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 integer Total connections opened */
  62         private $connsOpened = 0;
  63         /** @var ProcessCacheLRU */
  64         private $mProcCache;
  65
  66         /** @var integer Warn when this many connection are held */
  67         const CONN_HELD_WARN_THRESHOLD = 10;
  68
  69         /**
  70          * @param array $params Array with keys:
  71          *   servers           Required. Array of server info structures.
  72          *   loadMonitor       Name of a class used to fetch server lag and load.
  73          * @throws MWException
  74          */
  75         public function __construct( array $params ) {
  76                 if ( !isset( $params['servers'] ) ) {
  77                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  78                 }
  79                 $this->mServers = $params['servers'];
  80                 $this->mWaitTimeout = 10;
  81
  82                 $this->mReadIndex = -1;
  83                 $this->mWriteIndex = -1;
  84                 $this->mConns = array(
  85                         'local' => array(),
  86                         'foreignUsed' => array(),
  87                         'foreignFree' => array() );
  88                 $this->mLoads = array();
  89                 $this->mWaitForPos = false;
  90                 $this->mLaggedSlaveMode = false;
  91                 $this->mErrorConnection = false;
  92                 $this->mAllowLagged = false;
  93
  94                 if ( isset( $params['loadMonitor'] ) ) {
  95                         $this->mLoadMonitorClass = $params['loadMonitor'];
  96                 } else {
  97                         $master = reset( $params['servers'] );
  98                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  99                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 100                         } else {
 101                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 102                         }
 103                 }
 104
 105                 foreach ( $params['servers'] as $i => $server ) {
 106                         $this->mLoads[$i] = $server['load'];
 107                         if ( isset( $server['groupLoads'] ) ) {
 108                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 109                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 110                                                 $this->mGroupLoads[$group] = array();
 111                                         }
 112                                         $this->mGroupLoads[$group][$i] = $ratio;
 113                                 }
 114                         }
 115                 }
 116
 117                 $this->mProcCache = new ProcessCacheLRU( 30 );
 118         }
 119
 120         /**
 121          * Get a LoadMonitor instance
 122          *
 123          * @return LoadMonitor
 124          */
 125         private function getLoadMonitor() {
 126                 if ( !isset( $this->mLoadMonitor ) ) {
 127                         $class = $this->mLoadMonitorClass;
 128                         $this->mLoadMonitor = new $class( $this );
 129                 }
 130
 131                 return $this->mLoadMonitor;
 132         }
 133
 134         /**
 135          * Get or set arbitrary data used by the parent object, usually an LBFactory
 136          * @param mixed $x
 137          * @return mixed
 138          */
 139         public function parentInfo( $x = null ) {
 140                 return wfSetVar( $this->mParentInfo, $x );
 141         }
 142
 143         /**
 144          * Given an array of non-normalised probabilities, this function will select
 145          * an element and return the appropriate key
 146          *
 147          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 148          *
 149          * @param array $weights
 150          * @return bool|int|string
 151          */
 152         public function pickRandom( array $weights ) {
 153                 return ArrayUtils::pickRandom( $weights );
 154         }
 155
 156         /**
 157          * @param array $loads
 158          * @param bool|string $wiki Wiki to get non-lagged for
 159          * @param float $maxLag Restrict the maximum allowed lag to this many seconds
 160          * @return bool|int|string
 161          */
 162         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 163                 $lags = $this->getLagTimes( $wiki );
 164
 165                 # Unset excessively lagged servers
 166                 foreach ( $lags as $i => $lag ) {
 167                         if ( $i != 0 ) {
 168                                 $maxServerLag = $maxLag;
 169                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 170                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 171                                 }
 172                                 if ( $lag === false ) {
 173                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 174                                         unset( $loads[$i] );
 175                                 } elseif ( $lag > $maxServerLag ) {
 176                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 177                                         unset( $loads[$i] );
 178                                 }
 179                         }
 180                 }
 181
 182                 # Find out if all the slaves with non-zero load are lagged
 183                 $sum = 0;
 184                 foreach ( $loads as $load ) {
 185                         $sum += $load;
 186                 }
 187                 if ( $sum == 0 ) {
 188                         # No appropriate DB servers except maybe the master and some slaves with zero load
 189                         # Do NOT use the master
 190                         # Instead, this function will return false, triggering read-only mode,
 191                         # and a lagged slave will be used instead.
