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 */ var $mServers, $mConns, $mLoads, $mGroupLoads;
  17         /* private */ var $mErrorConnection;
  18         /* private */ var $mReadIndex, $mAllowLagged;
  19         /* private */ var $mWaitForPos, $mWaitTimeout;
  20         /* private */ var $mLaggedSlaveMode, $mLastError = 'Unknown error';
  21         /* private */ var $mParentInfo, $mLagTimes;
  22         /* private */ var $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         {
  32                 if ( !isset( $params['servers'] ) ) {
  33                         throw new MWException( __CLASS__.': missing servers parameter' );
  34                 }
  35                 $this->mServers = $params['servers'];
  36
  37                 if ( isset( $params['waitTimeout'] ) ) {
  38                         $this->mWaitTimeout = $params['waitTimeout'];
  39                 } else {
  40                         $this->mWaitTimeout = 10;
  41                 }
  42
  43                 $this->mReadIndex = -1;
  44                 $this->mWriteIndex = -1;
  45                 $this->mConns = array(
  46                         'local' => array(),
  47                         'foreignUsed' => array(),
  48                         'foreignFree' => array() );
  49                 $this->mLoads = array();
  50                 $this->mWaitForPos = false;
  51                 $this->mLaggedSlaveMode = false;
  52                 $this->mErrorConnection = false;
  53                 $this->mAllowLagged = false;
  54                 $this->mLoadMonitorClass = isset( $params['loadMonitor'] )
  55                         ? $params['loadMonitor'] : 'LoadMonitor_MySQL';
  56
  57                 foreach( $params['servers'] as $i => $server ) {
  58                         $this->mLoads[$i] = $server['load'];
  59                         if ( isset( $server['groupLoads'] ) ) {
  60                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  61                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  62                                                 $this->mGroupLoads[$group] = array();
  63                                         }
  64                                         $this->mGroupLoads[$group][$i] = $ratio;
  65                                 }
  66                         }
  67                 }
  68         }
  69
  70         /**
  71          * Get a LoadMonitor instance
  72          */
  73         function getLoadMonitor() {
  74                 if ( !isset( $this->mLoadMonitor ) ) {
  75                         $class = $this->mLoadMonitorClass;
  76                         $this->mLoadMonitor = new $class( $this );
  77                 }
  78                 return $this->mLoadMonitor;
  79         }
  80
  81         /**
  82          * Get or set arbitrary data used by the parent object, usually an LBFactory
  83          */
  84         function parentInfo( $x = null ) {
  85                 return wfSetVar( $this->mParentInfo, $x );
  86         }
  87
  88         /**
  89          * Given an array of non-normalised probabilities, this function will select
  90          * an element and return the appropriate key
  91          */
  92         function pickRandom( $weights )
  93         {
  94                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  95                         return false;
  96                 }
  97
  98                 $sum = array_sum( $weights );
  99                 if ( $sum == 0 ) {
 100                         # No loads on any of them
 101                         # In previous versions, this triggered an unweighted random selection,
 102                         # but this feature has been removed as of April 2006 to allow for strict
 103                         # separation of query groups.
 104                         return false;
 105                 }
 106                 $max = mt_getrandmax();
 107                 $rand = mt_rand(0, $max) / $max * $sum;
 108
 109                 $sum = 0;
 110                 foreach ( $weights as $i => $w ) {
 111                         $sum += $w;
 112                         if ( $sum >= $rand ) {
 113                                 break;
 114                         }
 115                 }
 116                 return $i;
 117         }
 118
 119         function getRandomNonLagged( $loads, $wiki = false ) {
 120                 # Unset excessively lagged servers
 121                 $lags = $this->getLagTimes( $wiki );
 122                 foreach ( $lags as $i => $lag ) {
 123                         if ( $i != 0 ) {
 124                                 if ( $lag === false ) {
 125                                         wfDebug( "Server #$i is not replicating\n" );
 126                                         unset( $loads[$i] );
 127                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 128                                         wfDebug( "Server #$i is excessively lagged ($lag seconds)\n" );
 129                                         unset( $loads[$i] );
 130                                 }
 131                         }
 132                 }
 133
 134                 # Find out if all the slaves with non-zero load are lagged
 135                 $sum = 0;
 136                 foreach ( $loads as $load ) {
 137                         $sum += $load;
 138                 }
 139                 if ( $sum == 0 ) {
 140                         # No appropriate DB servers except maybe the master and some slaves with zero load
 141                         # Do NOT use the master
 142                         # Instead, this function will return false, triggering read-only mode,
 143                         # and a lagged slave will be used instead.
