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
  54                 if ( isset( $params['loadMonitor'] ) ) {
  55                         $this->mLoadMonitorClass = $params['loadMonitor'];
  56                 } else {
  57                         $master = reset( $params['servers'] );
  58                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  59                                 $this->mLoadMonitorClass = 'LoadMonitor_MySQL';
  60                         } else {
  61                                 $this->mLoadMonitorClass = 'LoadMonitor_Null';
  62                         }
  63                 }
  64
  65                 foreach( $params['servers'] as $i => $server ) {
  66                         $this->mLoads[$i] = $server['load'];
  67                         if ( isset( $server['groupLoads'] ) ) {
  68                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  69                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  70                                                 $this->mGroupLoads[$group] = array();
  71                                         }
  72                                         $this->mGroupLoads[$group][$i] = $ratio;
  73                                 }
  74                         }
  75                 }
  76         }
  77
  78         /**
  79          * Get a LoadMonitor instance
  80          *
  81          * @return LoadMonitor
  82          */
  83         function getLoadMonitor() {
  84                 if ( !isset( $this->mLoadMonitor ) ) {
  85                         $class = $this->mLoadMonitorClass;
  86                         $this->mLoadMonitor = new $class( $this );
  87                 }
  88                 return $this->mLoadMonitor;
  89         }
  90
  91         /**
  92          * Get or set arbitrary data used by the parent object, usually an LBFactory
  93          */
  94         function parentInfo( $x = null ) {
  95                 return wfSetVar( $this->mParentInfo, $x );
  96         }
  97
  98         /**
  99          * Given an array of non-normalised probabilities, this function will select
 100          * an element and return the appropriate key
 101          *
 102          * @param $weights
 103          *
 104          * @return int
 105          */
 106         function pickRandom( $weights ) {
 107                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
 108                         return false;
 109                 }
 110
 111                 $sum = array_sum( $weights );
 112                 if ( $sum == 0 ) {
 113                         # No loads on any of them
 114                         # In previous versions, this triggered an unweighted random selection,
 115                         # but this feature has been removed as of April 2006 to allow for strict
 116                         # separation of query groups.
 117                         return false;
 118                 }
 119                 $max = mt_getrandmax();
 120                 $rand = mt_rand( 0, $max ) / $max * $sum;
 121
 122                 $sum = 0;
 123                 foreach ( $weights as $i => $w ) {
 124                         $sum += $w;
 125                         if ( $sum >= $rand ) {
 126                                 break;
 127                         }
 128                 }
 129                 return $i;
 130         }
 131
 132         /**
 133          * @param $loads
 134          * @param $wiki bool
 135          * @return bool|int|string
 136          */
 137         function getRandomNonLagged( $loads, $wiki = false ) {
 138                 # Unset excessively lagged servers
 139                 $lags = $this->getLagTimes( $wiki );
 140                 foreach ( $lags as $i => $lag ) {
 141                         if ( $i != 0 ) {
 142                                 if ( $lag === false ) {
 143                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 144                                         unset( $loads[$i] );
 145                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 146                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 147                                         unset( $loads[$i] );
 148                                 }
 149                         }
 150                 }
 151
 152                 # Find out if all the slaves with non-zero load are lagged
 153                 $sum = 0;
 154                 foreach ( $loads as $load ) {
 155                         $sum += $load;
 156                 }
 157                 if ( $sum == 0 ) {
 158                         # No appropriate DB servers except maybe the master and some slaves with zero load
 159                         # Do NOT use the master
 160                         # Instead, this function will return false, triggering read-only mode,
 161                         # and a lagged slave will be used instead.
