includes/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing object
   4  *
   5  * @todo document
   6  */
   7 class LoadBalancer {
   8         /* private */ var $mServers, $mConns, $mLoads, $mGroupLoads;
   9         /* private */ var $mFailFunction, $mErrorConnection;
  10         /* private */ var $mReadIndex, $mLastIndex, $mAllowLagged;
  11         /* private */ var $mWaitForPos, $mWaitTimeout;
  12         /* private */ var $mLaggedSlaveMode, $mLastError = 'Unknown error';
  13         /* private */ var $mParentInfo, $mLagTimes;
  14
  15         function __construct( $servers, $failFunction = false, $waitTimeout = 10, $unused = false )
  16         {
  17                 $this->mServers = $servers;
  18                 $this->mFailFunction = $failFunction;
  19                 $this->mReadIndex = -1;
  20                 $this->mWriteIndex = -1;
  21                 $this->mConns = array(
  22                         'local' => array(),
  23                         'foreignUsed' => array(),
  24                         'foreignFree' => array() );
  25                 $this->mLastIndex = -1;
  26                 $this->mLoads = array();
  27                 $this->mWaitForPos = false;
  28                 $this->mWaitTimeout = $waitTimeout;
  29                 $this->mLaggedSlaveMode = false;
  30                 $this->mErrorConnection = false;
  31                 $this->mAllowLag = false;
  32
  33                 foreach( $servers as $i => $server ) {
  34                         $this->mLoads[$i] = $server['load'];
  35                         if ( isset( $server['groupLoads'] ) ) {
  36                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  37                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  38                                                 $this->mGroupLoads[$group] = array();
  39                                         }
  40                                         $this->mGroupLoads[$group][$i] = $ratio;
  41                                 }
  42                         }
  43                 }
  44         }
  45
  46         static function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
  47         {
  48                 return new LoadBalancer( $servers, $failFunction, $waitTimeout );
  49         }
  50
  51         /**
  52          * Get or set arbitrary data used by the parent object, usually an LBFactory
  53          */
  54         function parentInfo( $x = null ) {
  55                 return wfSetVar( $this->mParentInfo, $x );
  56         }
  57
  58         /**
  59          * Given an array of non-normalised probabilities, this function will select
  60          * an element and return the appropriate key
  61          */
  62         function pickRandom( $weights )
  63         {
  64                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  65                         return false;
  66                 }
  67
  68                 $sum = array_sum( $weights );
  69                 if ( $sum == 0 ) {
  70                         # No loads on any of them
  71                         # In previous versions, this triggered an unweighted random selection,
  72                         # but this feature has been removed as of April 2006 to allow for strict
  73                         # separation of query groups.
  74                         return false;
  75                 }
  76                 $max = mt_getrandmax();
  77                 $rand = mt_rand(0, $max) / $max * $sum;
  78
  79                 $sum = 0;
  80                 foreach ( $weights as $i => $w ) {
  81                         $sum += $w;
  82                         if ( $sum >= $rand ) {
  83                                 break;
  84                         }
  85                 }
  86                 return $i;
  87         }
  88
  89         function getRandomNonLagged( $loads, $wiki = false ) {
  90                 # Unset excessively lagged servers
  91                 $lags = $this->getLagTimes( $wiki );
  92                 foreach ( $lags as $i => $lag ) {
  93                         if ( $i != 0 && isset( $this->mServers[$i]['max lag'] ) ) {
  94                                 if ( $lag === false ) {
  95                                         wfDebug( "Server #$i is not replicating\n" );
  96                                         unset( $loads[$i] );
  97                                 } elseif ( $lag > $this->mServers[$i]['max lag'] ) {
  98                                         wfDebug( "Server #$i is excessively lagged ($lag seconds)\n" );
  99                                         unset( $loads[$i] );
 100                                 }
 101                         }
 102                 }
 103
 104                 # Find out if all the slaves with non-zero load are lagged
 105                 $sum = 0;
 106                 foreach ( $loads as $load ) {
 107                         $sum += $load;
 108                 }
 109                 if ( $sum == 0 ) {
 110                         # No appropriate DB servers except maybe the master and some slaves with zero load
 111                         # Do NOT use the master
 112                         # Instead, this function will return false, triggering read-only mode,
 113                         # and a lagged slave will be used instead.
