includes/db/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing
   4  *
   5  * @file
   6  * @ingroup Database
   7  */
   8
   9 /**
  10  * Database load balancing object
  11  *
  12  * @todo document
  13  * @ingroup Database
  14  */
  15 class LoadBalancer {
  16         /* private */ var $mServers, $mConns, $mLoads, $mGroupLoads;
  17         /* private */ var $mErrorConnection;
  18         /* private */ var $mReadIndex, $mAllowLagged;
  19         /* private */ var $mWaitForPos, $mWaitTimeout;
  20         /* private */ var $mLaggedSlaveMode, $mLastError = 'Unknown error';
  21         /* private */ var $mParentInfo, $mLagTimes;
  22         /* private */ var $mLoadMonitorClass, $mLoadMonitor;
  23
  24         /**
  25          * @param $params Array with keys:
  26          *    servers           Required. Array of server info structures.
  27          *    masterWaitTimeout Replication lag wait timeout
  28          *    loadMonitor       Name of a class used to fetch server lag and load.
  29          */
  30         function __construct( $params )
  31         {
  32                 if ( !isset( $params['servers'] ) ) {
  33                         throw new MWException( __CLASS__.': missing servers parameter' );
  34                 }
  35                 $this->mServers = $params['servers'];
  36
  37                 if ( isset( $params['waitTimeout'] ) ) {
  38                         $this->mWaitTimeout = $params['waitTimeout'];
  39                 } else {
  40                         $this->mWaitTimeout = 10;
  41                 }
  42
  43                 $this->mReadIndex = -1;
  44                 $this->mWriteIndex = -1;
  45                 $this->mConns = array(
  46                         'local' => array(),
  47                         'foreignUsed' => array(),
  48                         'foreignFree' => array() );
  49                 $this->mLoads = array();
  50                 $this->mWaitForPos = false;
  51                 $this->mLaggedSlaveMode = false;
  52                 $this->mErrorConnection = false;
  53                 $this->mAllowLagged = false;
  54                 $this->mLoadMonitorClass = isset( $params['loadMonitor'] )
  55                         ? $params['loadMonitor'] : 'LoadMonitor_MySQL';
  56
  57                 foreach( $params['servers'] as $i => $server ) {
  58                         $this->mLoads[$i] = $server['load'];
  59                         if ( isset( $server['groupLoads'] ) ) {
  60                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  61                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  62                                                 $this->mGroupLoads[$group] = array();
  63                                         }
  64                                         $this->mGroupLoads[$group][$i] = $ratio;
  65                                 }
  66                         }
  67                 }
  68         }
  69
  70         /**
  71          * Get a LoadMonitor instance
  72          *
  73          * @return LoadMonitor
  74          */
  75         function getLoadMonitor() {
  76                 if ( !isset( $this->mLoadMonitor ) ) {
  77                         $class = $this->mLoadMonitorClass;
  78                         $this->mLoadMonitor = new $class( $this );
  79                 }
  80                 return $this->mLoadMonitor;
  81         }
  82
  83         /**
  84          * Get or set arbitrary data used by the parent object, usually an LBFactory
  85          */
  86         function parentInfo( $x = null ) {
  87                 return wfSetVar( $this->mParentInfo, $x );
  88         }
  89
  90         /**
  91          * Given an array of non-normalised probabilities, this function will select
  92          * an element and return the appropriate key
  93          */
  94         function pickRandom( $weights )
  95         {
  96                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  97                         return false;
  98                 }
  99
 100                 $sum = array_sum( $weights );
 101                 if ( $sum == 0 ) {
 102                         # No loads on any of them
 103                         # In previous versions, this triggered an unweighted random selection,
 104                         # but this feature has been removed as of April 2006 to allow for strict
 105                         # separation of query groups.