 162                         return false;
 163                 }
 164
 165                 if ( count( $loads ) == 0 ) {
 166                         return false;
 167                 }
 168
 169                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 170
 171                 # Return a random representative of the remainder
 172                 return $this->pickRandom( $loads );
 173         }
 174
 175         /**
 176          * Get the index of the reader connection, which may be a slave
 177          * This takes into account load ratios and lag times. It should
 178          * always return a consistent index during a given invocation
 179          *
 180          * Side effect: opens connections to databases
 181          * @param $group bool
 182          * @param $wiki bool
 183          * @return bool|int|string
 184          */
 185         function getReaderIndex( $group = false, $wiki = false ) {
 186                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 187
 188                 # @todo FIXME: For now, only go through all this for mysql databases
 189                 if ($wgDBtype != 'mysql') {
 190                         return $this->getWriterIndex();
 191                 }
 192
 193                 if ( count( $this->mServers ) == 1 )  {
 194                         # Skip the load balancing if there's only one server
 195                         return 0;
 196                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 197                         # Shortcut if generic reader exists already
 198                         return $this->mReadIndex;
 199                 }
 200
 201                 wfProfileIn( __METHOD__ );
 202
 203                 $totalElapsed = 0;
 204
 205                 # convert from seconds to microseconds
 206                 $timeout = $wgDBClusterTimeout * 1e6;
 207
 208                 # Find the relevant load array
 209                 if ( $group !== false ) {
 210                         if ( isset( $this->mGroupLoads[$group] ) ) {
 211                                 $nonErrorLoads = $this->mGroupLoads[$group];
 212                         } else {
 213                                 # No loads for this group, return false and the caller can use some other group
 214                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 215                                 wfProfileOut( __METHOD__ );
 216                                 return false;
 217                         }
 218                 } else {
 219                         $nonErrorLoads = $this->mLoads;
 220                 }
 221
 222                 if ( !$nonErrorLoads ) {
 223                         throw new MWException( "Empty server array given to LoadBalancer" );
 224                 }
 225
 226                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 227                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 228
 229                 $laggedSlaveMode = false;
 230
 231                 # First try quickly looking through the available servers for a server that
 232                 # meets our criteria
 233                 do {
 234                         $totalThreadsConnected = 0;
 235                         $overloadedServers = 0;
 236                         $currentLoads = $nonErrorLoads;
 237                         while ( count( $currentLoads ) ) {
 238                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 239                                         $i = $this->pickRandom( $currentLoads );
 240                                 } else {
 241                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 242                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 243                                                 # All slaves lagged. Switch to read-only mode
 244                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 245                                                 $wgReadOnly = 'The database has been automatically locked ' .
 246                                                         'while the slave database servers catch up to the master';
 247                                                 $i = $this->pickRandom( $currentLoads );
 248                                                 $laggedSlaveMode = true;
 249                                         }
 250                                 }
 251
 252                                 if ( $i === false ) {
 253                                         # pickRandom() returned false
 254                                         # This is permanent and means the configuration or the load monitor
 255                                         # wants us to return false.
 256                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 257                                         wfProfileOut( __METHOD__ );
 258                                         return false;
 259                                 }
 260
 261                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 262                                 $conn = $this->openConnection( $i, $wiki );
 263
 264                                 if ( !$conn ) {
 265                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 266                                         unset( $nonErrorLoads[$i] );
 267                                         unset( $currentLoads[$i] );
 268                                         continue;
 269                                 }
 270
 271                                 // Perform post-connection backoff
 272                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 273                                         ? $this->mServers[$i]['max threads'] : false;
 274                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 275
 276                                 // Decrement reference counter, we are finished with this connection.
 277                                 // It will be incremented for the caller later.
