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          * @throws MWException
  45          */
  46         function __construct( $params ) {
  47                 if ( !isset( $params['servers'] ) ) {
  48                         throw new MWException( __CLASS__.': missing servers parameter' );
  49                 }
  50                 $this->mServers = $params['servers'];
  51
  52                 if ( isset( $params['waitTimeout'] ) ) {
  53                         $this->mWaitTimeout = $params['waitTimeout'];
  54                 } else {
  55                         $this->mWaitTimeout = 10;
  56                 }
  57
  58                 $this->mReadIndex = -1;
  59                 $this->mWriteIndex = -1;
  60                 $this->mConns = array(
  61                         'local' => array(),
  62                         'foreignUsed' => array(),
  63                         'foreignFree' => array() );
  64                 $this->mLoads = array();
  65                 $this->mWaitForPos = false;
  66                 $this->mLaggedSlaveMode = false;
  67                 $this->mErrorConnection = false;
  68                 $this->mAllowLagged = false;
  69
  70                 if ( isset( $params['loadMonitor'] ) ) {
  71                         $this->mLoadMonitorClass = $params['loadMonitor'];
  72                 } else {
  73                         $master = reset( $params['servers'] );
  74                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  75                                 $this->mLoadMonitorClass = 'LoadMonitor_MySQL';
  76                         } else {
  77                                 $this->mLoadMonitorClass = 'LoadMonitor_Null';
  78                         }
  79                 }
  80
  81                 foreach( $params['servers'] as $i => $server ) {
  82                         $this->mLoads[$i] = $server['load'];
  83                         if ( isset( $server['groupLoads'] ) ) {
  84                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  85                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  86                                                 $this->mGroupLoads[$group] = array();
  87                                         }
  88                                         $this->mGroupLoads[$group][$i] = $ratio;
  89                                 }
  90                         }
  91                 }
  92         }
  93
  94         /**
  95          * Get a LoadMonitor instance
  96          *
  97          * @return LoadMonitor
  98          */
  99         function getLoadMonitor() {
 100                 if ( !isset( $this->mLoadMonitor ) ) {
 101                         $class = $this->mLoadMonitorClass;
 102                         $this->mLoadMonitor = new $class( $this );
 103                 }
 104                 return $this->mLoadMonitor;
 105         }
 106
 107         /**
 108          * Get or set arbitrary data used by the parent object, usually an LBFactory
 109          * @param $x
 110          * @return Mixed
 111          */
 112         function parentInfo( $x = null ) {
 113                 return wfSetVar( $this->mParentInfo, $x );
 114         }
 115
 116         /**
 117          * Given an array of non-normalised probabilities, this function will select
 118          * an element and return the appropriate key
 119          *
 120          * @param $weights array
 121          *
 122          * @return int
 123          */
 124         function pickRandom( $weights ) {
 125                 if ( !is_array( $weights ) || count( $weights ) == 0 ) {
 126                         return false;
 127                 }
 128
 129                 $sum = array_sum( $weights );
 130                 if ( $sum == 0 ) {
 131                         # No loads on any of them
 132                         # In previous versions, this triggered an unweighted random selection,
 133                         # but this feature has been removed as of April 2006 to allow for strict
 134                         # separation of query groups.
 135                         return false;
 136                 }
 137                 $max = mt_getrandmax();
 138                 $rand = mt_rand( 0, $max ) / $max * $sum;
 139
 140                 $sum = 0;
 141                 foreach ( $weights as $i => $w ) {
 142                         $sum += $w;
 143                         if ( $sum >= $rand ) {
 144                                 break;
 145                         }
 146                 }
 147                 return $i;
 148         }
 149
 150         /**
 151          * @param $loads array
 152          * @param $wiki bool
 153          * @return bool|int|string
 154          */
 155         function getRandomNonLagged( $loads, $wiki = false ) {
 156                 # Unset excessively lagged servers
 157                 $lags = $this->getLagTimes( $wiki );
 158                 foreach ( $lags as $i => $lag ) {
 159                         if ( $i != 0 ) {
 160                                 if ( $lag === false ) {
 161                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 162                                         unset( $loads[$i] );
 163                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 164                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 165                                         unset( $loads[$i] );
 166                                 }
 167                         }
 168                 }
 169
 170                 # Find out if all the slaves with non-zero load are lagged
 171                 $sum = 0;
 172                 foreach ( $loads as $load ) {
 173                         $sum += $load;
 174                 }
 175                 if ( $sum == 0 ) {
 176                         # No appropriate DB servers except maybe the master and some slaves with zero load
 177                         # Do NOT use the master
 178                         # Instead, this function will return false, triggering read-only mode,
 179                         # and a lagged slave will be used instead.