 106                         return false;
 107                 }
 108                 $max = mt_getrandmax();
 109                 $rand = mt_rand(0, $max) / $max * $sum;
 110
 111                 $sum = 0;
 112                 foreach ( $weights as $i => $w ) {
 113                         $sum += $w;
 114                         if ( $sum >= $rand ) {
 115                                 break;
 116                         }
 117                 }
 118                 return $i;
 119         }
 120
 121         function getRandomNonLagged( $loads, $wiki = false ) {
 122                 # Unset excessively lagged servers
 123                 $lags = $this->getLagTimes( $wiki );
 124                 foreach ( $lags as $i => $lag ) {
 125                         if ( $i != 0 ) {
 126                                 if ( $lag === false ) {
 127                                         wfDebug( "Server #$i is not replicating\n" );
 128                                         unset( $loads[$i] );
 129                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 130                                         wfDebug( "Server #$i is excessively lagged ($lag seconds)\n" );
 131                                         unset( $loads[$i] );
 132                                 }
 133                         }
 134                 }
 135
 136                 # Find out if all the slaves with non-zero load are lagged
 137                 $sum = 0;
 138                 foreach ( $loads as $load ) {
 139                         $sum += $load;
 140                 }
 141                 if ( $sum == 0 ) {
 142                         # No appropriate DB servers except maybe the master and some slaves with zero load
 143                         # Do NOT use the master
 144                         # Instead, this function will return false, triggering read-only mode,
 145                         # and a lagged slave will be used instead.
 146                         return false;
 147                 }
 148
 149                 if ( count( $loads ) == 0 ) {
 150                         return false;
 151                 }
 152
 153                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 154
 155                 # Return a random representative of the remainder
 156                 return $this->pickRandom( $loads );
 157         }
 158
 159         /**
 160          * Get the index of the reader connection, which may be a slave
 161          * This takes into account load ratios and lag times. It should
 162          * always return a consistent index during a given invocation
 163          *
 164          * Side effect: opens connections to databases
 165          */
 166         function getReaderIndex( $group = false, $wiki = false ) {
 167                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 168
 169                 # FIXME: For now, only go through all this for mysql databases
 170                 if ($wgDBtype != 'mysql') {
 171                         return $this->getWriterIndex();
 172                 }
 173
 174                 if ( count( $this->mServers ) == 1 )  {
 175                         # Skip the load balancing if there's only one server
 176                         return 0;
 177                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 178                         # Shortcut if generic reader exists already
 179                         return $this->mReadIndex;
 180                 }
 181
 182                 wfProfileIn( __METHOD__ );
 183
 184                 $totalElapsed = 0;
 185
 186                 # convert from seconds to microseconds
 187                 $timeout = $wgDBClusterTimeout * 1e6;
 188
 189                 # Find the relevant load array
 190                 if ( $group !== false ) {
 191                         if ( isset( $this->mGroupLoads[$group] ) ) {
 192                                 $nonErrorLoads = $this->mGroupLoads[$group];
 193                         } else {
 194                                 # No loads for this group, return false and the caller can use some other group
 195                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 196                                 wfProfileOut( __METHOD__ );
 197                                 return false;
 198                         }
 199                 } else {
 200                         $nonErrorLoads = $this->mLoads;
 201                 }
 202
 203                 if ( !$nonErrorLoads ) {
 204                         throw new MWException( "Empty server array given to LoadBalancer" );
 205                 }
 206
 207                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 208                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 209
 210                 $laggedSlaveMode = false;
 211
 212                 # First try quickly looking through the available servers for a server that
 213                 # meets our criteria
 214                 do {
 215                         $totalThreadsConnected = 0;
 216                         $overloadedServers = 0;
 217                         $currentLoads = $nonErrorLoads;
 218                         while ( count( $currentLoads ) ) {
 219                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 220                                         $i = $this->pickRandom( $currentLoads );
 221                                 } else {
 222                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 223                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 224                                                 # All slaves lagged. Switch to read-only mode
 225                                                 $wgReadOnly = wfMsgNoDBForContent( 'readonly_lag' );
 226                                                 $i = $this->pickRandom( $currentLoads );
 227                                                 $laggedSlaveMode = true;
 228                                         }
 229                                 }
 230
 231                                 if ( $i === false ) {
 232                                         # pickRandom() returned false
 233                                         # This is permanent and means the configuration or the load monitor
 234                                         # wants us to return false.
 235                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 236                                         wfProfileOut( __METHOD__ );
 237                                         return false;
 238                                 }
 239
 240                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 241                                 $conn = $this->openConnection( $i, $wiki );
 242
 243                                 if ( !$conn ) {
 244                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 245                                         unset( $nonErrorLoads[$i] );
 246                                         unset( $currentLoads[$i] );
 247                                         continue;
 248                                 }
 249
 250                                 // Perform post-connection backoff
 251                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 252                                         ? $this->mServers[$i]['max threads'] : false;
 253                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 254
 255                                 // Decrement reference counter, we are finished with this connection.