 278                                 if ( $wiki !== false ) {
 279                                         $this->reuseConnection( $conn );
 280                                 }
 281
 282                                 if ( $backoff ) {
 283                                         # Post-connection overload, don't use this server for now
 284                                         $totalThreadsConnected += $backoff;
 285                                         $overloadedServers++;
 286                                         unset( $currentLoads[$i] );
 287                                 } else {
 288                                         # Return this server
 289                                         break 2;
 290                                 }
 291                         }
 292
 293                         # No server found yet
 294                         $i = false;
 295
 296                         # If all servers were down, quit now
 297                         if ( !count( $nonErrorLoads ) ) {
 298                                 wfDebugLog( 'connect', "All servers down\n" );
 299                                 break;
 300                         }
 301
 302                         # Some servers must have been overloaded
 303                         if ( $overloadedServers == 0 ) {
 304                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 305                         }
 306                         # Back off for a while
 307                         # Scale the sleep time by the number of connected threads, to produce a
 308                         # roughly constant global poll rate
 309                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 310                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 311                 } while ( $totalElapsed < $timeout );
 312
 313                 if ( $totalElapsed >= $timeout ) {
 314                         wfDebugLog( 'connect', "All servers busy\n" );
 315                         $this->mErrorConnection = false;
 316                         $this->mLastError = 'All servers busy';
 317                 }
 318
 319                 if ( $i !== false ) {
 320                         # Slave connection successful
 321                         # Wait for the session master pos for a short time
 322                         if ( $this->mWaitForPos && $i > 0 ) {
 323                                 if ( !$this->doWait( $i ) ) {
 324                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 325                                 }
 326                         }
 327                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 328                                 $this->mReadIndex = $i;
 329                         }
 330                 }
 331                 wfProfileOut( __METHOD__ );
 332                 return $i;
 333         }
 334
 335         /**
 336          * Wait for a specified number of microseconds, and return the period waited
 337          */
 338         function sleep( $t ) {
 339                 wfProfileIn( __METHOD__ );
 340                 wfDebug( __METHOD__.": waiting $t us\n" );
 341                 usleep( $t );
 342                 wfProfileOut( __METHOD__ );
 343                 return $t;
 344         }
 345
 346         /**
 347          * Set the master wait position
 348          * If a DB_SLAVE connection has been opened already, waits
 349          * Otherwise sets a variable telling it to wait if such a connection is opened
 350          */
 351         public function waitFor( $pos ) {
 352                 wfProfileIn( __METHOD__ );
 353                 $this->mWaitForPos = $pos;
 354                 $i = $this->mReadIndex;
 355
 356                 if ( $i > 0 ) {
 357                         if ( !$this->doWait( $i ) ) {
 358                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 359                                 $this->mLaggedSlaveMode = true;
 360                         }
 361                 }
 362                 wfProfileOut( __METHOD__ );
 363         }
 364
 365         /**
 366          * Set the master wait position and wait for ALL slaves to catch up to it
 367          */
 368         public function waitForAll( $pos ) {
 369                 wfProfileIn( __METHOD__ );
 370                 $this->mWaitForPos = $pos;
 371                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 372                         $this->doWait( $i , true );
 373                 }
 374                 wfProfileOut( __METHOD__ );
 375         }
 376
 377         /**
 378          * Get any open connection to a given server index, local or foreign
 379          * Returns false if there is no connection open
 380          *
 381          * @return DatabaseBase
 382          */
 383         function getAnyOpenConnection( $i ) {
 384                 foreach ( $this->mConns as $conns ) {
 385                         if ( !empty( $conns[$i] ) ) {
 386                                 return reset( $conns[$i] );
 387                         }
 388                 }
 389                 return false;
 390         }
 391
 392         /**
 393          * Wait for a given slave to catch up to the master pos stored in $this
 394          * @param $index
 395          * @param $open bool
 396          * @return bool
 397          */
 398         function doWait( $index, $open = false ) {
 399                 # Find a connection to wait on
 400                 $conn = $this->getAnyOpenConnection( $index );
 401                 if ( !$conn ) {
 402                         if ( !$open ) {
 403                                 wfDebug( __METHOD__ . ": no connection open\n" );
 404                                 return false;
 405                         } else {
 406                                 $conn = $this->openConnection( $index );
 407                                 if ( !$conn ) {
 408                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 409                                         return false;
 410                                 }
 411                         }
 412                 }
 413
 414                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 415                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 416
 417                 if ( $result == -1 || is_null( $result ) ) {
 418                         # Timed out waiting for slave, use master instead
 419                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 420                         return false;
 421                 } else {
 422                         wfDebug( __METHOD__.": Done\n" );
 423                         return true;
 424                 }
 425         }
 426
 427         /**
 428          * Get a connection by index
 429          * This is the main entry point for this class.
