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
  33         /** @var bool|DatabaseBase Database connection that caused a problem */
  34         private $mErrorConnection;
  35         private $mReadIndex, $mAllowLagged;
  36
  37         /** @var bool|DBMasterPos False if not set */
  38         private $mWaitForPos;
  39
  40         private $mWaitTimeout;
  41         private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  42         private $mParentInfo, $mLagTimes;
  43         private $mLoadMonitorClass, $mLoadMonitor;
  44
  45         /**
  46          * @param array $params with keys:
  47          *   servers           Required. Array of server info structures.
  48          *   masterWaitTimeout Replication lag wait timeout
  49          *   loadMonitor       Name of a class used to fetch server lag and load.
  50          * @throws MWException
  51          */
  52         function __construct( $params ) {
  53                 if ( !isset( $params['servers'] ) ) {
  54                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  55                 }
  56                 $this->mServers = $params['servers'];
  57
  58                 if ( isset( $params['waitTimeout'] ) ) {
  59                         $this->mWaitTimeout = $params['waitTimeout'];
  60                 } else {
  61                         $this->mWaitTimeout = 10;
  62                 }
  63
  64                 $this->mReadIndex = -1;
  65                 $this->mWriteIndex = -1;
  66                 $this->mConns = array(
  67                         'local' => array(),
  68                         'foreignUsed' => array(),
  69                         'foreignFree' => array() );
  70                 $this->mLoads = array();
  71                 $this->mWaitForPos = false;
  72                 $this->mLaggedSlaveMode = false;
  73                 $this->mErrorConnection = false;
  74                 $this->mAllowLagged = false;
  75
  76                 if ( isset( $params['loadMonitor'] ) ) {
  77                         $this->mLoadMonitorClass = $params['loadMonitor'];
  78                 } else {
  79                         $master = reset( $params['servers'] );
  80                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  81                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  82                         } else {
  83                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
  84                         }
  85                 }
  86
  87                 foreach ( $params['servers'] as $i => $server ) {
  88                         $this->mLoads[$i] = $server['load'];
  89                         if ( isset( $server['groupLoads'] ) ) {
  90                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  91                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  92                                                 $this->mGroupLoads[$group] = array();
  93                                         }
  94                                         $this->mGroupLoads[$group][$i] = $ratio;
  95                                 }
  96                         }
  97                 }
  98         }
  99
 100         /**
 101          * Get a LoadMonitor instance
 102          *
 103          * @return LoadMonitor
 104          */
 105         function getLoadMonitor() {
 106                 if ( !isset( $this->mLoadMonitor ) ) {
 107                         $class = $this->mLoadMonitorClass;
 108                         $this->mLoadMonitor = new $class( $this );
 109                 }
 110
 111                 return $this->mLoadMonitor;
 112         }
 113
 114         /**
 115          * Get or set arbitrary data used by the parent object, usually an LBFactory
 116          * @param $x
 117          * @return mixed
 118          */
 119         function parentInfo( $x = null ) {
 120                 return wfSetVar( $this->mParentInfo, $x );
 121         }
 122
 123         /**
 124          * Given an array of non-normalised probabilities, this function will select
 125          * an element and return the appropriate key
 126          *
 127          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 128          *
 129          * @param array $weights
 130          * @return bool|int|string
 131          */
 132         function pickRandom( $weights ) {
 133                 return ArrayUtils::pickRandom( $weights );
 134         }
 135
 136         /**
 137          * @param array $loads
 138          * @param bool|string $wiki Wiki to get non-lagged for
 139          * @return bool|int|string
 140          */
 141         function getRandomNonLagged( $loads, $wiki = false ) {
 142                 # Unset excessively lagged servers
 143                 $lags = $this->getLagTimes( $wiki );
 144                 foreach ( $lags as $i => $lag ) {
 145                         if ( $i != 0 ) {
 146                                 if ( $lag === false ) {
 147                                         wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 148                                         unset( $loads[$i] );
 149                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 150                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 151                                         unset( $loads[$i] );
 152                                 }
 153                         }
 154                 }
 155
 156                 # Find out if all the slaves with non-zero load are lagged
 157                 $sum = 0;
 158                 foreach ( $loads as $load ) {
 159                         $sum += $load;
 160                 }
 161                 if ( $sum == 0 ) {
 162                         # No appropriate DB servers except maybe the master and some slaves with zero load
 163                         # Do NOT use the master
 164                         # Instead, this function will return false, triggering read-only mode,
 165                         # and a lagged slave will be used instead.
