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