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         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard slave lag as a factor in slave selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on slave lag to resolve */
  42         private $mWaitTimeout;
  43
  44         /** @var array LBFactory information */
  45         private $mParentInfo;
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50
  51         /** @var bool|DatabaseBase Database connection that caused a problem */
  52         private $mErrorConnection;
  53         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  54         private $mReadIndex;
  55         /** @var bool|DBMasterPos False if not set */
  56         private $mWaitForPos;
  57         /** @var bool Whether the generic reader fell back to a lagged slave */
  58         private $mLaggedSlaveMode;
  59         /** @var string The last DB selection or connection error */
  60         private $mLastError = 'Unknown error';
  61         /** @var ProcessCacheLRU */
  62         private $mProcCache;
  63
  64         /**
  65          * @param array $params Array with keys:
  66          *   servers           Required. Array of server info structures.
  67          *   loadMonitor       Name of a class used to fetch server lag and load.
  68          * @throws MWException
  69          */
  70         public function __construct( array $params ) {
  71                 if ( !isset( $params['servers'] ) ) {
  72                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  73                 }
  74                 $this->mServers = $params['servers'];
  75                 $this->mWaitTimeout = 10;
  76
  77                 $this->mReadIndex = -1;
  78                 $this->mWriteIndex = -1;
  79                 $this->mConns = array(
  80                         'local' => array(),
  81                         'foreignUsed' => array(),
  82                         'foreignFree' => array() );
  83                 $this->mLoads = array();
  84                 $this->mWaitForPos = false;
  85                 $this->mLaggedSlaveMode = false;
  86                 $this->mErrorConnection = false;
  87                 $this->mAllowLagged = false;
  88
  89                 if ( isset( $params['loadMonitor'] ) ) {
  90                         $this->mLoadMonitorClass = $params['loadMonitor'];
  91                 } else {
  92                         $master = reset( $params['servers'] );
  93                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  94                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  95                         } else {
  96                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
  97                         }
  98                 }
  99
 100                 foreach ( $params['servers'] as $i => $server ) {
 101                         $this->mLoads[$i] = $server['load'];
 102                         if ( isset( $server['groupLoads'] ) ) {
 103                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 104                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 105                                                 $this->mGroupLoads[$group] = array();
 106                                         }
 107                                         $this->mGroupLoads[$group][$i] = $ratio;
 108                                 }
 109                         }
 110                 }
 111
 112                 $this->mProcCache = new ProcessCacheLRU( 30 );
 113         }
 114
 115         /**
 116          * Get a LoadMonitor instance
 117          *
 118          * @return LoadMonitor
 119          */
 120         private function getLoadMonitor() {
 121                 if ( !isset( $this->mLoadMonitor ) ) {
 122                         $class = $this->mLoadMonitorClass;
 123                         $this->mLoadMonitor = new $class( $this );
 124                 }
 125
 126                 return $this->mLoadMonitor;
 127         }
 128
 129         /**
 130          * Get or set arbitrary data used by the parent object, usually an LBFactory
 131          * @param mixed $x
 132          * @return mixed
 133          */
 134         public function parentInfo( $x = null ) {
 135                 return wfSetVar( $this->mParentInfo, $x );
 136         }
 137
 138         /**
 139          * Given an array of non-normalised probabilities, this function will select
 140          * an element and return the appropriate key
 141          *
 142          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 143          *
 144          * @param array $weights
 145          * @return bool|int|string
 146          */
 147         public function pickRandom( array $weights ) {
 148                 return ArrayUtils::pickRandom( $weights );
 149         }
 150
 151         /**
 152          * @param array $loads
 153          * @param bool|string $wiki Wiki to get non-lagged for
 154          * @param float $maxLag Restrict the maximum allowed lag to this many seconds
 155          * @return bool|int|string
 156          */
 157         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 158                 $lags = $this->getLagTimes( $wiki );
 159
 160                 # Unset excessively lagged servers
 161                 foreach ( $lags as $i => $lag ) {
 162                         if ( $i != 0 ) {
 163                                 $maxServerLag = $maxLag;
 164                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 165                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 166                                 }
 167                                 if ( $lag === false ) {
 168                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 169                                         unset( $loads[$i] );
 170                                 } elseif ( $lag > $maxServerLag ) {
 171                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 172                                         unset( $loads[$i] );
 173                                 }
 174                         }
 175                 }
 176
 177                 # Find out if all the slaves with non-zero load are lagged
 178                 $sum = 0;
 179                 foreach ( $loads as $load ) {
 180                         $sum += $load;
 181                 }
 182                 if ( $sum == 0 ) {
 183                         # No appropriate DB servers except maybe the master and some slaves with zero load
 184                         # Do NOT use the master
 185                         # Instead, this function will return false, triggering read-only mode,
 186                         # and a lagged slave will be used instead.