 114                         return false;
 115                 }
 116
 117                 if ( count( $loads ) == 0 ) {
 118                         return false;
 119                 }
 120
 121                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 122
 123                 # Return a random representative of the remainder
 124                 return $this->pickRandom( $loads );
 125         }
 126
 127         /**
 128          * Get the index of the reader connection, which may be a slave
 129          * This takes into account load ratios and lag times. It should
 130          * always return a consistent index during a given invocation
 131          *
 132          * Side effect: opens connections to databases
 133          */
 134         function getReaderIndex( $group = false, $wiki = false ) {
 135                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 136
 137                 # FIXME: For now, only go through all this for mysql databases
 138                 if ($wgDBtype != 'mysql') {
 139                         return $this->getWriterIndex();
 140                 }
 141
 142                 if ( count( $this->mServers ) == 1 )  {
 143                         # Skip the load balancing if there's only one server
 144                         return 0;
 145                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 146                         # Shortcut if generic reader exists already
 147                         return $this->mReadIndex;
 148                 }
 149
 150                 wfProfileIn( __METHOD__ );
 151
 152                 $totalElapsed = 0;
 153
 154                 # convert from seconds to microseconds
 155                 $timeout = $wgDBClusterTimeout * 1e6;
 156
 157                 # Find the relevant load array
 158                 if ( $group !== false ) {
 159                         if ( isset( $this->mGroupLoads[$group] ) ) {
 160                                 $nonErrorLoads = $this->mGroupLoads[$group];
 161                         } else {
 162                                 # No loads for this group, return false and the caller can use some other group
 163                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 164                                 wfProfileOut( __METHOD__ );
 165                                 return false;
 166                         }
 167                 } else {
 168                         $nonErrorLoads = $this->mLoads;
 169                 }
 170
 171                 if ( !$nonErrorLoads ) {
 172                         throw new MWException( "Empty server array given to LoadBalancer" );
 173                 }
 174
 175                 $i = false;
 176                 $found = false;
 177                 $laggedSlaveMode = false;
 178
 179                 # First try quickly looking through the available servers for a server that
 180                 # meets our criteria
 181                 do {
 182                         $totalThreadsConnected = 0;
 183                         $overloadedServers = 0;
 184                         $currentLoads = $nonErrorLoads;
 185                         while ( count( $currentLoads ) ) {
 186                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 187                                         $i = $this->pickRandom( $currentLoads );
 188                                 } else {
 189                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 190                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 191                                                 # All slaves lagged. Switch to read-only mode
 192                                                 $wgReadOnly = wfMsgNoDBForContent( 'readonly_lag' );
 193                                                 $i = $this->pickRandom( $currentLoads );
 194                                                 $laggedSlaveMode = true;
 195                                         }
 196                                 }
 197
 198                                 if ( $i === false ) {
 199                                         # pickRandom() returned false
 200                                         # This is permanent and means the configuration wants us to return false
 201                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 202                                         wfProfileOut( __METHOD__ );
 203                                         return false;
 204                                 }
 205
 206                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 207                                 $conn = $this->openConnection( $i, $wiki );
 208
 209                                 if ( !$conn ) {
 210                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 211                                         unset( $nonErrorLoads[$i] );
 212                                         unset( $currentLoads[$i] );
 213                                         continue;
 214                                 }
 215
 216                                 if ( isset( $this->mServers[$i]['max threads'] ) ) {
 217                                         $status = $conn->getStatus("Thread%");
 218                                         if ( $wiki !== false ) {
 219                                                 $this->reuseConnection( $conn );
 220                                         }
 221                                         if ( $status['Threads_running'] > $this->mServers[$i]['max threads'] ) {
 222                                                 $totalThreadsConnected += $status['Threads_connected'];
 223                                                 $overloadedServers++;
 224                                                 unset( $currentLoads[$i] );
 225                                         } else {