 430          *
 431          * @param $i Integer: server index
 432          * @param $groups Array: query groups
 433          * @param $wiki String: wiki ID
 434          *
 435          * @return DatabaseBase
 436          */
 437         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 438                 wfProfileIn( __METHOD__ );
 439
 440                 if ( $i == DB_LAST ) {
 441                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 442                 } elseif ( $i === null || $i === false ) {
 443                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 444                 }
 445
 446                 if ( $wiki === wfWikiID() ) {
 447                         $wiki = false;
 448                 }
 449
 450                 # Query groups
 451                 if ( $i == DB_MASTER ) {
 452                         $i = $this->getWriterIndex();
 453                 } elseif ( !is_array( $groups ) ) {
 454                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 455                         if ( $groupIndex !== false ) {
 456                                 $serverName = $this->getServerName( $groupIndex );
 457                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 458                                 $i = $groupIndex;
 459                         }
 460                 } else {
 461                         foreach ( $groups as $group ) {
 462                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 463                                 if ( $groupIndex !== false ) {
 464                                         $serverName = $this->getServerName( $groupIndex );
 465                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 466                                         $i = $groupIndex;
 467                                         break;
 468                                 }
 469                         }
 470                 }
 471
 472                 # Operation-based index
 473                 if ( $i == DB_SLAVE ) {
 474                         $i = $this->getReaderIndex( false, $wiki );
 475                         # Couldn't find a working server in getReaderIndex()?
 476                         if ( $i === false ) {
 477                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 478                                 $this->reportConnectionError( $this->mErrorConnection );
 479                                 wfProfileOut( __METHOD__ );
 480                                 return false;
 481                         }
 482                 }
 483
 484                 # Now we have an explicit index into the servers array
 485                 $conn = $this->openConnection( $i, $wiki );
 486                 if ( !$conn ) {
 487                         $this->reportConnectionError( $this->mErrorConnection );
 488                 }
 489
 490                 wfProfileOut( __METHOD__ );
 491                 return $conn;
 492         }
 493
 494         /**
 495          * Mark a foreign connection as being available for reuse under a different
 496          * DB name or prefix. This mechanism is reference-counted, and must be called
 497          * the same number of times as getConnection() to work.
 498          *
 499          * @param DatabaseBase $conn
 500          */
 501         public function reuseConnection( $conn ) {
 502                 $serverIndex = $conn->getLBInfo('serverIndex');
 503                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 504                 $dbName = $conn->getDBname();
 505                 $prefix = $conn->tablePrefix();
 506                 if ( strval( $prefix ) !== '' ) {
 507                         $wiki = "$dbName-$prefix";
 508                 } else {
 509                         $wiki = $dbName;
 510                 }
 511                 if ( $serverIndex === null || $refCount === null ) {
 512                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 513                         /**
 514                          * This can happen in code like:
 515                          *   foreach ( $dbs as $db ) {
 516                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 517                          *     ...
 518                          *     $lb->reuseConnection( $conn );
 519                          *   }
 520                          * When a connection to the local DB is opened in this way, reuseConnection()
 521                          * should be ignored
 522                          */
 523                         return;
 524                 }
 525                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 526                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 527                 }
 528                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 529                 if ( $refCount <= 0 ) {
 530                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 531                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 532                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 533                 } else {
 534                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 535                 }
 536         }
 537
 538         /**
 539          * Open a connection to the server given by the specified index
 540          * Index must be an actual index into the array.
 541          * If the server is already open, returns it.
 542          *
 543          * On error, returns false, and the connection which caused the
 544          * error will be available via $this->mErrorConnection.