 187                         return false;
 188                 }
 189
 190                 if ( count( $loads ) == 0 ) {
 191                         return false;
 192                 }
 193
 194                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 195
 196                 # Return a random representative of the remainder
 197                 return ArrayUtils::pickRandom( $loads );
 198         }
 199
 200         /**
 201          * Get the index of the reader connection, which may be a slave
 202          * This takes into account load ratios and lag times. It should
 203          * always return a consistent index during a given invocation
 204          *
 205          * Side effect: opens connections to databases
 206          * @param string|bool $group Query group, or false for the generic reader
 207          * @param string|bool $wiki Wiki ID, or false for the current wiki
 208          * @throws MWException
 209          * @return bool|int|string
 210          */
 211         public function getReaderIndex( $group = false, $wiki = false ) {
 212                 global $wgReadOnly, $wgDBtype;
 213
 214                 # @todo FIXME: For now, only go through all this for mysql databases
 215                 if ( $wgDBtype != 'mysql' ) {
 216                         return $this->getWriterIndex();
 217                 }
 218
 219                 if ( count( $this->mServers ) == 1 ) {
 220                         # Skip the load balancing if there's only one server
 221                         return 0;
 222                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 223                         # Shortcut if generic reader exists already
 224                         return $this->mReadIndex;
 225                 }
 226
 227                 # Find the relevant load array
 228                 if ( $group !== false ) {
 229                         if ( isset( $this->mGroupLoads[$group] ) ) {
 230                                 $nonErrorLoads = $this->mGroupLoads[$group];
 231                         } else {
 232                                 # No loads for this group, return false and the caller can use some other group
 233                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 234
 235                                 return false;
 236                         }
 237                 } else {
 238                         $nonErrorLoads = $this->mLoads;
 239                 }
 240
 241                 if ( !count( $nonErrorLoads ) ) {
 242                         throw new MWException( "Empty server array given to LoadBalancer" );
 243                 }
 244
 245                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 246                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 247
 248                 $laggedSlaveMode = false;
 249
 250                 # No server found yet
 251                 $i = false;
 252                 # First try quickly looking through the available servers for a server that
 253                 # meets our criteria
 254                 $currentLoads = $nonErrorLoads;
 255                 while ( count( $currentLoads ) ) {
 256                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 257                                 $i = ArrayUtils::pickRandom( $currentLoads );
 258                         } else {
 259                                 $i = false;
 260                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 261                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 262                                         # This triggers doWait() after connect, so it's especially good to
 263                                         # avoid lagged servers so as to avoid just blocking in that method.
 264                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 265                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 266                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 267                                 }
 268                                 if ( $i === false ) {
 269                                         # Any server with less lag than it's 'max lag' param is preferable
 270                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 271                                 }
 272                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 273                                         # All slaves lagged. Switch to read-only mode
 274                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 275                                         $wgReadOnly = 'The database has been automatically locked ' .
 276                                                 'while the slave database servers catch up to the master';
 277                                         $i = ArrayUtils::pickRandom( $currentLoads );
 278                                         $laggedSlaveMode = true;
 279                                 }
 280                         }
 281
 282                         if ( $i === false ) {
 283                                 # pickRandom() returned false
 284                                 # This is permanent and means the configuration or the load monitor
 285                                 # wants us to return false.
 286                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 287
 288                                 return false;
 289                         }
 290
 291                         wfDebugLog( 'connect', __METHOD__ .
 292                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 293
 294                         $conn = $this->openConnection( $i, $wiki );
 295                         if ( !$conn ) {
 296                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 297                                 unset( $nonErrorLoads[$i] );
 298                                 unset( $currentLoads[$i] );
 299                                 $i = false;
 300                                 continue;
 301                         }
 302
 303                         // Decrement reference counter, we are finished with this connection.
 304                         // It will be incremented for the caller later.
