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 array $params 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          * @deprecated 1.21, use ArrayUtils::pickRandom()
 121          *
 122          * @param $weights array
 123          *
 124          * @return bool|int|string
 125          */
 126         function pickRandom( $weights ) {
 127                 return ArrayUtils::pickRandom( $weights );
 128         }
 129
 130         /**
 131          * @param $loads array
 132          * @param $wiki bool
 133          * @return bool|int|string
 134          */
 135         function getRandomNonLagged( $loads, $wiki = false ) {
 136                 # Unset excessively lagged servers
 137                 $lags = $this->getLagTimes( $wiki );
 138                 foreach ( $lags as $i => $lag ) {
 139                         if ( $i != 0 ) {
 140                                 if ( $lag === false ) {
 141                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 142                                         unset( $loads[$i] );
 143                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 144                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 145                                         unset( $loads[$i] );
 146                                 }
 147                         }
 148                 }
 149
 150                 # Find out if all the slaves with non-zero load are lagged
 151                 $sum = 0;
 152                 foreach ( $loads as $load ) {
 153                         $sum += $load;
 154                 }
 155                 if ( $sum == 0 ) {
 156                         # No appropriate DB servers except maybe the master and some slaves with zero load
 157                         # Do NOT use the master
 158                         # Instead, this function will return false, triggering read-only mode,
 159                         # and a lagged slave will be used instead.
 160                         return false;
 161                 }
 162
 163                 if ( count( $loads ) == 0 ) {
 164                         return false;
 165                 }
 166
 167                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 168
 169                 # Return a random representative of the remainder
 170                 return $this->pickRandom( $loads );
 171         }
 172
 173         /**
 174          * Get the index of the reader connection, which may be a slave
 175          * This takes into account load ratios and lag times. It should
 176          * always return a consistent index during a given invocation
 177          *
 178          * Side effect: opens connections to databases
 179          * @param $group bool
 180          * @param $wiki bool
 181          * @throws MWException
 182          * @return bool|int|string
 183          */
 184         function getReaderIndex( $group = false, $wiki = false ) {
 185                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 186
 187                 # @todo FIXME: For now, only go through all this for mysql databases
 188                 if ( $wgDBtype != 'mysql' ) {
 189                         return $this->getWriterIndex();
 190                 }
 191
 192                 if ( count( $this->mServers ) == 1 ) {
 193                         # Skip the load balancing if there's only one server
 194                         return 0;
 195                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 196                         # Shortcut if generic reader exists already
 197                         return $this->mReadIndex;
 198                 }
 199
 200                 wfProfileIn( __METHOD__ );
 201
 202                 $totalElapsed = 0;
 203
 204                 # convert from seconds to microseconds
 205                 $timeout = $wgDBClusterTimeout * 1e6;
 206
 207                 # Find the relevant load array
 208                 if ( $group !== false ) {
 209                         if ( isset( $this->mGroupLoads[$group] ) ) {
 210                                 $nonErrorLoads = $this->mGroupLoads[$group];
 211                         } else {
 212                                 # No loads for this group, return false and the caller can use some other group
 213                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 214                                 wfProfileOut( __METHOD__ );
 215                                 return false;
 216                         }
 217                 } else {
 218                         $nonErrorLoads = $this->mLoads;
 219                 }
 220
 221                 if ( !$nonErrorLoads ) {
 222                         wfProfileOut( __METHOD__ );
 223                         throw new MWException( "Empty server array given to LoadBalancer" );
 224                 }
 225
 226                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 227                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 228
 229                 $laggedSlaveMode = false;
 230
 231                 # First try quickly looking through the available servers for a server that
 232                 # meets our criteria
 233                 do {
 234                         $totalThreadsConnected = 0;
 235                         $overloadedServers = 0;
 236                         $currentLoads = $nonErrorLoads;
 237                         while ( count( $currentLoads ) ) {
 238                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 239                                         $i = $this->pickRandom( $currentLoads );
 240                                 } else {
 241                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 242                                         if ( $i === false && count( $currentLoads ) != 0 ) {
 243                                                 # All slaves lagged. Switch to read-only mode
 244                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 245                                                 $wgReadOnly = 'The database has been automatically locked ' .
