includes/db/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23
  24 /**
  25  * Database load balancing object
  26  *
  27  * @todo document
  28  * @ingroup Database
  29  */
  30 class LoadBalancer {
  31         private $mServers, $mConns, $mLoads, $mGroupLoads;
  32         private $mErrorConnection;
  33         private $mReadIndex, $mAllowLagged;
  34         private $mWaitForPos, $mWaitTimeout;
  35         private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  36         private $mParentInfo, $mLagTimes;
  37         private $mLoadMonitorClass, $mLoadMonitor;
  38
  39         /**
  40          * @param $params Array with keys:
  41          *    servers           Required. Array of server info structures.
  42          *    masterWaitTimeout Replication lag wait timeout
  43          *    loadMonitor       Name of a class used to fetch server lag and load.
  44          */
  45         function __construct( $params ) {
  46                 if ( !isset( $params['servers'] ) ) {
  47                         throw new MWException( __CLASS__.': missing servers parameter' );
  48                 }
  49                 $this->mServers = $params['servers'];
  50
  51                 if ( isset( $params['waitTimeout'] ) ) {
  52                         $this->mWaitTimeout = $params['waitTimeout'];
  53                 } else {
  54                         $this->mWaitTimeout = 10;
  55                 }
  56
  57                 $this->mReadIndex = -1;
  58                 $this->mWriteIndex = -1;
  59                 $this->mConns = array(
  60                         'local' => array(),
  61                         'foreignUsed' => array(),
  62                         'foreignFree' => array() );
  63                 $this->mLoads = array();
  64                 $this->mWaitForPos = false;
  65                 $this->mLaggedSlaveMode = false;
  66                 $this->mErrorConnection = false;
  67                 $this->mAllowLagged = false;
  68
  69                 if ( isset( $params['loadMonitor'] ) ) {
  70                         $this->mLoadMonitorClass = $params['loadMonitor'];
  71                 } else {
  72                         $master = reset( $params['servers'] );
  73                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  74                                 $this->mLoadMonitorClass = 'LoadMonitor_MySQL';
  75                         } else {
  76                                 $this->mLoadMonitorClass = 'LoadMonitor_Null';
  77                         }
  78                 }
  79
  80                 foreach( $params['servers'] as $i => $server ) {
  81                         $this->mLoads[$i] = $server['load'];
  82                         if ( isset( $server['groupLoads'] ) ) {
  83                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  84                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  85                                                 $this->mGroupLoads[$group] = array();
  86                                         }
  87                                         $this->mGroupLoads[$group][$i] = $ratio;
  88                                 }
  89                         }
  90                 }
  91         }
  92
  93         /**
  94          * Get a LoadMonitor instance
  95          *
  96          * @return LoadMonitor
  97          */
  98         function getLoadMonitor() {
  99                 if ( !isset( $this->mLoadMonitor ) ) {
 100                         $class = $this->mLoadMonitorClass;
 101                         $this->mLoadMonitor = new $class( $this );
 102                 }
 103                 return $this->mLoadMonitor;
 104         }
 105
 106         /**
 107          * Get or set arbitrary data used by the parent object, usually an LBFactory
 108          * @param $x
 109          * @return Mixed
 110          */
 111         function parentInfo( $x = null ) {
 112                 return wfSetVar( $this->mParentInfo, $x );
 113         }
 114
 115         /**
 116          * Given an array of non-normalised probabilities, this function will select
 117          * an element and return the appropriate key
 118          *
 119          * @param $weights array
 120          *
 121          * @return int
 122          */
 123         function pickRandom( $weights ) {
 124                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
 125                         return false;
 126                 }
 127
 128                 $sum = array_sum( $weights );
 129                 if ( $sum == 0 ) {
 130                         # No loads on any of them
 131                         # In previous versions, this triggered an unweighted random selection,
 132                         # but this feature has been removed as of April 2006 to allow for strict
 133                         # separation of query groups.
