOpenConnection( $server );
 529                         if ( $conn->isOpen() ) {
 530                                 $this->mConns['local'][$i][0] = $conn;
 531                         } else {
 532                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 533                                 $this->mErrorConnection = $conn;
 534                                 $conn = false;
 535                         }
 536                 }
 537                 $this->mLastIndex = $i;
 538                 wfProfileOut( __METHOD__ );
 539                 return $conn;
 540         }
 541
 542         /**
 543          * Open a connection to a foreign DB, or return one if it is already open.
 544          *
 545          * Increments a reference count on the returned connection which locks the
 546          * connection to the requested wiki. This reference count can be
 547          * decremented by calling reuseConnection().
 548          *
 549          * If a connection is open to the appropriate server already, but with the wrong
 550          * database, it will be switched to the right database and returned, as long as
 551          * it has been freed first with reuseConnection().
 552          *
 553          * On error, returns false, and the connection which caused the
 554          * error will be available via $this->mErrorConnection.
 555          *
 556          * @param integer $i Server index
 557          * @param string $wiki Wiki ID to open
 558          * @return Database
 559          */
 560         function openForeignConnection( $i, $wiki ) {
 561                 wfProfileIn(__METHOD__);
 562                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 563                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 564                         // Reuse an already-used connection
 565                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 566                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 567                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 568                         // Reuse a free connection for the same wiki
 569                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 570                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 571                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 572                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 573                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 574                         // Reuse a connection from another wiki
 575                         $conn = reset( $this->mConns['foreignFree'][$i] );
 576                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 577
 578                         if ( !$conn->selectDB( $dbName ) ) {
 579                                 global $wguname;
 580                                 $this->mLastError = "Error selecting database $dbName on server " .
 581                                         $conn->getServer() . " from client host {$wguname['nodename']}\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                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 602                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 603                         }
 604                 }
 605
 606                 // Increment reference count
 607                 if ( $conn ) {
 608                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 609                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 610                 }
 611                 wfProfileOut(__METHOD__);
 612                 return $conn;
 613         }
 614
 615         /**
 616          * Test if the specified index represents an open connection
 617          * @access private
 618          */
 619         function isOpen( $index ) {
 620                 if( !is_integer( $index ) ) {
 621                         return false;
 622                 }
 623                 return (bool)$this->getAnyOpenConnection( $index );
 624         }
 625
 626         /**
 627          * Really opens a connection. Uncached.
 628          * Returns a Database object whether or not the connection was successful.
 629          * @access private
 630          */
 631         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 632                 if( !is_array( $server ) ) {
 633                         throw new MWException( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 634                 }
 635
 636                 extract( $server );
 637                 if ( $dbNameOverride !== false ) {
 638                         $dbname = $dbNameOverride;
 639                 }
 640
 641                 # Get class for this database type
 642                 $class = 'Database' . ucfirst( $type );
 643
 644                 # Create object
 645                 wfDebug( "Connecting to $host $dbname...\n" );
 646                 $db = new $class( $host, $user, $password, $dbname, 1, $flags );
 647                 if ( $db->isOpen() ) {
 648                         wfDebug( "Connected\n" );
 649                 } else {
 650                         wfDebug( "Failed\n" );
 651                 }
 652                 $db->setLBInfo( $server );
 653                 if ( isset( $server['fakeSlaveLag'] ) ) {
 654                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 655                 }
 656                 if ( isset( $server['fakeMaster'] ) ) {
 657                         $db->setFakeMaster( true );
 658                 }
 659                 return $db;
 660         }
 661
 662         function reportConnectionError( &$conn ) {