 545          *
 546          * @param $i Integer server index
 547          * @param $wiki String wiki ID to open
 548          * @return DatabaseBase
 549          *
 550          * @access private
 551          */
 552         function openConnection( $i, $wiki = false ) {
 553                 wfProfileIn( __METHOD__ );
 554                 if ( $wiki !== false ) {
 555                         $conn = $this->openForeignConnection( $i, $wiki );
 556                         wfProfileOut( __METHOD__);
 557                         return $conn;
 558                 }
 559                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 560                         $conn = $this->mConns['local'][$i][0];
 561                 } else {
 562                         $server = $this->mServers[$i];
 563                         $server['serverIndex'] = $i;
 564                         $conn = $this->reallyOpenConnection( $server, false );
 565                         if ( $conn->isOpen() ) {
 566                                 $this->mConns['local'][$i][0] = $conn;
 567                         } else {
 568                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 569                                 $this->mErrorConnection = $conn;
 570                                 $conn = false;
 571                         }
 572                 }
 573                 wfProfileOut( __METHOD__ );
 574                 return $conn;
 575         }
 576
 577         /**
 578          * Open a connection to a foreign DB, or return one if it is already open.
 579          *
 580          * Increments a reference count on the returned connection which locks the
 581          * connection to the requested wiki. This reference count can be
 582          * decremented by calling reuseConnection().
 583          *
 584          * If a connection is open to the appropriate server already, but with the wrong
 585          * database, it will be switched to the right database and returned, as long as
 586          * it has been freed first with reuseConnection().
 587          *
 588          * On error, returns false, and the connection which caused the
 589          * error will be available via $this->mErrorConnection.
 590          *
 591          * @param $i Integer: server index
 592          * @param $wiki String: wiki ID to open
 593          * @return DatabaseBase
 594          */
 595         function openForeignConnection( $i, $wiki ) {
 596                 wfProfileIn(__METHOD__);
 597                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 598                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 599                         // Reuse an already-used connection
 600                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 601                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 602                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 603                         // Reuse a free connection for the same wiki
 604                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 605                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 606                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 607                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 608                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 609                         // Reuse a connection from another wiki
 610                         $conn = reset( $this->mConns['foreignFree'][$i] );
 611                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 612
 613                         if ( !$conn->selectDB( $dbName ) ) {
 614                                 $this->mLastError = "Error selecting database $dbName on server " .
 615                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 616                                 $this->mErrorConnection = $conn;
 617                                 $conn = false;
 618                         } else {
 619                                 $conn->tablePrefix( $prefix );
 620                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 621                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 622                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 623                         }
 624                 } else {
 625                         // Open a new connection
 626                         $server = $this->mServers[$i];
 627                         $server['serverIndex'] = $i;
 628                         $server['foreignPoolRefCount'] = 0;
 629                         $conn = $this->reallyOpenConnection( $server, $dbName );
 630                         if ( !$conn->isOpen() ) {
 631                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 632                                 $this->mErrorConnection = $conn;
 633                                 $conn = false;
 634                         } else {
 635                                 $conn->tablePrefix( $prefix );
 636                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 637                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 638                         }
 639                 }
 640
 641                 // Increment reference count
 642                 if ( $conn ) {
 643                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 644                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 645                 }
 646                 wfProfileOut(__METHOD__);
 647                 return $conn;
 648         }
 649
 650         /**
 651          * Test if the specified index represents an open connection
 652          *
 653          * @param $index Integer: server index
 654          * @access private
 655          * @return bool
 656          */
 657         function isOpen( $index ) {
 658                 if( !is_integer( $index ) ) {
 659                         return false;
 660                 }
 661                 return (bool)$this->getAnyOpenConnection( $index );
 662         }
 663
 664         /**
 665          * Really opens a connection. Uncached.
 666          * Returns a Database object whether or not the connection was successful.
