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 since 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                         $this->mLastError = 'Unknown error'; // reset error string
 483                         $i = $this->getReaderIndex( false, $wiki );
 484                         # Couldn't find a working server in getReaderIndex()?
 485                         if ( $i === false ) {
 486                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 487                                 wfProfileOut( __METHOD__ );
 488                                 return $this->reportConnectionError();
 489                         }
 490                 }
 491
 492                 # Now we have an explicit index into the servers array
 493                 $conn = $this->openConnection( $i, $wiki );
 494                 if ( !$conn ) {
 495                         wfProfileOut( __METHOD__ );
 496                         return $this->reportConnectionError();
 497                 }
 498
 499                 wfProfileOut( __METHOD__ );
 500                 return $conn;
 501         }
 502
 503         /**
 504          * Mark a foreign connection as being available for reuse under a different
 505          * DB name or prefix. This mechanism is reference-counted, and must be called
 506          * the same number of times as getConnection() to work.
 507          *
 508          * @param DatabaseBase $conn
 509          * @throws MWException
 510          */
 511         public function reuseConnection( $conn ) {
 512                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 513                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 514                 $dbName = $conn->getDBname();
 515                 $prefix = $conn->tablePrefix();
 516                 if ( strval( $prefix ) !== '' ) {
 517                         $wiki = "$dbName-$prefix";
 518                 } else {
 519                         $wiki = $dbName;
 520                 }
 521                 if ( $serverIndex === null || $refCount === null ) {
 522                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 523                         /**
 524                          * This can happen in code like:
 525                          *   foreach ( $dbs as $db ) {
 526                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 527                          *     ...
 528                          *     $lb->reuseConnection( $conn );
 529                          *   }
 530                          * When a connection to the local DB is opened in this way, reuseConnection()
 531                          * should be ignored
 532                          */
 533                         return;
 534                 }
 535                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 536                         throw new MWException( __METHOD__ . ": connection not found, has the connection been freed already?" );
 537                 }
 538                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 539                 if ( $refCount <= 0 ) {
 540                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 541                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 542                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 543                 } else {
 544                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 545                 }
 546         }
 547
 548         /**
 549          * Get a database connection handle reference
 550          *
 551          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 552          *
 553          * @see LoadBalancer::getConnection() for parameter information
 554          *
 555          * @param integer $db
 556          * @param mixed $groups
 557          * @param string $wiki
 558          * @return DBConnRef
 559          */
 560         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 561                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 562         }
 563
 564         /**
 565          * Open a connection to the server given by the specified index
 566          * Index must be an actual index into the array.
 567          * If the server is already open, returns it.
 568          *
 569          * On error, returns false, and the connection which caused the
 570          * error will be available via $this->mErrorConnection.
 571          *
 572          * @param $i Integer server index
 573          * @param string $wiki wiki ID to open
 574          * @return DatabaseBase
 575          *
 576          * @access private
 577          */
 578         function openConnection( $i, $wiki = false ) {
 579                 wfProfileIn( __METHOD__ );
 580                 if ( $wiki !== false ) {
 581                         $conn = $this->openForeignConnection( $i, $wiki );
 582                         wfProfileOut( __METHOD__ );
 583                         return $conn;
 584                 }
 585                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 586                         $conn = $this->mConns['local'][$i][0];
 587                 } else {
 588                         $server = $this->mServers[$i];
 589                         $server['serverIndex'] = $i;
 590                         $conn = $this->reallyOpenConnection( $server, false );
 591                         if ( $conn->isOpen() ) {
 592                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 593                                 $this->mConns['local'][$i][0] = $conn;
 594                         } else {
 595                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 596                                 $this->mErrorConnection = $conn;
 597                                 $conn = false;
 598                         }
 599                 }
 600                 wfProfileOut( __METHOD__ );
 601                 return $conn;
 602         }
 603
 604         /**
 605          * Open a connection to a foreign DB, or return one if it is already open.
