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 $mFailFunction, $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          *    failFunction      Deprecated, use exceptions instead.
  28          *    masterWaitTimeout Replication lag wait timeout
  29          *    loadMonitor       Name of a class used to fetch server lag and load.
  30          */
  31         function __construct( $params )
  32         {
  33                 if ( !isset( $params['servers'] ) ) {
  34                         throw new MWException( __CLASS__.': missing servers parameter' );
  35                 }
  36                 $this->mServers = $params['servers'];
  37
  38                 if ( isset( $params['failFunction'] ) ) {
  39                         $this->mFailFunction = $params['failFunction'];
  40                 } else {
  41                         $this->mFailFunction = false;
  42                 }
  43                 if ( isset( $params['waitTimeout'] ) ) {
  44                         $this->mWaitTimeout = $params['waitTimeout'];
  45                 } else {
  46                         $this->mWaitTimeout = 10;
  47                 }
  48
  49                 $this->mReadIndex = -1;
  50                 $this->mWriteIndex = -1;
  51                 $this->mConns = array(
  52                         'local' => array(),
  53                         'foreignUsed' => array(),
  54                         'foreignFree' => array() );
  55                 $this->mLoads = array();
  56                 $this->mWaitForPos = false;
  57                 $this->mLaggedSlaveMode = false;
  58                 $this->mErrorConnection = false;
  59                 $this->mAllowLag = false;
  60                 $this->mLoadMonitorClass = isset( $params['loadMonitor'] )
  61                         ? $params['loadMonitor'] : 'LoadMonitor_MySQL';
  62
  63                 foreach( $params['servers'] as $i => $server ) {
  64                         $this->mLoads[$i] = $server['load'];
  65                         if ( isset( $server['groupLoads'] ) ) {
  66                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  67                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  68                                                 $this->mGroupLoads[$group] = array();
  69                                         }
  70                                         $this->mGroupLoads[$group][$i] = $ratio;
  71                                 }
  72                         }
  73                 }
  74         }
  75
  76         static function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
  77         {
  78                 return new LoadBalancer( $servers, $failFunction, $waitTimeout );
  79         }
  80
  81         /**
  82          * Get a LoadMonitor instance
  83          */
  84         function getLoadMonitor() {
  85                 if ( !isset( $this->mLoadMonitor ) ) {
  86                         $class = $this->mLoadMonitorClass;
  87                         $this->mLoadMonitor = new $class( $this );
  88                 }
  89                 return $this->mLoadMonitor;
  90         }
  91
  92         /**
  93          * Get or set arbitrary data used by the parent object, usually an LBFactory
  94          */
  95         function parentInfo( $x = null ) {
  96                 return wfSetVar( $this->mParentInfo, $x );
  97         }
  98
  99         /**
 100          * Given an array of non-normalised probabilities, this function will select
 101          * an element and return the appropriate key
 102          */
 103         function pickRandom( $weights )
 104         {
 105                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
 106                         return false;
 107                 }
 108
 109                 $sum = array_sum( $weights );
 110                 if ( $sum == 0 ) {
 111                         # No loads on any of them
 112                         # In previous versions, this triggered an unweighted random selection,
 113                         # but this feature has been removed as of April 2006 to allow for strict
 114                         # separation of query groups.
