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