 305                         if ( $wiki !== false ) {
 306                                 $this->reuseConnection( $conn );
 307                         }
 308
 309                         # Return this server
 310                         break;
 311                 }
 312
 313                 # If all servers were down, quit now
 314                 if ( !count( $nonErrorLoads ) ) {
 315                         wfDebugLog( 'connect', "All servers down" );
 316                 }
 317
 318                 if ( $i !== false ) {
 319                         # Slave connection successful
 320                         # Wait for the session master pos for a short time
 321                         if ( $this->mWaitForPos && $i > 0 ) {
 322                                 if ( !$this->doWait( $i ) ) {
 323                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 324                                 }
 325                         }
 326                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group !== false ) {
 327                                 $this->mReadIndex = $i;
 328                         }
 329                 }
 330
 331                 return $i;
 332         }
 333
 334         /**
 335          * Set the master wait position
 336          * If a DB_SLAVE connection has been opened already, waits
 337          * Otherwise sets a variable telling it to wait if such a connection is opened
 338          * @param DBMasterPos $pos
 339          */
 340         public function waitFor( $pos ) {
 341                 $this->mWaitForPos = $pos;
 342                 $i = $this->mReadIndex;
 343
 344                 if ( $i > 0 ) {
 345                         if ( !$this->doWait( $i ) ) {
 346                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 347                                 $this->mLaggedSlaveMode = true;
 348                         }
 349                 }
 350         }
 351
 352         /**
 353          * Set the master wait position and wait for ALL slaves to catch up to it
 354          * @param DBMasterPos $pos
 355          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 356          * @return bool Success (able to connect and no timeouts reached)
 357          */
 358         public function waitForAll( $pos, $timeout = null ) {
 359                 $this->mWaitForPos = $pos;
 360                 $serverCount = count( $this->mServers );
 361
 362                 $ok = true;
 363                 for ( $i = 1; $i < $serverCount; $i++ ) {
 364                         if ( $this->mLoads[$i] > 0 ) {
 365                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 366                         }
 367                 }
 368
 369                 return $ok;
 370         }
 371
 372         /**
 373          * Get any open connection to a given server index, local or foreign
 374          * Returns false if there is no connection open
 375          *
 376          * @param int $i
 377          * @return DatabaseBase|bool False on failure
 378          */
 379         public function getAnyOpenConnection( $i ) {
 380                 foreach ( $this->mConns as $conns ) {
 381                         if ( !empty( $conns[$i] ) ) {
 382                                 return reset( $conns[$i] );
 383                         }
 384                 }
 385
 386                 return false;
 387         }
 388
 389         /**
 390          * Wait for a given slave to catch up to the master pos stored in $this
 391          * @param int $index Server index
 392          * @param bool $open Check the server even if a new connection has to be made
 393          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 394          * @return bool
 395          */
 396         protected function doWait( $index, $open = false, $timeout = null ) {
 397                 $close = false; // close the connection afterwards
 398
 399                 # Find a connection to wait on, creating one if needed and allowed
 400                 $conn = $this->getAnyOpenConnection( $index );
 401                 if ( !$conn ) {
 402                         if ( !$open ) {
 403                                 wfDebug( __METHOD__ . ": no connection open\n" );
 404
 405                                 return false;
 406                         } else {
 407                                 $conn = $this->openConnection( $index, '' );
 408                                 if ( !$conn ) {
 409                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 410
 411                                         return false;
 412                                 }
 413                                 // Avoid connection spam in waitForAll() when connections
 414                                 // are made just for the sake of doing this lag check.
 415                                 $close = true;
 416                         }
 417                 }
 418
 419                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 420                 $timeout = $timeout ?: $this->mWaitTimeout;
 421                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 422
 423                 if ( $result == -1 || is_null( $result ) ) {
 424                         # Timed out waiting for slave, use master instead
 425                         $server = $this->mServers[$index]['host'];
 426                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 427                         wfDebug( "$msg\n" );
 428                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 429                         $ok = false;
 430                 } else {
 431                         wfDebug( __METHOD__ . ": Done\n" );
 432                         $ok = true;
 433                 }
 434
 435                 if ( $close ) {
 436                         $this->closeConnection( $conn );
 437                 }
 438
 439                 return $ok;
 440         }
 441
 442         /**
 443          * Get a connection by index
 444          * This is the main entry point for this class.
 445          *
 446          * @param int $i Server index
 447          * @param array|string|bool $groups Query group(s), or false for the generic reader
 448          * @param string|bool $wiki Wiki ID, or false for the current wiki
 449          *
 450          * @throws MWException
 451          * @return DatabaseBase
 452          */
 453         public function getConnection( $i, $groups = array(), $wiki = false ) {
 454                 if ( $i === null || $i === false ) {
 455                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 456                                 ' with invalid server index' );
 457                 }
 458
 459                 if ( $wiki === wfWikiID() ) {
 460                         $wiki = false;
 461                 }
 462
 463                 $groups = ( $groups === false || $groups === array() )
 464                         ? array( false ) // check one "group": the generic pool
 465                         : (array)$groups;
 466
 467                 if ( $i == DB_MASTER ) {
 468                         $i = $this->getWriterIndex();
 469                 } else {
 470                         # Try to find an available server in any the query groups (in order)
 471                         foreach ( $groups as $group ) {
 472                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 473                                 if ( $groupIndex !== false ) {
 474                                         $serverName = $this->getServerName( $groupIndex );
 475                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 476                                         $i = $groupIndex;
 477                                         break;
 478                                 }
 479                         }
 480                 }
 481
 482                 # Operation-based index
 483                 if ( $i == DB_SLAVE ) {
 484                         $this->mLastError = 'Unknown error'; // reset error string
 485                         # Try the general server pool if $groups are unavailable.