 246                                                         'while the slave database servers catch up to the master';
 247                                                 $i = $this->pickRandom( $currentLoads );
 248                                                 $laggedSlaveMode = true;
 249                                         }
 250                                 }
 251
 252                                 if ( $i === false ) {
 253                                         # pickRandom() returned false
 254                                         # This is permanent and means the configuration or the load monitor
 255                                         # wants us to return false.
 256                                         wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 257                                         wfProfileOut( __METHOD__ );
 258                                         return false;
 259                                 }
 260
 261                                 wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 262                                 $conn = $this->openConnection( $i, $wiki );
 263
 264                                 if ( !$conn ) {
 265                                         wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 266                                         unset( $nonErrorLoads[$i] );
 267                                         unset( $currentLoads[$i] );
 268                                         continue;
 269                                 }
 270
 271                                 // Perform post-connection backoff
 272                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 273                                         ? $this->mServers[$i]['max threads'] : false;
 274                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 275
 276                                 // Decrement reference counter, we are finished with this connection.
 277                                 // It will be incremented for the caller later.
 278                                 if ( $wiki !== false ) {
 279                                         $this->reuseConnection( $conn );
 280                                 }
 281
 282                                 if ( $backoff ) {
 283                                         # Post-connection overload, don't use this server for now
 284                                         $totalThreadsConnected += $backoff;
 285                                         $overloadedServers++;
 286                                         unset( $currentLoads[$i] );
 287                                 } else {
 288                                         # Return this server
 289                                         break 2;
 290                                 }
 291                         }
 292
 293                         # No server found yet
 294                         $i = false;
 295
 296                         # If all servers were down, quit now
 297                         if ( !count( $nonErrorLoads ) ) {
 298                                 wfDebugLog( 'connect', "All servers down\n" );
 299                                 break;
 300                         }
 301
 302                         # Some servers must have been overloaded
 303                         if ( $overloadedServers == 0 ) {
 304                                 throw new MWException( __METHOD__ . ": unexpectedly found no overloaded servers" );
 305                         }
 306                         # Back off for a while
 307                         # Scale the sleep time by the number of connected threads, to produce a
 308                         # roughly constant global poll rate
 309                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 310                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 311                 } while ( $totalElapsed < $timeout );
 312
 313                 if ( $totalElapsed >= $timeout ) {
 314                         wfDebugLog( 'connect', "All servers busy\n" );
 315                         $this->mErrorConnection = false;
 316                         $this->mLastError = 'All servers busy';
 317                 }
 318
 319                 if ( $i !== false ) {
 320                         # Slave connection successful
 321                         # Wait for the session master pos for a short time
 322                         if ( $this->mWaitForPos && $i > 0 ) {
 323                                 if ( !$this->doWait( $i ) ) {
 324                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 325                                 }
 326                         }
 327                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
 328                                 $this->mReadIndex = $i;
 329                         }
 330                 }
 331                 wfProfileOut( __METHOD__ );
 332                 return $i;
 333         }
 334
 335         /**
 336          * Wait for a specified number of microseconds, and return the period waited
 337          * @param $t int
 338          * @return int
 339          */
 340         function sleep( $t ) {
 341                 wfProfileIn( __METHOD__ );
 342                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 343                 usleep( $t );
 344                 wfProfileOut( __METHOD__ );
 345                 return $t;
 346         }
 347
 348         /**
 349          * Set the master wait position
 350          * If a DB_SLAVE connection has been opened already, waits
 351          * Otherwise sets a variable telling it to wait if such a connection is opened
 352          * @param $pos DBMasterPos
 353          */
 354         public function waitFor( $pos ) {
 355                 wfProfileIn( __METHOD__ );
 356                 $this->mWaitForPos = $pos;
 357                 $i = $this->mReadIndex;
 358
 359                 if ( $i > 0 ) {
 360                         if ( !$this->doWait( $i ) ) {
 361                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 362                                 $this->mLaggedSlaveMode = true;
 363                         }
 364                 }
 365                 wfProfileOut( __METHOD__ );