 134                         return false;
 135                 }
 136                 $max = mt_getrandmax();
 137                 $rand = mt_rand( 0, $max ) / $max * $sum;
 138
 139                 $sum = 0;
 140                 foreach ( $weights as $i => $w ) {
 141                         $sum += $w;
 142                         if ( $sum >= $rand ) {
 143                                 break;
 144                         }
 145                 }
 146                 return $i;
 147         }
 148
 149         /**
 150          * @param $loads array
 151          * @param $wiki bool
 152          * @return bool|int|string
 153          */
 154         function getRandomNonLagged( $loads, $wiki = false ) {
 155                 # Unset excessively lagged servers
 156                 $lags = $this->getLagTimes( $wiki );
 157                 foreach ( $lags as $i => $lag ) {
 158                         if ( $i != 0 ) {
 159                                 if ( $lag === false ) {
 160                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 161                                         unset( $loads[$i] );
 162                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 163                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 164                                         unset( $loads[$i] );
 165                                 }
 166                         }
 167                 }
 168
 169                 # Find out if all the slaves with non-zero load are lagged
 170                 $sum = 0;
 171                 foreach ( $loads as $load ) {
 172                         $sum += $load;
 173                 }
 174                 if ( $sum == 0 ) {
 175                         # No appropriate DB servers except maybe the master and some slaves with zero load
 176                         # Do NOT use the master
 177                         # Instead, this function will return false, triggering read-only mode,
 178                         # and a lagged slave will be used instead.
 179                         return false;
 180                 }
 181
 182                 if ( count( $loads ) == 0 ) {
 183                         return false;
 184                 }
 185
 186                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 187
 188                 # Return a random representative of the remainder
 189                 return $this->pickRandom( $loads );
 190         }
 191
 192         /**
 193          * Get the index of the reader connection, which may be a slave
 194          * This takes into account load ratios and lag times. It should
 195          * always return a consistent index during a given invocation
 196          *
 197          * Side effect: opens connections to databases
 198          * @param $group bool
 199          * @param $wiki bool
 200          * @return bool|int|string
 201          */
 202         function getReaderIndex( $group = false, $wiki = false ) {
 203                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 204
 205                 # @todo FIXME: For now, only go through all this for mysql databases
 206                 if ($wgDBtype != 'mysql') {
 207                         return $this->getWriterIndex();
 208                 }
 209
 210                 if ( count( $this->mServers ) == 1 )  {
 211                         # Skip the load balancing if there's only one server
 212                         return 0;
 213                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 214                         # Shortcut if generic reader exists already
 215                         return $this->mReadIndex;
 216                 }
 217
 218                 wfProfileIn( __METHOD__ );
 219
 220                 $totalElapsed = 0;
 221
 222                 # convert from seconds to microseconds
 223                 $timeout = $wgDBClusterTimeout * 1e6;
 224
 225                 # Find the relevant load array
 226                 if ( $group !== false ) {
 227                         if ( isset( $this->mGroupLoads[$group] ) ) {
 228                                 $nonErrorLoads = $this->mGroupLoads[$group];
 229                         } else {
 230                                 # No loads for this group, return false and the caller can use some other group
 231                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 232                                 wfProfileOut( __METHOD__ );
 233                                 return false;
 234                         }
 235                 } else {
 236                         $nonErrorLoads = $this->mLoads;
 237                 }
 238
 239                 if ( !$nonErrorLoads ) {
 240                         throw new MWException( "Empty server array given to LoadBalancer" );
 241                 }
 242
 243                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 244                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 245
 246                 $laggedSlaveMode = false;
 247
 248                 # First try quickly looking through the available servers for a server that
 249                 # meets our criteria
 250                 do {
 251                         $totalThreadsConnected = 0;
 252                         $overloadedServers = 0;
 253                         $currentLoads = $nonErrorLoads;
 254                         while ( count( $currentLoads ) ) {
 255                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 256                                         $i = $this->pickRandom( $currentLoads );
 257                                 } else {
 258                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 259                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 260                                                 # All slaves lagged. Switch to read-only mode
 261                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 262                                                 $wgReadOnly = 'The database has been automatically locked ' .
 263                                                         'while the slave database servers catch up to the master';
 264                                                 $i = $this->pickRandom( $currentLoads );
 265                                                 $laggedSlaveMode = true;
 266                                         }
 267                                 }
 268
 269                                 if ( $i === false ) {
 270                                         # pickRandom() returned false
 271                                         # This is permanent and means the configuration or the load monitor
 272                                         # wants us to return false.