 256                                 // It will be incremented for the caller later.
 257                                 if ( $wiki !== false ) {
 258                                         $this->reuseConnection( $conn );
 259                                 }
 260
 261                                 if ( $backoff ) {
 262                                         # Post-connection overload, don't use this server for now
 263                                         $totalThreadsConnected += $backoff;
 264                                         $overloadedServers++;
 265                                         unset( $currentLoads[$i] );
 266                                 } else {
 267                                         # Return this server
 268                                         break 2;
 269                                 }
 270                         }
 271
 272                         # No server found yet
 273                         $i = false;
 274
 275                         # If all servers were down, quit now
 276                         if ( !count( $nonErrorLoads ) ) {
 277                                 wfDebugLog( 'connect', "All servers down\n" );
 278                                 break;
 279                         }
 280
 281                         # Some servers must have been overloaded
 282                         if ( $overloadedServers == 0 ) {
 283                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 284                         }
 285                         # Back off for a while
 286                         # Scale the sleep time by the number of connected threads, to produce a
 287                         # roughly constant global poll rate
 288                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 289                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 290                 } while ( $totalElapsed < $timeout );
 291
 292                 if ( $totalElapsed >= $timeout ) {
 293                         wfDebugLog( 'connect', "All servers busy\n" );
 294                         $this->mErrorConnection = false;
 295                         $this->mLastError = 'All servers busy';
 296                 }
 297
 298                 if ( $i !== false ) {
 299                         # Slave connection successful
 300                         # Wait for the session master pos for a short time
 301                         if ( $this->mWaitForPos && $i > 0 ) {
 302                                 if ( !$this->doWait( $i ) ) {
 303                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 304                                 }
 305                         }
 306                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 307                                 $this->mReadIndex = $i;
 308                         }
 309                 }
 310                 wfProfileOut( __METHOD__ );
 311                 return $i;
 312         }
 313
 314         /**
 315          * Wait for a specified number of microseconds, and return the period waited
 316          */
 317         function sleep( $t ) {
 318                 wfProfileIn( __METHOD__ );
 319                 wfDebug( __METHOD__.": waiting $t us\n" );
 320                 usleep( $t );
 321                 wfProfileOut( __METHOD__ );
 322                 return $t;
 323         }
 324
 325         /**
 326          * Set the master wait position
 327          * If a DB_SLAVE connection has been opened already, waits
 328          * Otherwise sets a variable telling it to wait if such a connection is opened
 329          */
 330         public function waitFor( $pos ) {
 331                 wfProfileIn( __METHOD__ );
 332                 $this->mWaitForPos = $pos;
 333                 $i = $this->mReadIndex;
 334
 335                 if ( $i > 0 ) {
 336                         if ( !$this->doWait( $i ) ) {
 337                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 338                                 $this->mLaggedSlaveMode = true;
 339                         }
 340                 }
 341                 wfProfileOut( __METHOD__ );
 342         }
 343
 344         /**
 345          * Set the master wait position and wait for ALL slaves to catch up to it
 346          */
 347         public function waitForAll( $pos ) {
 348                 wfProfileIn( __METHOD__ );
 349                 $this->mWaitForPos = $pos;
 350                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 351                         $this->doWait( $i , true );
 352                 }
 353                 wfProfileOut( __METHOD__ );
 354         }
 355
 356         /**
 357          * Get any open connection to a given server index, local or foreign
 358          * Returns false if there is no connection open
 359          *
 360          * @return DatabaseBase
 361          */
 362         function getAnyOpenConnection( $i ) {
 363                 foreach ( $this->mConns as $conns ) {
 364                         if ( !empty( $conns[$i] ) ) {
 365                                 return reset( $conns[$i] );
 366                         }
 367                 }
 368                 return false;
 369         }
 370
 371         /**
 372          * Wait for a given slave to catch up to the master pos stored in $this
 373          */
 374         function doWait( $index, $open = false ) {
 375                 # Find a connection to wait on
 376                 $conn = $this->getAnyOpenConnection( $index );
 377                 if ( !$conn ) {
 378                         if ( !$open ) {
 379                                 wfDebug( __METHOD__ . ": no connection open\n" );
 380                                 return false;
 381                         } else {
 382                                 $conn = $this->openConnection( $index );
 383                                 if ( !$conn ) {
 384                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 385                                         return false;
 386                                 }
 387                         }
 388                 }
 389
 390                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 391                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 392
 393                 if ( $result == -1 || is_null( $result ) ) {
 394                         # Timed out waiting for slave, use master instead
 395                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 396                         return false;
 397                 } else {
 398                         wfDebug( __METHOD__.": Done\n" );
 399                         return true;
 400                 }
 401         }
 402
 403         /**
 404          * Get a connection by index
 405          * This is the main entry point for this class.