 144                         return false;
 145                 }
 146
 147                 if ( count( $loads ) == 0 ) {
 148                         return false;
 149                 }
 150
 151                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 152
 153                 # Return a random representative of the remainder
 154                 return $this->pickRandom( $loads );
 155         }
 156
 157         /**
 158          * Get the index of the reader connection, which may be a slave
 159          * This takes into account load ratios and lag times. It should
 160          * always return a consistent index during a given invocation
 161          *
 162          * Side effect: opens connections to databases
 163          */
 164         function getReaderIndex( $group = false, $wiki = false ) {
 165                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 166
 167                 # FIXME: For now, only go through all this for mysql databases
 168                 if ($wgDBtype != 'mysql') {
 169                         return $this->getWriterIndex();
 170                 }
 171
 172                 if ( count( $this->mServers ) == 1 )  {
 173                         # Skip the load balancing if there's only one server
 174                         return 0;
 175                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 176                         # Shortcut if generic reader exists already
 177                         return $this->mReadIndex;
 178                 }
 179
 180                 wfProfileIn( __METHOD__ );
 181
 182                 $totalElapsed = 0;
 183
 184                 # convert from seconds to microseconds
 185                 $timeout = $wgDBClusterTimeout * 1e6;
 186
 187                 # Find the relevant load array
 188                 if ( $group !== false ) {
 189                         if ( isset( $this->mGroupLoads[$group] ) ) {
 190                                 $nonErrorLoads = $this->mGroupLoads[$group];
 191                         } else {
 192                                 # No loads for this group, return false and the caller can use some other group
 193                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 194                                 wfProfileOut( __METHOD__ );
 195                                 return false;
 196                         }
 197                 } else {
 198                         $nonErrorLoads = $this->mLoads;
 199                 }
 200
 201                 if ( !$nonErrorLoads ) {
 202                         throw new MWException( "Empty server array given to LoadBalancer" );
 203                 }
 204
 205                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 206                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 207
 208                 $laggedSlaveMode = false;
 209
 210                 # First try quickly looking through the available servers for a server that
 211                 # meets our criteria
 212                 do {
 213                         $totalThreadsConnected = 0;
 214                         $overloadedServers = 0;
 215                         $currentLoads = $nonErrorLoads;
 216                         while ( count( $currentLoads ) ) {
 217                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 218                                         $i = $this->pickRandom( $currentLoads );
 219                                 } else {
 220                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 221                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 222                                                 # All slaves lagged. Switch to read-only mode
 223                                                 $wgReadOnly = 'The database has been automatically locked ' .
 224                                                         'while the slave database servers catch up to the master';
 225                                                 $i = $this->pickRandom( $currentLoads );
 226                                                 $laggedSlaveMode = true;
 227                                         }
 228                                 }
 229
 230                                 if ( $i === false ) {
 231                                         # pickRandom() returned false
 232                                         # This is permanent and means the configuration or the load monitor
 233                                         # wants us to return false.
 234                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 235                                         wfProfileOut( __METHOD__ );
 236                                         return false;
 237                                 }
 238
 239                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 240                                 $conn = $this->openConnection( $i, $wiki );
 241
 242                                 if ( !$conn ) {
 243                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 244                                         unset( $nonErrorLoads[$i] );
 245                                         unset( $currentLoads[$i] );
 246                                         continue;
 247                                 }
 248
 249                                 // Perform post-connection backoff
 250                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 251                                         ? $this->mServers[$i]['max threads'] : false;
 252                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 253
 254                                 // Decrement reference counter, we are finished with this connection.
 255                                 // It will be incremented for the caller later.