 273                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 274                                         wfProfileOut( __METHOD__ );
 275                                         return false;
 276                                 }
 277
 278                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 279                                 $conn = $this->openConnection( $i, $wiki );
 280
 281                                 if ( !$conn ) {
 282                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 283                                         unset( $nonErrorLoads[$i] );
 284                                         unset( $currentLoads[$i] );
 285                                         continue;
 286                                 }
 287
 288                                 // Perform post-connection backoff
 289                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 290                                         ? $this->mServers[$i]['max threads'] : false;
 291                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 292
 293                                 // Decrement reference counter, we are finished with this connection.
 294                                 // It will be incremented for the caller later.
 295                                 if ( $wiki !== false ) {
 296                                         $this->reuseConnection( $conn );
 297                                 }
 298
 299                                 if ( $backoff ) {
 300                                         # Post-connection overload, don't use this server for now
 301                                         $totalThreadsConnected += $backoff;
 302                                         $overloadedServers++;
 303                                         unset( $currentLoads[$i] );
 304                                 } else {
 305                                         # Return this server
 306                                         break 2;
 307                                 }
 308                         }
 309
 310                         # No server found yet
 311                         $i = false;
 312
 313                         # If all servers were down, quit now
 314                         if ( !count( $nonErrorLoads ) ) {
 315                                 wfDebugLog( 'connect', "All servers down\n" );
 316                                 break;
 317                         }
 318
 319                         # Some servers must have been overloaded
 320                         if ( $overloadedServers == 0 ) {
 321                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 322                         }
 323                         # Back off for a while
 324                         # Scale the sleep time by the number of connected threads, to produce a
 325                         # roughly constant global poll rate
 326                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 327                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 328                 } while ( $totalElapsed < $timeout );
 329
 330                 if ( $totalElapsed >= $timeout ) {
 331                         wfDebugLog( 'connect', "All servers busy\n" );
 332                         $this->mErrorConnection = false;
 333                         $this->mLastError = 'All servers busy';
 334                 }
 335
 336                 if ( $i !== false ) {
 337                         # Slave connection successful
 338                         # Wait for the session master pos for a short time
 339                         if ( $this->mWaitForPos && $i > 0 ) {
 340                                 if ( !$this->doWait( $i ) ) {
 341                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 342                                 }
 343                         }
 344                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 345                                 $this->mReadIndex = $i;
 346                         }
 347                 }
 348                 wfProfileOut( __METHOD__ );
 349                 return $i;
 350         }
 351
 352         /**
 353          * Wait for a specified number of microseconds, and return the period waited
 354          * @param $t int
 355          * @return int
 356          */
 357         function sleep( $t ) {
 358                 wfProfileIn( __METHOD__ );
 359                 wfDebug( __METHOD__.": waiting $t us\n" );
 360                 usleep( $t );
 361                 wfProfileOut( __METHOD__ );
 362                 return $t;
 363         }
 364
 365         /**
 366          * Set the master wait position
 367          * If a DB_SLAVE connection has been opened already, waits
 368          * Otherwise sets a variable telling it to wait if such a connection is opened
 369          * @param $pos int
 370          */
 371         public function waitFor( $pos ) {
 372                 wfProfileIn( __METHOD__ );
 373                 $this->mWaitForPos = $pos;
 374                 $i = $this->mReadIndex;
 375
 376                 if ( $i > 0 ) {
 377                         if ( !$this->doWait( $i ) ) {
 378                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 379                                 $this->mLaggedSlaveMode = true;
 380                         }
 381                 }
 382                 wfProfileOut( __METHOD__ );
 383         }
 384
 385         /**
 386          * Set the master wait position and wait for ALL slaves to catch up to it
 387          * @param $pos int
 388          */
 389         public function waitForAll( $pos ) {
 390                 wfProfileIn( __METHOD__ );
 391                 $this->mWaitForPos = $pos;
 392                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 393                         $this->doWait( $i , true );
 394                 }
 395                 wfProfileOut( __METHOD__ );
 396         }
 397
 398         /**
 399          * Get any open connection to a given server index, local or foreign
 400          * Returns false if there is no connection open
 401          *
 402          * @param $i int
 403          * @return DatabaseBase|bool False on failure
 404          */
 405         function getAnyOpenConnection( $i ) {