 226                                                 # Max threads satisfied, return this server
 227                                                 break 2;
 228                                         }
 229                                 } else {
 230                                         # No maximum, return this server
 231                                         if ( $wiki !== false ) {
 232                                                 $this->reuseConnection( $conn );
 233                                         }
 234                                         $found = true;
 235                                         break 2;
 236                                 }
 237                         }
 238
 239                         # No server found yet
 240                         $i = false;
 241
 242                         # If all servers were down, quit now
 243                         if ( !count( $nonErrorLoads ) ) {
 244                                 wfDebugLog( 'connect', "All servers down\n" );
 245                                 break;
 246                         }
 247
 248                         # Some servers must have been overloaded
 249                         if ( $overloadedServers == 0 ) {
 250                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 251                         }
 252                         # Back off for a while
 253                         # Scale the sleep time by the number of connected threads, to produce a
 254                         # roughly constant global poll rate
 255                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 256                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 257                 } while ( $totalElapsed < $timeout );
 258
 259                 if ( $totalElapsed >= $timeout ) {
 260                         wfDebugLog( 'connect', "All servers busy\n" );
 261                         $this->mErrorConnection = false;
 262                         $this->mLastError = 'All servers busy';
 263                 }
 264
 265                 if ( $i !== false ) {
 266                         # Wait for the session master pos for a short time
 267                         if ( $this->mWaitForPos && $i > 0 ) {
 268                                 if ( !$this->doWait( $i ) ) {
 269                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 270                                 }
 271                         }
 272                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 273                                 $this->mReadIndex = $i;
 274                         }
 275                 }
 276                 wfProfileOut( __METHOD__ );
 277                 return $i;
 278         }
 279
 280         /**
 281          * Wait for a specified number of microseconds, and return the period waited
 282          */
 283         function sleep( $t ) {
 284                 wfProfileIn( __METHOD__ );
 285                 wfDebug( __METHOD__.": waiting $t us\n" );
 286                 usleep( $t );
 287                 wfProfileOut( __METHOD__ );
 288                 return $t;
 289         }
 290
 291         /**
 292          * Get a random server to use in a query group
 293          * @deprecated use getReaderIndex
 294          */
 295         function getGroupIndex( $group ) {
 296                 return $this->getReaderIndex( $group );
 297         }
 298
 299         /**
 300          * Set the master wait position
 301          * If a DB_SLAVE connection has been opened already, waits
 302          * Otherwise sets a variable telling it to wait if such a connection is opened
 303          */
 304         public function waitFor( $pos ) {
 305                 wfProfileIn( __METHOD__ );
 306                 $this->mWaitForPos = $pos;
 307                 $i = $this->mReadIndex;
 308
 309                 if ( $i > 0 ) {
 310                         if ( !$this->doWait( $i ) ) {
 311                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 312                                 $this->mLaggedSlaveMode = true;
 313                         }
 314                 }
 315                 wfProfileOut( __METHOD__ );
 316         }
 317
 318         /**
 319          * Get any open connection to a given server index, local or foreign
 320          * Returns false if there is no connection open
 321          */
 322         function getAnyOpenConnection( $i ) {
 323                 foreach ( $this->mConns as $type => $conns ) {
 324                         if ( !empty( $conns[$i] ) ) {
 325                                 return reset( $conns[$i] );
 326                         }
 327                 }
 328                 return false;
 329         }
 330
 331         /**
 332          * Wait for a given slave to catch up to the master pos stored in $this
 333          */
 334         function doWait( $index ) {
 335                 # Find a connection to wait on
 336                 $conn = $this->getAnyOpenConnection( $index );
 337                 if ( !$conn ) {
 338                         wfDebug( __METHOD__ . ": no connection open\n" );
 339                         return false;
 340                 }
 341
 342                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 343                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 344
 345                 if ( $result == -1 || is_null( $result ) ) {
 346                         # Timed out waiting for slave, use master instead
 347                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 348                         return false;
 349                 } else {
 350                         wfDebug( __METHOD__.": Done\n" );
 351                         return true;
 352                 }
 353         }
 354
 355         /**
 356          * Get a connection by index
 357          * This is the main entry point for this class.
