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 ( $lag === false ) {
 143                                         wfDebug( "Server #$i is not replicating\n" );
 144                                         unset( $loads[$i] );
 145                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 146                                         wfDebug( "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                                                 $wgReadOnly = wfMessage( 'readonly_lag' )->useDatabase( false )->plain();
 245                                                 $i = $this->pickRandom( $currentLoads );
 246                                                 $laggedSlaveMode = true;
 247                                         }
 248                                 }
 249
 250                                 if ( $i === false ) {
 251                                         # pickRandom() returned false
 252                                         # This is permanent and means the configuration or the load monitor
 253                                         # wants us to return false.
 254                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 255                                         wfProfileOut( __METHOD__ );
 256                                         return false;
 257                                 }
 258
 259                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 260                                 $conn = $this->openConnection( $i, $wiki );
 261
 262                                 if ( !$conn ) {
 263                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 264                                         unset( $nonErrorLoads[$i] );
 265                                         unset( $currentLoads[$i] );
 266                                         continue;
 267                                 }
 268
 269                                 // Perform post-connection backoff
 270                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 271                                         ? $this->mServers[$i]['max threads'] : false;
 272                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 273
 274                                 // Decrement reference counter, we are finished with this connection.
 275                                 // It will be incremented for the caller later.
 276                                 if ( $wiki !== false ) {
 277                                         $this->reuseConnection( $conn );
 278                                 }
 279
 280                                 if ( $backoff ) {
 281                                         # Post-connection overload, don't use this server for now
 282                                         $totalThreadsConnected += $backoff;
 283                                         $overloadedServers++;
 284                                         unset( $currentLoads[$i] );
 285                                 } else {
 286                                         # Return this server
 287                                         break 2;
 288                                 }
 289                         }
 290
 291                         # No server found yet
 292                         $i = false;
 293
 294                         # If all servers were down, quit now
 295                         if ( !count( $nonErrorLoads ) ) {
 296                                 wfDebugLog( 'connect', "All servers down\n" );
 297                                 break;
 298                         }
 299
 300                         # Some servers must have been overloaded
 301                         if ( $overloadedServers == 0 ) {
 302                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 303                         }
 304                         # Back off for a while
 305                         # Scale the sleep time by the number of connected threads, to produce a
 306                         # roughly constant global poll rate
 307                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 308                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 309                 } while ( $totalElapsed < $timeout );
 310
 311                 if ( $totalElapsed >= $timeout ) {
 312                         wfDebugLog( 'connect', "All servers busy\n" );
 313                         $this->mErrorConnection = false;
 314                         $this->mLastError = 'All servers busy';
 315                 }
 316
 317                 if ( $i !== false ) {
 318                         # Slave connection successful
 319                         # Wait for the session master pos for a short time
 320                         if ( $this->mWaitForPos && $i > 0 ) {
 321                                 if ( !$this->doWait( $i ) ) {
 322                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 323                                 }
 324                         }
 325                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 326                                 $this->mReadIndex = $i;
 327                         }
 328                 }
 329                 wfProfileOut( __METHOD__ );
 330                 return $i;
 331         }
 332
 333         /**
 334          * Wait for a specified number of microseconds, and return the period waited
 335          */
 336         function sleep( $t ) {
 337                 wfProfileIn( __METHOD__ );
 338                 wfDebug( __METHOD__.": waiting $t us\n" );
 339                 usleep( $t );
 340                 wfProfileOut( __METHOD__ );
 341                 return $t;
 342         }
 343
 344         /**
 345          * Set the master wait position
 346          * If a DB_SLAVE connection has been opened already, waits
 347          * Otherwise sets a variable telling it to wait if such a connection is opened
 348          */
 349         public function waitFor( $pos ) {
 350                 wfProfileIn( __METHOD__ );
 351                 $this->mWaitForPos = $pos;
 352                 $i = $this->mReadIndex;
 353
 354                 if ( $i > 0 ) {
 355                         if ( !$this->doWait( $i ) ) {