 256                                 if ( $wiki !== false ) {
 257                                         $this->reuseConnection( $conn );
 258                                 }
 259
 260                                 if ( $backoff ) {
 261                                         # Post-connection overload, don't use this server for now
 262                                         $totalThreadsConnected += $backoff;
 263                                         $overloadedServers++;
 264                                         unset( $currentLoads[$i] );
 265                                 } else {
 266                                         # Return this server
 267                                         break 2;
 268                                 }
 269                         }
 270
 271                         # No server found yet
 272                         $i = false;
 273
 274                         # If all servers were down, quit now
 275                         if ( !count( $nonErrorLoads ) ) {
 276                                 wfDebugLog( 'connect', "All servers down\n" );
 277                                 break;
 278                         }
 279
 280                         # Some servers must have been overloaded
 281                         if ( $overloadedServers == 0 ) {
 282                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 283                         }
 284                         # Back off for a while
 285                         # Scale the sleep time by the number of connected threads, to produce a
 286                         # roughly constant global poll rate
 287                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 288                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 289                 } while ( $totalElapsed < $timeout );
 290
 291                 if ( $totalElapsed >= $timeout ) {
 292                         wfDebugLog( 'connect', "All servers busy\n" );
 293                         $this->mErrorConnection = false;
 294                         $this->mLastError = 'All servers busy';
 295                 }
 296
 297                 if ( $i !== false ) {
 298                         # Slave connection successful
 299                         # Wait for the session master pos for a short time
 300                         if ( $this->mWaitForPos && $i > 0 ) {
 301                                 if ( !$this->doWait( $i ) ) {
 302                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 303                                 }
 304                         }
 305                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 306                                 $this->mReadIndex = $i;
 307                         }
 308                 }
 309                 wfProfileOut( __METHOD__ );
 310                 return $i;
 311         }
 312
 313         /**
 314          * Wait for a specified number of microseconds, and return the period waited
 315          */
 316         function sleep( $t ) {
 317                 wfProfileIn( __METHOD__ );
 318                 wfDebug( __METHOD__.": waiting $t us\n" );
 319                 usleep( $t );
 320                 wfProfileOut( __METHOD__ );
 321                 return $t;
 322         }
 323
 324         /**
 325          * Set the master wait position
 326          * If a DB_SLAVE connection has been opened already, waits
 327          * Otherwise sets a variable telling it to wait if such a connection is opened
 328          */
 329         public function waitFor( $pos ) {
 330                 wfProfileIn( __METHOD__ );
 331                 $this->mWaitForPos = $pos;
 332                 $i = $this->mReadIndex;
 333
 334                 if ( $i > 0 ) {
 335                         if ( !$this->doWait( $i ) ) {
 336                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 337                                 $this->mLaggedSlaveMode = true;
 338                         }
 339                 }
 340                 wfProfileOut( __METHOD__ );
 341         }
 342
 343         /**
 344          * Set the master wait position and wait for ALL slaves to catch up to it
 345          */
 346         public function waitForAll( $pos ) {
 347                 wfProfileIn( __METHOD__ );
 348                 $this->mWaitForPos = $pos;
 349                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 350                         $this->doWait( $i );
 351                 }
 352                 wfProfileOut( __METHOD__ );
 353         }
 354
 355         /**
 356          * Get any open connection to a given server index, local or foreign
 357          * Returns false if there is no connection open
 358          */
 359         function getAnyOpenConnection( $i ) {
 360                 foreach ( $this->mConns as $conns ) {
 361                         if ( !empty( $conns[$i] ) ) {
 362                                 return reset( $conns[$i] );
 363                         }
 364                 }
 365                 return false;
 366         }
 367
 368         /**
 369          * Wait for a given slave to catch up to the master pos stored in $this
 370          */
 371         function doWait( $index ) {
 372                 # Find a connection to wait on
 373                 $conn = $this->getAnyOpenConnection( $index );
 374                 if ( !$conn ) {
 375                         wfDebug( __METHOD__ . ": no connection open\n" );
 376                         return false;
 377                 }
 378
 379                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 380                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 381
 382                 if ( $result == -1 || is_null( $result ) ) {
 383                         # Timed out waiting for slave, use master instead
 384                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 385                         return false;
 386                 } else {
 387                         wfDebug( __METHOD__.": Done\n" );
 388                         return true;
 389                 }
 390         }
 391
 392         /**
 393          * Get a connection by index
 394          * This is the main entry point for this class.