 166                         return false;
 167                 }
 168
 169                 if ( count( $loads ) == 0 ) {
 170                         return false;
 171                 }
 172
 173                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 174
 175                 # Return a random representative of the remainder
 176                 return ArrayUtils::pickRandom( $loads );
 177         }
 178
 179         /**
 180          * Get the index of the reader connection, which may be a slave
 181          * This takes into account load ratios and lag times. It should
 182          * always return a consistent index during a given invocation
 183          *
 184          * Side effect: opens connections to databases
 185          * @param bool|string $group
 186          * @param bool|string $wiki
 187          * @throws MWException
 188          * @return bool|int|string
 189          */
 190         function getReaderIndex( $group = false, $wiki = false ) {
 191                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 192
 193                 # @todo FIXME: For now, only go through all this for mysql databases
 194                 if ( $wgDBtype != 'mysql' ) {
 195                         return $this->getWriterIndex();
 196                 }
 197
 198                 if ( count( $this->mServers ) == 1 ) {
 199                         # Skip the load balancing if there's only one server
 200                         return 0;
 201                 } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 202                         # Shortcut if generic reader exists already
 203                         return $this->mReadIndex;
 204                 }
 205
 206                 wfProfileIn( __METHOD__ );
 207
 208                 $totalElapsed = 0;
 209
 210                 # convert from seconds to microseconds
 211                 $timeout = $wgDBClusterTimeout * 1e6;
 212
 213                 # Find the relevant load array
 214                 if ( $group !== false ) {
 215                         if ( isset( $this->mGroupLoads[$group] ) ) {
 216                                 $nonErrorLoads = $this->mGroupLoads[$group];
 217                         } else {
 218                                 # No loads for this group, return false and the caller can use some other group
 219                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 220                                 wfProfileOut( __METHOD__ );
 221
 222                                 return false;
 223                         }
 224                 } else {
 225                         $nonErrorLoads = $this->mLoads;
 226                 }
 227
 228                 if ( !$nonErrorLoads ) {
 229                         wfProfileOut( __METHOD__ );
 230                         throw new MWException( "Empty server array given to LoadBalancer" );
 231                 }
 232
 233                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 234                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 235
 236                 $laggedSlaveMode = false;
 237
 238                 # First try quickly looking through the available servers for a server that
 239                 # meets our criteria
 240                 do {
 241                         $totalThreadsConnected = 0;
 242                         $overloadedServers = 0;
 243                         $currentLoads = $nonErrorLoads;
 244                         while ( count( $currentLoads ) ) {
 245                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 246                                         $i = ArrayUtils::pickRandom( $currentLoads );
 247                                 } else {
 248                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 249                                         if ( $i === false && count( $currentLoads ) != 0 ) {
 250                                                 # All slaves lagged. Switch to read-only mode
 251                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 252                                                 $wgReadOnly = 'The database has been automatically locked ' .
 253                                                         'while the slave database servers catch up to the master';
 254                                                 $i = ArrayUtils::pickRandom( $currentLoads );
 255                                                 $laggedSlaveMode = true;
 256                                         }
 257                                 }
 258
 259                                 if ( $i === false ) {
 260                                         # pickRandom() returned false
 261                                         # This is permanent and means the configuration or the load monitor
 262                                         # wants us to return false.
 263                                         wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 264                                         wfProfileOut( __METHOD__ );
 265
 266                                         return false;
 267                                 }
 268
 269                                 wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 270                                 $conn = $this->openConnection( $i, $wiki );
 271
 272                                 if ( !$conn ) {
 273                                         wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 274                                         unset( $nonErrorLoads[$i] );
 275                                         unset( $currentLoads[$i] );
 276                                         continue;
 277                                 }
 278
 279                                 // Perform post-connection backoff
 280                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 281                                         ? $this->mServers[$i]['max threads'] : 0;
 282                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 283
 284                                 // Decrement reference counter, we are finished with this connection.
 285                                 // It will be incremented for the caller later.
