includes/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         /* private */ var $mServers, $mConns, $mLoads, $mGroupLoads;
  15         /* private */ var $mFailFunction, $mErrorConnection;
  16         /* private */ var $mReadIndex, $mLastIndex, $mAllowLagged;
  17         /* private */ var $mWaitForPos, $mWaitTimeout;
  18         /* private */ var $mLaggedSlaveMode, $mLastError = 'Unknown error';
  19         /* private */ var $mParentInfo, $mLagTimes;
  20
  21         function __construct( $servers, $failFunction = false, $waitTimeout = 10, $unused = false )
  22         {
  23                 $this->mServers = $servers;
  24                 $this->mFailFunction = $failFunction;
  25                 $this->mReadIndex = -1;
  26                 $this->mWriteIndex = -1;
  27                 $this->mConns = array(
  28                         'local' => array(),
  29                         'foreignUsed' => array(),
  30                         'foreignFree' => array() );
  31                 $this->mLastIndex = -1;
  32                 $this->mLoads = array();
  33                 $this->mWaitForPos = false;
  34                 $this->mWaitTimeout = $waitTimeout;
  35                 $this->mLaggedSlaveMode = false;
  36                 $this->mErrorConnection = false;
  37                 $this->mAllowLag = false;
  38
  39                 foreach( $servers as $i => $server ) {
  40                         $this->mLoads[$i] = $server['load'];
  41                         if ( isset( $server['groupLoads'] ) ) {
  42                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  43                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  44                                                 $this->mGroupLoads[$group] = array();
  45                                         }
  46                                         $this->mGroupLoads[$group][$i] = $ratio;
  47                                 }
  48                         }
  49                 }
  50         }
  51
  52         static function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
  53         {
  54                 return new LoadBalancer( $servers, $failFunction, $waitTimeout );
  55         }
  56
  57         /**
  58          * Get or set arbitrary data used by the parent object, usually an LBFactory
  59          */
  60         function parentInfo( $x = null ) {
  61                 return wfSetVar( $this->mParentInfo, $x );
  62         }
  63
  64         /**
  65          * Given an array of non-normalised probabilities, this function will select
  66          * an element and return the appropriate key
  67          */
  68         function pickRandom( $weights )
  69         {
  70                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
  71                         return false;
  72                 }
  73
  74                 $sum = array_sum( $weights );
  75                 if ( $sum == 0 ) {
  76                         # No loads on any of them
  77                         # In previous versions, this triggered an unweighted random selection,
  78                         # but this feature has been removed as of April 2006 to allow for strict
  79                         # separation of query groups.
  80                         return false;
  81                 }
  82                 $max = mt_getrandmax();
  83                 $rand = mt_rand(0, $max) / $max * $sum;
  84
  85                 $sum = 0;
  86                 foreach ( $weights as $i => $w ) {
  87                         $sum += $w;
  88                         if ( $sum >= $rand ) {
  89                                 break;
  90                         }
  91                 }
  92                 return $i;
  93         }
  94
  95         function getRandomNonLagged( $loads, $wiki = false ) {
  96                 # Unset excessively lagged servers
  97                 $lags = $this->getLagTimes( $wiki );
  98                 foreach ( $lags as $i => $lag ) {
  99                         if ( $i != 0 && isset( $this->mServers[$i]['max lag'] ) ) {
 100                                 if ( $lag === false ) {
 101                                         wfDebug( "Server #$i is not replicating\n" );
 102                                         unset( $loads[$i] );
 103                                 } elseif ( $lag > $this->mServers[$i]['max lag'] ) {
 104                                         wfDebug( "Server #$i is excessively lagged ($lag seconds)\n" );
 105                                         unset( $loads[$i] );
 106                                 }
 107                         }
 108                 }
 109
 110                 # Find out if all the slaves with non-zero load are lagged
 111                 $sum = 0;
 112                 foreach ( $loads as $load ) {
 113                         $sum += $load;
 114                 }
 115                 if ( $sum == 0 ) {
 116                         # No appropriate DB servers except maybe the master and some slaves with zero load
 117                         # Do NOT use the master
 118                         # Instead, this function will return false, triggering read-only mode,
 119                         # and a lagged slave will be used instead.