 180                         return false;
 181                 }
 182
 183                 if ( count( $loads ) == 0 ) {
 184                         return false;
 185                 }
 186
 187                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 188
 189                 # Return a random representative of the remainder
 190                 return $this->pickRandom( $loads );
 191         }
 192
 193         /**
 194          * Get the index of the reader connection, which may be a slave
 195          * This takes into account load ratios and lag times. It should
 196          * always return a consistent index during a given invocation
 197          *
 198          * Side effect: opens connections to databases
 199          * @param $group bool
 200          * @param $wiki bool
 201          * @throws MWException
 202          * @return bool|int|string
 203          */
 204         function getReaderIndex( $group = false, $wiki = false ) {
 205                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 206
 207                 # @todo FIXME: For now, only go through all this for mysql databases
 208                 if ($wgDBtype != 'mysql') {
 209                         return $this->getWriterIndex();
 210                 }
 211
 212                 if ( count( $this->mServers ) == 1 )  {
 213                         # Skip the load balancing if there's only one server
 214                         return 0;
 215                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 216                         # Shortcut if generic reader exists already
 217                         return $this->mReadIndex;
 218                 }
 219
 220                 wfProfileIn( __METHOD__ );
 221
 222                 $totalElapsed = 0;
 223
 224                 # convert from seconds to microseconds
 225                 $timeout = $wgDBClusterTimeout * 1e6;
 226
 227                 # Find the relevant load array
 228                 if ( $group !== false ) {
 229                         if ( isset( $this->mGroupLoads[$group] ) ) {
 230                                 $nonErrorLoads = $this->mGroupLoads[$group];
 231                         } else {
 232                                 # No loads for this group, return false and the caller can use some other group
 233                                 wfDebug( __METHOD__.": no loads for group $group\n" );
 234                                 wfProfileOut( __METHOD__ );
 235                                 return false;
 236                         }
 237                 } else {
 238                         $nonErrorLoads = $this->mLoads;
 239                 }
 240
 241                 if ( !$nonErrorLoads ) {
 242                         throw new MWException( "Empty server array given to LoadBalancer" );
 243                 }
 244
 245                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 246                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 247
 248                 $laggedSlaveMode = false;
 249
 250                 # First try quickly looking through the available servers for a server that
 251                 # meets our criteria
 252                 do {
 253                         $totalThreadsConnected = 0;
 254                         $overloadedServers = 0;
 255                         $currentLoads = $nonErrorLoads;
 256                         while ( count( $currentLoads ) ) {
 257                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 258                                         $i = $this->pickRandom( $currentLoads );
 259                                 } else {
 260                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 261                                         if ( $i === false && count( $currentLoads ) != 0 )  {
 262                                                 # All slaves lagged. Switch to read-only mode
 263                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 264                                                 $wgReadOnly = 'The database has been automatically locked ' .
 265                                                         'while the slave database servers catch up to the master';
 266                                                 $i = $this->pickRandom( $currentLoads );
 267                                                 $laggedSlaveMode = true;
 268                                         }
 269                                 }
 270
 271                                 if ( $i === false ) {
 272                                         # pickRandom() returned false
 273                                         # This is permanent and means the configuration or the load monitor
 274                                         # wants us to return false.
 275                                         wfDebugLog( 'connect', __METHOD__.": pickRandom() returned false\n" );
 276                                         wfProfileOut( __METHOD__ );
 277                                         return false;
 278                                 }
 279
 280                                 wfDebugLog( 'connect', __METHOD__.": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 281                                 $conn = $this->openConnection( $i, $wiki );
 282
 283                                 if ( !$conn ) {
 284                                         wfDebugLog( 'connect', __METHOD__.": Failed connecting to $i/$wiki\n" );
 285                                         unset( $nonErrorLoads[$i] );
 286                                         unset( $currentLoads[$i] );
 287                                         continue;
 288                                 }
 289
 290                                 // Perform post-connection backoff
 291                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 292                                         ? $this->mServers[$i]['max threads'] : false;
 293                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 294
 295                                 // Decrement reference counter, we are finished with this connection.