 286                                 if ( $wiki !== false ) {
 287                                         $this->reuseConnection( $conn );
 288                                 }
 289
 290                                 if ( $backoff ) {
 291                                         # Post-connection overload, don't use this server for now
 292                                         $totalThreadsConnected += $backoff;
 293                                         $overloadedServers++;
 294                                         unset( $currentLoads[$i] );
 295                                 } else {
 296                                         # Return this server
 297                                         break 2;
 298                                 }
 299                         }
 300
 301                         # No server found yet
 302                         $i = false;
 303
 304                         # If all servers were down, quit now
 305                         if ( !count( $nonErrorLoads ) ) {
 306                                 wfDebugLog( 'connect', "All servers down\n" );
 307                                 break;
 308                         }
 309
 310                         # Some servers must have been overloaded
 311                         if ( $overloadedServers == 0 ) {
 312                                 throw new MWException( __METHOD__ . ": unexpectedly found no overloaded servers" );
 313                         }
 314                         # Back off for a while
 315                         # Scale the sleep time by the number of connected threads, to produce a
 316                         # roughly constant global poll rate
 317                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 318                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 319                 } while ( $totalElapsed < $timeout );
 320
 321                 if ( $totalElapsed >= $timeout ) {
 322                         wfDebugLog( 'connect', "All servers busy\n" );
 323                         $this->mErrorConnection = false;
 324                         $this->mLastError = 'All servers busy';
 325                 }
 326
 327                 if ( $i !== false ) {
 328                         # Slave connection successful
 329                         # Wait for the session master pos for a short time
 330                         if ( $this->mWaitForPos && $i > 0 ) {
 331                                 if ( !$this->doWait( $i ) ) {
 332                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 333                                 }
 334                         }
 335                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
 336                                 $this->mReadIndex = $i;
 337                         }
 338                 }
 339                 wfProfileOut( __METHOD__ );
 340
 341                 return $i;
 342         }
 343
 344         /**
 345          * Wait for a specified number of microseconds, and return the period waited
 346          * @param int $t
 347          * @return int
 348          */
 349         function sleep( $t ) {
 350                 wfProfileIn( __METHOD__ );
 351                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 352                 usleep( $t );
 353                 wfProfileOut( __METHOD__ );
 354
 355                 return $t;
 356         }
 357
 358         /**
 359          * Set the master wait position
 360          * If a DB_SLAVE connection has been opened already, waits
 361          * Otherwise sets a variable telling it to wait if such a connection is opened
 362          * @param DBMasterPos $pos
 363          */
 364         public function waitFor( $pos ) {
 365                 wfProfileIn( __METHOD__ );
 366                 $this->mWaitForPos = $pos;
 367                 $i = $this->mReadIndex;
 368
 369                 if ( $i > 0 ) {
 370                         if ( !$this->doWait( $i ) ) {
 371                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 372                                 $this->mLaggedSlaveMode = true;
 373                         }
 374                 }
 375                 wfProfileOut( __METHOD__ );
 376         }
 377
 378         /**
 379          * Set the master wait position and wait for ALL slaves to catch up to it
 380          * @param DBMasterPos $pos
 381          */
 382         public function waitForAll( $pos ) {
 383                 wfProfileIn( __METHOD__ );
 384                 $this->mWaitForPos = $pos;
 385                 $serverCount = count( $this->mServers );
 386                 for ( $i = 1; $i < $serverCount; $i++ ) {
 387                         if ( $this->mLoads[$i] > 0 ) {
 388                                 $this->doWait( $i, true );
 389                         }
 390                 }
 391                 wfProfileOut( __METHOD__ );
 392         }
 393
 394         /**
 395          * Get any open connection to a given server index, local or foreign
 396          * Returns false if there is no connection open
 397          *
 398          * @param int $i
 399          * @return DatabaseBase|bool False on failure
 400          */
 401         function getAnyOpenConnection( $i ) {
 402                 foreach ( $this->mConns as $conns ) {
 403                         if ( !empty( $conns[$i] ) ) {
 404                                 return reset( $conns[$i] );
 405                         }
 406                 }
 407
 408                 return false;
 409         }
 410
 411         /**
 412          * Wait for a given slave to catch up to the master pos stored in $this
 413          * @param $index
 414          * @param $open bool
 415          * @return bool
 416          */
 417         protected function doWait( $index, $open = false ) {
 418                 # Find a connection to wait on
 419                 $conn = $this->getAnyOpenConnection( $index );
 420                 if ( !$conn ) {
 421                         if ( !$open ) {
 422                                 wfDebug( __METHOD__ . ": no connection open\n" );
 423
 424                                 return false;
 425                         } else {
 426                                 $conn = $this->openConnection( $index, '' );
 427                                 if ( !$conn ) {
 428                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 429
 430                                         return false;
 431                                 }
 432                         }
 433                 }
 434
 435                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 436                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 437
 438                 if ( $result == -1 || is_null( $result ) ) {
 439                         # Timed out waiting for slave, use master instead
 440                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 441
 442                         return false;
 443                 } else {
 444                         wfDebug( __METHOD__ . ": Done\n" );
 445
 446                         return true;
 447                 }
 448         }
 449
 450         /**
 451          * Get a connection by index
 452          * This is the main entry point for this class.