 486                         $i = in_array( false, $groups, true )
 487                                 ? false // don't bother with this if that is what was tried above
 488                                 : $this->getReaderIndex( false, $wiki );
 489                         # Couldn't find a working server in getReaderIndex()?
 490                         if ( $i === false ) {
 491                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 492
 493                                 return $this->reportConnectionError();
 494                         }
 495                 }
 496
 497                 # Now we have an explicit index into the servers array
 498                 $conn = $this->openConnection( $i, $wiki );
 499                 if ( !$conn ) {
 500
 501                         return $this->reportConnectionError();
 502                 }
 503
 504
 505                 return $conn;
 506         }
 507
 508         /**
 509          * Mark a foreign connection as being available for reuse under a different
 510          * DB name or prefix. This mechanism is reference-counted, and must be called
 511          * the same number of times as getConnection() to work.
 512          *
 513          * @param DatabaseBase $conn
 514          * @throws MWException
 515          */
 516         public function reuseConnection( $conn ) {
 517                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 518                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 519                 if ( $serverIndex === null || $refCount === null ) {
 520                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 521
 522                         /**
 523                          * This can happen in code like:
 524                          *   foreach ( $dbs as $db ) {
 525                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 526                          *     ...
 527                          *     $lb->reuseConnection( $conn );
 528                          *   }
 529                          * When a connection to the local DB is opened in this way, reuseConnection()
 530                          * should be ignored
 531                          */
 532
 533                         return;
 534                 }
 535
 536                 $dbName = $conn->getDBname();
 537                 $prefix = $conn->tablePrefix();
 538                 if ( strval( $prefix ) !== '' ) {
 539                         $wiki = "$dbName-$prefix";
 540                 } else {
 541                         $wiki = $dbName;
 542                 }
 543                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 544                         throw new MWException( __METHOD__ . ": connection not found, has " .
 545                                 "the connection been freed already?" );
 546                 }
 547                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 548                 if ( $refCount <= 0 ) {
 549                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 550                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 551                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 552                 } else {
 553                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 554                 }
 555         }
 556
 557         /**
 558          * Get a database connection handle reference
 559          *
 560          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 561          *
 562          * @see LoadBalancer::getConnection() for parameter information
 563          *
 564          * @param int $db
 565          * @param array|string|bool $groups Query group(s), or false for the generic reader
 566          * @param string|bool $wiki Wiki ID, or false for the current wiki
 567          * @return DBConnRef
 568          */
 569         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 570                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 571         }
 572
 573         /**
 574          * Get a database connection handle reference without connecting yet
 575          *
 576          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 577          *
 578          * @see LoadBalancer::getConnection() for parameter information
 579          *
 580          * @param int $db
 581          * @param array|string|bool $groups Query group(s), or false for the generic reader
 582          * @param string|bool $wiki Wiki ID, or false for the current wiki
 583          * @return DBConnRef
 584          */
 585         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 586                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 587         }
 588
 589         /**
 590          * Open a connection to the server given by the specified index
 591          * Index must be an actual index into the array.
 592          * If the server is already open, returns it.
 593          *
 594          * On error, returns false, and the connection which caused the
 595          * error will be available via $this->mErrorConnection.
 596          *
 597          * @param int $i Server index
 598          * @param string|bool $wiki Wiki ID, or false for the current wiki
 599          * @return DatabaseBase
 600          *
 601          * @access private
 602          */
 603         public function openConnection( $i, $wiki = false ) {
 604                 if ( $wiki !== false ) {
 605                         $conn = $this->openForeignConnection( $i, $wiki );
 606
 607                         return $conn;
 608                 }
 609                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 610                         $conn = $this->mConns['local'][$i][0];
 611                 } else {
 612                         $server = $this->mServers[$i];
 613                         $server['serverIndex'] = $i;
 614                         $conn = $this->reallyOpenConnection( $server, false );
 615                         if ( $conn->isOpen() ) {
 616                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 617                                 $this->mConns['local'][$i][0] = $conn;
 618                         } else {
 619                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 620                                 $this->mErrorConnection = $conn;
 621                                 $conn = false;
 622                         }
 623                 }
 624
 625                 return $conn;
 626         }
 627
 628         /**
 629          * Open a connection to a foreign DB, or return one if it is already open.