 406                 foreach ( $this->mConns as $conns ) {
 407                         if ( !empty( $conns[$i] ) ) {
 408                                 return reset( $conns[$i] );
 409                         }
 410                 }
 411                 return false;
 412         }
 413
 414         /**
 415          * Wait for a given slave to catch up to the master pos stored in $this
 416          * @param $index
 417          * @param $open bool
 418          * @return bool
 419          */
 420         function doWait( $index, $open = false ) {
 421                 # Find a connection to wait on
 422                 $conn = $this->getAnyOpenConnection( $index );
 423                 if ( !$conn ) {
 424                         if ( !$open ) {
 425                                 wfDebug( __METHOD__ . ": no connection open\n" );
 426                                 return false;
 427                         } else {
 428                                 $conn = $this->openConnection( $index );
 429                                 if ( !$conn ) {
 430                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 431                                         return false;
 432                                 }
 433                         }
 434                 }
 435
 436                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 437                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 438
 439                 if ( $result == -1 || is_null( $result ) ) {
 440                         # Timed out waiting for slave, use master instead
 441                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 442                         return false;
 443                 } else {
 444                         wfDebug( __METHOD__.": Done\n" );
 445                         return true;
 446                 }
 447         }
 448
 449         /**
 450          * Get a connection by index
 451          * This is the main entry point for this class.
 452          *
 453          * @param $i Integer: server index
 454          * @param $groups Array: query groups
 455          * @param $wiki String: wiki ID
 456          *
 457          * @return DatabaseBase
 458          */
 459         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 460                 wfProfileIn( __METHOD__ );
 461
 462                 if ( $i == DB_LAST ) {
 463                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 464                 } elseif ( $i === null || $i === false ) {
 465                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 466                 }
 467
 468                 if ( $wiki === wfWikiID() ) {
 469                         $wiki = false;
 470                 }
 471
 472                 # Query groups
 473                 if ( $i == DB_MASTER ) {
 474                         $i = $this->getWriterIndex();
 475                 } elseif ( !is_array( $groups ) ) {
 476                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 477                         if ( $groupIndex !== false ) {
 478                                 $serverName = $this->getServerName( $groupIndex );
 479                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 480                                 $i = $groupIndex;
 481                         }
 482                 } else {
 483                         foreach ( $groups as $group ) {
 484                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 485                                 if ( $groupIndex !== false ) {
 486                                         $serverName = $this->getServerName( $groupIndex );
 487                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 488                                         $i = $groupIndex;
 489                                         break;
 490                                 }
 491                         }
 492                 }
 493
 494                 # Operation-based index
 495                 if ( $i == DB_SLAVE ) {
 496                         $i = $this->getReaderIndex( false, $wiki );
 497                         # Couldn't find a working server in getReaderIndex()?
 498                         if ( $i === false ) {
 499                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 500                                 wfProfileOut( __METHOD__ );
 501                                 $this->reportConnectionError( $this->mErrorConnection );
 502                                 return false;
 503                         }
 504                 }
 505
 506                 # Now we have an explicit index into the servers array
 507                 $conn = $this->openConnection( $i, $wiki );
 508                 if ( !$conn ) {
 509                         wfProfileOut( __METHOD__ );
 510                         $this->reportConnectionError( $this->mErrorConnection );
 511                 }
 512
 513                 wfProfileOut( __METHOD__ );
 514                 return $conn;
 515         }
 516
 517         /**
 518          * Mark a foreign connection as being available for reuse under a different
 519          * DB name or prefix. This mechanism is reference-counted, and must be called
 520          * the same number of times as getConnection() to work.
 521          *
 522          * @param DatabaseBase $conn
 523          */
 524         public function reuseConnection( $conn ) {
 525                 $serverIndex = $conn->getLBInfo('serverIndex');
 526                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 527                 $dbName = $conn->getDBname();
 528                 $prefix = $conn->tablePrefix();
 529                 if ( strval( $prefix ) !== '' ) {
 530                         $wiki = "$dbName-$prefix";
 531                 } else {
 532                         $wiki = $dbName;
 533                 }
 534                 if ( $serverIndex === null || $refCount === null ) {
 535                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 536                         /**
 537                          * This can happen in code like:
 538                          *   foreach ( $dbs as $db ) {
 539                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 540                          *     ...