 296                                 // It will be incremented for the caller later.
 297                                 if ( $wiki !== false ) {
 298                                         $this->reuseConnection( $conn );
 299                                 }
 300
 301                                 if ( $backoff ) {
 302                                         # Post-connection overload, don't use this server for now
 303                                         $totalThreadsConnected += $backoff;
 304                                         $overloadedServers++;
 305                                         unset( $currentLoads[$i] );
 306                                 } else {
 307                                         # Return this server
 308                                         break 2;
 309                                 }
 310                         }
 311
 312                         # No server found yet
 313                         $i = false;
 314
 315                         # If all servers were down, quit now
 316                         if ( !count( $nonErrorLoads ) ) {
 317                                 wfDebugLog( 'connect', "All servers down\n" );
 318                                 break;
 319                         }
 320
 321                         # Some servers must have been overloaded
 322                         if ( $overloadedServers == 0 ) {
 323                                 throw new MWException( __METHOD__.": unexpectedly found no overloaded servers" );
 324                         }
 325                         # Back off for a while
 326                         # Scale the sleep time by the number of connected threads, to produce a
 327                         # roughly constant global poll rate
 328                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 329                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 330                 } while ( $totalElapsed < $timeout );
 331
 332                 if ( $totalElapsed >= $timeout ) {
 333                         wfDebugLog( 'connect', "All servers busy\n" );
 334                         $this->mErrorConnection = false;
 335                         $this->mLastError = 'All servers busy';
 336                 }
 337
 338                 if ( $i !== false ) {
 339                         # Slave connection successful
 340                         # Wait for the session master pos for a short time
 341                         if ( $this->mWaitForPos && $i > 0 ) {
 342                                 if ( !$this->doWait( $i ) ) {
 343                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 344                                 }
 345                         }
 346                         if ( $this->mReadIndex <=0 && $this->mLoads[$i]>0 && $i !== false ) {
 347                                 $this->mReadIndex = $i;
 348                         }
 349                 }
 350                 wfProfileOut( __METHOD__ );
 351                 return $i;
 352         }
 353
 354         /**
 355          * Wait for a specified number of microseconds, and return the period waited
 356          * @param $t int
 357          * @return int
 358          */
 359         function sleep( $t ) {
 360                 wfProfileIn( __METHOD__ );
 361                 wfDebug( __METHOD__.": waiting $t us\n" );
 362                 usleep( $t );
 363                 wfProfileOut( __METHOD__ );
 364                 return $t;
 365         }
 366
 367         /**
 368          * Set the master wait position
 369          * If a DB_SLAVE connection has been opened already, waits
 370          * Otherwise sets a variable telling it to wait if such a connection is opened
 371          * @param $pos int
 372          */
 373         public function waitFor( $pos ) {
 374                 wfProfileIn( __METHOD__ );
 375                 $this->mWaitForPos = $pos;
 376                 $i = $this->mReadIndex;
 377
 378                 if ( $i > 0 ) {
 379                         if ( !$this->doWait( $i ) ) {
 380                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 381                                 $this->mLaggedSlaveMode = true;
 382                         }
 383                 }
 384                 wfProfileOut( __METHOD__ );
 385         }
 386
 387         /**
 388          * Set the master wait position and wait for ALL slaves to catch up to it
 389          * @param $pos int
 390          */
 391         public function waitForAll( $pos ) {
 392                 wfProfileIn( __METHOD__ );
 393                 $this->mWaitForPos = $pos;
 394                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 395                         $this->doWait( $i , true );
 396                 }
 397                 wfProfileOut( __METHOD__ );
 398         }
 399
 400         /**
 401          * Get any open connection to a given server index, local or foreign
 402          * Returns false if there is no connection open
 403          *
 404          * @param $i int
 405          * @return DatabaseBase|bool False on failure
 406          */
 407         function getAnyOpenConnection( $i ) {
 408                 foreach ( $this->mConns as $conns ) {
 409                         if ( !empty( $conns[$i] ) ) {
 410                                 return reset( $conns[$i] );
 411                         }
 412                 }
 413                 return false;
 414         }
 415
 416         /**
 417          * Wait for a given slave to catch up to the master pos stored in $this
 418          * @param $index
 419          * @param $open bool
 420          * @return bool
 421          */
 422         function doWait( $index, $open = false ) {
 423                 # Find a connection to wait on
 424                 $conn = $this->getAnyOpenConnection( $index );
 425                 if ( !$conn ) {
 426                         if ( !$open ) {
 427                                 wfDebug( __METHOD__ . ": no connection open\n" );
 428                                 return false;
 429                         } else {
 430                                 $conn = $this->openConnection( $index );
 431                                 if ( !$conn ) {
 432                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 433                                         return false;
 434                                 }
 435                         }
 436                 }
 437
 438                 wfDebug( __METHOD__.": Waiting for slave #$index to catch up...\n" );
 439                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 440
 441                 if ( $result == -1 || is_null( $result ) ) {
 442                         # Timed out waiting for slave, use master instead
 443                         wfDebug( __METHOD__.": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 444                         return false;
 445                 } else {
 446                         wfDebug( __METHOD__.": Done\n" );
 447                         return true;
 448                 }
 449         }
 450
 451         /**
 452          * Get a connection by index
 453          * This is the main entry point for this class.