 395          *
 396          * @param $i Integer: server index
 397          * @param $groups Array: query groups
 398          * @param $wiki String: wiki ID
 399          *
 400          * @return DatabaseBase
 401          */
 402         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 403                 wfProfileIn( __METHOD__ );
 404
 405                 if ( $i == DB_LAST ) {
 406                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 407                 } elseif ( $i === null || $i === false ) {
 408                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 409                 }
 410
 411                 if ( $wiki === wfWikiID() ) {
 412                         $wiki = false;
 413                 }
 414
 415                 # Query groups
 416                 if ( $i == DB_MASTER ) {
 417                         $i = $this->getWriterIndex();
 418                 } elseif ( !is_array( $groups ) ) {
 419                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 420                         if ( $groupIndex !== false ) {
 421                                 $serverName = $this->getServerName( $groupIndex );
 422                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 423                                 $i = $groupIndex;
 424                         }
 425                 } else {
 426                         foreach ( $groups as $group ) {
 427                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 428                                 if ( $groupIndex !== false ) {
 429                                         $serverName = $this->getServerName( $groupIndex );
 430                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 431                                         $i = $groupIndex;
 432                                         break;
 433                                 }
 434                         }
 435                 }
 436
 437                 # Operation-based index
 438                 if ( $i == DB_SLAVE ) {
 439                         $i = $this->getReaderIndex( false, $wiki );
 440                         # Couldn't find a working server in getReaderIndex()?
 441                         if ( $i === false ) {
 442                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 443                                 $this->reportConnectionError( $this->mErrorConnection );
 444                                 wfProfileOut( __METHOD__ );
 445                                 return false;
 446                         }
 447                 }
 448
 449                 # Now we have an explicit index into the servers array
 450                 $conn = $this->openConnection( $i, $wiki );
 451                 if ( !$conn ) {
 452                         $this->reportConnectionError( $this->mErrorConnection );
 453                 }
 454
 455                 wfProfileOut( __METHOD__ );
 456                 return $conn;
 457         }
 458
 459         /**
 460          * Mark a foreign connection as being available for reuse under a different
 461          * DB name or prefix. This mechanism is reference-counted, and must be called
 462          * the same number of times as getConnection() to work.
 463          */
 464         public function reuseConnection( $conn ) {
 465                 $serverIndex = $conn->getLBInfo('serverIndex');
 466                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 467                 $dbName = $conn->getDBname();
 468                 $prefix = $conn->tablePrefix();
 469                 if ( strval( $prefix ) !== '' ) {
 470                         $wiki = "$dbName-$prefix";
 471                 } else {
 472                         $wiki = $dbName;
 473                 }
 474                 if ( $serverIndex === null || $refCount === null ) {
 475                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 476                         /**
 477                          * This can happen in code like:
 478                          *   foreach ( $dbs as $db ) {
 479                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 480                          *     ...
 481                          *     $lb->reuseConnection( $conn );
 482                          *   }
 483                          * When a connection to the local DB is opened in this way, reuseConnection()
 484                          * should be ignored
 485                          */
 486                         return;
 487                 }
 488                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 489                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 490                 }
 491                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 492                 if ( $refCount <= 0 ) {
 493                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 494                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 495                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 496                 } else {
 497                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 498                 }
 499         }
 500
 501         /**
 502          * Open a connection to the server given by the specified index
 503          * Index must be an actual index into the array.
 504          * If the server is already open, returns it.
 505          *
 506          * On error, returns false, and the connection which caused the
 507          * error will be available via $this->mErrorConnection.
 508          *
 509          * @param $i Integer: server index
 510          * @param $wiki String: wiki ID to open
 511          * @return DatabaseBase
 512          *
 513          * @access private
 514          */
 515         function openConnection( $i, $wiki = false ) {
 516                 wfProfileIn( __METHOD__ );
 517                 if ( $wiki !== false ) {
 518                         $conn = $this->openForeignConnection( $i, $wiki );
 519                         wfProfileOut( __METHOD__);
 520                         return $conn;
 521                 }
 522                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 523                         $conn = $this->mConns['local'][$i][0];
 524                 } else {
 525                         $server = $this->mServers[$i];
 526                         $server['serverIndex'] = $i;
 527                         $conn = $this->reallyOpenConnection( $server, false );
 528                         if ( $conn->isOpen() ) {
 529                                 $this->mConns['local'][$i][0] = $conn;
 530                         } else {
 531                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 532                                 $this->mErrorConnection = $conn;
 533                                 $conn = false;
 534                         }
 535                 }
 536                 wfProfileOut( __METHOD__ );
 537                 return $conn;
 538         }
 539
 540         /**
 541          * Open a connection to a foreign DB, or return one if it is already open.
 542          *
 543          * Increments a reference count on the returned connection which locks the
 544          * connection to the requested wiki. This reference count can be
 545          * decremented by calling reuseConnection().