 406          *
 407          * @param $i Integer: server index
 408          * @param $groups Array: query groups
 409          * @param $wiki String: wiki ID
 410          *
 411          * @return DatabaseBase
 412          */
 413         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 414                 wfProfileIn( __METHOD__ );
 415
 416                 if ( $i == DB_LAST ) {
 417                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 418                 } elseif ( $i === null || $i === false ) {
 419                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 420                 }
 421
 422                 if ( $wiki === wfWikiID() ) {
 423                         $wiki = false;
 424                 }
 425
 426                 # Query groups
 427                 if ( $i == DB_MASTER ) {
 428                         $i = $this->getWriterIndex();
 429                 } elseif ( !is_array( $groups ) ) {
 430                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 431                         if ( $groupIndex !== false ) {
 432                                 $serverName = $this->getServerName( $groupIndex );
 433                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 434                                 $i = $groupIndex;
 435                         }
 436                 } else {
 437                         foreach ( $groups as $group ) {
 438                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 439                                 if ( $groupIndex !== false ) {
 440                                         $serverName = $this->getServerName( $groupIndex );
 441                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 442                                         $i = $groupIndex;
 443                                         break;
 444                                 }
 445                         }
 446                 }
 447
 448                 # Operation-based index
 449                 if ( $i == DB_SLAVE ) {
 450                         $i = $this->getReaderIndex( false, $wiki );
 451                         # Couldn't find a working server in getReaderIndex()?
 452                         if ( $i === false ) {
 453                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 454                                 $this->reportConnectionError( $this->mErrorConnection );
 455                                 wfProfileOut( __METHOD__ );
 456                                 return false;
 457                         }
 458                 }
 459
 460                 # Now we have an explicit index into the servers array
 461                 $conn = $this->openConnection( $i, $wiki );
 462                 if ( !$conn ) {
 463                         $this->reportConnectionError( $this->mErrorConnection );
 464                 }
 465
 466                 wfProfileOut( __METHOD__ );
 467                 return $conn;
 468         }
 469
 470         /**
 471          * Mark a foreign connection as being available for reuse under a different
 472          * DB name or prefix. This mechanism is reference-counted, and must be called
 473          * the same number of times as getConnection() to work.
 474          *
 475          * @param DatabaseBase $conn
 476          */
 477         public function reuseConnection( $conn ) {
 478                 $serverIndex = $conn->getLBInfo('serverIndex');
 479                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 480                 $dbName = $conn->getDBname();
 481                 $prefix = $conn->tablePrefix();
 482                 if ( strval( $prefix ) !== '' ) {
 483                         $wiki = "$dbName-$prefix";
 484                 } else {
 485                         $wiki = $dbName;
 486                 }
 487                 if ( $serverIndex === null || $refCount === null ) {
 488                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 489                         /**
 490                          * This can happen in code like:
 491                          *   foreach ( $dbs as $db ) {
 492                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 493                          *     ...
 494                          *     $lb->reuseConnection( $conn );
 495                          *   }
 496                          * When a connection to the local DB is opened in this way, reuseConnection()
 497                          * should be ignored
 498                          */
 499                         return;
 500                 }
 501                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 502                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 503                 }
 504                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 505                 if ( $refCount <= 0 ) {
 506                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 507                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 508                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 509                 } else {
 510                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 511                 }
 512         }
 513
 514         /**
 515          * Open a connection to the server given by the specified index
 516          * Index must be an actual index into the array.
 517          * If the server is already open, returns it.
 518          *
 519          * On error, returns false, and the connection which caused the
 520          * error will be available via $this->mErrorConnection.