 606          *
 607          * Increments a reference count on the returned connection which locks the
 608          * connection to the requested wiki. This reference count can be
 609          * decremented by calling reuseConnection().
 610          *
 611          * If a connection is open to the appropriate server already, but with the wrong
 612          * database, it will be switched to the right database and returned, as long as
 613          * it has been freed first with reuseConnection().
 614          *
 615          * On error, returns false, and the connection which caused the
 616          * error will be available via $this->mErrorConnection.
 617          *
 618          * @param $i Integer: server index
 619          * @param string $wiki wiki ID to open
 620          * @return DatabaseBase
 621          */
 622         function openForeignConnection( $i, $wiki ) {
 623                 wfProfileIn( __METHOD__ );
 624                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 625                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 626                         // Reuse an already-used connection
 627                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 628                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 629                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 630                         // Reuse a free connection for the same wiki
 631                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 632                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 633                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 634                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 635                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 636                         // Reuse a connection from another wiki
 637                         $conn = reset( $this->mConns['foreignFree'][$i] );
 638                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 639
 640                         if ( !$conn->selectDB( $dbName ) ) {
 641                                 $this->mLastError = "Error selecting database $dbName on server " .
 642                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 643                                 $this->mErrorConnection = $conn;
 644                                 $conn = false;
 645                         } else {
 646                                 $conn->tablePrefix( $prefix );
 647                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 648                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 649                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 650                         }
 651                 } else {
 652                         // Open a new connection
 653                         $server = $this->mServers[$i];
 654                         $server['serverIndex'] = $i;
 655                         $server['foreignPoolRefCount'] = 0;
 656                         $server['foreign'] = true;
 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                 if ( $dbNameOverride !== false ) {
 709                         $server['dbname'] = $dbNameOverride;
 710                 }
 711
 712                 # Create object
 713                 try {
 714                         $db = DatabaseBase::factory( $server['type'], $server );
 715                 } catch ( DBConnectionError $e ) {
 716                         // FIXME: This is probably the ugliest thing I have ever done to
 717                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 718                         $db = $e->db;
 719                 }
 720
 721                 $db->setLBInfo( $server );
 722                 if ( isset( $server['fakeSlaveLag'] ) ) {
 723                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 724                 }
 725                 if ( isset( $server['fakeMaster'] ) ) {
 726                         $db->setFakeMaster( true );
 727                 }
 728                 return $db;
 729         }
 730
 731         /**
 732          * @throws DBConnectionError
 733          * @return bool
 734          */
 735         private function reportConnectionError() {
 736                 $conn = $this->mErrorConnection; // The connection which caused the error
 737
 738                 if ( !is_object( $conn ) ) {
 739                         // No last connection, probably due to all servers being too busy
 740                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 741
 742                         // If all servers were busy, mLastError will contain something sensible
 743                         throw new DBConnectionError( null, $this->mLastError );
 744                 } else {
 745                         $server = $conn->getProperty( 'mServer' );
 746                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 747                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 748                 }
 749                 return false; /* not reached */
 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                 return $this->mAllowLagged;
 962         }
 963
 964         /**
 965          * @return bool
 966          */
 967         function pingAll() {
 968                 $success = true;
 969                 foreach ( $this->mConns as $conns2 ) {
 970                         foreach ( $conns2 as $conns3 ) {
 971                                 foreach ( $conns3 as $conn ) {
 972                                         if ( !$conn->ping() ) {
 973                                                 $success = false;
 974                                         }
 975                                 }
 976                         }
 977                 }
 978                 return $success;
 979         }
 980
 981         /**
 982          * Call a function with each open connection object
 983          * @param $callback
 984          * @param array $params
 985          */
 986         function forEachOpenConnection( $callback, $params = array() ) {
 987                 foreach ( $this->mConns as $conns2 ) {
 988                         foreach ( $conns2 as $conns3 ) {
 989                                 foreach ( $conns3 as $conn ) {
 990                                         $mergedParams = array_merge( array( $conn ), $params );
 991                                         call_user_func_array( $callback, $mergedParams );
 992                                 }
 993                         }
 994                 }
 995         }
 996
 997         /**
 998          * Get the hostname and lag time of the most-lagged slave.