 366         }
 367
 368         /**
 369          * Set the master wait position and wait for ALL slaves to catch up to it
 370          * @param $pos DBMasterPos
 371          */
 372         public function waitForAll( $pos ) {
 373                 wfProfileIn( __METHOD__ );
 374                 $this->mWaitForPos = $pos;
 375                 for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 376                         $this->doWait( $i, true );
 377                 }
 378                 wfProfileOut( __METHOD__ );
 379         }
 380
 381         /**
 382          * Get any open connection to a given server index, local or foreign
 383          * Returns false if there is no connection open
 384          *
 385          * @param $i int
 386          * @return DatabaseBase|bool False on failure
 387          */
 388         function getAnyOpenConnection( $i ) {
 389                 foreach ( $this->mConns as $conns ) {
 390                         if ( !empty( $conns[$i] ) ) {
 391                                 return reset( $conns[$i] );
 392                         }
 393                 }
 394                 return false;
 395         }
 396
 397         /**
 398          * Wait for a given slave to catch up to the master pos stored in $this
 399          * @param $index
 400          * @param $open bool
 401          * @return bool
 402          */
 403         protected function doWait( $index, $open = false ) {
 404                 # Find a connection to wait on
 405                 $conn = $this->getAnyOpenConnection( $index );
 406                 if ( !$conn ) {
 407                         if ( !$open ) {
 408                                 wfDebug( __METHOD__ . ": no connection open\n" );
 409                                 return false;
 410                         } else {
 411                                 $conn = $this->openConnection( $index, '' );
 412                                 if ( !$conn ) {
 413                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 414                                         return false;
 415                                 }
 416                         }
 417                 }
 418
 419                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 420                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 421
 422                 if ( $result == -1 || is_null( $result ) ) {
 423                         # Timed out waiting for slave, use master instead
 424                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 425                         return false;
 426                 } else {
 427                         wfDebug( __METHOD__ . ": Done\n" );
 428                         return true;
 429                 }
 430         }
 431
 432         /**
 433          * Get a connection by index
 434          * This is the main entry point for this class.
 435          *
 436          * @param $i Integer: server index
 437          * @param array $groups query groups
 438          * @param bool|string $wiki Wiki ID
 439          *
 440          * @throws MWException
 441          * @return DatabaseBase
 442          */
 443         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 444                 wfProfileIn( __METHOD__ );
 445
 446                 if ( $i == DB_LAST ) {
 447                         wfProfileOut( __METHOD__ );
 448                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 449                 } elseif ( $i === null || $i === false ) {
 450                         wfProfileOut( __METHOD__ );
 451                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 452                 }
 453
 454                 if ( $wiki === wfWikiID() ) {
 455                         $wiki = false;
 456                 }
 457
 458                 # Query groups
 459                 if ( $i == DB_MASTER ) {
 460                         $i = $this->getWriterIndex();
 461                 } elseif ( !is_array( $groups ) ) {
 462                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 463                         if ( $groupIndex !== false ) {
 464                                 $serverName = $this->getServerName( $groupIndex );
 465                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 466                                 $i = $groupIndex;
 467                         }
 468                 } else {
 469                         foreach ( $groups as $group ) {
 470                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 471                                 if ( $groupIndex !== false ) {
 472                                         $serverName = $this->getServerName( $groupIndex );
 473                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 474                                         $i = $groupIndex;
 475                                         break;
 476                                 }
 477                         }
 478                 }
 479
 480                 # Operation-based index
 481                 if ( $i == DB_SLAVE ) {
 482                         $i = $this->getReaderIndex( false, $wiki );
 483                         # Couldn't find a working server in getReaderIndex()?
 484                         if ( $i === false ) {
 485                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 486                                 wfProfileOut( __METHOD__ );
 487                                 return $this->reportConnectionError();
 488                         }
 489                 }
 490
 491                 # Now we have an explicit index into the servers array
 492                 $conn = $this->openConnection( $i, $wiki );
 493                 if ( !$conn ) {
 494                         wfProfileOut( __METHOD__ );
 495                         return $this->reportConnectionError();
 496                 }
 497
 498                 wfProfileOut( __METHOD__ );
 499                 return $conn;
 500         }
 501
 502         /**
 503          * Mark a foreign connection as being available for reuse under a different
 504          * DB name or prefix. This mechanism is reference-counted, and must be called
 505          * the same number of times as getConnection() to work.