 453          *
 454          * @param $i Integer: server index
 455          * @param array $groups query groups
 456          * @param bool|string $wiki Wiki ID
 457          *
 458          * @throws MWException
 459          * @return DatabaseBase
 460          */
 461         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 462                 wfProfileIn( __METHOD__ );
 463
 464                 if ( $i == DB_LAST ) {
 465                         wfProfileOut( __METHOD__ );
 466                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 467                                 ' with deprecated server index DB_LAST' );
 468                 } elseif ( $i === null || $i === false ) {
 469                         wfProfileOut( __METHOD__ );
 470                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 471                                 ' with invalid server index' );
 472                 }
 473
 474                 if ( $wiki === wfWikiID() ) {
 475                         $wiki = false;
 476                 }
 477
 478                 # Query groups
 479                 if ( $i == DB_MASTER ) {
 480                         $i = $this->getWriterIndex();
 481                 } elseif ( !is_array( $groups ) ) {
 482                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 483                         if ( $groupIndex !== false ) {
 484                                 $serverName = $this->getServerName( $groupIndex );
 485                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 486                                 $i = $groupIndex;
 487                         }
 488                 } else {
 489                         foreach ( $groups as $group ) {
 490                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 491                                 if ( $groupIndex !== false ) {
 492                                         $serverName = $this->getServerName( $groupIndex );
 493                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 494                                         $i = $groupIndex;
 495                                         break;
 496                                 }
 497                         }
 498                 }
 499
 500                 # Operation-based index
 501                 if ( $i == DB_SLAVE ) {
 502                         $this->mLastError = 'Unknown error'; // reset error string
 503                         $i = $this->getReaderIndex( false, $wiki );
 504                         # Couldn't find a working server in getReaderIndex()?
 505                         if ( $i === false ) {
 506                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 507                                 wfProfileOut( __METHOD__ );
 508
 509                                 return $this->reportConnectionError();
 510                         }
 511                 }
 512
 513                 # Now we have an explicit index into the servers array
 514                 $conn = $this->openConnection( $i, $wiki );
 515                 if ( !$conn ) {
 516                         wfProfileOut( __METHOD__ );
 517
 518                         return $this->reportConnectionError();
 519                 }
 520
 521                 wfProfileOut( __METHOD__ );
 522
 523                 return $conn;
 524         }
 525
 526         /**
 527          * Mark a foreign connection as being available for reuse under a different
 528          * DB name or prefix. This mechanism is reference-counted, and must be called
 529          * the same number of times as getConnection() to work.
 530          *
 531          * @param DatabaseBase $conn
 532          * @throws MWException
 533          */
 534         public function reuseConnection( $conn ) {
 535                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 536                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 537                 $dbName = $conn->getDBname();
 538                 $prefix = $conn->tablePrefix();
 539                 if ( strval( $prefix ) !== '' ) {
 540                         $wiki = "$dbName-$prefix";
 541                 } else {
 542                         $wiki = $dbName;
 543                 }
 544                 if ( $serverIndex === null || $refCount === null ) {
 545                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 546
 547                         /**
 548                          * This can happen in code like:
 549                          *   foreach ( $dbs as $db ) {
 550                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 551                          *     ...
 552                          *     $lb->reuseConnection( $conn );
 553                          *   }
 554                          * When a connection to the local DB is opened in this way, reuseConnection()
 555                          * should be ignored
 556                          */
 557
 558                         return;
 559                 }
 560                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 561                         throw new MWException( __METHOD__ . ": connection not found, has " .
 562                                 "the connection been freed already?" );
 563                 }
 564                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 565                 if ( $refCount <= 0 ) {
 566                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 567                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 568                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 569                 } else {
 570                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 571                 }
 572         }
 573
 574         /**
 575          * Get a database connection handle reference
 576          *
 577          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 578          *
 579          * @see LoadBalancer::getConnection() for parameter information
 580          *
 581          * @param integer $db
 582          * @param mixed $groups
 583          * @param bool|string $wiki
 584          * @return DBConnRef
 585          */
 586         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 587                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 588         }
 589
 590         /**
 591          * Get a database connection handle reference without connecting yet
 592          *
 593          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 594          *
 595          * @see LoadBalancer::getConnection() for parameter information
 596          *
 597          * @param integer $db
 598          * @param mixed $groups
 599          * @param bool|string $wiki
 600          * @return DBConnRef
 601          */
 602         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 603                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 604         }
 605
 606         /**
 607          * Open a connection to the server given by the specified index
 608          * Index must be an actual index into the array.