 120                         return false;
 121                 }
 122
 123                 if ( count( $loads ) == 0 ) {
 124                         return false;
 125                 }
 126
 127                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 128
 129                 # Return a random representative of the remainder
 130                 return $this->pickRandom( $loads );
 131         }
 132
 133         /**
 134          * Get the index of the reader connection, which may be a slave
 135          * This takes into account load ratios and lag times. It should
 136          * always return a consistent index during a given invocation
 137          *
 138          * Side effect: opens connections to databases
 139          */
 140         function getReaderIndex( $group = false, $wiki = false ) {
 141                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 142
 143                 # FIXME: For now, only go through all this for mysql databases
 144                 if ($wgDBtype != 'mysql') {
 145                         return $this->getWriterIndex();
 146                 }
 147
 148                 if ( count( $this->mServers ) == 1 )  {
 149                         # Skip the load balancing if there's only one server
 150                         return 0;
 151                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 152                         # Shortcut if generic reader exists already
 153                         return $this->mReadIndex;
 154                 }
 155
 156                 wfProfileIn( __METHOD__ );
 157
 158                 $totalElapsed = 0;
 159
 160                 # convert from seconds to microseconds
 161                 $timeout = $wgDBClusterTimeout * 1e6;
 162
 163                 # Find the relevant load array
 164                 if ( $group !== false ) {
 165                         if ( isset( $this->mGroupLoads[$group] ) ) {
 166                                 $nonErrorLoads = $this->mGroupLoads[$group];
 167                         } else {
 168                                 # No loads for this group, return false and the caller can use some other group
 169                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 170                                 wfProfileOut( __METHOD__ );
 171                                 return false;
 172                         }
 173                 } else {
 174                         $nonErrorLoads = $this->mLoads;
 175                 }
 176
 177                 if ( !$nonErrorLoads ) {
 178                         throw new MWException( "Empty server array given to LoadBalancer" );
 179                 }
 180
 181                 $i = false;
 182                 $found = false;
 183                 $laggedSlaveMode = false;
 184
 185                 # First try quickly looking through the available servers for a server that
 186                 # meets our criteria
 187                 do {
 188                         $totalThreadsConnected = 0;
 189                         $overloadedServers = 0;
 190                         $currentLoads = $nonErrorLoads;
 191                         while ( count( $currentLoads ) ) {
 192                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 193                                         $i = $this->pickRandom( $currentLoads );
 194                                 } else {
 195                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 196                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 197                                                 # All slaves lagged. Switch to read-only mode
 198                                                 $wgReadOnly = wfMsgNoDBForContent( 'readonly_lag' );
 199                                                 $i = $this->pickRandom( $currentLoads );
 200                                                 $laggedSlaveMode = true;
 201                                         }
 202                                 }
 203
 204                                 if ( $i === false ) {
 205                                         # pickRandom() returned false
 206                                         # This is permanent and means the configuration wants us to return false
 207                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 208                                         wfProfileOut( __METHOD__ );
 209                                         return false;
 210                                 }
 211
 212                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 213                                 $conn = $this->openConnection( $i, $wiki );
 214
 215                                 if ( !$conn ) {
 216                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 217                                         unset( $nonErrorLoads[$i] );
 218                                         unset( $currentLoads[$i] );
 219                                         continue;
 220                                 }
 221
 222                                 if ( isset( $this->mServers[$i]['max threads'] ) ) {
 223                                         $status = $conn->getStatus("Thread%");
 224                                         if ( $wiki !== false ) {
 225                                                 $this->reuseConnection( $conn );
 226                                         }
 227                                         if ( $status['Threads_running'] > $this->mServers[$i]['max threads'] ) {
 228                                                 $totalThreadsConnected += $status['Threads_connected'];
 229                                                 $overloadedServers++;
 230                                                 unset( $currentLoads[$i] );
 231                                         } else {