 506          *
 507          * @param DatabaseBase $conn
 508          * @throws MWException
 509          */
 510         public function reuseConnection( $conn ) {
 511                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 512                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 513                 $dbName = $conn->getDBname();
 514                 $prefix = $conn->tablePrefix();
 515                 if ( strval( $prefix ) !== '' ) {
 516                         $wiki = "$dbName-$prefix";
 517                 } else {
 518                         $wiki = $dbName;
 519                 }
 520                 if ( $serverIndex === null || $refCount === null ) {
 521                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 522                         /**
 523                          * This can happen in code like:
 524                          *   foreach ( $dbs as $db ) {
 525                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 526                          *     ...
 527                          *     $lb->reuseConnection( $conn );
 528                          *   }
 529                          * When a connection to the local DB is opened in this way, reuseConnection()
 530                          * should be ignored
 531                          */
 532                         return;
 533                 }
 534                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 535                         throw new MWException( __METHOD__ . ": connection not found, has the connection been freed already?" );
 536                 }
 537                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 538                 if ( $refCount <= 0 ) {
 539                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 540                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 541                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 542                 } else {
 543                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 544                 }
 545         }
 546
 547         /**
 548          * Open a connection to the server given by the specified index
 549          * Index must be an actual index into the array.
 550          * If the server is already open, returns it.
 551          *
 552          * On error, returns false, and the connection which caused the
 553          * error will be available via $this->mErrorConnection.
 554          *
 555          * @param $i Integer server index
 556          * @param string $wiki wiki ID to open
 557          * @return DatabaseBase
 558          *
 559          * @access private
 560          */
 561         function openConnection( $i, $wiki = false ) {
 562                 wfProfileIn( __METHOD__ );
 563                 if ( $wiki !== false ) {
 564                         $conn = $this->openForeignConnection( $i, $wiki );
 565                         wfProfileOut( __METHOD__ );
 566                         return $conn;
 567                 }
 568                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 569                         $conn = $this->mConns['local'][$i][0];
 570                 } else {
 571                         $server = $this->mServers[$i];
 572                         $server['serverIndex'] = $i;
 573                         $conn = $this->reallyOpenConnection( $server, false );
 574                         if ( $conn->isOpen() ) {
 575                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 576                                 $this->mConns['local'][$i][0] = $conn;
 577                         } else {
 578                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 579                                 $this->mErrorConnection = $conn;
 580                                 $conn = false;
 581                         }
 582                 }
 583                 wfProfileOut( __METHOD__ );
 584                 return $conn;
 585         }
 586
 587         /**
 588          * Open a connection to a foreign DB, or return one if it is already open.
 589          *
 590          * Increments a reference count on the returned connection which locks the
 591          * connection to the requested wiki. This reference count can be
 592          * decremented by calling reuseConnection().
 593          *
 594          * If a connection is open to the appropriate server already, but with the wrong
 595          * database, it will be switched to the right database and returned, as long as
 596          * it has been freed first with reuseConnection().
 597          *
 598          * On error, returns false, and the connection which caused the
 599          * error will be available via $this->mErrorConnection.
 600          *
 601          * @param $i Integer: server index
 602          * @param string $wiki wiki ID to open
 603          * @return DatabaseBase
 604          */
 605         function openForeignConnection( $i, $wiki ) {
 606                 wfProfileIn( __METHOD__ );
 607                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 608                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 609                         // Reuse an already-used connection
 610                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 611                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 612                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 613                         // Reuse a free connection for the same wiki
 614                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 615                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 616                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 617                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 618                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 619                         // Reuse a connection from another wiki
 620                         $conn = reset( $this->mConns['foreignFree'][$i] );
 621                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 622
 623                         if ( !$conn->selectDB( $dbName ) ) {
 624                                 $this->mLastError = "Error selecting database $dbName on server " .
 625                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 626                                 $this->mErrorConnection = $conn;
 627                                 $conn = false;
 628                         } else {
 629                                 $conn->tablePrefix( $prefix );
 630                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 631                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 632                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 633                         }
 634                 } else {
 635                         // Open a new connection
 636                         $server = $this->mServers[$i];
 637                         $server['serverIndex'] = $i;
 638                         $server['foreignPoolRefCount'] = 0;
 639                         $conn = $this->reallyOpenConnection( $server, $dbName );
 640                         if ( !$conn->isOpen() ) {
 641                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 642                                 $this->mErrorConnection = $conn;
 643                                 $conn = false;
 644                         } else {
 645                                 $conn->tablePrefix( $prefix );
 646                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 647                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 648                         }
 649                 }
 650
 651                 // Increment reference count
 652                 if ( $conn ) {
 653                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 654                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 655                 }
 656                 wfProfileOut( __METHOD__ );
 657                 return $conn;
 658         }
 659
 660         /**
 661          * Test if the specified index represents an open connection
 662          *
 663          * @param $index Integer: server index
 664          * @access private
 665          * @return bool
 666          */
 667         function isOpen( $index ) {
 668                 if ( !is_integer( $index ) ) {
 669                         return false;
 670                 }
 671                 return (bool)$this->getAnyOpenConnection( $index );
 672         }
 673
 674         /**
 675          * Really opens a connection. Uncached.