 663                 wfProfileIn( __METHOD__ );
 664                 # Prevent infinite recursion
 665
 666                 static $reporting = false;
 667                 if ( !$reporting ) {
 668                         $reporting = true;
 669                         if ( !is_object( $conn ) ) {
 670                                 // No last connection, probably due to all servers being too busy
 671                                 $conn = new Database;
 672                                 if ( $this->mFailFunction ) {
 673                                         $conn->failFunction( $this->mFailFunction );
 674                                         $conn->reportConnectionError( $this->mLastError );
 675                                 } else {
 676                                         // If all servers were busy, mLastError will contain something sensible
 677                                         throw new DBConnectionError( $conn, $this->mLastError );
 678                                 }
 679                         } else {
 680                                 if ( $this->mFailFunction ) {
 681                                         $conn->failFunction( $this->mFailFunction );
 682                                 } else {
 683                                         $conn->failFunction( false );
 684                                 }
 685                                 $server = $conn->getProperty( 'mServer' );
 686                                 $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 687                         }
 688                         $reporting = false;
 689                 }
 690                 wfProfileOut( __METHOD__ );
 691         }
 692
 693         function getWriterIndex() {
 694                 return 0;
 695         }
 696
 697         /**
 698          * Returns true if the specified index is a valid server index
 699          */
 700         function haveIndex( $i ) {
 701                 return array_key_exists( $i, $this->mServers );
 702         }
 703
 704         /**
 705          * Returns true if the specified index is valid and has non-zero load
 706          */
 707         function isNonZeroLoad( $i ) {
 708                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 709         }
 710
 711         /**
 712          * Get the number of defined servers (not the number of open connections)
 713          */
 714         function getServerCount() {
 715                 return count( $this->mServers );
 716         }
 717
 718         /**
 719          * Get the host name or IP address of the server with the specified index
 720          * Prefer a readable name if available.
 721          */
 722         function getServerName( $i ) {
 723                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 724                         return $this->mServers[$i]['hostName'];
 725                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 726                         return $this->mServers[$i]['host'];
 727                 } else {
 728                         return '';
 729                 }
 730         }
 731
 732         /**
 733          * Return the server info structure for a given index, or false if the index is invalid.
 734          */
 735         function getServerInfo( $i ) {
 736                 if ( isset( $this->mServers[$i] ) ) {
 737                         return $this->mServers[$i];
 738                 } else {
 739                         return false;
 740                 }
 741         }
 742
 743         /**
 744          * Get the current master position for chronology control purposes
 745          * @return mixed
 746          */
 747         function getMasterPos() {
 748                 # If this entire request was served from a slave without opening a connection to the
 749                 # master (however unlikely that may be), then we can fetch the position from the slave.
 750                 $masterConn = $this->getAnyOpenConnection( 0 );
 751                 if ( !$masterConn ) {
 752                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 753                                 $conn = $this->getAnyOpenConnection( $i );
 754                                 if ( $conn ) {
 755                                         wfDebug( "Master pos fetched from slave\n" );
 756                                         return $conn->getSlavePos();
 757                                 }
 758                         }
 759                 } else {
 760                         wfDebug( "Master pos fetched from master\n" );
 761                         return $masterConn->getMasterPos();
 762                 }
 763                 return false;
 764         }
 765
 766         /**
 767          * Close all open connections
 768          */
 769         function closeAll() {
 770                 foreach ( $this->mConns as $conns2 ) {
 771                         foreach  ( $conns2 as $conns3 ) {
 772                                 foreach ( $conns3 as $conn ) {
 773                                         $conn->close();
 774                                 }
 775                         }
 776                 }
 777                 $this->mConns = array(
 778                         'local' => array(),
 779                         'foreignFree' => array(),
 780                         'foreignUsed' => array(),
 781                 );
 782         }
 783
 784         /**
 785          * Close a connection
 786          * Using this function makes sure the LoadBalancer knows the connection is closed.
 787          * If you use $conn->close() directly, the load balancer won't update its state.