 630          *
 631          * Increments a reference count on the returned connection which locks the
 632          * connection to the requested wiki. This reference count can be
 633          * decremented by calling reuseConnection().
 634          *
 635          * If a connection is open to the appropriate server already, but with the wrong
 636          * database, it will be switched to the right database and returned, as long as
 637          * it has been freed first with reuseConnection().
 638          *
 639          * On error, returns false, and the connection which caused the
 640          * error will be available via $this->mErrorConnection.
 641          *
 642          * @param int $i Server index
 643          * @param string $wiki Wiki ID to open
 644          * @return DatabaseBase
 645          */
 646         private function openForeignConnection( $i, $wiki ) {
 647                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 648                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 649                         // Reuse an already-used connection
 650                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 651                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 652                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 653                         // Reuse a free connection for the same wiki
 654                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 655                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 656                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 657                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 658                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 659                         // Reuse a connection from another wiki
 660                         $conn = reset( $this->mConns['foreignFree'][$i] );
 661                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 662
 663                         // The empty string as a DB name means "don't care".
 664                         // DatabaseMysqlBase::open() already handle this on connection.
 665                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 666                                 $this->mLastError = "Error selecting database $dbName on server " .
 667                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 668                                 $this->mErrorConnection = $conn;
 669                                 $conn = false;
 670                         } else {
 671                                 $conn->tablePrefix( $prefix );
 672                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 673                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 674                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 675                         }
 676                 } else {
 677                         // Open a new connection
 678                         $server = $this->mServers[$i];
 679                         $server['serverIndex'] = $i;
 680                         $server['foreignPoolRefCount'] = 0;
 681                         $server['foreign'] = true;
 682                         $conn = $this->reallyOpenConnection( $server, $dbName );
 683                         if ( !$conn->isOpen() ) {
 684                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 685                                 $this->mErrorConnection = $conn;
 686                                 $conn = false;
 687                         } else {
 688                                 $conn->tablePrefix( $prefix );
 689                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 690                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 691                         }
 692                 }
 693
 694                 // Increment reference count
 695                 if ( $conn ) {
 696                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 697                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 698                 }
 699
 700                 return $conn;
 701         }
 702
 703         /**
 704          * Test if the specified index represents an open connection
 705          *
 706          * @param int $index Server index
 707          * @access private
 708          * @return bool
 709          */
 710         private function isOpen( $index ) {
 711                 if ( !is_integer( $index ) ) {
 712                         return false;
 713                 }
 714
 715                 return (bool)$this->getAnyOpenConnection( $index );
 716         }
 717
 718         /**
 719          * Really opens a connection. Uncached.
 720          * Returns a Database object whether or not the connection was successful.
 721          * @access private
 722          *
 723          * @param array $server
 724          * @param bool $dbNameOverride
 725          * @throws MWException
 726          * @return DatabaseBase
 727          */
 728         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 729                 if ( !is_array( $server ) ) {
 730                         throw new MWException( 'You must update your load-balancing configuration. ' .