 609          * If the server is already open, returns it.
 610          *
 611          * On error, returns false, and the connection which caused the
 612          * error will be available via $this->mErrorConnection.
 613          *
 614          * @param $i Integer server index
 615          * @param bool|string $wiki wiki ID to open
 616          * @return DatabaseBase
 617          *
 618          * @access private
 619          */
 620         function openConnection( $i, $wiki = false ) {
 621                 wfProfileIn( __METHOD__ );
 622                 if ( $wiki !== false ) {
 623                         $conn = $this->openForeignConnection( $i, $wiki );
 624                         wfProfileOut( __METHOD__ );
 625
 626                         return $conn;
 627                 }
 628                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 629                         $conn = $this->mConns['local'][$i][0];
 630                 } else {
 631                         $server = $this->mServers[$i];
 632                         $server['serverIndex'] = $i;
 633                         $conn = $this->reallyOpenConnection( $server, false );
 634                         if ( $conn->isOpen() ) {
 635                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 636                                 $this->mConns['local'][$i][0] = $conn;
 637                         } else {
 638                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 639                                 $this->mErrorConnection = $conn;
 640                                 $conn = false;
 641                         }
 642                 }
 643                 wfProfileOut( __METHOD__ );
 644
 645                 return $conn;
 646         }
 647
 648         /**
 649          * Open a connection to a foreign DB, or return one if it is already open.
 650          *
 651          * Increments a reference count on the returned connection which locks the
 652          * connection to the requested wiki. This reference count can be
 653          * decremented by calling reuseConnection().
 654          *
 655          * If a connection is open to the appropriate server already, but with the wrong
 656          * database, it will be switched to the right database and returned, as long as
 657          * it has been freed first with reuseConnection().
 658          *
 659          * On error, returns false, and the connection which caused the
 660          * error will be available via $this->mErrorConnection.
 661          *
 662          * @param $i Integer: server index
 663          * @param string $wiki wiki ID to open
 664          * @return DatabaseBase
 665          */
 666         function openForeignConnection( $i, $wiki ) {
 667                 wfProfileIn( __METHOD__ );
 668                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 669                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 670                         // Reuse an already-used connection
 671                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 672                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 673                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 674                         // Reuse a free connection for the same wiki
 675                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 676                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 677                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 678                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 679                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 680                         // Reuse a connection from another wiki
 681                         $conn = reset( $this->mConns['foreignFree'][$i] );
 682                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 683
 684                         if ( !$conn->selectDB( $dbName ) ) {
 685                                 $this->mLastError = "Error selecting database $dbName on server " .
 686                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 687                                 $this->mErrorConnection = $conn;
 688                                 $conn = false;
 689                         } else {
 690                                 $conn->tablePrefix( $prefix );
 691                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 692                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 693                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 694                         }
 695                 } else {
 696                         // Open a new connection
 697                         $server = $this->mServers[$i];
 698                         $server['serverIndex'] = $i;
 699                         $server['foreignPoolRefCount'] = 0;
 700                         $server['foreign'] = true;
 701                         $conn = $this->reallyOpenConnection( $server, $dbName );
 702                         if ( !$conn->isOpen() ) {
 703                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 704                                 $this->mErrorConnection = $conn;
 705                                 $conn = false;
 706                         } else {
 707                                 $conn->tablePrefix( $prefix );
 708                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 709                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 710                         }
 711                 }
 712
 713                 // Increment reference count
 714                 if ( $conn ) {
 715                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 716                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 717                 }
 718                 wfProfileOut( __METHOD__ );
 719
 720                 return $conn;
 721         }
 722
 723         /**
 724          * Test if the specified index represents an open connection
 725          *
 726          * @param $index Integer: server index
 727          * @access private
 728          * @return bool
 729          */
 730         function isOpen( $index ) {
 731                 if ( !is_integer( $index ) ) {
 732                         return false;
 733                 }
 734
 735                 return (bool)$this->getAnyOpenConnection( $index );
 736         }
 737
 738         /**
 739          * Really opens a connection. Uncached.
 740          * Returns a Database object whether or not the connection was successful.
 741          * @access private
 742          *
 743          * @param $server
 744          * @param $dbNameOverride bool
 745          * @throws MWException
 746          * @return DatabaseBase
 747          */
 748         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 749                 if ( !is_array( $server ) ) {
 750                         throw new MWException( 'You must update your load-balancing configuration. ' .