 232                                                 # Max threads satisfied, return this server
 233                                                 break 2;
 234                                         }
 235                                 } else {
 236                                         # No maximum, return this server
 237                                         if ( $wiki !== false ) {
 238                                                 $this->reuseConnection( $conn );
 239                                         }
 240                                         $found = true;
 241                                         break 2;
 242                                 }
 243                         }
 244
 245                         # No server found yet
 246                         $i = false;
 247
 248                         # If all servers were down, quit now
 249                         if ( !count( $nonErrorLoads ) ) {
 250                                 wfDebugLog( 'connect', "All servers down\n" );
 251                                 break;
 252                         }
 253
 254                         # Some servers must have been overloaded
 255                         if ( $overloadedServers == 0 ) {
 256                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 257                         }
 258                         # Back off for a while
 259                         # Scale the sleep time by the number of connected threads, to produce a
 260                         # roughly constant global poll rate
 261                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 262                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 263                 } while ( $totalElapsed < $timeout );
 264
 265                 if ( $totalElapsed >= $timeout ) {
 266                         wfDebugLog( 'connect', "All servers busy\n" );
 267                         $this->mErrorConnection = false;
 268                         $this->mLastError = 'All servers busy';
 269                 }
 270
 271                 if ( $i !== false ) {
 272                         # Wait for the session master pos for a short time
 273                         if ( $this->mWaitForPos && $i > 0 ) {
 274                                 if ( !$this->doWait( $i ) ) {
 275                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 276                                 }
 277                         }
 278                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 279                                 $this->mReadIndex = $i;
 280                         }
 281                 }
 282                 wfProfileOut( __METHOD__ );
 283                 return $i;
 284         }
 285
 286         /**
 287          * Wait for a specified number of microseconds, and return the period waited
 288          */
 289         function sleep( $t ) {
 290                 wfProfileIn( __METHOD__ );
 291                 wfDebug( __METHOD__.": waiting $t us\n" );
 292                 usleep( $t );
 293                 wfProfileOut( __METHOD__ );
 294                 return $t;
 295         }
 296
 297         /**
 298          * Get a random server to use in a query group
 299          * @deprecated use getReaderIndex
 300          */
 301         function getGroupIndex( $group ) {
 302                 return $this->getReaderIndex( $group );
 303         }
 304
 305         /**
 306          * Set the master wait position
 307          * If a DB_SLAVE connection has been opened already, waits
 308          * Otherwise sets a variable telling it to wait if such a connection is opened
 309          */
 310         public function waitFor( $pos ) {
 311                 wfProfileIn( __METHOD__ );
 312                 $this->mWaitForPos = $pos;
 313                 $i = $this->mReadIndex;
 314
 315                 if ( $i > 0 ) {
 316                         if ( !$this->doWait( $i ) ) {
 317                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 318                                 $this->mLaggedSlaveMode = true;
 319                         }
 320                 }
 321                 wfProfileOut( __METHOD__ );
 322         }
 323
 324         /**
 325          * Get any open connection to a given server index, local or foreign
 326          * Returns false if there is no connection open
 327          */
 328         function getAnyOpenConnection( $i ) {
 329                 foreach ( $this->mConns as $type => $conns ) {
 330                         if ( !empty( $conns[$i] ) ) {
 331                                 return reset( $conns[$i] );
 332                         }
 333                 }
 334                 return false;
 335         }
 336
 337         /**
 338          * Wait for a given slave to catch up to the master pos stored in $this
 339          */
 340         function doWait( $index ) {
 341                 # Find a connection to wait on
 342                 $conn = $this->getAnyOpenConnection( $index );
 343                 if ( !$conn ) {
 344                         wfDebug( __METHOD__ . ": no connection open\n" );
 345                         return false;
 346                 }
 347
 348                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 349                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 350
 351                 if ( $result == -1 || is_null( $result ) ) {
 352                         # Timed out waiting for slave, use master instead
 353                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 354                         return false;
 355                 } else {
 356                         wfDebug( __METHOD__.": Done\n" );
 357                         return true;
 358                 }
 359         }
 360
 361         /**
 362          * Get a connection by index
 363          * This is the main entry point for this class.