 731                                 'See DefaultSettings.php entry for $wgDBservers.' );
 732                 }
 733
 734                 if ( $dbNameOverride !== false ) {
 735                         $server['dbname'] = $dbNameOverride;
 736                 }
 737
 738                 # Create object
 739                 try {
 740                         $db = DatabaseBase::factory( $server['type'], $server );
 741                 } catch ( DBConnectionError $e ) {
 742                         // FIXME: This is probably the ugliest thing I have ever done to
 743                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 744                         $db = $e->db;
 745                 }
 746
 747                 $db->setLBInfo( $server );
 748                 if ( isset( $server['fakeSlaveLag'] ) ) {
 749                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 750                 }
 751                 if ( isset( $server['fakeMaster'] ) ) {
 752                         $db->setFakeMaster( true );
 753                 }
 754
 755                 return $db;
 756         }
 757
 758         /**
 759          * @throws DBConnectionError
 760          * @return bool
 761          */
 762         private function reportConnectionError() {
 763                 $conn = $this->mErrorConnection; // The connection which caused the error
 764                 $context = array(
 765                         'method' => __METHOD__,
 766                         'last_error' => $this->mLastError,
 767                 );
 768
 769                 if ( !is_object( $conn ) ) {
 770                         // No last connection, probably due to all servers being too busy
 771                         wfLogDBError(
 772                                 "LB failure with no last connection. Connection error: {last_error}",
 773                                 $context
 774                         );
 775
 776                         // If all servers were busy, mLastError will contain something sensible
 777                         throw new DBConnectionError( null, $this->mLastError );
 778                 } else {
 779                         $context['db_server'] = $conn->getProperty( 'mServer' );
 780                         wfLogDBError(
 781                                 "Connection error: {last_error} ({db_server})",
 782                                 $context
 783                         );
 784                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
 785                 }
 786
 787                 return false; /* not reached */
 788         }
 789
 790         /**
 791          * @return int
 792          */
 793         private function getWriterIndex() {
 794                 return 0;
 795         }
 796
 797         /**
 798          * Returns true if the specified index is a valid server index
 799          *
 800          * @param string $i
 801          * @return bool
 802          */
 803         public function haveIndex( $i ) {
 804                 return array_key_exists( $i, $this->mServers );
 805         }
 806
 807         /**
 808          * Returns true if the specified index is valid and has non-zero load
 809          *
 810          * @param string $i
 811          * @return bool
 812          */
 813         public function isNonZeroLoad( $i ) {
 814                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 815         }
 816
 817         /**
 818          * Get the number of defined servers (not the number of open connections)
 819          *
 820          * @return int
 821          */
 822         public function getServerCount() {
 823                 return count( $this->mServers );
 824         }
 825
 826         /**
 827          * Get the host name or IP address of the server with the specified index
 828          * Prefer a readable name if available.
 829          * @param string $i
 830          * @return string
 831          */
 832         public function getServerName( $i ) {
 833                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 834                         return $this->mServers[$i]['hostName'];
 835                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 836                         return $this->mServers[$i]['host'];
 837                 } else {
 838                         return '';
 839                 }
 840         }
 841
 842         /**
 843          * Return the server info structure for a given index, or false if the index is invalid.
 844          * @param int $i
 845          * @return array|bool
 846          */
 847         public function getServerInfo( $i ) {
 848                 if ( isset( $this->mServers[$i] ) ) {
 849                         return $this->mServers[$i];
 850                 } else {
 851                         return false;
 852                 }
 853         }
 854
 855         /**
 856          * Sets the server info structure for the given index. Entry at index $i
 857          * is created if it doesn't exist
 858          * @param int $i
 859          * @param array $serverInfo
 860          */
 861         public function setServerInfo( $i, array $serverInfo ) {
 862                 $this->mServers[$i] = $serverInfo;
 863         }
 864
 865         /**
 866          * Get the current master position for chronology control purposes
 867          * @return mixed
 868          */
 869         public function getMasterPos() {
 870                 # If this entire request was served from a slave without opening a connection to the
 871                 # master (however unlikely that may be), then we can fetch the position from the slave.
 872                 $masterConn = $this->getAnyOpenConnection( 0 );
 873                 if ( !$masterConn ) {
 874                         $serverCount = count( $this->mServers );
 875                         for ( $i = 1; $i < $serverCount; $i++ ) {
 876                                 $conn = $this->getAnyOpenConnection( $i );
 877                                 if ( $conn ) {
 878                                         wfDebug( "Master pos fetched from slave\n" );
 879
 880                                         return $conn->getSlavePos();
 881                                 }
 882                         }
 883                 } else {
 884                         wfDebug( "Master pos fetched from master\n" );
 885
 886                         return $masterConn->getMasterPos();
 887                 }
 888
 889                 return false;
 890         }
 891
 892         /**
 893          * Close all open connections
 894          */
 895         public function closeAll() {
 896                 foreach ( $this->mConns as $conns2 ) {
 897                         foreach ( $conns2 as $conns3 ) {
 898                                 /** @var DatabaseBase $conn */
 899                                 foreach ( $conns3 as $conn ) {
 900                                         $conn->close();
 901                                 }
 902                         }
 903                 }
 904                 $this->mConns = array(
 905                         'local' => array(),
 906                         'foreignFree' => array(),
 907                         'foreignUsed' => array(),
 908                 );
 909         }
 910
 911         /**
 912          * Close a connection
 913          * Using this function makes sure the LoadBalancer knows the connection is closed.
 914          * If you use $conn->close() directly, the load balancer won't update its state.