 676          * Returns a Database object whether or not the connection was successful.
 677          * @access private
 678          *
 679          * @param $server
 680          * @param $dbNameOverride bool
 681          * @throws MWException
 682          * @return DatabaseBase
 683          */
 684         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 685                 if ( !is_array( $server ) ) {
 686                         throw new MWException( 'You must update your load-balancing configuration. ' .
 687                                 'See DefaultSettings.php entry for $wgDBservers.' );
 688                 }
 689
 690                 if ( $dbNameOverride !== false ) {
 691                         $server['dbname'] = $dbNameOverride;
 692                 }
 693
 694                 # Create object
 695                 try {
 696                         $db = DatabaseBase::factory( $server['type'], $server );
 697                 } catch ( DBConnectionError $e ) {
 698                         // FIXME: This is probably the ugliest thing I have ever done to
 699                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 700                         $db = $e->db;
 701                 }
 702
 703                 $db->setLBInfo( $server );
 704                 if ( isset( $server['fakeSlaveLag'] ) ) {
 705                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 706                 }
 707                 if ( isset( $server['fakeMaster'] ) ) {
 708                         $db->setFakeMaster( true );
 709                 }
 710                 return $db;
 711         }
 712
 713         /**
 714          * @throws DBConnectionError
 715          * @return bool
 716          */
 717         private function reportConnectionError() {
 718                 $conn = $this->mErrorConnection; // The connection which caused the error
 719
 720                 if ( !is_object( $conn ) ) {
 721                         // No last connection, probably due to all servers being too busy
 722                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 723
 724                         // If all servers were busy, mLastError will contain something sensible
 725                         throw new DBConnectionError( null, $this->mLastError );
 726                 } else {
 727                         $server = $conn->getProperty( 'mServer' );
 728                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 729                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 730                 }
 731                 return false; /* not reached */
 732         }
 733
 734         /**
 735          * @return int
 736          */
 737         function getWriterIndex() {
 738                 return 0;
 739         }
 740
 741         /**
 742          * Returns true if the specified index is a valid server index
 743          *
 744          * @param $i
 745          * @return bool
 746          */
 747         function haveIndex( $i ) {
 748                 return array_key_exists( $i, $this->mServers );
 749         }
 750
 751         /**
 752          * Returns true if the specified index is valid and has non-zero load
 753          *
 754          * @param $i
 755          * @return bool
 756          */
 757         function isNonZeroLoad( $i ) {
 758                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 759         }
 760
 761         /**
 762          * Get the number of defined servers (not the number of open connections)
 763          *
 764          * @return int
 765          */
 766         function getServerCount() {
 767                 return count( $this->mServers );
 768         }
 769
 770         /**
 771          * Get the host name or IP address of the server with the specified index
 772          * Prefer a readable name if available.
 773          * @param $i
 774          * @return string
 775          */
 776         function getServerName( $i ) {
 777                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 778                         return $this->mServers[$i]['hostName'];
 779                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 780                         return $this->mServers[$i]['host'];
 781                 } else {
 782                         return '';
 783                 }
 784         }
 785
 786         /**
 787          * Return the server info structure for a given index, or false if the index is invalid.
 788          * @param $i
 789          * @return bool
 790          */
 791         function getServerInfo( $i ) {
 792                 if ( isset( $this->mServers[$i] ) ) {
 793                         return $this->mServers[$i];
 794                 } else {
 795                         return false;
 796                 }
 797         }
 798
 799         /**
 800          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 801          * @param $i
 802          * @param $serverInfo
 803          */
 804         function setServerInfo( $i, $serverInfo ) {
 805                 $this->mServers[$i] = $serverInfo;
 806         }
 807
 808         /**
 809          * Get the current master position for chronology control purposes
 810          * @return mixed
 811          */
 812         function getMasterPos() {
 813                 # If this entire request was served from a slave without opening a connection to the
 814                 # master (however unlikely that may be), then we can fetch the position from the slave.
