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