 358          */
 359         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 360                 global $wgDBtype;
 361                 wfProfileIn( __METHOD__ );
 362
 363                 if ( $wiki === wfWikiID() ) {
 364                         $wiki = false;
 365                 }
 366
 367                 # Query groups
 368                 if ( $i == DB_MASTER ) {
 369                         $i = $this->getWriterIndex();
 370                 } elseif ( !is_array( $groups ) ) {
 371                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 372                         if ( $groupIndex !== false ) {
 373                                 $serverName = $this->getServerName( $groupIndex );
 374                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 375                                 $i = $groupIndex;
 376                         }
 377                 } else {
 378                         foreach ( $groups as $group ) {
 379                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 380                                 if ( $groupIndex !== false ) {
 381                                         $serverName = $this->getServerName( $groupIndex );
 382                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 383                                         $i = $groupIndex;
 384                                         break;
 385                                 }
 386                         }
 387                 }
 388
 389                 # Operation-based index
 390                 if ( $i == DB_SLAVE ) {
 391                         $i = $this->getReaderIndex( false, $wiki );
 392                 } elseif ( $i == DB_LAST ) {
 393                         # Just use $this->mLastIndex, which should already be set
 394                         $i = $this->mLastIndex;
 395                         if ( $i === -1 ) {
 396                                 # Oh dear, not set, best to use the writer for safety
 397                                 wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
 398                                 $i = $this->getWriterIndex();
 399                         }
 400                 }
 401                 # Couldn't find a working server in getReaderIndex()?
 402                 if ( $i === false ) {
 403                         $this->reportConnectionError( $this->mErrorConnection );
 404                 }
 405
 406                 # Now we have an explicit index into the servers array
 407                 $conn = $this->openConnection( $i, $wiki );
 408                 if ( !$conn ) {
 409                         $this->reportConnectionError( $this->mErrorConnection );
 410                 }
 411
 412                 wfProfileOut( __METHOD__ );
 413                 return $conn;
 414         }
 415
 416         /**
 417          * Mark a foreign connection as being available for reuse under a different
 418          * DB name or prefix. This mechanism is reference-counted, and must be called
 419          * the same number of times as getConnection() to work.
 420          */
 421         public function reuseConnection( $conn ) {
 422                 $serverIndex = $conn->getLBInfo('serverIndex');
 423                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 424                 $dbName = $conn->getDBname();
 425                 $prefix = $conn->tablePrefix();
 426                 if ( strval( $prefix ) !== '' ) {
 427                         $wiki = "$dbName-$prefix";
 428                 } else {
 429                         $wiki = $dbName;
 430                 }
 431                 if ( $serverIndex === null || $refCount === null ) {
 432                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 433                         /**
 434                          * This can happen in code like:
 435                          *   foreach ( $dbs as $db ) {
 436                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 437                          *     ...
 438                          *     $lb->reuseConnection( $conn );
 439                          *   }
 440                          * When a connection to the local DB is opened in this way, reuseConnection()
 441                          * should be ignored
 442                          */
 443                         return;
 444                 }
 445                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 446                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 447                 }
 448                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 449                 if ( $refCount <= 0 ) {
 450                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 451                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 452                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 453                 } else {
 454                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 455                 }
 456         }
 457
 458         /**
 459          * Open a connection to the server given by the specified index
 460          * Index must be an actual index into the array.
 461          * If the server is already open, returns it.
 462          *
 463          * On error, returns false, and the connection which caused the
 464          * error will be available via $this->mErrorConnection.
 465          *
 466          * @param integer $i Server index
 467          * @param string $wiki Wiki ID to open
 468          * @return Database
 469          *
 470          * @access private
 471          */
 472         function openConnection( $i, $wiki = false ) {
 473                 wfProfileIn( __METHOD__ );
 474                 if ( $wiki !== false ) {
 475                         $conn = $this->openForeignConnection( $i, $wiki );
 476                         wfProfileOut( __METHOD__);
 477                         return $conn;
 478                 }
 479                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 480                         $conn = $this->mConns['local'][$i][0];
 481                 } else {
 482                         $server = $this->mServers[$i];
 483                         $server['serverIndex'] = $i;
 484                         $conn = $this->reallyOpenConnection( $server );
 485                         if ( $conn->isOpen() ) {
 486                                 $this->mConns['local'][$i][0] = $conn;
 487                         } else {
 488                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 489                                 $this->mErrorConnection = $conn;
 490                                 $conn = false;
 491                         }
 492                 }
 493                 $this->mLastIndex = $i;
 494                 wfProfileOut( __METHOD__ );
 495                 return $conn;
 496         }
 497
 498         /**
 499          * Open a connection to a foreign DB, or return one if it is already open.
 500          *
 501          * Increments a reference count on the returned connection which locks the
 502          * connection to the requested wiki. This reference count can be
 503          * decremented by calling reuseConnection().