 546          *
 547          * If a connection is open to the appropriate server already, but with the wrong
 548          * database, it will be switched to the right database and returned, as long as
 549          * it has been freed first with reuseConnection().
 550          *
 551          * On error, returns false, and the connection which caused the
 552          * error will be available via $this->mErrorConnection.
 553          *
 554          * @param $i Integer: server index
 555          * @param $wiki String: wiki ID to open
 556          * @return DatabaseBase
 557          */
 558         function openForeignConnection( $i, $wiki ) {
 559                 wfProfileIn(__METHOD__);
 560                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 561                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 562                         // Reuse an already-used connection
 563                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 564                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 565                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 566                         // Reuse a free connection for the same wiki
 567                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 568                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 569                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 570                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 571                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 572                         // Reuse a connection from another wiki
 573                         $conn = reset( $this->mConns['foreignFree'][$i] );
 574                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 575
 576                         if ( !$conn->selectDB( $dbName ) ) {
 577                                 $this->mLastError = "Error selecting database $dbName on server " .
 578                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 579                                 $this->mErrorConnection = $conn;
 580                                 $conn = false;
 581                         } else {
 582                                 $conn->tablePrefix( $prefix );
 583                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 584                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 585                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 586                         }
 587                 } else {
 588                         // Open a new connection
 589                         $server = $this->mServers[$i];
 590                         $server['serverIndex'] = $i;
 591                         $server['foreignPoolRefCount'] = 0;
 592                         $conn = $this->reallyOpenConnection( $server, $dbName );
 593                         if ( !$conn->isOpen() ) {
 594                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 595                                 $this->mErrorConnection = $conn;
 596                                 $conn = false;
 597                         } else {
 598                                 $conn->tablePrefix( $prefix );
 599                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 600                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 601                         }
 602                 }
 603
 604                 // Increment reference count
 605                 if ( $conn ) {
 606                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 607                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 608                 }
 609                 wfProfileOut(__METHOD__);
 610                 return $conn;
 611         }
 612
 613         /**
 614          * Test if the specified index represents an open connection
 615          *
 616          * @param $index Integer: server index
 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                 $host = $server['host'];
 637                 $dbname = $server['dbname'];
 638
 639                 if ( $dbNameOverride !== false ) {
 640                         $server['dbname'] = $dbname = $dbNameOverride;
 641                 }
 642
 643                 # Create object
 644                 wfDebug( "Connecting to $host $dbname...\n" );
 645                 try {
 646                         $db = DatabaseBase::newFromType( $server['type'], $server );
 647                 } catch ( DBConnectionError $e ) {
 648                         // FIXME: This is probably the ugliest thing I have ever done to
 649                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 650                         $db = $e->db;
 651                 }
 652                 if ( $db->isOpen() ) {
 653                         wfDebug( "Connected to $host $dbname.\n" );
 654                 } else {
 655                         wfDebug( "Connection failed to $host $dbname.\n" );
 656                 }
 657                 $db->setLBInfo( $server );
 658                 if ( isset( $server['fakeSlaveLag'] ) ) {
 659                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 660                 }
 661                 if ( isset( $server['fakeMaster'] ) ) {
 662                         $db->setFakeMaster( true );
 663                 }
 664                 return $db;
 665         }
 666
 667         function reportConnectionError( &$conn ) {
 668                 wfProfileIn( __METHOD__ );
 669
 670                 if ( !is_object( $conn ) ) {
 671                         // No last connection, probably due to all servers being too busy
 672                         wfLogDBError( "LB failure with no last connection\n" );
 673                         $conn = new Database;
 674                         // If all servers were busy, mLastError will contain something sensible
 675                         throw new DBConnectionError( $conn, $this->mLastError );
 676                 } else {
 677                         $server = $conn->getProperty( 'mServer' );
 678                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 679                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 680                 }
 681                 wfProfileOut( __METHOD__ );
 682         }
 683
 684         function getWriterIndex() {
 685                 return 0;
 686         }
 687
 688         /**
 689          * Returns true if the specified index is a valid server index
 690          */
 691         function haveIndex( $i ) {
 692                 return array_key_exists( $i, $this->mServers );
 693         }
 694
 695         /**
 696          * Returns true if the specified index is valid and has non-zero load
 697          */
 698         function isNonZeroLoad( $i ) {
 699                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 700         }
 701
 702         /**
 703          * Get the number of defined servers (not the number of open connections)
 704          */
 705         function getServerCount() {
 706                 return count( $this->mServers );
 707         }
 708
 709         /**
 710          * Get the host name or IP address of the server with the specified index
 711          * Prefer a readable name if available.