 356                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 357                                 $this->mLaggedSlaveMode = true;
 358                         }
 359                 }
 360                 wfProfileOut( __METHOD__ );
 361         }
 362
 363         /**
 364          * Set the master wait position and wait for ALL slaves to catch up to it
 365          */
 366         public function waitForAll( $pos ) {
 367                 wfProfileIn( __METHOD__ );
 368                 $this->mWaitForPos = $pos;
 369                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 370                         $this->doWait( $i , true );
 371                 }
 372                 wfProfileOut( __METHOD__ );
 373         }
 374
 375         /**
 376          * Get any open connection to a given server index, local or foreign
 377          * Returns false if there is no connection open
 378          *
 379          * @return DatabaseBase
 380          */
 381         function getAnyOpenConnection( $i ) {
 382                 foreach ( $this->mConns as $conns ) {
 383                         if ( !empty( $conns[$i] ) ) {
 384                                 return reset( $conns[$i] );
 385                         }
 386                 }
 387                 return false;
 388         }
 389
 390         /**
 391          * Wait for a given slave to catch up to the master pos stored in $this
 392          */
 393         function doWait( $index, $open = false ) {
 394                 # Find a connection to wait on
 395                 $conn = $this->getAnyOpenConnection( $index );
 396                 if ( !$conn ) {
 397                         if ( !$open ) {
 398                                 wfDebug( __METHOD__ . ": no connection open\n" );
 399                                 return false;
 400                         } else {
 401                                 $conn = $this->openConnection( $index );
 402                                 if ( !$conn ) {
 403                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 404                                         return false;
 405                                 }
 406                         }
 407                 }
 408
 409                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 410                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 411
 412                 if ( $result == -1 || is_null( $result ) ) {
 413                         # Timed out waiting for slave, use master instead
 414                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 415                         return false;
 416                 } else {
 417                         wfDebug( __METHOD__.": Done\n" );
 418                         return true;
 419                 }
 420         }
 421
 422         /**
 423          * Get a connection by index
 424          * This is the main entry point for this class.
 425          *
 426          * @param $i Integer: server index
 427          * @param $groups Array: query groups
 428          * @param $wiki String: wiki ID
 429          *
 430          * @return DatabaseBase
 431          */
 432         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 433                 wfProfileIn( __METHOD__ );
 434
 435                 if ( $i == DB_LAST ) {
 436                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 437                 } elseif ( $i === null || $i === false ) {
 438                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 439                 }
 440
 441                 if ( $wiki === wfWikiID() ) {
 442                         $wiki = false;
 443                 }
 444
 445                 # Query groups
 446                 if ( $i == DB_MASTER ) {
 447                         $i = $this->getWriterIndex();
 448                 } elseif ( !is_array( $groups ) ) {
 449                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 450                         if ( $groupIndex !== false ) {
 451                                 $serverName = $this->getServerName( $groupIndex );
 452                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 453                                 $i = $groupIndex;
 454                         }
 455                 } else {
 456                         foreach ( $groups as $group ) {
 457                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 458                                 if ( $groupIndex !== false ) {
 459                                         $serverName = $this->getServerName( $groupIndex );
 460                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 461                                         $i = $groupIndex;
 462                                         break;
 463                                 }
 464                         }
 465                 }
 466
 467                 # Operation-based index
 468                 if ( $i == DB_SLAVE ) {
 469                         $i = $this->getReaderIndex( false, $wiki );
 470                         # Couldn't find a working server in getReaderIndex()?
 471                         if ( $i === false ) {
 472                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 473                                 $this->reportConnectionError( $this->mErrorConnection );
 474                                 wfProfileOut( __METHOD__ );
 475                                 return false;
 476                         }
 477                 }
 478
 479                 # Now we have an explicit index into the servers array
 480                 $conn = $this->openConnection( $i, $wiki );
 481                 if ( !$conn ) {
 482                         $this->reportConnectionError( $this->mErrorConnection );
 483                 }
 484
 485                 wfProfileOut( __METHOD__ );
 486                 return $conn;
 487         }
 488
 489         /**
 490          * Mark a foreign connection as being available for reuse under a different
 491          * DB name or prefix. This mechanism is reference-counted, and must be called
 492          * the same number of times as getConnection() to work.