 115                         return false;
 116                 }
 117                 $max = mt_getrandmax();
 118                 $rand = mt_rand(0, $max) / $max * $sum;
 119
 120                 $sum = 0;
 121                 foreach ( $weights as $i => $w ) {
 122                         $sum += $w;
 123                         if ( $sum >= $rand ) {
 124                                 break;
 125                         }
 126                 }
 127                 return $i;
 128         }
 129
 130         function getRandomNonLagged( $loads, $wiki = false ) {
 131                 # Unset excessively lagged servers
 132                 $lags = $this->getLagTimes( $wiki );
 133                 foreach ( $lags as $i => $lag ) {
 134                         if ( $i != 0 && isset( $this->mServers[$i]['max lag'] ) ) {
 135                                 if ( $lag === false ) {
 136                                         wfDebug( "Server #$i is not replicating\n" );
 137                                         unset( $loads[$i] );
 138                                 } elseif ( $lag > $this->mServers[$i]['max lag'] ) {
 139                                         wfDebug( "Server #$i is excessively lagged ($lag seconds)\n" );
 140                                         unset( $loads[$i] );
 141                                 }
 142                         }
 143                 }
 144
 145                 # Find out if all the slaves with non-zero load are lagged
 146                 $sum = 0;
 147                 foreach ( $loads as $load ) {
 148                         $sum += $load;
 149                 }
 150                 if ( $sum == 0 ) {
 151                         # No appropriate DB servers except maybe the master and some slaves with zero load
 152                         # Do NOT use the master
 153                         # Instead, this function will return false, triggering read-only mode,
 154                         # and a lagged slave will be used instead.
 155                         return false;
 156                 }
 157
 158                 if ( count( $loads ) == 0 ) {
 159                         return false;
 160                 }
 161
 162                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 163
 164                 # Return a random representative of the remainder
 165                 return $this->pickRandom( $loads );
 166         }
 167
 168         /**
 169          * Get the index of the reader connection, which may be a slave
 170          * This takes into account load ratios and lag times. It should
 171          * always return a consistent index during a given invocation
 172          *
 173          * Side effect: opens connections to databases
 174          */
 175         function getReaderIndex( $group = false, $wiki = false ) {
 176                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 177
 178                 # FIXME: For now, only go through all this for mysql databases
 179                 if ($wgDBtype != 'mysql') {
 180                         return $this->getWriterIndex();
 181                 }
 182
 183                 if ( count( $this->mServers ) == 1 )  {
 184                         # Skip the load balancing if there's only one server
 185                         return 0;
 186                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 187                         # Shortcut if generic reader exists already
 188                         return $this->mReadIndex;
 189                 }
 190
 191                 wfProfileIn( __METHOD__ );
 192
 193                 $totalElapsed = 0;
 194
 195                 # convert from seconds to microseconds
 196                 $timeout = $wgDBClusterTimeout * 1e6;
 197
 198                 # Find the relevant load array
 199                 if ( $group !== false ) {
 200                         if ( isset( $this->mGroupLoads[$group] ) ) {
 201                                 $nonErrorLoads = $this->mGroupLoads[$group];
 202                         } else {
 203                                 # No loads for this group, return false and the caller can use some other group
 204                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 205                                 wfProfileOut( __METHOD__ );
 206                                 return false;
 207                         }
 208                 } else {
 209                         $nonErrorLoads = $this->mLoads;
 210                 }
 211
 212                 if ( !$nonErrorLoads ) {
 213                         throw new MWException( "Empty server array given to LoadBalancer" );
 214                 }
 215
 216                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 217                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 218
 219                 $i = 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          * @param $i Integer: server index
 404          * @param $groups Array: query groups
 405          * @param $wiki String: wiki ID
 406          *
 407          * @return DatabaseBase
 408          */
 409         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 410                 wfProfileIn( __METHOD__ );
 411
 412                 if ( $i == DB_LAST ) {
 413                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 414                 } elseif ( $i === null || $i === false ) {
 415                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 416                 }
 417
 418                 if ( $wiki === wfWikiID() ) {
 419                         $wiki = false;
 420                 }
 421
 422                 # Query groups
 423                 if ( $i == DB_MASTER ) {
 424                         $i = $this->getWriterIndex();
 425                 } elseif ( !is_array( $groups ) ) {
 426                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 427                         if ( $groupIndex !== false ) {
 428                                 $serverName = $this->getServerName( $groupIndex );
 429                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 430                                 $i = $groupIndex;
 431                         }
 432                 } else {
 433                         foreach ( $groups as $group ) {
 434                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 435                                 if ( $groupIndex !== false ) {
 436                                         $serverName = $this->getServerName( $groupIndex );
 437                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 438                                         $i = $groupIndex;
 439                                         break;
 440                                 }
 441                         }
 442                 }
 443
 444                 # Operation-based index
 445                 if ( $i == DB_SLAVE ) {
 446                         $i = $this->getReaderIndex( false, $wiki );
 447                         # Couldn't find a working server in getReaderIndex()?