 667          * @access private
 668          *
 669          * @return DatabaseBase
 670          */
 671         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 672                 if( !is_array( $server ) ) {
 673                         throw new MWException( 'You must update your load-balancing configuration. ' .
 674                                 'See DefaultSettings.php entry for $wgDBservers.' );
 675                 }
 676
 677                 $host = $server['host'];
 678                 $dbname = $server['dbname'];
 679
 680                 if ( $dbNameOverride !== false ) {
 681                         $server['dbname'] = $dbname = $dbNameOverride;
 682                 }
 683
 684                 # Create object
 685                 wfDebug( "Connecting to $host $dbname...\n" );
 686                 try {
 687                         $db = DatabaseBase::factory( $server['type'], $server );
 688                 } catch ( DBConnectionError $e ) {
 689                         // FIXME: This is probably the ugliest thing I have ever done to
 690                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 691                         $db = $e->db;
 692                 }
 693
 694                 if ( $db->isOpen() ) {
 695                         wfDebug( "Connected to $host $dbname.\n" );
 696                 } else {
 697                         wfDebug( "Connection failed to $host $dbname.\n" );
 698                 }
 699                 $db->setLBInfo( $server );
 700                 if ( isset( $server['fakeSlaveLag'] ) ) {
 701                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 702                 }
 703                 if ( isset( $server['fakeMaster'] ) ) {
 704                         $db->setFakeMaster( true );
 705                 }
 706                 return $db;
 707         }
 708
 709         function reportConnectionError( &$conn ) {
 710                 wfProfileIn( __METHOD__ );
 711
 712                 if ( !is_object( $conn ) ) {
 713                         // No last connection, probably due to all servers being too busy
 714                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 715                         $conn = new Database;
 716                         // If all servers were busy, mLastError will contain something sensible
 717                         throw new DBConnectionError( $conn, $this->mLastError );
 718                 } else {
 719                         $server = $conn->getProperty( 'mServer' );
 720                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 721                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 722                 }
 723                 wfProfileOut( __METHOD__ );
 724         }
 725
 726         /**
 727          * @return int
 728          */
 729         function getWriterIndex() {
 730                 return 0;
 731         }
 732
 733         /**
 734          * Returns true if the specified index is a valid server index
 735          *
 736          * @return bool
 737          */
 738         function haveIndex( $i ) {
 739                 return array_key_exists( $i, $this->mServers );
 740         }
 741
 742         /**
 743          * Returns true if the specified index is valid and has non-zero load
 744          *
 745          * @return bool
 746          */
 747         function isNonZeroLoad( $i ) {
 748                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 749         }
 750
 751         /**
 752          * Get the number of defined servers (not the number of open connections)
 753          *
 754          * @return int
 755          */
 756         function getServerCount() {
 757                 return count( $this->mServers );
 758         }
 759
 760         /**
 761          * Get the host name or IP address of the server with the specified index
 762          * Prefer a readable name if available.
 763          */
 764         function getServerName( $i ) {
 765                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 766                         return $this->mServers[$i]['hostName'];
 767                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 768                         return $this->mServers[$i]['host'];
 769                 } else {
 770                         return '';
 771                 }
 772         }
 773
 774         /**
 775          * Return the server info structure for a given index, or false if the index is invalid.
 776          */
 777         function getServerInfo( $i ) {
 778                 if ( isset( $this->mServers[$i] ) ) {
 779                         return $this->mServers[$i];
 780                 } else {
 781                         return false;
 782                 }
 783         }
 784
 785         /**
 786          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 787          */
 788         function setServerInfo( $i, $serverInfo ) {
 789                 $this->mServers[$i] = $serverInfo;
 790         }
 791
 792         /**
 793          * Get the current master position for chronology control purposes
 794          * @return mixed
 795          */
 796         function getMasterPos() {
 797                 # If this entire request was served from a slave without opening a connection to the
 798                 # master (however unlikely that may be), then we can fetch the position from the slave.