 521          *
 522          * @param $i Integer: server index
 523          * @param $wiki String: wiki ID to open
 524          * @return DatabaseBase
 525          *
 526          * @access private
 527          */
 528         function openConnection( $i, $wiki = false ) {
 529                 wfProfileIn( __METHOD__ );
 530                 if ( $wiki !== false ) {
 531                         $conn = $this->openForeignConnection( $i, $wiki );
 532                         wfProfileOut( __METHOD__);
 533                         return $conn;
 534                 }
 535                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 536                         $conn = $this->mConns['local'][$i][0];
 537                 } else {
 538                         $server = $this->mServers[$i];
 539                         $server['serverIndex'] = $i;
 540                         $conn = $this->reallyOpenConnection( $server, false );
 541                         if ( $conn->isOpen() ) {
 542                                 $this->mConns['local'][$i][0] = $conn;
 543                         } else {
 544                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 545                                 $this->mErrorConnection = $conn;
 546                                 $conn = false;
 547                         }
 548                 }
 549                 wfProfileOut( __METHOD__ );
 550                 return $conn;
 551         }
 552
 553         /**
 554          * Open a connection to a foreign DB, or return one if it is already open.
 555          *
 556          * Increments a reference count on the returned connection which locks the
 557          * connection to the requested wiki. This reference count can be
 558          * decremented by calling reuseConnection().
 559          *
 560          * If a connection is open to the appropriate server already, but with the wrong
 561          * database, it will be switched to the right database and returned, as long as
 562          * it has been freed first with reuseConnection().
 563          *
 564          * On error, returns false, and the connection which caused the
 565          * error will be available via $this->mErrorConnection.
 566          *
 567          * @param $i Integer: server index
 568          * @param $wiki String: wiki ID to open
 569          * @return DatabaseBase
 570          */
 571         function openForeignConnection( $i, $wiki ) {
 572                 wfProfileIn(__METHOD__);
 573                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 574                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 575                         // Reuse an already-used connection
 576                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 577                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 578                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 579                         // Reuse a free connection for the same wiki
 580                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 581                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 582                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 583                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 584                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 585                         // Reuse a connection from another wiki
 586                         $conn = reset( $this->mConns['foreignFree'][$i] );
 587                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 588
 589                         if ( !$conn->selectDB( $dbName ) ) {
 590                                 $this->mLastError = "Error selecting database $dbName on server " .
 591                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 592                                 $this->mErrorConnection = $conn;
 593                                 $conn = false;
 594                         } else {
 595                                 $conn->tablePrefix( $prefix );
 596                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 597                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 598                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 599                         }
 600                 } else {
 601                         // Open a new connection
 602                         $server = $this->mServers[$i];
 603                         $server['serverIndex'] = $i;
 604                         $server['foreignPoolRefCount'] = 0;
 605                         $conn = $this->reallyOpenConnection( $server, $dbName );
 606                         if ( !$conn->isOpen() ) {
 607                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 608                                 $this->mErrorConnection = $conn;
 609                                 $conn = false;
 610                         } else {
 611                                 $conn->tablePrefix( $prefix );
 612                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 613                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 614                         }
 615                 }
 616
 617                 // Increment reference count
 618                 if ( $conn ) {
 619                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 620                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 621                 }
 622                 wfProfileOut(__METHOD__);
 623                 return $conn;
 624         }
 625
 626         /**
 627          * Test if the specified index represents an open connection
 628          *
 629          * @param $index Integer: server index
 630          * @access private
 631          */
 632         function isOpen( $index ) {
 633                 if( !is_integer( $index ) ) {
 634                         return false;
 635                 }
 636                 return (bool)$this->getAnyOpenConnection( $index );
 637         }
 638
 639         /**
 640          * Really opens a connection. Uncached.
 641          * Returns a Database object whether or not the connection was successful.
 642          * @access private
 643          */
 644         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 645                 if( !is_array( $server ) ) {
 646                         throw new MWException( 'You must update your load-balancing configuration. ' .