 454          *
 455          * @param $i Integer: server index
 456          * @param $groups Array: query groups
 457          * @param bool|string $wiki Wiki ID
 458          *
 459          * @throws MWException
 460          * @return DatabaseBase
 461          */
 462         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 463                 wfProfileIn( __METHOD__ );
 464
 465                 if ( $i == DB_LAST ) {
 466                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 467                 } elseif ( $i === null || $i === false ) {
 468                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 469                 }
 470
 471                 if ( $wiki === wfWikiID() ) {
 472                         $wiki = false;
 473                 }
 474
 475                 # Query groups
 476                 if ( $i == DB_MASTER ) {
 477                         $i = $this->getWriterIndex();
 478                 } elseif ( !is_array( $groups ) ) {
 479                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 480                         if ( $groupIndex !== false ) {
 481                                 $serverName = $this->getServerName( $groupIndex );
 482                                 wfDebug( __METHOD__.": using server $serverName for group $groups\n" );
 483                                 $i = $groupIndex;
 484                         }
 485                 } else {
 486                         foreach ( $groups as $group ) {
 487                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 488                                 if ( $groupIndex !== false ) {
 489                                         $serverName = $this->getServerName( $groupIndex );
 490                                         wfDebug( __METHOD__.": using server $serverName for group $group\n" );
 491                                         $i = $groupIndex;
 492                                         break;
 493                                 }
 494                         }
 495                 }
 496
 497                 # Operation-based index
 498                 if ( $i == DB_SLAVE ) {
 499                         $i = $this->getReaderIndex( false, $wiki );
 500                         # Couldn't find a working server in getReaderIndex()?
 501                         if ( $i === false ) {
 502                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 503                                 wfProfileOut( __METHOD__ );
 504                                 $this->reportConnectionError( $this->mErrorConnection );
 505                                 return false;
 506                         }
 507                 }
 508
 509                 # Now we have an explicit index into the servers array
 510                 $conn = $this->openConnection( $i, $wiki );
 511                 if ( !$conn ) {
 512                         wfProfileOut( __METHOD__ );
 513                         $this->reportConnectionError( $this->mErrorConnection );
 514                 }
 515
 516                 wfProfileOut( __METHOD__ );
 517                 return $conn;
 518         }
 519
 520         /**
 521          * Mark a foreign connection as being available for reuse under a different
 522          * DB name or prefix. This mechanism is reference-counted, and must be called
 523          * the same number of times as getConnection() to work.
 524          *
 525          * @param DatabaseBase $conn
 526          * @throws MWException
 527          */
 528         public function reuseConnection( $conn ) {
 529                 $serverIndex = $conn->getLBInfo('serverIndex');
 530                 $refCount = $conn->getLBInfo('foreignPoolRefCount');
 531                 $dbName = $conn->getDBname();
 532                 $prefix = $conn->tablePrefix();
 533                 if ( strval( $prefix ) !== '' ) {
 534                         $wiki = "$dbName-$prefix";
 535                 } else {
 536                         $wiki = $dbName;
 537                 }
 538                 if ( $serverIndex === null || $refCount === null ) {
 539                         wfDebug( __METHOD__.": this connection was not opened as a foreign connection\n" );
 540                         /**
 541                          * This can happen in code like:
 542                          *   foreach ( $dbs as $db ) {
 543                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 544                          *     ...