 192                         return false;
 193                 }
 194
 195                 if ( count( $loads ) == 0 ) {
 196                         return false;
 197                 }
 198
 199                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 200
 201                 # Return a random representative of the remainder
 202                 return ArrayUtils::pickRandom( $loads );
 203         }
 204
 205         /**
 206          * Get the index of the reader connection, which may be a slave
 207          * This takes into account load ratios and lag times. It should
 208          * always return a consistent index during a given invocation
 209          *
 210          * Side effect: opens connections to databases
 211          * @param string|bool $group Query group, or false for the generic reader
 212          * @param string|bool $wiki Wiki ID, or false for the current wiki
 213          * @throws MWException
 214          * @return bool|int|string
 215          */
 216         public function getReaderIndex( $group = false, $wiki = false ) {
 217                 global $wgReadOnly, $wgDBtype;
 218
 219                 # @todo FIXME: For now, only go through all this for mysql databases
 220                 if ( $wgDBtype != 'mysql' ) {
 221                         return $this->getWriterIndex();
 222                 }
 223
 224                 if ( count( $this->mServers ) == 1 ) {
 225                         # Skip the load balancing if there's only one server
 226                         return 0;
 227                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 228                         # Shortcut if generic reader exists already
 229                         return $this->mReadIndex;
 230                 }
 231
 232                 # Find the relevant load array
 233                 if ( $group !== false ) {
 234                         if ( isset( $this->mGroupLoads[$group] ) ) {
 235                                 $nonErrorLoads = $this->mGroupLoads[$group];
 236                         } else {
 237                                 # No loads for this group, return false and the caller can use some other group
 238                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 239
 240                                 return false;
 241                         }
 242                 } else {
 243                         $nonErrorLoads = $this->mLoads;
 244                 }
 245
 246                 if ( !count( $nonErrorLoads ) ) {
 247                         throw new MWException( "Empty server array given to LoadBalancer" );
 248                 }
 249
 250                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 251                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 252
 253                 $laggedSlaveMode = false;
 254
 255                 # No server found yet
 256                 $i = false;
 257                 # First try quickly looking through the available servers for a server that
 258                 # meets our criteria
 259                 $currentLoads = $nonErrorLoads;
 260                 while ( count( $currentLoads ) ) {
 261                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 262                                 $i = ArrayUtils::pickRandom( $currentLoads );
 263                         } else {
 264                                 $i = false;
 265                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 266                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 267                                         # This triggers doWait() after connect, so it's especially good to
 268                                         # avoid lagged servers so as to avoid just blocking in that method.
 269                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 270                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 271                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 272                                 }
 273                                 if ( $i === false ) {
 274                                         # Any server with less lag than it's 'max lag' param is preferable
 275                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 276                                 }
 277                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 278                                         # All slaves lagged. Switch to read-only mode
 279                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 280                                         $wgReadOnly = 'The database has been automatically locked ' .
 281                                                 'while the slave database servers catch up to the master';
 282                                         $i = ArrayUtils::pickRandom( $currentLoads );
 283                                         $laggedSlaveMode = true;
 284                                 }
 285                         }
 286
 287                         if ( $i === false ) {
 288                                 # pickRandom() returned false
 289                                 # This is permanent and means the configuration or the load monitor
 290                                 # wants us to return false.
 291                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 292
 293                                 return false;
 294                         }
 295
 296                         wfDebugLog( 'connect', __METHOD__ .
 297                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 298
 299                         $conn = $this->openConnection( $i, $wiki );
 300                         if ( !$conn ) {
 301                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 302                                 unset( $nonErrorLoads[$i] );
 303                                 unset( $currentLoads[$i] );
 304                                 $i = false;
 305                                 continue;
 306                         }
 307
 308                         // Decrement reference counter, we are finished with this connection.
 309                         // It will be incremented for the caller later.
 310                         if ( $wiki !== false ) {
 311                                 $this->reuseConnection( $conn );
 312                         }
 313
 314                         # Return this server
 315                         break;
 316                 }
 317
 318                 # If all servers were down, quit now
 319                 if ( !count( $nonErrorLoads ) ) {
 320                         wfDebugLog( 'connect', "All servers down" );
 321                 }
 322
 323                 if ( $i !== false ) {
 324                         # Slave connection successful
 325                         # Wait for the session master pos for a short time
 326                         if ( $this->mWaitForPos && $i > 0 ) {
 327                                 if ( !$this->doWait( $i ) ) {
 328                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 329                                 }
 330                         }
 331                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 332                                 $this->mReadIndex = $i;
 333                         }
 334                         $serverName = $this->getServerName( $i );
 335                         wfDebug( __METHOD__ . ": using server $serverName for group '$group'\n" );
 336                 }
 337
 338                 return $i;
 339         }
 340
 341         /**
 342          * Set the master wait position
 343          * If a DB_SLAVE connection has been opened already, waits
 344          * Otherwise sets a variable telling it to wait if such a connection is opened