 448                         if ( $i === false ) {
 449                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 450                                 $this->reportConnectionError( $this->mErrorConnection );
 451                                 return false;
 452                         }
 453                 }
 454
 455                 # Now we have an explicit index into the servers array
 456                 $conn = $this->openConnection( $i, $wiki );
 457                 if ( !$conn ) {
 458                         $this->reportConnectionError( $this->mErrorConnection );
 459                 }
 460
 461                 wfProfileOut( __METHOD__ );
 462                 return $conn;
 463         }
 464
 465         /**
 466          * Mark a foreign connection as being available for reuse under a different
 467          * DB name or prefix. This mechanism is reference-counted, and must be called
 468          * the same number of times as getConnection() to work.
 469          */
 470         public function reuseConnection( $conn ) {
 471                 $serverIndex = $conn->getLBInfo('serverIndex');
 472                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 473                 $dbName = $conn->getDBname();
 474                 $prefix = $conn->tablePrefix();
 475                 if ( strval( $prefix ) !== '' ) {
 476                         $wiki = "$dbName-$prefix";
 477                 } else {
 478                         $wiki = $dbName;
 479                 }
 480                 if ( $serverIndex === null || $refCount === null ) {
 481                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 482                         /**
 483                          * This can happen in code like:
 484                          *   foreach ( $dbs as $db ) {
 485                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 486                          *     ...
 487                          *     $lb->reuseConnection( $conn );
 488                          *   }
 489                          * When a connection to the local DB is opened in this way, reuseConnection()
 490                          * should be ignored
 491                          */
 492                         return;
 493                 }
 494                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 495                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 496                 }
 497                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 498                 if ( $refCount <= 0 ) {
 499                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 500                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 501                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 502                 } else {
 503                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 504                 }
 505         }
 506
 507         /**
 508          * Open a connection to the server given by the specified index
 509          * Index must be an actual index into the array.
 510          * If the server is already open, returns it.
 511          *
 512          * On error, returns false, and the connection which caused the
 513          * error will be available via $this->mErrorConnection.
 514          *
 515          * @param $i Integer: server index
 516          * @param $wiki String: wiki ID to open
 517          * @return DatabaseBase
 518          *
 519          * @access private
 520          */
 521         function openConnection( $i, $wiki = false ) {
 522                 wfProfileIn( __METHOD__ );
 523                 if ( $wiki !== false ) {
 524                         $conn = $this->openForeignConnection( $i, $wiki );
 525                         wfProfileOut( __METHOD__);
 526                         return $conn;
 527                 }
 528                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 529                         $conn = $this->mConns['local'][$i][0];
 530                 } else {
 531                         $server = $this->mServers[$i];
 532                         $server['serverIndex'] = $i;
 533                         $conn = $this->reallyOpenConnection( $server, false );
 534                         if ( $conn->isOpen() ) {
 535                                 $this->mConns['local'][$i][0] = $conn;
 536                         } else {
 537                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 538                                 $this->mErrorConnection = $conn;
 539                                 $conn = false;
 540                         }
 541                 }
 542                 wfProfileOut( __METHOD__ );
 543                 return $conn;
 544         }
 545
 546         /**
 547          * Open a connection to a foreign DB, or return one if it is already open.
 548          *
 549          * Increments a reference count on the returned connection which locks the
 550          * connection to the requested wiki. This reference count can be
 551          * decremented by calling reuseConnection().
 552          *
 553          * If a connection is open to the appropriate server already, but with the wrong
 554          * database, it will be switched to the right database and returned, as long as
 555          * it has been freed first with reuseConnection().
 556          *
 557          * On error, returns false, and the connection which caused the
 558          * error will be available via $this->mErrorConnection.