 545                          *     $lb->reuseConnection( $conn );
 546                          *   }
 547                          * When a connection to the local DB is opened in this way, reuseConnection()
 548                          * should be ignored
 549                          */
 550                         return;
 551                 }
 552                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 553                         throw new MWException( __METHOD__.": connection not found, has the connection been freed already?" );
 554                 }
 555                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 556                 if ( $refCount <= 0 ) {
 557                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 558                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 559                         wfDebug( __METHOD__.": freed connection $serverIndex/$wiki\n" );
 560                 } else {
 561                         wfDebug( __METHOD__.": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 562                 }
 563         }
 564
 565         /**
 566          * Open a connection to the server given by the specified index
 567          * Index must be an actual index into the array.
 568          * If the server is already open, returns it.
 569          *
 570          * On error, returns false, and the connection which caused the
 571          * error will be available via $this->mErrorConnection.
 572          *
 573          * @param $i Integer server index
 574          * @param $wiki String wiki ID to open
 575          * @return DatabaseBase
 576          *
 577          * @access private
 578          */
 579         function openConnection( $i, $wiki = false ) {
 580                 wfProfileIn( __METHOD__ );
 581                 if ( $wiki !== false ) {
 582                         $conn = $this->openForeignConnection( $i, $wiki );
 583                         wfProfileOut( __METHOD__);
 584                         return $conn;
 585                 }
 586                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 587                         $conn = $this->mConns['local'][$i][0];
 588                 } else {
 589                         $server = $this->mServers[$i];
 590                         $server['serverIndex'] = $i;
 591                         $conn = $this->reallyOpenConnection( $server, false );
 592                         if ( $conn->isOpen() ) {
 593                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 594                                 $this->mConns['local'][$i][0] = $conn;
 595                         } else {
 596                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 597                                 $this->mErrorConnection = $conn;
 598                                 $conn = false;
 599                         }
 600                 }
 601                 wfProfileOut( __METHOD__ );
 602                 return $conn;
 603         }
 604
 605         /**
 606          * Open a connection to a foreign DB, or return one if it is already open.
 607          *
 608          * Increments a reference count on the returned connection which locks the
 609          * connection to the requested wiki. This reference count can be
 610          * decremented by calling reuseConnection().
 611          *
 612          * If a connection is open to the appropriate server already, but with the wrong
 613          * database, it will be switched to the right database and returned, as long as
 614          * it has been freed first with reuseConnection().
 615          *
 616          * On error, returns false, and the connection which caused the
 617          * error will be available via $this->mErrorConnection.
 618          *
 619          * @param $i Integer: server index
 620          * @param $wiki String: wiki ID to open
 621          * @return DatabaseBase
 622          */
 623         function openForeignConnection( $i, $wiki ) {
 624                 wfProfileIn(__METHOD__);
 625                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 626                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 627                         // Reuse an already-used connection
 628                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 629                         wfDebug( __METHOD__.": reusing connection $i/$wiki\n" );
 630                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 631                         // Reuse a free connection for the same wiki
 632                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 633                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 634                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 635                         wfDebug( __METHOD__.": reusing free connection $i/$wiki\n" );
 636                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 637                         // Reuse a connection from another wiki
 638                         $conn = reset( $this->mConns['foreignFree'][$i] );
 639                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 640
 641                         if ( !$conn->selectDB( $dbName ) ) {
 642                                 $this->mLastError = "Error selecting database $dbName on server " .