 788          */
 789         function closeConnecton( $conn ) {
 790                 $done = false;
 791                 foreach ( $this->mConns as $i1 => $conns2 ) {
 792                         foreach ( $conns2 as $i2 => $conns3 ) {
 793                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 794                                         if ( $conn === $candidateConn ) {
 795                                                 $conn->close();
 796                                                 unset( $this->mConns[$i1][$i2][$i3] );
 797                                                 $done = true;
 798                                                 break;
 799                                         }
 800                                 }
 801                         }
 802                 }
 803                 if ( !$done ) {
 804                         $conn->close();
 805                 }
 806         }
 807
 808         /**
 809          * Commit transactions on all open connections
 810          */
 811         function commitAll() {
 812                 foreach ( $this->mConns as $conns2 ) {
 813                         foreach ( $conns2 as $conns3 ) {
 814                                 foreach ( $conns3 as $conn ) {
 815                                         $conn->immediateCommit();
 816                                 }
 817                         }
 818                 }
 819         }
 820
 821         /* Issue COMMIT only on master, only if queries were done on connection */
 822         function commitMasterChanges() {
 823                 // Always 0, but who knows.. :)
 824                 $masterIndex = $this->getWriterIndex();
 825                 foreach ( $this->mConns as $type => $conns2 ) {
 826                         if ( empty( $conns2[$masterIndex] ) ) {
 827                                 continue;
 828                         }
 829                         foreach ( $conns2[$masterIndex] as $conn ) {
 830                                 if ( $conn->lastQuery() != '' ) {
 831                                         $conn->commit();
 832                                 }
 833                         }
 834                 }
 835         }
 836
 837         function waitTimeout( $value = NULL ) {
 838                 return wfSetVar( $this->mWaitTimeout, $value );
 839         }
 840
 841         function getLaggedSlaveMode() {
 842                 return $this->mLaggedSlaveMode;
 843         }
 844
 845         /* Disables/enables lag checks */
 846         function allowLagged($mode=null) {
 847                 if ($mode===null)
 848                         return $this->mAllowLagged;
 849                 $this->mAllowLagged=$mode;
 850         }
 851
 852         function pingAll() {
 853                 $success = true;
 854                 foreach ( $this->mConns as $conns2 ) {
 855                         foreach ( $conns2 as $conns3 ) {
 856                                 foreach ( $conns3 as $conn ) {
 857                                         if ( !$conn->ping() ) {
 858                                                 $success = false;
 859                                         }
 860                                 }
 861                         }
 862                 }
 863                 return $success;
 864         }
 865
 866         /**
 867          * Call a function with each open connection object
 868          */
 869         function forEachOpenConnection( $callback, $params = array() ) {
 870                 foreach ( $this->mConns as $conns2 ) {
 871                         foreach ( $conns2 as $conns3 ) {
 872                                 foreach ( $conns3 as $conn ) {
 873                                         $mergedParams = array_merge( array( $conn ), $params );
 874                                         call_user_func_array( $callback, $mergedParams );
 875                                 }
 876                         }
 877                 }
 878         }
 879
 880         /**
 881          * Get the hostname and lag time of the most-lagged slave.
 882          * This is useful for maintenance scripts that need to throttle their updates.
 883          * May attempt to open connections to slaves on the default DB.
 884          */
 885         function getMaxLag() {
 886                 $maxLag = -1;
 887                 $host = '';
 888                 foreach ( $this->mServers as $i => $conn ) {
 889                         $conn = $this->getAnyOpenConnection( $i );
 890                         if ( !$conn ) {
 891                                 $conn = $this->openConnection( $i );
 892                         }
 893                         if ( !$conn ) {
 894                                 continue;
 895                         }
 896                         $lag = $conn->getLag();
 897                         if ( $lag > $maxLag ) {
 898                                 $maxLag = $lag;
 899                                 $host = $this->mServers[$i]['host'];
 900                         }
 901                 }
 902                 return array( $host, $maxLag );
 903         }
 904
 905         /**
 906          * Get lag time for each server
 907          * Results are cached for a short time in memcached, and indefinitely in the process cache
 908          */
 909         function getLagTimes( $wiki = false ) {
 910                 # Try process cache
 911                 if ( isset( $this->mLagTimes ) ) {
 912                         return $this->mLagTimes;
 913                 }
 914                 # No, send the request to the load monitor
 915                 $this->mLagTimes = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
 916                 return $this->mLagTimes;
 917         }
 918 }