includes/db/LoadBalancer.php

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