 799                 $masterConn = $this->getAnyOpenConnection( 0 );
 800                 if ( !$masterConn ) {
 801                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 802                                 $conn = $this->getAnyOpenConnection( $i );
 803                                 if ( $conn ) {
 804                                         wfDebug( "Master pos fetched from slave\n" );
 805                                         return $conn->getSlavePos();
 806                                 }
 807                         }
 808                 } else {
 809                         wfDebug( "Master pos fetched from master\n" );
 810                         return $masterConn->getMasterPos();
 811                 }
 812                 return false;
 813         }
 814
 815         /**
 816          * Close all open connections
 817          */
 818         function closeAll() {
 819                 foreach ( $this->mConns as $conns2 ) {
 820                         foreach  ( $conns2 as $conns3 ) {
 821                                 foreach ( $conns3 as $conn ) {
 822                                         $conn->close();
 823                                 }
 824                         }
 825                 }
 826                 $this->mConns = array(
 827                         'local' => array(),
 828                         'foreignFree' => array(),
 829                         'foreignUsed' => array(),
 830                 );
 831         }
 832
 833         /**
 834          * Deprecated function, typo in function name
 835          *
 836          * @deprecated in 1.18
 837          */
 838         function closeConnecton( $conn ) {
 839                 $this->closeConnection( $conn );
 840         }
 841
 842         /**
 843          * Close a connection
 844          * Using this function makes sure the LoadBalancer knows the connection is closed.
 845          * If you use $conn->close() directly, the load balancer won't update its state.
 846          * @param $conn DatabaseBase
 847          */
 848         function closeConnection( $conn ) {
 849                 $done = false;
 850                 foreach ( $this->mConns as $i1 => $conns2 ) {
 851                         foreach ( $conns2 as $i2 => $conns3 ) {
 852                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 853                                         if ( $conn === $candidateConn ) {
 854                                                 $conn->close();
 855                                                 unset( $this->mConns[$i1][$i2][$i3] );
 856                                                 $done = true;
 857                                                 break;
 858                                         }
 859                                 }
 860                         }
 861                 }
 862                 if ( !$done ) {
 863                         $conn->close();
 864                 }
 865         }
 866
 867         /**
 868          * Commit transactions on all open connections
 869          */
 870         function commitAll() {
 871                 foreach ( $this->mConns as $conns2 ) {
 872                         foreach ( $conns2 as $conns3 ) {
 873                                 foreach ( $conns3 as $conn ) {
 874                                         $conn->commit();
 875                                 }
 876                         }
 877                 }
 878         }
 879
 880         /**
 881          *  Issue COMMIT only on master, only if queries were done on connection
 882          */
 883         function commitMasterChanges() {
 884                 // Always 0, but who knows.. :)
 885                 $masterIndex = $this->getWriterIndex();
 886                 foreach ( $this->mConns as $conns2 ) {
 887                         if ( empty( $conns2[$masterIndex] ) ) {
 888                                 continue;
 889                         }
 890                         foreach ( $conns2[$masterIndex] as $conn ) {
 891                                 if ( $conn->doneWrites() ) {
 892                                         $conn->commit();
 893                                 }
 894                         }
 895                 }
 896         }
 897
 898         /**
 899          * @param $value null
 900          * @return Mixed
 901          */
 902         function waitTimeout( $value = null ) {
 903                 return wfSetVar( $this->mWaitTimeout, $value );
 904         }
 905
 906         /**
 907          * @return bool
 908          */
 909         function getLaggedSlaveMode() {
 910                 return $this->mLaggedSlaveMode;
 911         }
 912
 913         /* Disables/enables lag checks */
 914         function allowLagged( $mode = null ) {
 915                 if ( $mode === null) {
 916                         return $this->mAllowLagged;
 917                 }
 918                 $this->mAllowLagged = $mode;
 919         }
 920
 921         /**
 922          * @return bool
 923          */
 924         function pingAll() {
 925                 $success = true;
 926                 foreach ( $this->mConns as $conns2 ) {
 927                         foreach ( $conns2 as $conns3 ) {
 928                                 foreach ( $conns3 as $conn ) {
 929                                         if ( !$conn->ping() ) {
 930                                                 $success = false;
 931                                         }
 932                                 }
 933                         }
 934                 }
 935                 return $success;
 936         }
 937
 938         /**
 939          * Call a function with each open connection object
 940          */
 941         function forEachOpenConnection( $callback, $params = array() ) {
 942                 foreach ( $this->mConns as $conns2 ) {
 943                         foreach ( $conns2 as $conns3 ) {
 944                                 foreach ( $conns3 as $conn ) {
 945                                         $mergedParams = array_merge( array( $conn ), $params );
 946                                         call_user_func_array( $callback, $mergedParams );
 947                                 }
 948                         }
 949                 }
 950         }
 951
 952         /**
 953          * Get the hostname and lag time of the most-lagged slave.