 504          *
 505          * If a connection is open to the appropriate server already, but with the wrong
 506          * database, it will be switched to the right database and returned, as long as
 507          * it has been freed first with reuseConnection().
 508          *
 509          * On error, returns false, and the connection which caused the
 510          * error will be available via $this->mErrorConnection.
 511          *
 512          * @param integer $i Server index
 513          * @param string $wiki Wiki ID to open
 514          * @return Database
 515          */
 516         function openForeignConnection( $i, $wiki ) {
 517                 wfProfileIn(__METHOD__);
 518                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 519                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 520                         // Reuse an already-used connection
 521                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 522                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 523                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 524                         // Reuse a free connection for the same wiki
 525                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 526                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 527                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 528                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 529                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 530                         // Reuse a connection from another wiki
 531                         $conn = reset( $this->mConns['foreignFree'][$i] );
 532                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 533
 534                         if ( !$conn->selectDB( $dbName ) ) {
 535                                 global $wguname;
 536                                 $this->mLastError = "Error selecting database $dbName on server " .
 537                                         $conn->getServer() . " from client host {$wguname['nodename']}\n";
 538                                 $this->mErrorConnection = $conn;
 539                                 $conn = false;
 540                         } else {
 541                                 $conn->tablePrefix( $prefix );
 542                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 543                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 544                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 545                         }
 546                 } else {
 547                         // Open a new connection
 548                         $server = $this->mServers[$i];
 549                         $server['serverIndex'] = $i;
 550                         $server['foreignPoolRefCount'] = 0;
 551                         $conn = $this->reallyOpenConnection( $server, $dbName );
 552                         if ( !$conn->isOpen() ) {
 553                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 554                                 $this->mErrorConnection = $conn;
 555                                 $conn = false;
 556                         } else {
 557                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 558                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 559                         }
 560                 }
 561
 562                 // Increment reference count
 563                 if ( $conn ) {
 564                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 565                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 566                 }
 567                 wfProfileOut(__METHOD__);
 568                 return $conn;
 569         }
 570
 571         /**
 572          * Test if the specified index represents an open connection
 573          * @access private
 574          */
 575         function isOpen( $index ) {
 576                 if( !is_integer( $index ) ) {
 577                         return false;
 578                 }
 579                 return (bool)$this->getAnyOpenConnection( $index );
 580         }
 581
 582         /**
 583          * Really opens a connection. Uncached.
 584          * Returns a Database object whether or not the connection was successful.
 585          * @access private
 586          */
 587         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 588                 if( !is_array( $server ) ) {
 589                         throw new MWException( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 590                 }
 591
 592                 extract( $server );
 593                 if ( $dbNameOverride !== false ) {
 594                         $dbname = $dbNameOverride;
 595                 }
 596
 597                 # Get class for this database type
 598                 $class = 'Database' . ucfirst( $type );
 599
 600                 # Create object
 601                 wfDebug( "Connecting to $host $dbname...\n" );
 602                 $db = new $class( $host, $user, $password, $dbname, 1, $flags );
 603                 if ( $db->isOpen() ) {
 604                         wfDebug( "Connected\n" );
 605                 } else {
 606                         wfDebug( "Failed\n" );
 607                 }
 608                 $db->setLBInfo( $server );
 609                 if ( isset( $server['fakeSlaveLag'] ) ) {
 610                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 611                 }
 612                 if ( isset( $server['fakeMaster'] ) ) {
 613                         $db->setFakeMaster( true );
 614                 }
 615                 return $db;
 616         }
 617
 618         function reportConnectionError( &$conn ) {
 619                 wfProfileIn( __METHOD__ );
 620                 # Prevent infinite recursion
 621
 622                 static $reporting = false;
 623                 if ( !$reporting ) {
 624                         $reporting = true;
 625                         if ( !is_object( $conn ) ) {
 626                                 // No last connection, probably due to all servers being too busy
 627                                 $conn = new Database;
 628                                 if ( $this->mFailFunction ) {
 629                                         $conn->failFunction( $this->mFailFunction );
 630                                         $conn->reportConnectionError( $this->mLastError );
 631                                 } else {
 632                                         // If all servers were busy, mLastError will contain something sensible
 633                                         throw new DBConnectionError( $conn, $this->mLastError );
 634                                 }
 635                         } else {
 636                                 if ( $this->mFailFunction ) {
 637                                         $conn->failFunction( $this->mFailFunction );
 638                                 } else {
 639                                         $conn->failFunction( false );
 640                                 }
 641                                 $server = $conn->getProperty( 'mServer' );