 643                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 644                                 $this->mErrorConnection = $conn;
 645                                 $conn = false;
 646                         } else {
 647                                 $conn->tablePrefix( $prefix );
 648                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 649                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 650                                 wfDebug( __METHOD__.": reusing free connection from $oldWiki for $wiki\n" );
 651                         }
 652                 } else {
 653                         // Open a new connection
 654                         $server = $this->mServers[$i];
 655                         $server['serverIndex'] = $i;
 656                         $server['foreignPoolRefCount'] = 0;
 657                         $conn = $this->reallyOpenConnection( $server, $dbName );
 658                         if ( !$conn->isOpen() ) {
 659                                 wfDebug( __METHOD__.": error opening connection for $i/$wiki\n" );
 660                                 $this->mErrorConnection = $conn;
 661                                 $conn = false;
 662                         } else {
 663                                 $conn->tablePrefix( $prefix );
 664                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 665                                 wfDebug( __METHOD__.": opened new connection for $i/$wiki\n" );
 666                         }
 667                 }
 668
 669                 // Increment reference count
 670                 if ( $conn ) {
 671                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 672                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 673                 }
 674                 wfProfileOut(__METHOD__);
 675                 return $conn;
 676         }
 677
 678         /**
 679          * Test if the specified index represents an open connection
 680          *
 681          * @param $index Integer: server index
 682          * @access private
 683          * @return bool
 684          */
 685         function isOpen( $index ) {
 686                 if( !is_integer( $index ) ) {
 687                         return false;
 688                 }
 689                 return (bool)$this->getAnyOpenConnection( $index );
 690         }
 691
 692         /**
 693          * Really opens a connection. Uncached.
 694          * Returns a Database object whether or not the connection was successful.
 695          * @access private
 696          *
 697          * @param $server
 698          * @param $dbNameOverride bool
 699          * @throws MWException
 700          * @return DatabaseBase
 701          */
 702         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 703                 if( !is_array( $server ) ) {
 704                         throw new MWException( 'You must update your load-balancing configuration. ' .
 705                                 'See DefaultSettings.php entry for $wgDBservers.' );
 706                 }
 707
 708                 $host = $server['host'];
 709                 $dbname = $server['dbname'];
 710
 711                 if ( $dbNameOverride !== false ) {
 712                         $server['dbname'] = $dbname = $dbNameOverride;
 713                 }
 714
 715                 # Create object
 716                 try {
 717                         $db = DatabaseBase::factory( $server['type'], $server );
 718                 } catch ( DBConnectionError $e ) {
 719                         // FIXME: This is probably the ugliest thing I have ever done to
 720                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 721                         $db = $e->db;
 722                 }
 723
 724                 $db->setLBInfo( $server );
 725                 if ( isset( $server['fakeSlaveLag'] ) ) {
 726                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 727                 }
 728                 if ( isset( $server['fakeMaster'] ) ) {
 729                         $db->setFakeMaster( true );
 730                 }
 731                 return $db;
 732         }
 733
 734         /**
 735          * @param $conn
 736          * @throws DBConnectionError
 737          */
 738         function reportConnectionError( &$conn ) {
 739                 if ( !is_object( $conn ) ) {
 740                         // No last connection, probably due to all servers being too busy
 741                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 742                         $conn = new Database;
 743                         // If all servers were busy, mLastError will contain something sensible
 744                         throw new DBConnectionError( $conn, $this->mLastError );
 745                 } else {
 746                         $server = $conn->getProperty( 'mServer' );
 747                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 748                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" );
 749                 }
 750         }
 751
 752         /**
 753          * @return int
 754          */
 755         function getWriterIndex() {
 756                 return 0;
 757         }
 758
 759         /**
 760          * Returns true if the specified index is a valid server index
 761          *
 762          * @param $i
 763          * @return bool
 764          */
 765         function haveIndex( $i ) {
 766                 return array_key_exists( $i, $this->mServers );
 767         }
 768
 769         /**
 770          * Returns true if the specified index is valid and has non-zero load
 771          *
 772          * @param $i
 773          * @return bool
 774          */
 775         function isNonZeroLoad( $i ) {
 776                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 777         }
 778
 779         /**
 780          * Get the number of defined servers (not the number of open connections)
 781          *
 782          * @return int
 783          */
 784         function getServerCount() {
 785                 return count( $this->mServers );
 786         }
 787
 788         /**
 789          * Get the host name or IP address of the server with the specified index
 790          * Prefer a readable name if available.
 791          * @param $i
 792          * @return string
 793          */
 794         function getServerName( $i ) {
 795                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 796                         return $this->mServers[$i]['hostName'];
 797                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 798                         return $this->mServers[$i]['host'];
 799                 } else {
 800                         return '';
 801                 }
 802         }
 803
 804         /**
 805          * Return the server info structure for a given index, or false if the index is invalid.