 751                                 'See DefaultSettings.php entry for $wgDBservers.' );
 752                 }
 753
 754                 if ( $dbNameOverride !== false ) {
 755                         $server['dbname'] = $dbNameOverride;
 756                 }
 757
 758                 # Create object
 759                 try {
 760                         $db = DatabaseBase::factory( $server['type'], $server );
 761                 } catch ( DBConnectionError $e ) {
 762                         // FIXME: This is probably the ugliest thing I have ever done to
 763                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 764                         $db = $e->db;
 765                 }
 766
 767                 $db->setLBInfo( $server );
 768                 if ( isset( $server['fakeSlaveLag'] ) ) {
 769                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 770                 }
 771                 if ( isset( $server['fakeMaster'] ) ) {
 772                         $db->setFakeMaster( true );
 773                 }
 774
 775                 return $db;
 776         }
 777
 778         /**
 779          * @throws DBConnectionError
 780          * @return bool
 781          */
 782         private function reportConnectionError() {
 783                 $conn = $this->mErrorConnection; // The connection which caused the error
 784
 785                 if ( !is_object( $conn ) ) {
 786                         // No last connection, probably due to all servers being too busy
 787                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 788
 789                         // If all servers were busy, mLastError will contain something sensible
 790                         throw new DBConnectionError( null, $this->mLastError );
 791                 } else {
 792                         $server = $conn->getProperty( 'mServer' );
 793                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 794                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 795                 }
 796
 797                 return false; /* not reached */
 798         }
 799
 800         /**
 801          * @return int
 802          */
 803         function getWriterIndex() {
 804                 return 0;
 805         }
 806
 807         /**
 808          * Returns true if the specified index is a valid server index
 809          *
 810          * @param string $i
 811          * @return bool
 812          */
 813         function haveIndex( $i ) {
 814                 return array_key_exists( $i, $this->mServers );
 815         }
 816
 817         /**
 818          * Returns true if the specified index is valid and has non-zero load
 819          *
 820          * @param string $i
 821          * @return bool
 822          */
 823         function isNonZeroLoad( $i ) {
 824                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 825         }
 826
 827         /**
 828          * Get the number of defined servers (not the number of open connections)
 829          *
 830          * @return int
 831          */
 832         function getServerCount() {
 833                 return count( $this->mServers );
 834         }
 835
 836         /**
 837          * Get the host name or IP address of the server with the specified index
 838          * Prefer a readable name if available.
 839          * @param string $i
 840          * @return string
 841          */
 842         function getServerName( $i ) {
 843                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 844                         return $this->mServers[$i]['hostName'];
 845                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 846                         return $this->mServers[$i]['host'];
 847                 } else {
 848                         return '';
 849                 }
 850         }
 851
 852         /**
 853          * Return the server info structure for a given index, or false if the index is invalid.
 854          * @param $i
 855          * @return bool
 856          */
 857         function getServerInfo( $i ) {
 858                 if ( isset( $this->mServers[$i] ) ) {
 859                         return $this->mServers[$i];
 860                 } else {
 861                         return false;
 862                 }
 863         }
 864
 865         /**
 866          * Sets the server info structure for the given index. Entry at index $i
 867          * is created if it doesn't exist
 868          * @param $i
 869          * @param $serverInfo
 870          */
 871         function setServerInfo( $i, $serverInfo ) {
 872                 $this->mServers[$i] = $serverInfo;
 873         }
 874
 875         /**
 876          * Get the current master position for chronology control purposes
 877          * @return mixed
 878          */
 879         function getMasterPos() {
 880                 # If this entire request was served from a slave without opening a connection to the
 881                 # master (however unlikely that may be), then we can fetch the position from the slave.