 493          *
 494          * @param DatabaseBase $conn
 495          */
 496         public function reuseConnection( $conn ) {
 497                 $serverIndex = $conn->getLBInfo('serverIndex');
 498                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 499                 $dbName = $conn->getDBname();
 500                 $prefix = $conn->tablePrefix();
 501                 if ( strval( $prefix ) !== '' ) {
 502                         $wiki = "$dbName-$prefix";
 503                 } else {
 504                         $wiki = $dbName;
 505                 }
 506                 if ( $serverIndex === null || $refCount === null ) {
 507                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 508                         /**
 509                          * This can happen in code like:
 510                          *   foreach ( $dbs as $db ) {
 511                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 512                          *     ...
 513                          *     $lb->reuseConnection( $conn );
 514                          *   }
 515                          * When a connection to the local DB is opened in this way, reuseConnection()
 516                          * should be ignored
 517                          */
 518                         return;
 519                 }
 520                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 521                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 522                 }
 523                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 524                 if ( $refCount <= 0 ) {
 525                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 526                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 527                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 528                 } else {
 529                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 530                 }
 531         }
 532
 533         /**
 534          * Open a connection to the server given by the specified index
 535          * Index must be an actual index into the array.
 536          * If the server is already open, returns it.
 537          *
 538          * On error, returns false, and the connection which caused the
 539          * error will be available via $this->mErrorConnection.
 540          *
 541          * @param $i Integer server index
 542          * @param $wiki String wiki ID to open
 543          * @return DatabaseBase
 544          *
 545          * @access private
 546          */
 547         function openConnection( $i, $wiki = false ) {
 548                 wfProfileIn( __METHOD__ );
 549                 if ( $wiki !== false ) {
 550                         $conn = $this->openForeignConnection( $i, $wiki );
 551                         wfProfileOut( __METHOD__);
 552                         return $conn;
 553                 }
 554                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 555                         $conn = $this->mConns['local'][$i][0];
 556                 } else {
 557                         $server = $this->mServers[$i];
 558                         $server['serverIndex'] = $i;
 559                         $conn = $this->reallyOpenConnection( $server, false );
 560                         if ( $conn->isOpen() ) {
 561                                 $this->mConns['local'][$i][0] = $conn;
 562                         } else {
 563                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 564                                 $this->mErrorConnection = $conn;
 565                                 $conn = false;
 566                         }
 567                 }
 568                 wfProfileOut( __METHOD__ );
 569                 return $conn;
 570         }
 571
 572         /**
 573          * Open a connection to a foreign DB, or return one if it is already open.
 574          *
 575          * Increments a reference count on the returned connection which locks the
 576          * connection to the requested wiki. This reference count can be
 577          * decremented by calling reuseConnection().
 578          *
 579          * If a connection is open to the appropriate server already, but with the wrong
 580          * database, it will be switched to the right database and returned, as long as
 581          * it has been freed first with reuseConnection().
 582          *
 583          * On error, returns false, and the connection which caused the
 584          * error will be available via $this->mErrorConnection.
 585          *
 586          * @param $i Integer: server index
 587          * @param $wiki String: wiki ID to open
 588          * @return DatabaseBase
 589          */
 590         function openForeignConnection( $i, $wiki ) {
 591                 wfProfileIn(__METHOD__);
 592                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 593                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 594                         // Reuse an already-used connection
 595                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 596                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 597                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 598                         // Reuse a free connection for the same wiki
 599                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 600                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 601                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 602                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 603                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 604                         // Reuse a connection from another wiki
 605                         $conn = reset( $this->mConns['foreignFree'][$i] );
 606                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 607
 608                         if ( !$conn->selectDB( $dbName ) ) {
 609                                 $this->mLastError = "Error selecting database $dbName on server " .