 806          * @param $i
 807          * @return bool
 808          */
 809         function getServerInfo( $i ) {
 810                 if ( isset( $this->mServers[$i] ) ) {
 811                         return $this->mServers[$i];
 812                 } else {
 813                         return false;
 814                 }
 815         }
 816
 817         /**
 818          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 819          * @param $i
 820          * @param $serverInfo
 821          */
 822         function setServerInfo( $i, $serverInfo ) {
 823                 $this->mServers[$i] = $serverInfo;
 824         }
 825
 826         /**
 827          * Get the current master position for chronology control purposes
 828          * @return mixed
 829          */
 830         function getMasterPos() {
 831                 # If this entire request was served from a slave without opening a connection to the
 832                 # master (however unlikely that may be), then we can fetch the position from the slave.
 833                 $masterConn = $this->getAnyOpenConnection( 0 );
 834                 if ( !$masterConn ) {
 835                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 836                                 $conn = $this->getAnyOpenConnection( $i );
 837                                 if ( $conn ) {
 838                                         wfDebug( "Master pos fetched from slave\n" );
 839                                         return $conn->getSlavePos();
 840                                 }
 841                         }
 842                 } else {
 843                         wfDebug( "Master pos fetched from master\n" );
 844                         return $masterConn->getMasterPos();
 845                 }
 846                 return false;
 847         }
 848
 849         /**
 850          * Close all open connections
 851          */
 852         function closeAll() {
 853                 foreach ( $this->mConns as $conns2 ) {
 854                         foreach  ( $conns2 as $conns3 ) {
 855                                 foreach ( $conns3 as $conn ) {
 856                                         $conn->close();
 857                                 }
 858                         }
 859                 }
 860                 $this->mConns = array(
 861                         'local' => array(),
 862                         'foreignFree' => array(),
 863                         'foreignUsed' => array(),
 864                 );
 865         }
 866
 867         /**
 868          * Deprecated function, typo in function name
 869          *
 870          * @deprecated in 1.18
 871          * @param $conn
 872          */
 873         function closeConnecton( $conn ) {
 874                 wfDeprecated( __METHOD__, '1.18' );
 875                 $this->closeConnection( $conn );
 876         }
 877
 878         /**
 879          * Close a connection
 880          * Using this function makes sure the LoadBalancer knows the connection is closed.
 881          * If you use $conn->close() directly, the load balancer won't update its state.
 882          * @param $conn DatabaseBase
 883          */
 884         function closeConnection( $conn ) {
 885                 $done = false;
 886                 foreach ( $this->mConns as $i1 => $conns2 ) {
 887                         foreach ( $conns2 as $i2 => $conns3 ) {
 888                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 889                                         if ( $conn === $candidateConn ) {
 890                                                 $conn->close();
 891                                                 unset( $this->mConns[$i1][$i2][$i3] );
 892                                                 $done = true;
 893                                                 break;
 894                                         }
 895                                 }
 896                         }
 897                 }
 898                 if ( !$done ) {
 899                         $conn->close();
 900                 }
 901         }
 902
 903         /**
 904          * Commit transactions on all open connections
 905          */
 906         function commitAll() {
 907                 foreach ( $this->mConns as $conns2 ) {
 908                         foreach ( $conns2 as $conns3 ) {
 909                                 foreach ( $conns3 as $conn ) {
 910                                         if ( $conn->trxLevel() ) {
 911                                                 $conn->commit( __METHOD__, 'flush' );
 912                                         }
 913                                 }
 914                         }
 915                 }
 916         }
 917
 918         /**
 919          *  Issue COMMIT only on master, only if queries were done on connection
 920          */
 921         function commitMasterChanges() {
 922                 // Always 0, but who knows.. :)
 923                 $masterIndex = $this->getWriterIndex();
 924                 foreach ( $this->mConns as $conns2 ) {
 925                         if ( empty( $conns2[$masterIndex] ) ) {
 926                                 continue;
 927                         }
 928                         foreach ( $conns2[$masterIndex] as $conn ) {
 929                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 930                                         $conn->commit( __METHOD__, 'flush' );
 931                                 }
 932                         }
 933                 }
 934         }
 935
 936         /**
 937          * @param $value null
 938          * @return Mixed
 939          */
 940         function waitTimeout( $value = null ) {
 941                 return wfSetVar( $this->mWaitTimeout, $value );
 942         }
 943
 944         /**
 945          * @return bool
 946          */
 947         function getLaggedSlaveMode() {