 815                 $masterConn = $this->getAnyOpenConnection( 0 );
 816                 if ( !$masterConn ) {
 817                         for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 818                                 $conn = $this->getAnyOpenConnection( $i );
 819                                 if ( $conn ) {
 820                                         wfDebug( "Master pos fetched from slave\n" );
 821                                         return $conn->getSlavePos();
 822                                 }
 823                         }
 824                 } else {
 825                         wfDebug( "Master pos fetched from master\n" );
 826                         return $masterConn->getMasterPos();
 827                 }
 828                 return false;
 829         }
 830
 831         /**
 832          * Close all open connections
 833          */
 834         function closeAll() {
 835                 foreach ( $this->mConns as $conns2 ) {
 836                         foreach ( $conns2 as $conns3 ) {
 837                                 foreach ( $conns3 as $conn ) {
 838                                         $conn->close();
 839                                 }
 840                         }
 841                 }
 842                 $this->mConns = array(
 843                         'local' => array(),
 844                         'foreignFree' => array(),
 845                         'foreignUsed' => array(),
 846                 );
 847         }
 848
 849         /**
 850          * Deprecated function, typo in function name
 851          *
 852          * @deprecated in 1.18
 853          * @param $conn
 854          */
 855         function closeConnecton( $conn ) {
 856                 wfDeprecated( __METHOD__, '1.18' );
 857                 $this->closeConnection( $conn );
 858         }
 859
 860         /**
 861          * Close a connection
 862          * Using this function makes sure the LoadBalancer knows the connection is closed.
 863          * If you use $conn->close() directly, the load balancer won't update its state.
 864          * @param $conn DatabaseBase
 865          */
 866         function closeConnection( $conn ) {
 867                 $done = false;
 868                 foreach ( $this->mConns as $i1 => $conns2 ) {
 869                         foreach ( $conns2 as $i2 => $conns3 ) {
 870                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 871                                         if ( $conn === $candidateConn ) {
 872                                                 $conn->close();
 873                                                 unset( $this->mConns[$i1][$i2][$i3] );
 874                                                 $done = true;
 875                                                 break;
 876                                         }
 877                                 }
 878                         }
 879                 }
 880                 if ( !$done ) {
 881                         $conn->close();
 882                 }
 883         }
 884
 885         /**
 886          * Commit transactions on all open connections
 887          */
 888         function commitAll() {
 889                 foreach ( $this->mConns as $conns2 ) {
 890                         foreach ( $conns2 as $conns3 ) {
 891                                 foreach ( $conns3 as $conn ) {
 892                                         if ( $conn->trxLevel() ) {
 893                                                 $conn->commit( __METHOD__, 'flush' );
 894                                         }
 895                                 }
 896                         }
 897                 }
 898         }
 899
 900         /**
 901          *  Issue COMMIT only on master, only if queries were done on connection
 902          */
 903         function commitMasterChanges() {
 904                 // Always 0, but who knows.. :)
 905                 $masterIndex = $this->getWriterIndex();
 906                 foreach ( $this->mConns as $conns2 ) {
 907                         if ( empty( $conns2[$masterIndex] ) ) {
 908                                 continue;
 909                         }
 910                         foreach ( $conns2[$masterIndex] as $conn ) {
 911                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 912                                         $conn->commit( __METHOD__, 'flush' );
 913                                 }
 914                         }
 915                 }
 916         }
 917
 918         /**
 919          * @param $value null
 920          * @return Mixed
 921          */
 922         function waitTimeout( $value = null ) {
 923                 return wfSetVar( $this->mWaitTimeout, $value );
 924         }
 925
 926         /**
 927          * @return bool
 928          */
 929         function getLaggedSlaveMode() {
 930                 return $this->mLaggedSlaveMode;
 931         }
 932
 933         /**
 934          * Disables/enables lag checks
 935          * @param $mode null
 936          * @return bool
 937          */
 938         function allowLagged( $mode = null ) {
 939                 if ( $mode === null ) {
 940                         return $this->mAllowLagged;
 941                 }
 942                 $this->mAllowLagged = $mode;
 943                 return $this->mAllowLagged;
 944         }
 945
 946         /**
 947          * @return bool