 541                          *     $lb->reuseConnection( $conn );
 542                          *   }
 543                          * When a connection to the local DB is opened in this way, reuseConnection()
 544                          * should be ignored
 545                          */
 546                         return;
 547                 }
 548                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 549                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 550                 }
 551                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 552                 if ( $refCount <= 0 ) {
 553                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 554                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 555                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 556                 } else {
 557                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 558                 }
 559         }
 560
 561         /**
 562          * Open a connection to the server given by the specified index
 563          * Index must be an actual index into the array.
 564          * If the server is already open, returns it.
 565          *
 566          * On error, returns false, and the connection which caused the
 567          * error will be available via $this->mErrorConnection.
 568          *
 569          * @param $i Integer server index
 570          * @param $wiki String wiki ID to open
 571          * @return DatabaseBase
 572          *
 573          * @access private
 574          */
 575         function openConnection( $i, $wiki = false ) {
 576                 wfProfileIn( __METHOD__ );
 577                 if ( $wiki !== false ) {
 578                         $conn = $this->openForeignConnection( $i, $wiki );
 579                         wfProfileOut( __METHOD__);
 580                         return $conn;
 581                 }
 582                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 583                         $conn = $this->mConns['local'][$i][0];
 584                 } else {
 585                         $server = $this->mServers[$i];
 586                         $server['serverIndex'] = $i;
 587                         $conn = $this->reallyOpenConnection( $server, false );
 588                         if ( $conn->isOpen() ) {
 589                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 590                                 $this->mConns['local'][$i][0] = $conn;
 591                         } else {
 592                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 593                                 $this->mErrorConnection = $conn;
 594                                 $conn = false;
 595                         }
 596                 }
 597                 wfProfileOut( __METHOD__ );
 598                 return $conn;
 599         }
 600
 601         /**
 602          * Open a connection to a foreign DB, or return one if it is already open.
 603          *
 604          * Increments a reference count on the returned connection which locks the
 605          * connection to the requested wiki. This reference count can be
 606          * decremented by calling reuseConnection().
 607          *
 608          * If a connection is open to the appropriate server already, but with the wrong
 609          * database, it will be switched to the right database and returned, as long as
 610          * it has been freed first with reuseConnection().
 611          *
 612          * On error, returns false, and the connection which caused the
 613          * error will be available via $this->mErrorConnection.
 614          *
 615          * @param $i Integer: server index
 616          * @param $wiki String: wiki ID to open
 617          * @return DatabaseBase
 618          */
 619         function openForeignConnection( $i, $wiki ) {
 620                 wfProfileIn(__METHOD__);
 621                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 622                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 623                         // Reuse an already-used connection
 624                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 625                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 626                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 627                         // Reuse a free connection for the same wiki
 628                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 629                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 630                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 631                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 632                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 633                         // Reuse a connection from another wiki
 634                         $conn = reset( $this->mConns['foreignFree'][$i] );
 635                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 636
 637                         if ( !$conn->selectDB( $dbName ) ) {
 638                                 $this->mLastError = "Error selecting database $dbName on server " .
 639                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 640                                 $this->mErrorConnection = $conn;
 641                                 $conn = false;
 642                         } else {
 643                                 $conn->tablePrefix( $prefix );
 644                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 645                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 646                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 647                         }
 648                 } else {
 649                         // Open a new connection
 650                         $server = $this->mServers[$i];
 651                         $server['serverIndex'] = $i;
 652                         $server['foreignPoolRefCount'] = 0;
 653                         $conn = $this->reallyOpenConnection( $server, $dbName );
 654                         if ( !$conn->isOpen() ) {
 655                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 656                                 $this->mErrorConnection = $conn;
 657                                 $conn = false;
 658                         } else {
 659                                 $conn->tablePrefix( $prefix );
 660                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 661                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 662                         }
 663                 }
 664
 665                 // Increment reference count
 666                 if ( $conn ) {
 667                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 668                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 669                 }
 670                 wfProfileOut(__METHOD__);
 671                 return $conn;
 672         }
 673
 674         /**
 675          * Test if the specified index represents an open connection
 676          *
 677          * @param $index Integer: server index
 678          * @access private
 679          * @return bool
 680          */
 681         function isOpen( $index ) {
 682                 if( !is_integer( $index ) ) {
 683                         return false;
 684                 }
 685                 return (bool)$this->getAnyOpenConnection( $index );
 686         }
 687
 688         /**
 689          * Really opens a connection. Uncached.