 559          *
 560          * @param $i Integer: server index
 561          * @param $wiki String: wiki ID to open
 562          * @return DatabaseBase
 563          */
 564         function openForeignConnection( $i, $wiki ) {
 565                 wfProfileIn(__METHOD__);
 566                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 567                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 568                         // Reuse an already-used connection
 569                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 570                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 571                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 572                         // Reuse a free connection for the same wiki
 573                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 574                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 575                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 576                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 577                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 578                         // Reuse a connection from another wiki
 579                         $conn = reset( $this->mConns['foreignFree'][$i] );
 580                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 581
 582                         if ( !$conn->selectDB( $dbName ) ) {
 583                                 $this->mLastError = "Error selecting database $dbName on server " .
 584                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 585                                 $this->mErrorConnection = $conn;
 586                                 $conn = false;
 587                         } else {
 588                                 $conn->tablePrefix( $prefix );
 589                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 590                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 591                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 592                         }
 593                 } else {
 594                         // Open a new connection
 595                         $server = $this->mServers[$i];
 596                         $server['serverIndex'] = $i;
 597                         $server['foreignPoolRefCount'] = 0;
 598                         $conn = $this->reallyOpenConnection( $server, $dbName );
 599                         if ( !$conn->isOpen() ) {
 600                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 601                                 $this->mErrorConnection = $conn;
 602                                 $conn = false;
 603                         } else {
 604                                 $conn->tablePrefix( $prefix );
 605                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 606                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 607                         }
 608                 }
 609
 610                 // Increment reference count
 611                 if ( $conn ) {
 612                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 613                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 614                 }
 615                 wfProfileOut(__METHOD__);
 616                 return $conn;
 617         }
 618
 619         /**
 620          * Test if the specified index represents an open connection
 621          *
 622          * @param $index Integer: server index
 623          * @access private
 624          */
 625         function isOpen( $index ) {
 626                 if( !is_integer( $index ) ) {
 627                         return false;
 628                 }
 629                 return (bool)$this->getAnyOpenConnection( $index );
 630         }
 631
 632         /**
 633          * Really opens a connection. Uncached.
 634          * Returns a Database object whether or not the connection was successful.
 635          * @access private
 636          */
 637         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 638                 if( !is_array( $server ) ) {
 639                         throw new MWException( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 640                 }
 641
 642                 extract( $server );
 643                 if ( $dbNameOverride !== false ) {
 644                         $dbname = $dbNameOverride;
 645                 }
 646
 647                 # Get class for this database type
 648                 $class = 'Database' . ucfirst( $type );
 649
 650                 # Create object
 651                 wfDebug( "Connecting to $host $dbname...\n" );
 652                 $db = new $class( $host, $user, $password, $dbname, 1, $flags );
 653                 if ( $db->isOpen() ) {
 654                         wfDebug( "Connected\n" );
 655                 } else {
 656                         wfDebug( "Failed\n" );
 657                 }
 658                 $db->setLBInfo( $server );
 659                 if ( isset( $server['fakeSlaveLag'] ) ) {
 660                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 661                 }
 662                 if ( isset( $server['fakeMaster'] ) ) {
 663                         $db->setFakeMaster( true );
 664                 }
 665                 return $db;
 666         }
 667
 668         function reportConnectionError( &$conn ) {
 669                 wfProfileIn( __METHOD__ );
 670
 671                 if ( !is_object( $conn ) ) {
 672                         // No last connection, probably due to all servers being too busy
 673                         wfLogDBError( "LB failure with no last connection\n" );
 674                         $conn = new Database;
 675                         if ( $this->mFailFunction ) {
 676                                 $conn->failFunction( $this->mFailFunction );
 677                                 $conn->reportConnectionError( $this->mLastError );
 678                         } else {
 679                                 // If all servers were busy, mLastError will contain something sensible
 680                                 throw new DBConnectionError( $conn, $this->mLastError );
 681                         }
 682                 } else {
 683                         if ( $this->mFailFunction ) {
 684                                 $conn->failFunction( $this->mFailFunction );
 685                         } else {
 686                                 $conn->failFunction( false );
 687                         }
 688                         $server = $conn->getProperty( 'mServer' );
 689                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 690                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 691                 }
 692                 wfProfileOut( __METHOD__ );
 693         }
 694
 695         function getWriterIndex() {
 696                 return 0;
 697         }
 698
 699         /**
 700          * Returns true if the specified index is a valid server index
 701          */
 702         function haveIndex( $i ) {
 703                 return array_key_exists( $i, $this->mServers );
 704         }
 705
 706         /**
 707          * Returns true if the specified index is valid and has non-zero load
 708          */
 709         function isNonZeroLoad( $i ) {
 710                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 711         }
 712
 713         /**
 714          * Get the number of defined servers (not the number of open connections)
 715          */
 716         function getServerCount() {
 717                 return count( $this->mServers );
 718         }
 719
 720         /**
 721          * Get the host name or IP address of the server with the specified index
 722          * Prefer a readable name if available.