 642                                 $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 643                         }
 644                         $reporting = false;
 645                 }
 646                 wfProfileOut( __METHOD__ );
 647         }
 648
 649         function getWriterIndex() {
 650                 return 0;
 651         }
 652
 653         /**
 654          * Returns true if the specified index is a valid server index
 655          */
 656         function haveIndex( $i ) {
 657                 return array_key_exists( $i, $this->mServers );
 658         }
 659
 660         /**
 661          * Returns true if the specified index is valid and has non-zero load
 662          */
 663         function isNonZeroLoad( $i ) {
 664                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 665         }
 666
 667         /**
 668          * Get the number of defined servers (not the number of open connections)
 669          */
 670         function getServerCount() {
 671                 return count( $this->mServers );
 672         }
 673
 674         /**
 675          * Get the host name or IP address of the server with the specified index
 676          */
 677         function getServerName( $i ) {
 678                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 679                         return $this->mServers[$i]['hostName'];
 680                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 681                         return $this->mServers[$i]['host'];
 682                 } else {
 683                         return '';
 684                 }
 685         }
 686
 687         /**
 688          * Get the current master position for chronology control purposes
 689          * @return mixed
 690          */
 691         function getMasterPos() {
 692                 # If this entire request was served from a slave without opening a connection to the
 693                 # master (however unlikely that may be), then we can fetch the position from the slave.
 694                 $masterConn = $this->getAnyOpenConnection( 0 );
 695                 if ( !$masterConn ) {
 696                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 697                                 $conn = $this->getAnyOpenConnection( $i );
 698                                 if ( $conn ) {
 699                                         wfDebug( "Master pos fetched from slave\n" );
 700                                         return $conn->getSlavePos();
 701                                 }
 702                         }
 703                 } else {
 704                         wfDebug( "Master pos fetched from master\n" );
 705                         return $masterConn->getMasterPos();
 706                 }
 707                 return false;
 708         }
 709
 710         /**
 711          * Close all open connections
 712          */
 713         function closeAll() {
 714                 foreach ( $this->mConns as $conns2 ) {
 715                         foreach  ( $conns2 as $conns3 ) {
 716                                 foreach ( $conns3 as $conn ) {
 717                                         $conn->close();
 718                                 }
 719                         }
 720                 }
 721                 $this->mConns = array(
 722                         'local' => array(),
 723                         'foreignFree' => array(),
 724                         'foreignUsed' => array(),
 725                 );
 726         }
 727
 728         /**
 729          * Close a connection
 730          * Using this function makes sure the LoadBalancer knows the connection is closed.
 731          * If you use $conn->close() directly, the load balancer won't update its state.
 732          */
 733         function closeConnecton( $conn ) {
 734                 $done = false;
 735                 foreach ( $this->mConns as $i1 => $conns2 ) {
 736                         foreach ( $conns2 as $i2 => $conns3 ) {
 737                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 738                                         if ( $conn === $candidateConn ) {
 739                                                 $conn->close();
 740                                                 unset( $this->mConns[$i1][$i2][$i3] );
 741                                                 $done = true;
 742                                                 break;
 743                                         }
 744                                 }
 745                         }
 746                 }
 747                 if ( !$done ) {
 748                         $conn->close();
 749                 }
 750         }
 751
 752         /**
 753          * Commit transactions on all open connections
 754          */
 755         function commitAll() {
 756                 foreach ( $this->mConns as $conns2 ) {
 757                         foreach ( $conns2 as $conns3 ) {
 758                                 foreach ( $conns3 as $conn ) {
 759                                         $conn->immediateCommit();
 760                                 }
 761                         }
 762                 }
 763         }
 764
 765         /* Issue COMMIT only on master, only if queries were done on connection */
 766         function commitMasterChanges() {
 767                 // Always 0, but who knows.. :)
 768                 $masterIndex = $this->getWriterIndex();
 769                 foreach ( $this->mConns as $type => $conns2 ) {
 770                         if ( empty( $conns2[$masterIndex] ) ) {
 771                                 continue;
 772                         }
 773                         foreach ( $conns2[$masterIndex] as $conn ) {
 774                                 if ( $conn->lastQuery() != '' ) {
 775                                         $conn->commit();
 776                                 }
 777                         }
 778                 }
 779         }
 780
 781         function waitTimeout( $value = NULL ) {
 782                 return wfSetVar( $this->mWaitTimeout, $value );
 783         }
 784
 785         function getLaggedSlaveMode() {
 786                 return $this->mLaggedSlaveMode;
 787         }
 788
 789         /* Disables/enables lag checks */
 790         function allowLagged($mode=null) {
 791                 if ($mode===null)
 792                         return $this->mAllowLagged;
 793                 $this->mAllowLagged=$mode;
 794         }
 795
 796         function pingAll() {
 797                 $success = true;
 798                 foreach ( $this->mConns as $conns2 ) {
 799                         foreach ( $conns2 as $conns3 ) {
 800                                 foreach ( $conns3 as $conn ) {
 801                                         if ( !$conn->ping() ) {
 802                                                 $success = false;
 803                                         }
 804                                 }
 805                         }
 806                 }
 807                 return $success;
 808         }
 809
 810         /**
 811          * Get the hostname and lag time of the most-lagged slave.