 690          * Returns a Database object whether or not the connection was successful.
 691          * @access private
 692          *
 693          * @param $server
 694          * @param $dbNameOverride bool
 695          * @return DatabaseBase
 696          */
 697         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 698                 if( !is_array( $server ) ) {
 699                         throw new MWException( 'You must update your load-balancing configuration. ' .
 700                                 'See DefaultSettings.php entry for $wgDBservers.' );
 701                 }
 702
 703                 $host = $server['host'];
 704                 $dbname = $server['dbname'];
 705
 706                 if ( $dbNameOverride !== false ) {
 707                         $server['dbname'] = $dbname = $dbNameOverride;
 708                 }
 709
 710                 # Create object
 711                 try {
 712                         $db = DatabaseBase::factory( $server['type'], $server );
 713                 } catch ( DBConnectionError $e ) {
 714                         // FIXME: This is probably the ugliest thing I have ever done to
 715                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 716                         $db = $e->db;
 717                 }
 718
 719                 $db->setLBInfo( $server );
 720                 if ( isset( $server['fakeSlaveLag'] ) ) {
 721                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 722                 }
 723                 if ( isset( $server['fakeMaster'] ) ) {
 724                         $db->setFakeMaster( true );
 725                 }
 726                 return $db;
 727         }
 728
 729         /**
 730          * @param $conn
 731          * @throws DBConnectionError
 732          */
 733         function reportConnectionError( &$conn ) {
 734                 if ( !is_object( $conn ) ) {
 735                         // No last connection, probably due to all servers being too busy
 736                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 737                         $conn = new Database;
 738                         // If all servers were busy, mLastError will contain something sensible
 739                         throw new DBConnectionError( $conn, $this->mLastError );
 740                 } else {
 741                         $server = $conn->getProperty( 'mServer' );
 742                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 743                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 744                 }
 745         }
 746
 747         /**
 748          * @return int
 749          */
 750         function getWriterIndex() {
 751                 return 0;
 752         }
 753
 754         /**
 755          * Returns true if the specified index is a valid server index
 756          *
 757          * @param $i
 758          * @return bool
 759          */
 760         function haveIndex( $i ) {
 761                 return array_key_exists( $i, $this->mServers );
 762         }
 763
 764         /**
 765          * Returns true if the specified index is valid and has non-zero load
 766          *
 767          * @param $i
 768          * @return bool
 769          */
 770         function isNonZeroLoad( $i ) {
 771                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 772         }
 773
 774         /**
 775          * Get the number of defined servers (not the number of open connections)
 776          *
 777          * @return int
 778          */
 779         function getServerCount() {
 780                 return count( $this->mServers );
 781         }
 782
 783         /**
 784          * Get the host name or IP address of the server with the specified index
 785          * Prefer a readable name if available.
 786          * @param $i
 787          * @return string
 788          */
 789         function getServerName( $i ) {
 790                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 791                         return $this->mServers[$i]['hostName'];
 792                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 793                         return $this->mServers[$i]['host'];
 794                 } else {
 795                         return '';
 796                 }
 797         }
 798
 799         /**
 800          * Return the server info structure for a given index, or false if the index is invalid.
 801          * @param $i
 802          * @return bool
 803          */
 804         function getServerInfo( $i ) {
 805                 if ( isset( $this->mServers[$i] ) ) {
 806                         return $this->mServers[$i];
 807                 } else {
 808                         return false;
 809                 }
 810         }
 811
 812         /**
 813          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 814          * @param $i
 815          * @param $serverInfo
 816          */
 817         function setServerInfo( $i, $serverInfo ) {
 818                 $this->mServers[$i] = $serverInfo;
 819         }
 820
 821         /**
 822          * Get the current master position for chronology control purposes
 823          * @return mixed
 824          */
 825         function getMasterPos() {
 826                 # If this entire request was served from a slave without opening a connection to the
 827                 # master (however unlikely that may be), then we can fetch the position from the slave.