 948                 return $this->mLaggedSlaveMode;
 949         }
 950
 951         /**
 952          * Disables/enables lag checks
 953          * @param $mode null
 954          * @return bool
 955          */
 956         function allowLagged( $mode = null ) {
 957                 if ( $mode === null) {
 958                         return $this->mAllowLagged;
 959                 }
 960                 $this->mAllowLagged = $mode;
 961         }
 962
 963         /**
 964          * @return bool
 965          */
 966         function pingAll() {
 967                 $success = true;
 968                 foreach ( $this->mConns as $conns2 ) {
 969                         foreach ( $conns2 as $conns3 ) {
 970                                 foreach ( $conns3 as $conn ) {
 971                                         if ( !$conn->ping() ) {
 972                                                 $success = false;
 973                                         }
 974                                 }
 975                         }
 976                 }
 977                 return $success;
 978         }
 979
 980         /**
 981          * Call a function with each open connection object
 982          * @param $callback
 983          * @param array $params
 984          */
 985         function forEachOpenConnection( $callback, $params = array() ) {
 986                 foreach ( $this->mConns as $conns2 ) {
 987                         foreach ( $conns2 as $conns3 ) {
 988                                 foreach ( $conns3 as $conn ) {
 989                                         $mergedParams = array_merge( array( $conn ), $params );
 990                                         call_user_func_array( $callback, $mergedParams );
 991                                 }
 992                         }
 993                 }
 994         }
 995
 996         /**
 997          * Get the hostname and lag time of the most-lagged slave.
 998          * This is useful for maintenance scripts that need to throttle their updates.
 999          * May attempt to open connections to slaves on the default DB. If there is
1000          * no lag, the maximum lag will be reported as -1.
1001          *
1002          * @param $wiki string Wiki ID, or false for the default database
1003          *
1004          * @return array ( host, max lag, index of max lagged host )
1005          */
1006         function getMaxLag( $wiki = false ) {
1007                 $maxLag = -1;
1008                 $host = '';
1009                 $maxIndex = 0;
1010                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1011                         foreach ( $this->mServers as $i => $conn ) {
1012                                 $conn = false;
1013                                 if ( $wiki === false ) {
1014                                         $conn = $this->getAnyOpenConnection( $i );
1015                                 }
1016                                 if ( !$conn ) {
1017                                         $conn = $this->openConnection( $i, $wiki );
1018                                 }
1019                                 if ( !$conn ) {
1020                                         continue;
1021                                 }
1022                                 $lag = $conn->getLag();
1023                                 if ( $lag > $maxLag ) {
1024                                         $maxLag = $lag;
1025                                         $host = $this->mServers[$i]['host'];
1026                                         $maxIndex = $i;
1027                                 }
1028                         }
1029                 }
1030                 return array( $host, $maxLag, $maxIndex );
1031         }
1032
1033         /**
1034          * Get lag time for each server
1035          * Results are cached for a short time in memcached, and indefinitely in the process cache
1036          *
1037          * @param $wiki
1038          *
1039          * @return array
1040          */
1041         function getLagTimes( $wiki = false ) {
1042                 # Try process cache
1043                 if ( isset( $this->mLagTimes ) ) {
1044                         return $this->mLagTimes;
1045                 }
1046                 if ( $this->getServerCount() == 1 ) {
1047                         # No replication
1048                         $this->mLagTimes = array( 0 => 0 );
1049                 } else {
1050                         # Send the request to the load monitor
1051                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1052                                 array_keys( $this->mServers ), $wiki );
1053                 }
1054                 return $this->mLagTimes;
1055         }
1056
1057         /**
1058          * Get the lag in seconds for a given connection, or zero if this load
1059          * balancer does not have replication enabled.
1060          *
1061          * This should be used in preference to Database::getLag() in cases where
1062          * replication may not be in use, since there is no way to determine if
1063          * replication is in use at the connection level without running
1064          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1065          * function instead of Database::getLag() avoids a fatal error in this
1066          * case on many installations.
1067          *
1068          * @param $conn DatabaseBase
1069          *
1070          * @return int
1071          */
1072         function safeGetLag( $conn ) {
1073                 if ( $this->getServerCount() == 1 ) {
1074                         return 0;
1075                 } else {
1076                         return $conn->getLag();
1077                 }
1078         }
1079
1080         /**
1081          * Clear the cache for getLagTimes
1082          */
1083         function clearLagTimeCache() {
1084                 $this->mLagTimes = null;
1085         }
1086 }