 610                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 611                                 $this->mErrorConnection = $conn;
 612                                 $conn = false;
 613                         } else {
 614                                 $conn->tablePrefix( $prefix );
 615                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 616                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 617                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 618                         }
 619                 } else {
 620                         // Open a new connection
 621                         $server = $this->mServers[$i];
 622                         $server['serverIndex'] = $i;
 623                         $server['foreignPoolRefCount'] = 0;
 624                         $conn = $this->reallyOpenConnection( $server, $dbName );
 625                         if ( !$conn->isOpen() ) {
 626                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 627                                 $this->mErrorConnection = $conn;
 628                                 $conn = false;
 629                         } else {
 630                                 $conn->tablePrefix( $prefix );
 631                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 632                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 633                         }
 634                 }
 635
 636                 // Increment reference count
 637                 if ( $conn ) {
 638                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 639                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 640                 }
 641                 wfProfileOut(__METHOD__);
 642                 return $conn;
 643         }
 644
 645         /**
 646          * Test if the specified index represents an open connection
 647          *
 648          * @param $index Integer: server index
 649          * @access private
 650          * @return bool
 651          */
 652         function isOpen( $index ) {
 653                 if( !is_integer( $index ) ) {
 654                         return false;
 655                 }
 656                 return (bool)$this->getAnyOpenConnection( $index );
 657         }
 658
 659         /**
 660          * Really opens a connection. Uncached.
 661          * Returns a Database object whether or not the connection was successful.
 662          * @access private
 663          *
 664          * @return DatabaseBase
 665          */
 666         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 667                 if( !is_array( $server ) ) {
 668                         throw new MWException( 'You must update your load-balancing configuration. ' .
 669                                                'See DefaultSettings.php entry for $wgDBservers.' );
 670                 }
 671
 672                 $host = $server['host'];
 673                 $dbname = $server['dbname'];
 674
 675                 if ( $dbNameOverride !== false ) {
 676                         $server['dbname'] = $dbname = $dbNameOverride;
 677                 }
 678
 679                 # Create object
 680                 wfDebug( "Connecting to $host $dbname...\n" );
 681                 $db = DatabaseBase::factory( $server['type'], $server );
 682                 if ( $db->isOpen() ) {
 683                         wfDebug( "Connected to $host $dbname.\n" );
 684                 } else {
 685                         wfDebug( "Connection failed to $host $dbname.\n" );
 686                 }
 687                 $db->setLBInfo( $server );
 688                 if ( isset( $server['fakeSlaveLag'] ) ) {
 689                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 690                 }
 691                 if ( isset( $server['fakeMaster'] ) ) {
 692                         $db->setFakeMaster( true );
 693                 }
 694                 return $db;
 695         }
 696
 697         function reportConnectionError( &$conn ) {
 698                 wfProfileIn( __METHOD__ );
 699
 700                 if ( !is_object( $conn ) ) {
 701                         // No last connection, probably due to all servers being too busy
 702                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 703                         $conn = new Database;
 704                         // If all servers were busy, mLastError will contain something sensible
 705                         throw new DBConnectionError( $conn, $this->mLastError );
 706                 } else {
 707                         $server = $conn->getProperty( 'mServer' );
 708                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 709                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 710                 }
 711                 wfProfileOut( __METHOD__ );
 712         }
 713
 714         function getWriterIndex() {
 715                 return 0;
 716         }
 717
 718         /**
 719          * Returns true if the specified index is a valid server index
 720          *
 721          * @return bool
 722          */
 723         function haveIndex( $i ) {
 724                 return array_key_exists( $i, $this->mServers );
 725         }
 726
 727         /**
 728          * Returns true if the specified index is valid and has non-zero load
 729          *
 730          * @return bool
 731          */
 732         function isNonZeroLoad( $i ) {
 733                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 734         }
 735
 736         /**
 737          * Get the number of defined servers (not the number of open connections)
 738          *
 739          * @return int
 740          */
 741         function getServerCount() {
 742                 return count( $this->mServers );
 743         }
 744
 745         /**
 746          * Get the host name or IP address of the server with the specified index
 747          * Prefer a readable name if available.