 364          */
 365         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 366                 global $wgDBtype;
 367                 wfProfileIn( __METHOD__ );
 368
 369                 if ( $wiki === wfWikiID() ) {
 370                         $wiki = false;
 371                 }
 372
 373                 # Query groups
 374                 if ( $i == DB_MASTER ) {
 375                         $i = $this->getWriterIndex();
 376                 } elseif ( !is_array( $groups ) ) {
 377                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 378                         if ( $groupIndex !== false ) {
 379                                 $serverName = $this->getServerName( $groupIndex );
 380                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 381                                 $i = $groupIndex;
 382                         }
 383                 } else {
 384                         foreach ( $groups as $group ) {
 385                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 386                                 if ( $groupIndex !== false ) {
 387                                         $serverName = $this->getServerName( $groupIndex );
 388                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 389                                         $i = $groupIndex;
 390                                         break;
 391                                 }
 392                         }
 393                 }
 394
 395                 # Operation-based index
 396                 if ( $i == DB_SLAVE ) {
 397                         $i = $this->getReaderIndex( false, $wiki );
 398                 } elseif ( $i == DB_LAST ) {
 399                         # Just use $this->mLastIndex, which should already be set
 400                         $i = $this->mLastIndex;
 401                         if ( $i === -1 ) {
 402                                 # Oh dear, not set, best to use the writer for safety
 403                                 wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
 404                                 $i = $this->getWriterIndex();
 405                         }
 406                 }
 407                 # Couldn't find a working server in getReaderIndex()?
 408                 if ( $i === false ) {
 409                         $this->reportConnectionError( $this->mErrorConnection );
 410                 }
 411
 412                 # Now we have an explicit index into the servers array
 413                 $conn = $this->openConnection( $i, $wiki );
 414                 if ( !$conn ) {
 415                         $this->reportConnectionError( $this->mErrorConnection );
 416                 }
 417
 418                 wfProfileOut( __METHOD__ );
 419                 return $conn;
 420         }
 421
 422         /**
 423          * Mark a foreign connection as being available for reuse under a different
 424          * DB name or prefix. This mechanism is reference-counted, and must be called
 425          * the same number of times as getConnection() to work.
 426          */
 427         public function reuseConnection( $conn ) {
 428                 $serverIndex = $conn->getLBInfo('serverIndex');
 429                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 430                 $dbName = $conn->getDBname();
 431                 $prefix = $conn->tablePrefix();
 432                 if ( strval( $prefix ) !== '' ) {
 433                         $wiki = "$dbName-$prefix";
 434                 } else {
 435                         $wiki = $dbName;
 436                 }
 437                 if ( $serverIndex === null || $refCount === null ) {
 438                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 439                         /**
 440                          * This can happen in code like:
 441                          *   foreach ( $dbs as $db ) {
 442                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 443                          *     ...
 444                          *     $lb->reuseConnection( $conn );
 445                          *   }
 446                          * When a connection to the local DB is opened in this way, reuseConnection()
 447                          * should be ignored
 448                          */
 449                         return;
 450                 }
 451                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 452                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 453                 }
 454                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 455                 if ( $refCount <= 0 ) {
 456                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 457                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 458                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 459                 } else {
 460                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 461                 }
 462         }
 463
 464         /**
 465          * Open a connection to the server given by the specified index
 466          * Index must be an actual index into the array.
 467          * If the server is already open, returns it.
 468          *
 469          * On error, returns false, and the connection which caused the
 470          * error will be available via $this->mErrorConnection.
 471          *
 472          * @param integer $i Server index
 473          * @param string $wiki Wiki ID to open
 474          * @return Database
 475          *
 476          * @access private
 477          */
 478         function openConnection( $i, $wiki = false ) {
 479                 wfProfileIn( __METHOD__ );
 480                 if ( $wiki !== false ) {
 481                         $conn = $this->openForeignConnection( $i, $wiki );
 482                         wfProfileOut( __METHOD__);
 483                         return $conn;
 484                 }
 485                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 486                         $conn = $this->mConns['local'][$i][0];
 487                 } else {
 488                         $server = $this->mServers[$i];
 489                         $server['serverIndex'] = $i;
 490                         $conn = $this->reallyOpenConnection( $server );
 491                         if ( $conn->isOpen() ) {
 492                                 $this->mConns['local'][$i][0] = $conn;
 493                         } else {
 494                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 495                                 $this->mErrorConnection = $conn;
 496                                 $conn = false;
 497                         }
 498                 }
 499                 $this->mLastIndex = $i;
 500                 wfProfileOut( __METHOD__ );
 501                 return $conn;
 502         }
 503
 504         /**
 505          * Open a connection to a foreign DB, or return one if it is already open.
 506          *
 507          * Increments a reference count on the returned connection which locks the
 508          * connection to the requested wiki. This reference count can be
 509          * decremented by calling reuseConnection().