 647                                                'See DefaultSettings.php entry for $wgDBservers.' );
 648                 }
 649
 650                 $host = $server['host'];
 651                 $dbname = $server['dbname'];
 652
 653                 if ( $dbNameOverride !== false ) {
 654                         $server['dbname'] = $dbname = $dbNameOverride;
 655                 }
 656
 657                 # Create object
 658                 wfDebug( "Connecting to $host $dbname...\n" );
 659                 $db = DatabaseBase::newFromType( $server['type'], $server );
 660                 if ( $db->isOpen() ) {
 661                         wfDebug( "Connected to $host $dbname.\n" );
 662                 } else {
 663                         wfDebug( "Connection failed to $host $dbname.\n" );
 664                 }
 665                 $db->setLBInfo( $server );
 666                 if ( isset( $server['fakeSlaveLag'] ) ) {
 667                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 668                 }
 669                 if ( isset( $server['fakeMaster'] ) ) {
 670                         $db->setFakeMaster( true );
 671                 }
 672                 return $db;
 673         }
 674
 675         function reportConnectionError( &$conn ) {
 676                 wfProfileIn( __METHOD__ );
 677
 678                 if ( !is_object( $conn ) ) {
 679                         // No last connection, probably due to all servers being too busy
 680                         wfLogDBError( "LB failure with no last connection\n" );
 681                         $conn = new Database;
 682                         // If all servers were busy, mLastError will contain something sensible
 683                         throw new DBConnectionError( $conn, $this->mLastError );
 684                 } else {
 685                         $server = $conn->getProperty( 'mServer' );
 686                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 687                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 688                 }
 689                 wfProfileOut( __METHOD__ );
 690         }
 691
 692         function getWriterIndex() {
 693                 return 0;
 694         }
 695
 696         /**
 697          * Returns true if the specified index is a valid server index
 698          */
 699         function haveIndex( $i ) {
 700                 return array_key_exists( $i, $this->mServers );
 701         }
 702
 703         /**
 704          * Returns true if the specified index is valid and has non-zero load
 705          */
 706         function isNonZeroLoad( $i ) {
 707                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 708         }
 709
 710         /**
 711          * Get the number of defined servers (not the number of open connections)
 712          */
 713         function getServerCount() {
 714                 return count( $this->mServers );
 715         }
 716
 717         /**
 718          * Get the host name or IP address of the server with the specified index
 719          * Prefer a readable name if available.
 720          */
 721         function getServerName( $i ) {
 722                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 723                         return $this->mServers[$i]['hostName'];
 724                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 725                         return $this->mServers[$i]['host'];
 726                 } else {
 727                         return '';
 728                 }
 729         }
 730
 731         /**
 732          * Return the server info structure for a given index, or false if the index is invalid.
 733          */
 734         function getServerInfo( $i ) {
 735                 if ( isset( $this->mServers[$i] ) ) {
 736                         return $this->mServers[$i];
 737                 } else {
 738                         return false;
 739                 }
 740         }
 741
 742         /**
 743          * Get the current master position for chronology control purposes
 744          * @return mixed
 745          */
 746         function getMasterPos() {
 747                 # If this entire request was served from a slave without opening a connection to the
 748                 # master (however unlikely that may be), then we can fetch the position from the slave.
 749                 $masterConn = $this->getAnyOpenConnection( 0 );
 750                 if ( !$masterConn ) {
 751                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 752                                 $conn = $this->getAnyOpenConnection( $i );
 753                                 if ( $conn ) {
 754                                         wfDebug( "Master pos fetched from slave\n" );
 755                                         return $conn->getSlavePos();
 756                                 }
 757                         }
 758                 } else {
 759                         wfDebug( "Master pos fetched from master\n" );
 760                         return $masterConn->getMasterPos();
 761                 }
 762                 return false;
 763         }
 764
 765         /**
 766          * Close all open connections
 767          */
 768         function closeAll() {
 769                 foreach ( $this->mConns as $conns2 ) {
 770                         foreach  ( $conns2 as $conns3 ) {
 771                                 foreach ( $conns3 as $conn ) {
 772                                         $conn->close();
 773                                 }
 774                         }
 775                 }
 776                 $this->mConns = array(
 777                         'local' => array(),
 778                         'foreignFree' => array(),
 779                         'foreignUsed' => array(),
 780                 );
 781         }
 782
 783         /**
 784          * Deprecated function, typo in function name
 785          */
 786         function closeConnecton( $conn ) {
 787                 $this->closeConnection( $conn );
 788         }
 789
 790         /**
 791          * Close a connection
 792          * Using this function makes sure the LoadBalancer knows the connection is closed.
 793          * If you use $conn->close() directly, the load balancer won't update its state.