 828                 $masterConn = $this->getAnyOpenConnection( 0 );
 829                 if ( !$masterConn ) {
 830                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 831                                 $conn = $this->getAnyOpenConnection( $i );
 832                                 if ( $conn ) {
 833                                         wfDebug( "Master pos fetched from slave\n" );
 834                                         return $conn->getSlavePos();
 835                                 }
 836                         }
 837                 } else {
 838                         wfDebug( "Master pos fetched from master\n" );
 839                         return $masterConn->getMasterPos();
 840                 }
 841                 return false;
 842         }
 843
 844         /**
 845          * Close all open connections
 846          */
 847         function closeAll() {
 848                 foreach ( $this->mConns as $conns2 ) {
 849                         foreach  ( $conns2 as $conns3 ) {
 850                                 foreach ( $conns3 as $conn ) {
 851                                         $conn->close();
 852                                 }
 853                         }
 854                 }
 855                 $this->mConns = array(
 856                         'local' => array(),
 857                         'foreignFree' => array(),
 858                         'foreignUsed' => array(),
 859                 );
 860         }
 861
 862         /**
 863          * Deprecated function, typo in function name
 864          *
 865          * @deprecated in 1.18
 866          * @param $conn
 867          */
 868         function closeConnecton( $conn ) {
 869                 wfDeprecated( __METHOD__, '1.18' );
 870                 $this->closeConnection( $conn );
 871         }
 872
 873         /**
 874          * Close a connection
 875          * Using this function makes sure the LoadBalancer knows the connection is closed.
 876          * If you use $conn->close() directly, the load balancer won't update its state.
 877          * @param $conn DatabaseBase
 878          */
 879         function closeConnection( $conn ) {
 880                 $done = false;
 881                 foreach ( $this->mConns as $i1 => $conns2 ) {
 882                         foreach ( $conns2 as $i2 => $conns3 ) {
 883                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 884                                         if ( $conn === $candidateConn ) {
 885                                                 $conn->close();
 886                                                 unset( $this->mConns[$i1][$i2][$i3] );
 887                                                 $done = true;
 888                                                 break;
 889                                         }
 890                                 }
 891                         }
 892                 }
 893                 if ( !$done ) {
 894                         $conn->close();
 895                 }
 896         }
 897
 898         /**
 899          * Commit transactions on all open connections
 900          */
 901         function commitAll() {
 902                 foreach ( $this->mConns as $conns2 ) {
 903                         foreach ( $conns2 as $conns3 ) {
 904                                 foreach ( $conns3 as $conn ) {
 905                                         $conn->commit( __METHOD__ );
 906                                 }
 907                         }
 908                 }
 909         }
 910
 911         /**
 912          *  Issue COMMIT only on master, only if queries were done on connection
 913          */
 914         function commitMasterChanges() {
 915                 // Always 0, but who knows.. :)
 916                 $masterIndex = $this->getWriterIndex();
 917                 foreach ( $this->mConns as $conns2 ) {
 918                         if ( empty( $conns2[$masterIndex] ) ) {
 919                                 continue;
 920                         }
 921                         foreach ( $conns2[$masterIndex] as $conn ) {
 922                                 if ( $conn->trxLevel() && $conn->doneWrites() ) {
 923                                         $conn->commit( __METHOD__ );
 924                                 }
 925                         }
 926                 }
 927         }
 928
 929         /**
 930          * @param $value null
 931          * @return Mixed
 932          */
 933         function waitTimeout( $value = null ) {
 934                 return wfSetVar( $this->mWaitTimeout, $value );
 935         }
 936
 937         /**
 938          * @return bool
 939          */
 940         function getLaggedSlaveMode() {
 941                 return $this->mLaggedSlaveMode;
 942         }
 943
 944         /**
 945          * Disables/enables lag checks
 946          * @param $mode null
 947          * @return bool
 948          */
 949         function allowLagged( $mode = null ) {
 950                 if ( $mode === null) {
 951                         return $this->mAllowLagged;
 952                 }
 953                 $this->mAllowLagged = $mode;
 954         }
 955
 956         /**
 957          * @return bool
 958          */
 959         function pingAll() {
 960                 $success = true;
 961                 foreach ( $this->mConns as $conns2 ) {
 962                         foreach ( $conns2 as $conns3 ) {
 963                                 foreach ( $conns3 as $conn ) {
 964                                         if ( !$conn->ping() ) {
 965                                                 $success = false;
 966                                         }
 967                                 }
 968                         }
 969                 }
 970                 return $success;
 971         }
 972
 973         /**
 974          * Call a function with each open connection object
 975          * @param $callback
 976          * @param array $params
 977          */
 978         function forEachOpenConnection( $callback, $params = array() ) {
 979                 foreach ( $this->mConns as $conns2 ) {
 980                         foreach ( $conns2 as $conns3 ) {
 981                                 foreach ( $conns3 as $conn ) {
 982                                         $mergedParams = array_merge( array( $conn ), $params );
 983                                         call_user_func_array( $callback, $mergedParams );
 984                                 }
 985                         }
 986                 }
 987         }
 988
 989         /**
 990          * Get the hostname and lag time of the most-lagged slave.