 999          * This is useful for maintenance scripts that need to throttle their updates.
1000          * May attempt to open connections to slaves on the default DB. If there is
1001          * no lag, the maximum lag will be reported as -1.
1002          *
1003          * @param string $wiki Wiki ID, or false for the default database
1004          *
1005          * @return array ( host, max lag, index of max lagged host )
1006          */
1007         function getMaxLag( $wiki = false ) {
1008                 $maxLag = -1;
1009                 $host = '';
1010                 $maxIndex = 0;
1011                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1012                         foreach ( $this->mServers as $i => $conn ) {
1013                                 $conn = false;
1014                                 if ( $wiki === false ) {
1015                                         $conn = $this->getAnyOpenConnection( $i );
1016                                 }
1017                                 if ( !$conn ) {
1018                                         $conn = $this->openConnection( $i, $wiki );
1019                                 }
1020                                 if ( !$conn ) {
1021                                         continue;
1022                                 }
1023                                 $lag = $conn->getLag();
1024                                 if ( $lag > $maxLag ) {
1025                                         $maxLag = $lag;
1026                                         $host = $this->mServers[$i]['host'];
1027                                         $maxIndex = $i;
1028                                 }
1029                         }
1030                 }
1031                 return array( $host, $maxLag, $maxIndex );
1032         }
1033
1034         /**
1035          * Get lag time for each server
1036          * Results are cached for a short time in memcached, and indefinitely in the process cache
1037          *
1038          * @param $wiki
1039          *
1040          * @return array
1041          */
1042         function getLagTimes( $wiki = false ) {
1043                 # Try process cache
1044                 if ( isset( $this->mLagTimes ) ) {
1045                         return $this->mLagTimes;
1046                 }
1047                 if ( $this->getServerCount() == 1 ) {
1048                         # No replication
1049                         $this->mLagTimes = array( 0 => 0 );
1050                 } else {
1051                         # Send the request to the load monitor
1052                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1053                                 array_keys( $this->mServers ), $wiki );
1054                 }
1055                 return $this->mLagTimes;
1056         }
1057
1058         /**
1059          * Get the lag in seconds for a given connection, or zero if this load
1060          * balancer does not have replication enabled.
1061          *
1062          * This should be used in preference to Database::getLag() in cases where
1063          * replication may not be in use, since there is no way to determine if
1064          * replication is in use at the connection level without running
1065          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1066          * function instead of Database::getLag() avoids a fatal error in this
1067          * case on many installations.
1068          *
1069          * @param $conn DatabaseBase
1070          *
1071          * @return int
1072          */
1073         function safeGetLag( $conn ) {
1074                 if ( $this->getServerCount() == 1 ) {
1075                         return 0;
1076                 } else {
1077                         return $conn->getLag();
1078                 }
1079         }
1080
1081         /**
1082          * Clear the cache for getLagTimes
1083          */
1084         function clearLagTimeCache() {
1085                 $this->mLagTimes = null;
1086         }
1087 }
1088
1089 /**
1090  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1091  *
1092  * @ingroup Database
1093  * @since 1.22
1094  */
1095 class DBConnRef implements IDatabase {
1096         /** @var LoadBalancer */
1097         protected $lb;
1098         /** @var DatabaseBase */
1099         protected $conn;
1100
1101         /**
1102          * @param $lb LoadBalancer
1103          * @param $conn DatabaseBase
1104          */
1105         public function __construct( LoadBalancer $lb, DatabaseBase $conn ) {
1106                 $this->lb = $lb;
1107                 $this->conn = $conn;
1108         }
1109
1110         public function __call( $name, $arguments ) {
1111                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1112         }
1113
1114         function __destruct() {
1115                 $this->lb->reuseConnection( $this->conn );
1116         }
1117 }