 882                 $masterConn = $this->getAnyOpenConnection( 0 );
 883                 if ( !$masterConn ) {
 884                         $serverCount = count( $this->mServers );
 885                         for ( $i = 1; $i < $serverCount; $i++ ) {
 886                                 $conn = $this->getAnyOpenConnection( $i );
 887                                 if ( $conn ) {
 888                                         wfDebug( "Master pos fetched from slave\n" );
 889
 890                                         return $conn->getSlavePos();
 891                                 }
 892                         }
 893                 } else {
 894                         wfDebug( "Master pos fetched from master\n" );
 895
 896                         return $masterConn->getMasterPos();
 897                 }
 898
 899                 return false;
 900         }
 901
 902         /**
 903          * Close all open connections
 904          */
 905         function closeAll() {
 906                 foreach ( $this->mConns as $conns2 ) {
 907                         foreach ( $conns2 as $conns3 ) {
 908                                 /** @var DatabaseBase $conn */
 909                                 foreach ( $conns3 as $conn ) {
 910                                         $conn->close();
 911                                 }
 912                         }
 913                 }
 914                 $this->mConns = array(
 915                         'local' => array(),
 916                         'foreignFree' => array(),
 917                         'foreignUsed' => array(),
 918                 );
 919         }
 920
 921         /**
 922          * Deprecated function, typo in function name
 923          *
 924          * @deprecated in 1.18
 925          * @param DatabaseBase $conn
 926          */
 927         function closeConnecton( $conn ) {
 928                 wfDeprecated( __METHOD__, '1.18' );
 929                 $this->closeConnection( $conn );
 930         }
 931
 932         /**
 933          * Close a connection
 934          * Using this function makes sure the LoadBalancer knows the connection is closed.
 935          * If you use $conn->close() directly, the load balancer won't update its state.
 936          * @param DatabaseBase $conn
 937          */
 938         function closeConnection( $conn ) {
 939                 $done = false;
 940                 foreach ( $this->mConns as $i1 => $conns2 ) {
 941                         foreach ( $conns2 as $i2 => $conns3 ) {
 942                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 943                                         if ( $conn === $candidateConn ) {
 944                                                 $conn->close();
 945                                                 unset( $this->mConns[$i1][$i2][$i3] );
 946                                                 $done = true;
 947                                                 break;
 948                                         }
 949                                 }
 950                         }
 951                 }
 952                 if ( !$done ) {
 953                         $conn->close();
 954                 }
 955         }
 956
 957         /**
 958          * Commit transactions on all open connections
 959          */
 960         function commitAll() {
 961                 foreach ( $this->mConns as $conns2 ) {
 962                         foreach ( $conns2 as $conns3 ) {
 963                                 /** @var DatabaseBase[] $conns3 */
 964                                 foreach ( $conns3 as $conn ) {
 965                                         if ( $conn->trxLevel() ) {
 966                                                 $conn->commit( __METHOD__, 'flush' );
 967                                         }
 968                                 }
 969                         }
 970                 }
 971         }
 972
 973         /**
 974          *  Issue COMMIT only on master, only if queries were done on connection
 975          */
 976         function commitMasterChanges() {
 977                 // Always 0, but who knows.. :)
 978                 $masterIndex = $this->getWriterIndex();
 979                 foreach ( $this->mConns as $conns2 ) {
 980                         if ( empty( $conns2[$masterIndex] ) ) {
 981                                 continue;
 982                         }
 983                         /** @var DatabaseBase $conn */
 984                         foreach ( $conns2[$masterIndex] as $conn ) {
 985                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 986                                         $conn->commit( __METHOD__, 'flush' );
 987                                 }
 988                         }
 989                 }
 990         }
 991
 992         /**
 993          * @param $value null
 994          * @return Mixed
 995          */
 996         function waitTimeout( $value = null ) {
 997                 return wfSetVar( $this->mWaitTimeout, $value );
 998         }
 999
1000         /**
1001          * @return bool
1002          */
1003         function getLaggedSlaveMode() {
1004                 return $this->mLaggedSlaveMode;
1005         }
1006
1007         /**
1008          * Disables/enables lag checks
1009          * @param null|bool $mode
1010          * @return bool
1011          */
1012         function allowLagged( $mode = null ) {
1013                 if ( $mode === null ) {
1014                         return $this->mAllowLagged;
1015                 }
1016                 $this->mAllowLagged = $mode;
1017
1018                 return $this->mAllowLagged;
1019         }
1020
1021         /**
1022          * @return bool
1023          */
1024         function pingAll() {
1025                 $success = true;
1026                 foreach ( $this->mConns as $conns2 ) {
1027                         foreach ( $conns2 as $conns3 ) {
1028                                 /** @var DatabaseBase[] $conns3 */
1029                                 foreach ( $conns3 as $conn ) {
1030                                         if ( !$conn->ping() ) {
1031                                                 $success = false;
1032                                         }
1033                                 }
1034                         }
1035                 }
1036
1037                 return $success;
1038         }
1039
1040         /**
1041          * Call a function with each open connection object
1042          * @param callable $callback
1043          * @param array $params
1044          */
1045         function forEachOpenConnection( $callback, $params = array() ) {
1046                 foreach ( $this->mConns as $conns2 ) {
1047                         foreach ( $conns2 as $conns3 ) {
1048                                 foreach ( $conns3 as $conn ) {
1049                                         $mergedParams = array_merge( array( $conn ), $params );
1050                                         call_user_func_array( $callback, $mergedParams );
1051                                 }
1052                         }
1053                 }
1054         }
1055
1056         /**
1057          * Get the hostname and lag time of the most-lagged slave.