 510          *
 511          * If a connection is open to the appropriate server already, but with the wrong
 512          * database, it will be switched to the right database and returned, as long as
 513          * it has been freed first with reuseConnection().
 514          *
 515          * On error, returns false, and the connection which caused the
 516          * error will be available via $this->mErrorConnection.
 517          *
 518          * @param integer $i Server index
 519          * @param string $wiki Wiki ID to open
 520          * @return Database
 521          */
 522         function openForeignConnection( $i, $wiki ) {
 523                 wfProfileIn(__METHOD__);
 524                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 525                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 526                         // Reuse an already-used connection
 527                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 528                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 529                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 530                         // Reuse a free connection for the same wiki
 531                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 532                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 533                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 534                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 535                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 536                         // Reuse a connection from another wiki
 537                         $conn = reset( $this->mConns['foreignFree'][$i] );
 538                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 539
 540                         if ( !$conn->selectDB( $dbName ) ) {
 541                                 global $wguname;
 542                                 $this->mLastError = "Error selecting database $dbName on server " .
 543                                         $conn->getServer() . " from client host {$wguname['nodename']}\n";
 544                                 $this->mErrorConnection = $conn;
 545                                 $conn = false;
 546                         } else {
 547                                 $conn->tablePrefix( $prefix );
 548                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 549                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 550                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 551                         }
 552                 } else {
 553                         // Open a new connection
 554                         $server = $this->mServers[$i];
 555                         $server['serverIndex'] = $i;
 556                         $server['foreignPoolRefCount'] = 0;
 557                         $conn = $this->reallyOpenConnection( $server, $dbName );
 558                         if ( !$conn->isOpen() ) {
 559                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 560                                 $this->mErrorConnection = $conn;
 561                                 $conn = false;
 562                         } else {
 563                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 564                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 565                         }
 566                 }
 567
 568                 // Increment reference count
 569                 if ( $conn ) {
 570                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 571                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 572                 }
 573                 wfProfileOut(__METHOD__);
 574                 return $conn;
 575         }
 576
 577         /**
 578          * Test if the specified index represents an open connection
 579          * @access private
 580          */
 581         function isOpen( $index ) {
 582                 if( !is_integer( $index ) ) {
 583                         return false;
 584                 }
 585                 return (bool)$this->getAnyOpenConnection( $index );
 586         }
 587
 588         /**
 589          * Really opens a connection. Uncached.
 590          * Returns a Database object whether or not the connection was successful.
 591          * @access private
 592          */
 593         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 594                 if( !is_array( $server ) ) {
 595                         throw new MWException( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
 596                 }
 597
 598                 extract( $server );
 599                 if ( $dbNameOverride !== false ) {
 600                         $dbname = $dbNameOverride;
 601                 }
 602
 603                 # Get class for this database type
 604                 $class = 'Database' . ucfirst( $type );
 605
 606                 # Create object
 607                 wfDebug( "Connecting to $host $dbname...\n" );
 608                 $db = new $class( $host, $user, $password, $dbname, 1, $flags );
 609                 if ( $db->isOpen() ) {
 610                         wfDebug( "Connected\n" );
 611                 } else {
 612                         wfDebug( "Failed\n" );
 613                 }
 614                 $db->setLBInfo( $server );
 615                 if ( isset( $server['fakeSlaveLag'] ) ) {
 616                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 617                 }
 618                 if ( isset( $server['fakeMaster'] ) ) {
 619                         $db->setFakeMaster( true );
 620                 }
 621                 return $db;
 622         }
 623
 624         function reportConnectionError( &$conn ) {
 625                 wfProfileIn( __METHOD__ );
 626                 # Prevent infinite recursion
 627
 628                 static $reporting = false;
 629                 if ( !$reporting ) {
 630                         $reporting = true;
 631                         if ( !is_object( $conn ) ) {
 632                                 // No last connection, probably due to all servers being too busy
 633                                 $conn = new Database;
 634                                 if ( $this->mFailFunction ) {
 635                                         $conn->failFunction( $this->mFailFunction );
 636                                         $conn->reportConnectionError( $this->mLastError );
 637                                 } else {
 638                                         // If all servers were busy, mLastError will contain something sensible
 639                                         throw new DBConnectionError( $conn, $this->mLastError );
 640                                 }
 641                         } else {
 642                                 if ( $this->mFailFunction ) {
 643                                         $conn->failFunction( $this->mFailFunction );
 644                                 } else {
 645                                         $conn->failFunction( false );
 646                                 }
 647                                 $server = $conn->getProperty( 'mServer' );