 948          */
 949         function pingAll() {
 950                 $success = true;
 951                 foreach ( $this->mConns as $conns2 ) {
 952                         foreach ( $conns2 as $conns3 ) {
 953                                 foreach ( $conns3 as $conn ) {
 954                                         if ( !$conn->ping() ) {
 955                                                 $success = false;
 956                                         }
 957                                 }
 958                         }
 959                 }
 960                 return $success;
 961         }
 962
 963         /**
 964          * Call a function with each open connection object
 965          * @param $callback
 966          * @param array $params
 967          */
 968         function forEachOpenConnection( $callback, $params = array() ) {
 969                 foreach ( $this->mConns as $conns2 ) {
 970                         foreach ( $conns2 as $conns3 ) {
 971                                 foreach ( $conns3 as $conn ) {
 972                                         $mergedParams = array_merge( array( $conn ), $params );
 973                                         call_user_func_array( $callback, $mergedParams );
 974                                 }
 975                         }
 976                 }
 977         }
 978
 979         /**
 980          * Get the hostname and lag time of the most-lagged slave.
 981          * This is useful for maintenance scripts that need to throttle their updates.
 982          * May attempt to open connections to slaves on the default DB. If there is
 983          * no lag, the maximum lag will be reported as -1.
 984          *
 985          * @param string $wiki Wiki ID, or false for the default database
 986          *
 987          * @return array ( host, max lag, index of max lagged host )
 988          */
 989         function getMaxLag( $wiki = false ) {
 990                 $maxLag = -1;
 991                 $host = '';
 992                 $maxIndex = 0;
 993                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
 994                         foreach ( $this->mServers as $i => $conn ) {
 995                                 $conn = false;
 996                                 if ( $wiki === false ) {
 997                                         $conn = $this->getAnyOpenConnection( $i );
 998                                 }
 999                                 if ( !$conn ) {
1000                                         $conn = $this->openConnection( $i, $wiki );
1001                                 }
1002                                 if ( !$conn ) {
1003                                         continue;
1004                                 }
1005                                 $lag = $conn->getLag();
1006                                 if ( $lag > $maxLag ) {
1007                                         $maxLag = $lag;
1008                                         $host = $this->mServers[$i]['host'];
1009                                         $maxIndex = $i;
1010                                 }
1011                         }
1012                 }
1013                 return array( $host, $maxLag, $maxIndex );
1014         }
1015
1016         /**
1017          * Get lag time for each server
1018          * Results are cached for a short time in memcached, and indefinitely in the process cache
1019          *
1020          * @param $wiki
1021          *
1022          * @return array
1023          */
1024         function getLagTimes( $wiki = false ) {
1025                 # Try process cache
1026                 if ( isset( $this->mLagTimes ) ) {
1027                         return $this->mLagTimes;
1028                 }
1029                 if ( $this->getServerCount() == 1 ) {
1030                         # No replication
1031                         $this->mLagTimes = array( 0 => 0 );
1032                 } else {
1033                         # Send the request to the load monitor
1034                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1035                                 array_keys( $this->mServers ), $wiki );
1036                 }
1037                 return $this->mLagTimes;
1038         }
1039
1040         /**
1041          * Get the lag in seconds for a given connection, or zero if this load
1042          * balancer does not have replication enabled.
1043          *
1044          * This should be used in preference to Database::getLag() in cases where
1045          * replication may not be in use, since there is no way to determine if
1046          * replication is in use at the connection level without running
1047          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1048          * function instead of Database::getLag() avoids a fatal error in this
1049          * case on many installations.
1050          *
1051          * @param $conn DatabaseBase
1052          *
1053          * @return int
1054          */
1055         function safeGetLag( $conn ) {
1056                 if ( $this->getServerCount() == 1 ) {
1057                         return 0;
1058                 } else {
1059                         return $conn->getLag();
1060                 }
1061         }
1062
1063         /**
1064          * Clear the cache for getLagTimes
1065          */
1066         function clearLagTimeCache() {
1067                 $this->mLagTimes = null;
1068         }
1069 }