 723          */
 724         function getServerName( $i ) {
 725                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 726                         return $this->mServers[$i]['hostName'];
 727                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 728                         return $this->mServers[$i]['host'];
 729                 } else {
 730                         return '';
 731                 }
 732         }
 733
 734         /**
 735          * Return the server info structure for a given index, or false if the index is invalid.
 736          */
 737         function getServerInfo( $i ) {
 738                 if ( isset( $this->mServers[$i] ) ) {
 739                         return $this->mServers[$i];
 740                 } else {
 741                         return false;
 742                 }
 743         }
 744
 745         /**
 746          * Get the current master position for chronology control purposes
 747          * @return mixed
 748          */
 749         function getMasterPos() {
 750                 # If this entire request was served from a slave without opening a connection to the
 751                 # master (however unlikely that may be), then we can fetch the position from the slave.
 752                 $masterConn = $this->getAnyOpenConnection( 0 );
 753                 if ( !$masterConn ) {
 754                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 755                                 $conn = $this->getAnyOpenConnection( $i );
 756                                 if ( $conn ) {
 757                                         wfDebug( "Master pos fetched from slave\n" );
 758                                         return $conn->getSlavePos();
 759                                 }
 760                         }
 761                 } else {
 762                         wfDebug( "Master pos fetched from master\n" );
 763                         return $masterConn->getMasterPos();
 764                 }
 765                 return false;
 766         }
 767
 768         /**
 769          * Close all open connections
 770          */
 771         function closeAll() {
 772                 foreach ( $this->mConns as $conns2 ) {
 773                         foreach  ( $conns2 as $conns3 ) {
 774                                 foreach ( $conns3 as $conn ) {
 775                                         $conn->close();
 776                                 }
 777                         }
 778                 }
 779                 $this->mConns = array(
 780                         'local' => array(),
 781                         'foreignFree' => array(),
 782                         'foreignUsed' => array(),
 783                 );
 784         }
 785
 786         /**
 787          * Close a connection
 788          * Using this function makes sure the LoadBalancer knows the connection is closed.
 789          * If you use $conn->close() directly, the load balancer won't update its state.