 712          */
 713         function getServerName( $i ) {
 714                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 715                         return $this->mServers[$i]['hostName'];
 716                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 717                         return $this->mServers[$i]['host'];
 718                 } else {
 719                         return '';
 720                 }
 721         }
 722
 723         /**
 724          * Return the server info structure for a given index, or false if the index is invalid.
 725          */
 726         function getServerInfo( $i ) {
 727                 if ( isset( $this->mServers[$i] ) ) {
 728                         return $this->mServers[$i];
 729                 } else {
 730                         return false;
 731                 }
 732         }
 733
 734         /**
 735          * Get the current master position for chronology control purposes
 736          * @return mixed
 737          */
 738         function getMasterPos() {
 739                 # If this entire request was served from a slave without opening a connection to the
 740                 # master (however unlikely that may be), then we can fetch the position from the slave.
 741                 $masterConn = $this->getAnyOpenConnection( 0 );
 742                 if ( !$masterConn ) {
 743                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 744                                 $conn = $this->getAnyOpenConnection( $i );
 745                                 if ( $conn ) {
 746                                         wfDebug( "Master pos fetched from slave\n" );
 747                                         return $conn->getSlavePos();
 748                                 }
 749                         }
 750                 } else {
 751                         wfDebug( "Master pos fetched from master\n" );
 752                         return $masterConn->getMasterPos();
 753                 }
 754                 return false;
 755         }
 756
 757         /**
 758          * Close all open connections
 759          */
 760         function closeAll() {
 761                 foreach ( $this->mConns as $conns2 ) {
 762                         foreach  ( $conns2 as $conns3 ) {
 763                                 foreach ( $conns3 as $conn ) {
 764                                         $conn->close();
 765                                 }
 766                         }
 767                 }
 768                 $this->mConns = array(
 769                         'local' => array(),
 770                         'foreignFree' => array(),
 771                         'foreignUsed' => array(),
 772                 );
 773         }
 774
 775         /**
 776          * Deprecated function, typo in function name
 777          */
 778         function closeConnecton( $conn ) {
 779                 $this->closeConnection( $conn );
 780         }
 781
 782         /**
 783          * Close a connection
 784          * Using this function makes sure the LoadBalancer knows the connection is closed.
 785          * If you use $conn->close() directly, the load balancer won't update its state.
 786          * @param  $conn
 787          * @return void
 788          */
 789         function closeConnection( $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->commit();
 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 $conns2 ) {
 826                         if ( empty( $conns2[$masterIndex] ) ) {
 827                                 continue;
 828                         }
 829                         foreach ( $conns2[$masterIndex] as $conn ) {
 830                                 if ( $conn->doneWrites() ) {
 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          * @param $wiki string Wiki ID, or false for the default database
 885          */
 886         function getMaxLag( $wiki = false ) {
 887                 $maxLag = -1;
 888                 $host = '';
 889                 foreach ( $this->mServers as $i => $conn ) {
 890                         $conn = false;
 891                         if ( $wiki === false ) {
 892                                 $conn = $this->getAnyOpenConnection( $i );
 893                         }
 894                         if ( !$conn ) {
 895                                 $conn = $this->openConnection( $i, $wiki );
 896                         }
 897                         if ( !$conn ) {
 898                                 continue;
 899                         }
 900                         $lag = $conn->getLag();
 901                         if ( $lag > $maxLag ) {
 902                                 $maxLag = $lag;
 903                                 $host = $this->mServers[$i]['host'];
 904                         }
 905                 }
 906                 return array( $host, $maxLag );
 907         }
 908
 909         /**
 910          * Get lag time for each server
 911          * Results are cached for a short time in memcached, and indefinitely in the process cache
 912          */
 913         function getLagTimes( $wiki = false ) {
 914                 # Try process cache
 915                 if ( isset( $this->mLagTimes ) ) {
 916                         return $this->mLagTimes;
 917                 }
 918                 # No, send the request to the load monitor
 919                 $this->mLagTimes = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
 920                 return $this->mLagTimes;
 921         }
 922
 923         /**
 924          * Clear the cache for getLagTimes
 925          */
 926         function clearLagTimeCache() {
 927                 $this->mLagTimes = null;
 928         }
 929 }