 648                                 $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 649                         }
 650                         $reporting = false;
 651                 }
 652                 wfProfileOut( __METHOD__ );
 653         }
 654
 655         function getWriterIndex() {
 656                 return 0;
 657         }
 658
 659         /**
 660          * Returns true if the specified index is a valid server index
 661          */
 662         function haveIndex( $i ) {
 663                 return array_key_exists( $i, $this->mServers );
 664         }
 665
 666         /**
 667          * Returns true if the specified index is valid and has non-zero load
 668          */
 669         function isNonZeroLoad( $i ) {
 670                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 671         }
 672
 673         /**
 674          * Get the number of defined servers (not the number of open connections)
 675          */
 676         function getServerCount() {
 677                 return count( $this->mServers );
 678         }
 679
 680         /**
 681          * Get the host name or IP address of the server with the specified index
 682          */
 683         function getServerName( $i ) {
 684                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 685                         return $this->mServers[$i]['hostName'];
 686                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 687                         return $this->mServers[$i]['host'];
 688                 } else {
 689                         return '';
 690                 }
 691         }
 692
 693         /**
 694          * Get the current master position for chronology control purposes
 695          * @return mixed
 696          */
 697         function getMasterPos() {
 698                 # If this entire request was served from a slave without opening a connection to the
 699                 # master (however unlikely that may be), then we can fetch the position from the slave.
 700                 $masterConn = $this->getAnyOpenConnection( 0 );
 701                 if ( !$masterConn ) {
 702                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 703                                 $conn = $this->getAnyOpenConnection( $i );
 704                                 if ( $conn ) {
 705                                         wfDebug( "Master pos fetched from slave\n" );
 706                                         return $conn->getSlavePos();
 707                                 }
 708                         }
 709                 } else {
 710                         wfDebug( "Master pos fetched from master\n" );
 711                         return $masterConn->getMasterPos();
 712                 }
 713                 return false;
 714         }
 715
 716         /**
 717          * Close all open connections
 718          */
 719         function closeAll() {
 720                 foreach ( $this->mConns as $conns2 ) {
 721                         foreach  ( $conns2 as $conns3 ) {
 722                                 foreach ( $conns3 as $conn ) {
 723                                         $conn->close();
 724                                 }
 725                         }
 726                 }
 727                 $this->mConns = array(
 728                         'local' => array(),
 729                         'foreignFree' => array(),
 730                         'foreignUsed' => array(),
 731                 );
 732         }
 733
 734         /**
 735          * Close a connection
 736          * Using this function makes sure the LoadBalancer knows the connection is closed.
 737          * If you use $conn->close() directly, the load balancer won't update its state.
 738          */
 739         function closeConnecton( $conn ) {
 740                 $done = false;
 741                 foreach ( $this->mConns as $i1 => $conns2 ) {
 742                         foreach ( $conns2 as $i2 => $conns3 ) {
 743                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 744                                         if ( $conn === $candidateConn ) {
 745                                                 $conn->close();
 746                                                 unset( $this->mConns[$i1][$i2][$i3] );
 747                                                 $done = true;
 748                                                 break;
 749                                         }
 750                                 }
 751                         }
 752                 }
 753                 if ( !$done ) {
 754                         $conn->close();
 755                 }
 756         }
 757
 758         /**
 759          * Commit transactions on all open connections
 760          */
 761         function commitAll() {
 762                 foreach ( $this->mConns as $conns2 ) {
 763                         foreach ( $conns2 as $conns3 ) {
 764                                 foreach ( $conns3 as $conn ) {
 765                                         $conn->immediateCommit();
 766                                 }
 767                         }
 768                 }
 769         }
 770
 771         /* Issue COMMIT only on master, only if queries were done on connection */
 772         function commitMasterChanges() {
 773                 // Always 0, but who knows.. :)
 774                 $masterIndex = $this->getWriterIndex();
 775                 foreach ( $this->mConns as $type => $conns2 ) {
 776                         if ( empty( $conns2[$masterIndex] ) ) {
 777                                 continue;
 778                         }
 779                         foreach ( $conns2[$masterIndex] as $conn ) {
 780                                 if ( $conn->lastQuery() != '' ) {
 781                                         $conn->commit();
 782                                 }
 783                         }
 784                 }
 785         }
 786
 787         function waitTimeout( $value = NULL ) {
 788                 return wfSetVar( $this->mWaitTimeout, $value );
 789         }
 790
 791         function getLaggedSlaveMode() {
 792                 return $this->mLaggedSlaveMode;
 793         }
 794
 795         /* Disables/enables lag checks */
 796         function allowLagged($mode=null) {
 797                 if ($mode===null)
 798                         return $this->mAllowLagged;
 799                 $this->mAllowLagged=$mode;
 800         }
 801
 802         function pingAll() {
 803                 $success = true;
 804                 foreach ( $this->mConns as $conns2 ) {
 805                         foreach ( $conns2 as $conns3 ) {
 806                                 foreach ( $conns3 as $conn ) {
 807                                         if ( !$conn->ping() ) {
 808                                                 $success = false;
 809                                         }
 810                                 }
 811                         }
 812                 }
 813                 return $success;
 814         }
 815
 816         /**
 817          * Get the hostname and lag time of the most-lagged slave.