 790          */
 791         function closeConnecton( $conn ) {
 792                 $done = false;
 793                 foreach ( $this->mConns as $i1 => $conns2 ) {
 794                         foreach ( $conns2 as $i2 => $conns3 ) {
 795                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 796                                         if ( $conn === $candidateConn ) {
 797                                                 $conn->close();
 798                                                 unset( $this->mConns[$i1][$i2][$i3] );
 799                                                 $done = true;
 800                                                 break;
 801                                         }
 802                                 }
 803                         }
 804                 }
 805                 if ( !$done ) {
 806                         $conn->close();
 807                 }
 808         }
 809
 810         /**
 811          * Commit transactions on all open connections
 812          */
 813         function commitAll() {
 814                 foreach ( $this->mConns as $conns2 ) {
 815                         foreach ( $conns2 as $conns3 ) {
 816                                 foreach ( $conns3 as $conn ) {
 817                                         $conn->commit();
 818                                 }
 819                         }
 820                 }
 821         }
 822
 823         /* Issue COMMIT only on master, only if queries were done on connection */
 824         function commitMasterChanges() {
 825                 // Always 0, but who knows.. :)
 826                 $masterIndex = $this->getWriterIndex();
 827                 foreach ( $this->mConns as $type => $conns2 ) {
 828                         if ( empty( $conns2[$masterIndex] ) ) {
 829                                 continue;
 830                         }
 831                         foreach ( $conns2[$masterIndex] as $conn ) {
 832                                 if ( $conn->doneWrites() ) {
 833                                         $conn->commit();
 834                                 }
 835                         }
 836                 }
 837         }
 838
 839         function waitTimeout( $value = null ) {
 840                 return wfSetVar( $this->mWaitTimeout, $value );
 841         }
 842
 843         function getLaggedSlaveMode() {
 844                 return $this->mLaggedSlaveMode;
 845         }
 846
 847         /* Disables/enables lag checks */
 848         function allowLagged($mode=null) {
 849                 if ($mode===null)
 850                         return $this->mAllowLagged;
 851                 $this->mAllowLagged=$mode;
 852         }
 853
 854         function pingAll() {
 855                 $success = true;
 856                 foreach ( $this->mConns as $conns2 ) {
 857                         foreach ( $conns2 as $conns3 ) {
 858                                 foreach ( $conns3 as $conn ) {
 859                                         if ( !$conn->ping() ) {
 860                                                 $success = false;
 861                                         }
 862                                 }
 863                         }
 864                 }
 865                 return $success;
 866         }
 867
 868         /**
 869          * Call a function with each open connection object
 870          */
 871         function forEachOpenConnection( $callback, $params = array() ) {
 872                 foreach ( $this->mConns as $conns2 ) {
 873                         foreach ( $conns2 as $conns3 ) {
 874                                 foreach ( $conns3 as $conn ) {
 875                                         $mergedParams = array_merge( array( $conn ), $params );
 876                                         call_user_func_array( $callback, $mergedParams );
 877                                 }
 878                         }
 879                 }
 880         }
 881
 882         /**
 883          * Get the hostname and lag time of the most-lagged slave.
 884          * This is useful for maintenance scripts that need to throttle their updates.
 885          * May attempt to open connections to slaves on the default DB.
 886          * @param $wiki string Wiki ID, or false for the default database
 887          */
 888         function getMaxLag( $wiki = false ) {
 889                 $maxLag = -1;
 890                 $host = '';
 891                 foreach ( $this->mServers as $i => $conn ) {
 892                         $conn = false;
 893                         if ( $wiki === false ) {
 894                                 $conn = $this->getAnyOpenConnection( $i );
 895                         }
 896                         if ( !$conn ) {
 897                                 $conn = $this->openConnection( $i, $wiki );
 898                         }
 899                         if ( !$conn ) {
 900                                 continue;
 901                         }
 902                         $lag = $conn->getLag();
 903                         if ( $lag > $maxLag ) {
 904                                 $maxLag = $lag;
 905                                 $host = $this->mServers[$i]['host'];
 906                         }
 907                 }
 908                 return array( $host, $maxLag );
 909         }
 910
 911         /**
 912          * Get lag time for each server
 913          * Results are cached for a short time in memcached, and indefinitely in the process cache
 914          */
 915         function getLagTimes( $wiki = false ) {
 916                 # Try process cache
 917                 if ( isset( $this->mLagTimes ) ) {
 918                         return $this->mLagTimes;
 919                 }
 920                 # No, send the request to the load monitor
 921                 $this->mLagTimes = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
 922                 return $this->mLagTimes;
 923         }
 924
 925         /**
 926          * Clear the cache for getLagTimes
 927          */
 928         function clearLagTimeCache() {
 929                 $this->mLagTimes = null;
 930         }
 931 }