 915          * @param DatabaseBase $conn
 916          */
 917         public function closeConnection( $conn ) {
 918                 $done = false;
 919                 foreach ( $this->mConns as $i1 => $conns2 ) {
 920                         foreach ( $conns2 as $i2 => $conns3 ) {
 921                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 922                                         if ( $conn === $candidateConn ) {
 923                                                 $conn->close();
 924                                                 unset( $this->mConns[$i1][$i2][$i3] );
 925                                                 $done = true;
 926                                                 break;
 927                                         }
 928                                 }
 929                         }
 930                 }
 931                 if ( !$done ) {
 932                         $conn->close();
 933                 }
 934         }
 935
 936         /**
 937          * Commit transactions on all open connections
 938          */
 939         public function commitAll() {
 940                 foreach ( $this->mConns as $conns2 ) {
 941                         foreach ( $conns2 as $conns3 ) {
 942                                 /** @var DatabaseBase[] $conns3 */
 943                                 foreach ( $conns3 as $conn ) {
 944                                         if ( $conn->trxLevel() ) {
 945                                                 $conn->commit( __METHOD__, 'flush' );
 946                                         }
 947                                 }
 948                         }
 949                 }
 950         }
 951
 952         /**
 953          *  Issue COMMIT only on master, only if queries were done on connection
 954          */
 955         public function commitMasterChanges() {
 956                 // Always 0, but who knows.. :)
 957                 $masterIndex = $this->getWriterIndex();
 958                 foreach ( $this->mConns as $conns2 ) {
 959                         if ( empty( $conns2[$masterIndex] ) ) {
 960                                 continue;
 961                         }
 962                         /** @var DatabaseBase $conn */
 963                         foreach ( $conns2[$masterIndex] as $conn ) {
 964                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 965                                         $conn->commit( __METHOD__, 'flush' );
 966                                 }
 967                         }
 968                 }
 969         }
 970
 971         /**
 972          * Issue ROLLBACK only on master, only if queries were done on connection
 973          * @since 1.23
 974          */
 975         public function rollbackMasterChanges() {
 976                 // Always 0, but who knows.. :)
 977                 $masterIndex = $this->getWriterIndex();
 978                 foreach ( $this->mConns as $conns2 ) {
 979                         if ( empty( $conns2[$masterIndex] ) ) {
 980                                 continue;
 981                         }
 982                         /** @var DatabaseBase $conn */
 983                         foreach ( $conns2[$masterIndex] as $conn ) {
 984                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 985                                         $conn->rollback( __METHOD__, 'flush' );
 986                                 }
 987                         }
 988                 }
 989         }
 990
 991         /**
 992          * @return bool Whether a master connection is already open
 993          * @since 1.24
 994          */
 995         public function hasMasterConnection() {
 996                 return $this->isOpen( $this->getWriterIndex() );
 997         }
 998
 999         /**
1000          * Determine if there are any pending changes that need to be rolled back
1001          * or committed.
1002          * @since 1.23
1003          * @return bool
1004          */
1005         public function hasMasterChanges() {
1006                 // Always 0, but who knows.. :)
1007                 $masterIndex = $this->getWriterIndex();
1008                 foreach ( $this->mConns as $conns2 ) {
1009                         if ( empty( $conns2[$masterIndex] ) ) {
1010                                 continue;
1011                         }
1012                         /** @var DatabaseBase $conn */
1013                         foreach ( $conns2[$masterIndex] as $conn ) {
1014                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1015                                         return true;
1016                                 }
1017                         }
1018                 }
1019                 return false;
1020         }
1021
1022         /**
1023          * @param mixed $value
1024          * @return mixed
1025          */
1026         public function waitTimeout( $value = null ) {
1027                 return wfSetVar( $this->mWaitTimeout, $value );
1028         }
1029
1030         /**
1031          * @return bool
1032          */
1033         public function getLaggedSlaveMode() {
1034                 return $this->mLaggedSlaveMode;
1035         }
1036
1037         /**
1038          * Disables/enables lag checks
1039          * @param null|bool $mode
1040          * @return bool
1041          */
1042         public function allowLagged( $mode = null ) {
1043                 if ( $mode === null ) {
1044                         return $this->mAllowLagged;
1045                 }
1046                 $this->mAllowLagged = $mode;
1047
1048                 return $this->mAllowLagged;
1049         }
1050
1051         /**
1052          * @return bool
1053          */
1054         public function pingAll() {
1055                 $success = true;
1056                 foreach ( $this->mConns as $conns2 ) {
1057                         foreach ( $conns2 as $conns3 ) {
1058                                 /** @var DatabaseBase[] $conns3 */
1059                                 foreach ( $conns3 as $conn ) {
1060                                         if ( !$conn->ping() ) {
1061                                                 $success = false;
1062                                         }
1063                                 }
1064                         }
1065                 }
1066
1067                 return $success;
1068         }
1069
1070         /**
1071          * Call a function with each open connection object
1072          * @param callable $callback
1073          * @param array $params
1074          */
1075         public function forEachOpenConnection( $callback, array $params = array() ) {
1076                 foreach ( $this->mConns as $conns2 ) {
1077                         foreach ( $conns2 as $conns3 ) {
1078                                 foreach ( $conns3 as $conn ) {
1079                                         $mergedParams = array_merge( array( $conn ), $params );
1080                                         call_user_func_array( $callback, $mergedParams );
1081                                 }
1082                         }
1083                 }
1084         }
1085
1086         /**
1087          * Get the hostname and lag time of the most-lagged slave
1088          *
1089          * This is useful for maintenance scripts that need to throttle their updates.