 991          * This is useful for maintenance scripts that need to throttle their updates.
 992          * May attempt to open connections to slaves on the default DB. If there is
 993          * no lag, the maximum lag will be reported as -1.
 994          *
 995          * @param $wiki string Wiki ID, or false for the default database
 996          *
 997          * @return array ( host, max lag, index of max lagged host )
 998          */
 999         function getMaxLag( $wiki = false ) {
1000                 $maxLag = -1;
1001                 $host = '';
1002                 $maxIndex = 0;
1003                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1004                         foreach ( $this->mServers as $i => $conn ) {
1005                                 $conn = false;
1006                                 if ( $wiki === false ) {
1007                                         $conn = $this->getAnyOpenConnection( $i );
1008                                 }
1009                                 if ( !$conn ) {
1010                                         $conn = $this->openConnection( $i, $wiki );
1011                                 }
1012                                 if ( !$conn ) {
1013                                         continue;
1014                                 }
1015                                 $lag = $conn->getLag();
1016                                 if ( $lag > $maxLag ) {
1017                                         $maxLag = $lag;
1018                                         $host = $this->mServers[$i]['host'];
1019                                         $maxIndex = $i;
1020                                 }
1021                         }
1022                 }
1023                 return array( $host, $maxLag, $maxIndex );
1024         }
1025
1026         /**
1027          * Get lag time for each server
1028          * Results are cached for a short time in memcached, and indefinitely in the process cache
1029          *
1030          * @param $wiki
1031          *
1032          * @return array
1033          */
1034         function getLagTimes( $wiki = false ) {
1035                 # Try process cache
1036                 if ( isset( $this->mLagTimes ) ) {
1037                         return $this->mLagTimes;
1038                 }
1039                 if ( $this->getServerCount() == 1 ) {
1040                         # No replication
1041                         $this->mLagTimes = array( 0 => 0 );
1042                 } else {
1043                         # Send the request to the load monitor
1044                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1045                                 array_keys( $this->mServers ), $wiki );
1046                 }
1047                 return $this->mLagTimes;
1048         }
1049
1050         /**
1051          * Get the lag in seconds for a given connection, or zero if this load
1052          * balancer does not have replication enabled.
1053          *
1054          * This should be used in preference to Database::getLag() in cases where
1055          * replication may not be in use, since there is no way to determine if
1056          * replication is in use at the connection level without running
1057          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1058          * function instead of Database::getLag() avoids a fatal error in this
1059          * case on many installations.
1060          *
1061          * @param $conn DatabaseBase
1062          *
1063          * @return int
1064          */
1065         function safeGetLag( $conn ) {
1066                 if ( $this->getServerCount() == 1 ) {
1067                         return 0;
1068                 } else {
1069                         return $conn->getLag();
1070                 }
1071         }
1072
1073         /**
1074          * Clear the cache for getLagTimes
1075          */
1076         function clearLagTimeCache() {
1077                 $this->mLagTimes = null;
1078         }
1079 }