 818          * This is useful for maintenance scripts that need to throttle their updates.
 819          * May attempt to open connections to slaves on the default DB.
 820          */
 821         function getMaxLag() {
 822                 $maxLag = -1;
 823                 $host = '';
 824                 foreach ( $this->mServers as $i => $conn ) {
 825                         $conn = $this->getAnyOpenConnection( $i );
 826                         if ( !$conn ) {
 827                                 $conn = $this->openConnection( $i );
 828                         }
 829                         if ( !$conn ) {
 830                                 continue;
 831                         }
 832                         $lag = $conn->getLag();
 833                         if ( $lag > $maxLag ) {
 834                                 $maxLag = $lag;
 835                                 $host = $this->mServers[$i]['host'];
 836                         }
 837                 }
 838                 return array( $host, $maxLag );
 839         }
 840
 841         /**
 842          * Get lag time for each server
 843          * Results are cached for a short time in memcached, and indefinitely in the process cache
 844          */
 845         function getLagTimes( $wiki = false ) {
 846                 wfProfileIn( __METHOD__ );
 847
 848                 if ( !isset( $this->mLagTimes ) ) {
 849                         $expiry = 5;
 850                         $requestRate = 10;
 851
 852                         global $wgMemc;
 853                         $masterName = $this->getServerName( 0 );
 854                         $memcKey = wfMemcKey( 'lag_times', $masterName );
 855                         $times = $wgMemc->get( $memcKey );
 856                         if ( $times ) {
 857                                 # Randomly recache with probability rising over $expiry
 858                                 $elapsed = time() - $times['timestamp'];
 859                                 $chance = max( 0, ( $expiry - $elapsed ) * $requestRate );
 860                                 if ( mt_rand( 0, $chance ) != 0 ) {
 861                                         unset( $times['timestamp'] );
 862                                         wfProfileOut( __METHOD__ );
 863                                         return $times;
 864                                 }
 865                                 wfIncrStats( 'lag_cache_miss_expired' );
 866                         } else {
 867                                 wfIncrStats( 'lag_cache_miss_absent' );
 868                         }
 869
 870                         # Cache key missing or expired
 871
 872                         $times = array();
 873                         foreach ( $this->mServers as $i => $conn ) {
 874                                 if ($i == 0) { # Master
 875                                         $times[$i] = 0;
 876                                 } elseif ( false !== ( $conn = $this->getAnyOpenConnection( $i ) ) ) {
 877                                         $times[$i] = $conn->getLag();
 878                                 } elseif ( false !== ( $conn = $this->openConnection( $i, $wiki ) ) ) {
 879                                         $times[$i] = $conn->getLag();
 880                                 }
 881                         }
 882
 883                         # Add a timestamp key so we know when it was cached
 884                         $times['timestamp'] = time();
 885                         $wgMemc->set( $memcKey, $times, $expiry );
 886
 887                         # But don't give the timestamp to the caller
 888                         unset($times['timestamp']);
 889                         $this->mLagTimes = $times;
 890                 }
 891                 wfProfileOut( __METHOD__ );
 892                 return $this->mLagTimes;
 893         }
 894 }