 794          * @param  $conn
 795          * @return void
 796          */
 797         function closeConnection( $conn ) {
 798                 $done = false;
 799                 foreach ( $this->mConns as $i1 => $conns2 ) {
 800                         foreach ( $conns2 as $i2 => $conns3 ) {
 801                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 802                                         if ( $conn === $candidateConn ) {
 803                                                 $conn->close();
 804                                                 unset( $this->mConns[$i1][$i2][$i3] );
 805                                                 $done = true;
 806                                                 break;
 807                                         }
 808                                 }
 809                         }
 810                 }
 811                 if ( !$done ) {
 812                         $conn->close();
 813                 }
 814         }
 815
 816         /**
 817          * Commit transactions on all open connections
 818          */
 819         function commitAll() {
 820                 foreach ( $this->mConns as $conns2 ) {
 821                         foreach ( $conns2 as $conns3 ) {
 822                                 foreach ( $conns3 as $conn ) {
 823                                         $conn->commit();
 824                                 }
 825                         }
 826                 }
 827         }
 828
 829         /* Issue COMMIT only on master, only if queries were done on connection */
 830         function commitMasterChanges() {
 831                 // Always 0, but who knows.. :)
 832                 $masterIndex = $this->getWriterIndex();
 833                 foreach ( $this->mConns as $conns2 ) {
 834                         if ( empty( $conns2[$masterIndex] ) ) {
 835                                 continue;
 836                         }
 837                         foreach ( $conns2[$masterIndex] as $conn ) {
 838                                 if ( $conn->doneWrites() ) {
 839                                         $conn->commit();
 840                                 }
 841                         }
 842                 }
 843         }
 844
 845         function waitTimeout( $value = null ) {
 846                 return wfSetVar( $this->mWaitTimeout, $value );
 847         }
 848
 849         function getLaggedSlaveMode() {
 850                 return $this->mLaggedSlaveMode;
 851         }
 852
 853         /* Disables/enables lag checks */
 854         function allowLagged($mode=null) {
 855                 if ($mode===null)
 856                         return $this->mAllowLagged;
 857                 $this->mAllowLagged=$mode;
 858         }
 859
 860         function pingAll() {
 861                 $success = true;
 862                 foreach ( $this->mConns as $conns2 ) {
 863                         foreach ( $conns2 as $conns3 ) {
 864                                 foreach ( $conns3 as $conn ) {
 865                                         if ( !$conn->ping() ) {
 866                                                 $success = false;
 867                                         }
 868                                 }
 869                         }
 870                 }
 871                 return $success;
 872         }
 873
 874         /**
 875          * Call a function with each open connection object
 876          */
 877         function forEachOpenConnection( $callback, $params = array() ) {
 878                 foreach ( $this->mConns as $conns2 ) {
 879                         foreach ( $conns2 as $conns3 ) {
 880                                 foreach ( $conns3 as $conn ) {
 881                                         $mergedParams = array_merge( array( $conn ), $params );
 882                                         call_user_func_array( $callback, $mergedParams );
 883                                 }
 884                         }
 885                 }
 886         }
 887
 888         /**
 889          * Get the hostname and lag time of the most-lagged slave.
 890          * This is useful for maintenance scripts that need to throttle their updates.
 891          * May attempt to open connections to slaves on the default DB.
 892          * @param $wiki string Wiki ID, or false for the default database
 893          */
 894         function getMaxLag( $wiki = false ) {
 895                 $maxLag = -1;
 896                 $host = '';
 897                 foreach ( $this->mServers as $i => $conn ) {
 898                         $conn = false;
 899                         if ( $wiki === false ) {
 900                                 $conn = $this->getAnyOpenConnection( $i );
 901                         }
 902                         if ( !$conn ) {
 903                                 $conn = $this->openConnection( $i, $wiki );
 904                         }
 905                         if ( !$conn ) {
 906                                 continue;
 907                         }
 908                         $lag = $conn->getLag();
 909                         if ( $lag > $maxLag ) {
 910                                 $maxLag = $lag;
 911                                 $host = $this->mServers[$i]['host'];
 912                         }
 913                 }
 914                 return array( $host, $maxLag );
 915         }
 916
 917         /**
 918          * Get lag time for each server
 919          * Results are cached for a short time in memcached, and indefinitely in the process cache
 920          */
 921         function getLagTimes( $wiki = false ) {
 922                 # Try process cache
 923                 if ( isset( $this->mLagTimes ) ) {
 924                         return $this->mLagTimes;
 925                 }
 926                 # No, send the request to the load monitor
 927                 $this->mLagTimes = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
 928                 return $this->mLagTimes;
 929         }
 930
 931         /**
 932          * Clear the cache for getLagTimes
 933          */
 934         function clearLagTimeCache() {
 935                 $this->mLagTimes = null;
 936         }
 937 }