includes/db/LoadBalancer.php

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