1090          * May attempt to open connections to slaves on the default DB. If there is
1091          * no lag, the maximum lag will be reported as -1.
1092          *
1093          * @param bool|string $wiki Wiki ID, or false for the default database
1094          * @return array ( host, max lag, index of max lagged host )
1095          */
1096         public function getMaxLag( $wiki = false ) {
1097                 $maxLag = -1;
1098                 $host = '';
1099                 $maxIndex = 0;
1100
1101                 if ( $this->getServerCount() <= 1 ) {
1102                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1103                 }
1104
1105                 $lagTimes = $this->getLagTimes( $wiki );
1106                 foreach ( $lagTimes as $i => $lag ) {
1107                         if ( $lag > $maxLag ) {
1108                                 $maxLag = $lag;
1109                                 $host = $this->mServers[$i]['host'];
1110                                 $maxIndex = $i;
1111                         }
1112                 }
1113
1114                 return array( $host, $maxLag, $maxIndex );
1115         }
1116
1117         /**
1118          * Get lag time for each server
1119          *
1120          * Results are cached for a short time in memcached/process cache
1121          *
1122          * @param string|bool $wiki
1123          * @return int[] Map of (server index => seconds)
1124          */
1125         public function getLagTimes( $wiki = false ) {
1126                 if ( $this->getServerCount() <= 1 ) {
1127                         return array( 0 => 0 ); // no replication = no lag
1128                 }
1129
1130                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1131                         return $this->mProcCache->get( 'slave_lag', 'times' );
1132                 }
1133
1134                 # Send the request to the load monitor
1135                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1136
1137                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1138
1139                 return $times;
1140         }
1141
1142         /**
1143          * Get the lag in seconds for a given connection, or zero if this load
1144          * balancer does not have replication enabled.
1145          *
1146          * This should be used in preference to Database::getLag() in cases where
1147          * replication may not be in use, since there is no way to determine if
1148          * replication is in use at the connection level without running
1149          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1150          * function instead of Database::getLag() avoids a fatal error in this
1151          * case on many installations.
1152          *
1153          * @param DatabaseBase $conn
1154          * @return int
1155          */
1156         public function safeGetLag( $conn ) {
1157                 if ( $this->getServerCount() == 1 ) {
1158                         return 0;
1159                 } else {
1160                         return $conn->getLag();
1161                 }
1162         }
1163
1164         /**
1165          * Clear the cache for slag lag delay times
1166          */
1167         public function clearLagTimeCache() {
1168                 $this->mProcCache->clear( 'slave_lag' );
1169         }
1170 }
1171
1172 /**
1173  * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1174  * as well handling deferring the actual network connection until the handle is used
1175  *
1176  * @ingroup Database
1177  * @since 1.22
1178  */
1179 class DBConnRef implements IDatabase {
1180         /** @var LoadBalancer */
1181         private $lb;
1182
1183         /** @var DatabaseBase|null */
1184         private $conn;
1185
1186         /** @var array|null */
1187         private $params;
1188
1189         /**
1190          * @param LoadBalancer $lb
1191          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1192          */
1193         public function __construct( LoadBalancer $lb, $conn ) {
1194                 $this->lb = $lb;
1195                 if ( $conn instanceof DatabaseBase ) {
1196                         $this->conn = $conn;
1197                 } else {
1198                         $this->params = $conn;
1199                 }
1200         }
1201
1202         public function __call( $name, $arguments ) {
1203                 if ( $this->conn === null ) {
1204                         list( $db, $groups, $wiki ) = $this->params;
1205                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1206                 }
1207
1208                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1209         }
1210
1211         public function __destruct() {
1212                 if ( $this->conn !== null ) {
1213                         $this->lb->reuseConnection( $this->conn );
1214                 }
1215         }
1216 }