 748          */
 749         function getServerName( $i ) {
 750                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 751                         return $this->mServers[$i]['hostName'];
 752                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 753                         return $this->mServers[$i]['host'];
 754                 } else {
 755                         return '';
 756                 }
 757         }
 758
 759         /**
 760          * Return the server info structure for a given index, or false if the index is invalid.
 761          */
 762         function getServerInfo( $i ) {
 763                 if ( isset( $this->mServers[$i] ) ) {
 764                         return $this->mServers[$i];
 765                 } else {
 766                         return false;
 767                 }
 768         }
 769
 770         /**
 771          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 772          */
 773         function setServerInfo( $i, $serverInfo ) {
 774                 $this->mServers[$i] = $serverInfo;
 775         }
 776
 777         /**
 778          * Get the current master position for chronology control purposes
 779          * @return mixed
 780          */
 781         function getMasterPos() {
 782                 # If this entire request was served from a slave without opening a connection to the
 783                 # master (however unlikely that may be), then we can fetch the position from the slave.
 784                 $masterConn = $this->getAnyOpenConnection( 0 );
 785                 if ( !$masterConn ) {
 786                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 787                                 $conn = $this->getAnyOpenConnection( $i );
 788                                 if ( $conn ) {
 789                                         wfDebug( "Master pos fetched from slave\n" );
 790                                         return $conn->getSlavePos();
 791                                 }
 792                         }
 793                 } else {
 794                         wfDebug( "Master pos fetched from master\n" );
 795                         return $masterConn->getMasterPos();
 796                 }
 797                 return false;
 798         }
 799
 800         /**
 801          * Close all open connections
 802          */
 803         function closeAll() {
 804                 foreach ( $this->mConns as $conns2 ) {
 805                         foreach  ( $conns2 as $conns3 ) {
 806                                 foreach ( $conns3 as $conn ) {
 807                                         $conn->close();
 808                                 }
 809                         }
 810                 }
 811                 $this->mConns = array(
 812                         'local' => array(),
 813                         'foreignFree' => array(),
 814                         'foreignUsed' => array(),
 815                 );
 816         }
 817
 818         /**
 819          * Deprecated function, typo in function name
 820          *
 821          * @deprecated in 1.18
 822          */
 823         function closeConnecton( $conn ) {
 824                 $this->closeConnection( $conn );
 825         }
 826
 827         /**
 828          * Close a connection
 829          * Using this function makes sure the LoadBalancer knows the connection is closed.
 830          * If you use $conn->close() directly, the load balancer won't update its state.