 812          * This is useful for maintenance scripts that need to throttle their updates.
 813          * May attempt to open connections to slaves on the default DB.
 814          */
 815         function getMaxLag() {
 816                 $maxLag = -1;
 817                 $host = '';
 818                 foreach ( $this->mServers as $i => $conn ) {
 819                         $conn = $this->getAnyOpenConnection( $i );
 820                         if ( !$conn ) {
 821                                 $conn = $this->openConnection( $i );
 822                         }
 823                         if ( !$conn ) {
 824                                 continue;
 825                         }
 826                         $lag = $conn->getLag();
 827                         if ( $lag > $maxLag ) {
 828                                 $maxLag = $lag;
 829                                 $host = $this->mServers[$i]['host'];
 830                         }
 831                 }
 832                 return array( $host, $maxLag );
 833         }
 834
 835         /**
 836          * Get lag time for each server
 837          * Results are cached for a short time in memcached, and indefinitely in the process cache
 838          */
 839         function getLagTimes( $wiki = false ) {
 840                 wfProfileIn( __METHOD__ );
 841
 842                 if ( !isset( $this->mLagTimes ) ) {
 843                         $expiry = 5;
 844                         $requestRate = 10;
 845
 846                         global $wgMemc;
 847                         $masterName = $this->getServerName( 0 );
 848                         $memcKey = wfMemcKey( 'lag_times', $masterName );
 849                         $times = $wgMemc->get( $memcKey );
 850                         if ( $times ) {
 851                                 # Randomly recache with probability rising over $expiry
 852                                 $elapsed = time() - $times['timestamp'];
 853                                 $chance = max( 0, ( $expiry - $elapsed ) * $requestRate );
 854                                 if ( mt_rand( 0, $chance ) != 0 ) {
 855                                         unset( $times['timestamp'] );
 856                                         wfProfileOut( __METHOD__ );
 857                                         return $times;
 858                                 }
 859                                 wfIncrStats( 'lag_cache_miss_expired' );
 860                         } else {
 861                                 wfIncrStats( 'lag_cache_miss_absent' );
 862                         }
 863
 864                         # Cache key missing or expired
 865
 866                         $times = array();
 867                         foreach ( $this->mServers as $i => $conn ) {
 868                                 if ($i == 0) { # Master
 869                                         $times[$i] = 0;
 870                                 } elseif ( false !== ( $conn = $this->getAnyOpenConnection( $i ) ) ) {
 871                                         $times[$i] = $conn->getLag();
 872                                 } elseif ( false !== ( $conn = $this->openConnection( $i, $wiki ) ) ) {
 873                                         $times[$i] = $conn->getLag();
 874                                 }
 875                         }
 876
 877                         # Add a timestamp key so we know when it was cached
 878                         $times['timestamp'] = time();
 879                         $wgMemc->set( $memcKey, $times, $expiry );
 880
 881                         # But don't give the timestamp to the caller
 882                         unset($times['timestamp']);
 883                         $this->mLagTimes = $times;
 884                 }
 885                 wfProfileOut( __METHOD__ );
 886                 return $this->mLagTimes;
 887         }
 888 }