1058          * This is useful for maintenance scripts that need to throttle their updates.
1059          * May attempt to open connections to slaves on the default DB. If there is
1060          * no lag, the maximum lag will be reported as -1.
1061          *
1062          * @param bool|string $wiki Wiki ID, or false for the default database
1063          * @return array ( host, max lag, index of max lagged host )
1064          */
1065         function getMaxLag( $wiki = false ) {
1066                 $maxLag = -1;
1067                 $host = '';
1068                 $maxIndex = 0;
1069                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1070                         foreach ( $this->mServers as $i => $conn ) {
1071                                 $conn = false;
1072                                 if ( $wiki === false ) {
1073                                         $conn = $this->getAnyOpenConnection( $i );
1074                                 }
1075                                 if ( !$conn ) {
1076                                         $conn = $this->openConnection( $i, $wiki );
1077                                 }
1078                                 if ( !$conn ) {
1079                                         continue;
1080                                 }
1081                                 $lag = $conn->getLag();
1082                                 if ( $lag > $maxLag ) {
1083                                         $maxLag = $lag;
1084                                         $host = $this->mServers[$i]['host'];
1085                                         $maxIndex = $i;
1086                                 }
1087                         }
1088                 }
1089
1090                 return array( $host, $maxLag, $maxIndex );
1091         }
1092
1093         /**
1094          * Get lag time for each server
1095          * Results are cached for a short time in memcached, and indefinitely in the process cache
1096          *
1097          * @param string|bool $wiki
1098          * @return array
1099          */
1100         function getLagTimes( $wiki = false ) {
1101                 # Try process cache
1102                 if ( isset( $this->mLagTimes ) ) {
1103                         return $this->mLagTimes;
1104                 }
1105                 if ( $this->getServerCount() == 1 ) {
1106                         # No replication
1107                         $this->mLagTimes = array( 0 => 0 );
1108                 } else {
1109                         # Send the request to the load monitor
1110                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1111                                 array_keys( $this->mServers ), $wiki );
1112                 }
1113
1114                 return $this->mLagTimes;
1115         }
1116
1117         /**
1118          * Get the lag in seconds for a given connection, or zero if this load
1119          * balancer does not have replication enabled.
1120          *
1121          * This should be used in preference to Database::getLag() in cases where
1122          * replication may not be in use, since there is no way to determine if
1123          * replication is in use at the connection level without running
1124          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1125          * function instead of Database::getLag() avoids a fatal error in this
1126          * case on many installations.
1127          *
1128          * @param DatabaseBase $conn
1129          * @return int
1130          */
1131         function safeGetLag( $conn ) {
1132                 if ( $this->getServerCount() == 1 ) {
1133                         return 0;
1134                 } else {
1135                         return $conn->getLag();
1136                 }
1137         }
1138
1139         /**
1140          * Clear the cache for getLagTimes
1141          */
1142         function clearLagTimeCache() {
1143                 $this->mLagTimes = null;
1144         }
1145 }
1146
1147 /**
1148  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1149  * as well handling deferring the actual network connection until the handle is used
1150  *
1151  * @ingroup Database
1152  * @since 1.22
1153  */
1154 class DBConnRef implements IDatabase {
1155         /** @var LoadBalancer */
1156         protected $lb;
1157
1158         /** @var DatabaseBase|null */
1159         protected $conn;
1160
1161         /** @var array|null */
1162         protected $params;
1163
1164         /**
1165          * @param LoadBalancer $lb
1166          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1167          */
1168         public function __construct( LoadBalancer $lb, $conn ) {
1169                 $this->lb = $lb;
1170                 if ( $conn instanceof DatabaseBase ) {
1171                         $this->conn = $conn;
1172                 } else {
1173                         $this->params = $conn;
1174                 }
1175         }
1176
1177         public function __call( $name, $arguments ) {
1178                 if ( $this->conn === null ) {
1179                         list( $db, $groups, $wiki ) = $this->params;
1180                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1181                 }
1182
1183                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1184         }
1185
1186         function __destruct() {
1187                 if ( $this->conn !== null ) {
1188                         $this->lb->reuseConnection( $this->conn );
1189                 }
1190         }
1191 }