 831          * @param $conn
 832          * @return void
 833          */
 834         function closeConnection( $conn ) {
 835                 $done = false;
 836                 foreach ( $this->mConns as $i1 => $conns2 ) {
 837                         foreach ( $conns2 as $i2 => $conns3 ) {
 838                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 839                                         if ( $conn === $candidateConn ) {
 840                                                 $conn->close();
 841                                                 unset( $this->mConns[$i1][$i2][$i3] );
 842                                                 $done = true;
 843                                                 break;
 844                                         }
 845                                 }
 846                         }
 847                 }
 848                 if ( !$done ) {
 849                         $conn->close();
 850                 }
 851         }
 852
 853         /**
 854          * Commit transactions on all open connections
 855          */
 856         function commitAll() {
 857                 foreach ( $this->mConns as $conns2 ) {
 858                         foreach ( $conns2 as $conns3 ) {
 859                                 foreach ( $conns3 as $conn ) {
 860                                         $conn->commit();
 861                                 }
 862                         }
 863                 }
 864         }
 865
 866         /**
 867          *  Issue COMMIT only on master, only if queries were done on connection
 868          */
 869         function commitMasterChanges() {
 870                 // Always 0, but who knows.. :)
 871                 $masterIndex = $this->getWriterIndex();
 872                 foreach ( $this->mConns as $conns2 ) {
 873                         if ( empty( $conns2[$masterIndex] ) ) {
 874                                 continue;
 875                         }
 876                         foreach ( $conns2[$masterIndex] as $conn ) {
 877                                 if ( $conn->doneWrites() ) {
 878                                         $conn->commit();
 879                                 }
 880                         }
 881                 }
 882         }
 883
 884         function waitTimeout( $value = null ) {
 885                 return wfSetVar( $this->mWaitTimeout, $value );
 886         }
 887
 888         function getLaggedSlaveMode() {
 889                 return $this->mLaggedSlaveMode;
 890         }
 891
 892         /* Disables/enables lag checks */
 893         function allowLagged( $mode = null ) {
 894                 if ( $mode === null) {
 895                         return $this->mAllowLagged;
 896                 }
 897                 $this->mAllowLagged = $mode;
 898         }
 899
 900         function pingAll() {
 901                 $success = true;
 902                 foreach ( $this->mConns as $conns2 ) {
 903                         foreach ( $conns2 as $conns3 ) {
 904                                 foreach ( $conns3 as $conn ) {
 905                                         if ( !$conn->ping() ) {
 906                                                 $success = false;
 907                                         }
 908                                 }
 909                         }
 910                 }
 911                 return $success;
 912         }
 913
 914         /**
 915          * Call a function with each open connection object
 916          */
 917         function forEachOpenConnection( $callback, $params = array() ) {
 918                 foreach ( $this->mConns as $conns2 ) {
 919                         foreach ( $conns2 as $conns3 ) {
 920                                 foreach ( $conns3 as $conn ) {
 921                                         $mergedParams = array_merge( array( $conn ), $params );
 922                                         call_user_func_array( $callback, $mergedParams );
 923                                 }
 924                         }
 925                 }
 926         }
 927
 928         /**
 929          * Get the hostname and lag time of the most-lagged slave.
 930          * This is useful for maintenance scripts that need to throttle their updates.
 931          * May attempt to open connections to slaves on the default DB.
 932          * @param $wiki string Wiki ID, or false for the default database
 933          *
 934          * @return array ( host, max lag, index of max lagged host )
 935          */
 936         function getMaxLag( $wiki = false ) {
 937                 $maxLag = -1;
 938                 $host = '';
 939                 $maxIndex = 0;
 940                 foreach ( $this->mServers as $i => $conn ) {
 941                         $conn = false;
 942                         if ( $wiki === false ) {
 943                                 $conn = $this->getAnyOpenConnection( $i );
 944                         }
 945                         if ( !$conn ) {
 946                                 $conn = $this->openConnection( $i, $wiki );
 947                         }
 948                         if ( !$conn ) {
 949                                 continue;
 950                         }
 951                         $lag = $conn->getLag();
 952                         if ( $lag > $maxLag ) {
 953                                 $maxLag = $lag;
 954                                 $host = $this->mServers[$i]['host'];
 955                                 $maxIndex = $i;
 956                         }
 957                 }
 958                 return array( $host, $maxLag, $maxIndex );
 959         }
 960
 961         /**
 962          * Get lag time for each server
 963          * Results are cached for a short time in memcached, and indefinitely in the process cache
 964          *
 965          * @param $wiki
 966          *
 967          * @return array
 968          */
 969         function getLagTimes( $wiki = false ) {
 970                 # Try process cache
 971                 if ( isset( $this->mLagTimes ) ) {
 972                         return $this->mLagTimes;
 973                 }
 974                 # No, send the request to the load monitor
 975                 $this->mLagTimes = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
 976                 return $this->mLagTimes;
 977         }
 978
 979         /**
 980          * Clear the cache for getLagTimes
 981          */
 982         function clearLagTimeCache() {
 983                 $this->mLagTimes = null;
 984         }
 985 }