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