 954          * This is useful for maintenance scripts that need to throttle their updates.
 955          * May attempt to open connections to slaves on the default DB. If there is
 956          * no lag, the maximum lag will be reported as -1.
 957          *
 958          * @param $wiki string Wiki ID, or false for the default database
 959          *
 960          * @return array ( host, max lag, index of max lagged host )
 961          */
 962         function getMaxLag( $wiki = false ) {
 963                 $maxLag = -1;
 964                 $host = '';
 965                 $maxIndex = 0;
 966                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
 967                         foreach ( $this->mServers as $i => $conn ) {
 968                                 $conn = false;
 969                                 if ( $wiki === false ) {
 970                                         $conn = $this->getAnyOpenConnection( $i );
 971                                 }
 972                                 if ( !$conn ) {
 973                                         $conn = $this->openConnection( $i, $wiki );
 974                                 }
 975                                 if ( !$conn ) {
 976                                         continue;
 977                                 }
 978                                 $lag = $conn->getLag();
 979                                 if ( $lag > $maxLag ) {
 980                                         $maxLag = $lag;
 981                                         $host = $this->mServers[$i]['host'];
 982                                         $maxIndex = $i;
 983                                 }
 984                         }
 985                 }
 986                 return array( $host, $maxLag, $maxIndex );
 987         }
 988
 989         /**
 990          * Get lag time for each server
 991          * Results are cached for a short time in memcached, and indefinitely in the process cache
 992          *
 993          * @param $wiki
 994          *
 995          * @return array
 996          */
 997         function getLagTimes( $wiki = false ) {
 998                 # Try process cache
 999                 if ( isset( $this->mLagTimes ) ) {
1000                         return $this->mLagTimes;
1001                 }
1002                 if ( $this->getServerCount() == 1 ) {
1003                         # No replication
1004                         $this->mLagTimes = array( 0 => 0 );
1005                 } else {
1006                         # Send the request to the load monitor
1007                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1008                                 array_keys( $this->mServers ), $wiki );
1009                 }
1010                 return $this->mLagTimes;
1011         }
1012
1013         /**
1014          * Get the lag in seconds for a given connection, or zero if this load
1015          * balancer does not have replication enabled.
1016          *
1017          * This should be used in preference to Database::getLag() in cases where
1018          * replication may not be in use, since there is no way to determine if
1019          * replication is in use at the connection level without running
1020          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1021          * function instead of Database::getLag() avoids a fatal error in this
1022          * case on many installations.
1023          *
1024          * @param $conn DatabaseBase
1025          *
1026          * @return int
1027          */
1028         function safeGetLag( $conn ) {
1029                 if ( $this->getServerCount() == 1 ) {
1030                         return 0;
1031                 } else {
1032                         return $conn->getLag();
1033                 }
1034         }
1035
1036         /**
1037          * Clear the cache for getLagTimes
1038          */
1039         function clearLagTimeCache() {
1040                 $this->mLagTimes = null;
1041         }
1042 }