 345          * @param DBMasterPos $pos
 346          */
 347         public function waitFor( $pos ) {
 348                 $this->mWaitForPos = $pos;
 349                 $i = $this->mReadIndex;
 350
 351                 if ( $i > 0 ) {
 352                         if ( !$this->doWait( $i ) ) {
 353                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 354                                 $this->mLaggedSlaveMode = true;
 355                         }
 356                 }
 357         }
 358
 359         /**
 360          * Set the master wait position and wait for ALL slaves to catch up to it
 361          * @param DBMasterPos $pos
 362          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 363          * @return bool Success (able to connect and no timeouts reached)
 364          */
 365         public function waitForAll( $pos, $timeout = null ) {
 366                 $this->mWaitForPos = $pos;
 367                 $serverCount = count( $this->mServers );
 368
 369                 $ok = true;
 370                 for ( $i = 1; $i < $serverCount; $i++ ) {
 371                         if ( $this->mLoads[$i] > 0 ) {
 372                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 373                         }
 374                 }
 375
 376                 return $ok;
 377         }
 378
 379         /**
 380          * Get any open connection to a given server index, local or foreign
 381          * Returns false if there is no connection open
 382          *
 383          * @param int $i
 384          * @return DatabaseBase|bool False on failure
 385          */
 386         public function getAnyOpenConnection( $i ) {
 387                 foreach ( $this->mConns as $conns ) {
 388                         if ( !empty( $conns[$i] ) ) {
 389                                 return reset( $conns[$i] );
 390                         }
 391                 }
 392
 393                 return false;
 394         }
 395
 396         /**
 397          * Wait for a given slave to catch up to the master pos stored in $this
 398          * @param int $index Server index
 399          * @param bool $open Check the server even if a new connection has to be made
 400          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 401          * @return bool
 402          */
 403         protected function doWait( $index, $open = false, $timeout = null ) {
 404                 $close = false; // close the connection afterwards
 405
 406                 # Find a connection to wait on, creating one if needed and allowed
 407                 $conn = $this->getAnyOpenConnection( $index );
 408                 if ( !$conn ) {
 409                         if ( !$open ) {
 410                                 wfDebug( __METHOD__ . ": no connection open\n" );
 411
 412                                 return false;
 413                         } else {
 414                                 $conn = $this->openConnection( $index, '' );
 415                                 if ( !$conn ) {
 416                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 417
 418                                         return false;
 419                                 }
 420                                 // Avoid connection spam in waitForAll() when connections
 421                                 // are made just for the sake of doing this lag check.
 422                                 $close = true;
 423                         }
 424                 }
 425
 426                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 427                 $timeout = $timeout ?: $this->mWaitTimeout;
 428                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 429
 430                 if ( $result == -1 || is_null( $result ) ) {
 431                         # Timed out waiting for slave, use master instead
 432                         $server = $this->mServers[$index]['host'];
 433                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 434                         wfDebug( "$msg\n" );
 435                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 436                         $ok = false;
 437                 } else {
 438                         wfDebug( __METHOD__ . ": Done\n" );
 439                         $ok = true;
 440                 }
 441
 442                 if ( $close ) {
 443                         $this->closeConnection( $conn );
 444                 }
 445
 446                 return $ok;
 447         }
 448
 449         /**
 450          * Get a connection by index
 451          * This is the main entry point for this class.
 452          *
 453          * @param int $i Server index
 454          * @param array|string|bool $groups Query group(s), or false for the generic reader
 455          * @param string|bool $wiki Wiki ID, or false for the current wiki
 456          *
 457          * @throws MWException
 458          * @return DatabaseBase
 459          */
 460         public function getConnection( $i, $groups = array(), $wiki = false ) {
 461                 if ( $i === null || $i === false ) {
 462                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 463                                 ' with invalid server index' );
 464                 }
 465
 466                 if ( $wiki === wfWikiID() ) {
 467                         $wiki = false;
 468                 }
 469
 470                 $groups = ( $groups === false || $groups === array() )
 471                         ? array( false ) // check one "group": the generic pool
 472                         : (array)$groups;
 473
 474                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 475                 $oldConnsOpened = $this->connsOpened; // connections open now
 476
 477                 if ( $i == DB_MASTER ) {
 478                         $i = $this->getWriterIndex();
 479                 } else {
 480                         # Try to find an available server in any the query groups (in order)
 481                         foreach ( $groups as $group ) {
 482                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 483                                 if ( $groupIndex !== false ) {
 484                                         $i = $groupIndex;
 485                                         break;
 486                                 }
 487                         }
 488                 }
 489
 490                 # Operation-based index
 491                 if ( $i == DB_SLAVE ) {
 492                         $this->mLastError = 'Unknown error'; // reset error string
 493                         # Try the general server pool if $groups are unavailable.
 494                         $i = in_array( false, $groups, true )
 495                                 ? false // don't bother with this if that is what was tried above
 496                                 : $this->getReaderIndex( false, $wiki );
 497                         # Couldn't find a working server in getReaderIndex()?
 498                         if ( $i === false ) {
 499                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 500
 501                                 return $this->reportConnectionError();
 502                         }
 503                 }
 504
 505                 # Now we have an explicit index into the servers array
 506                 $conn = $this->openConnection( $i, $wiki );
 507                 if ( !$conn ) {
 508
 509                         return $this->reportConnectionError();
 510                 }
 511
 512                 # Profile any new connections that happen
 513                 if ( $this->connsOpened > $oldConnsOpened ) {
 514                         $host = $conn->getServer();
 515                         $dbname = $conn->getDBname();
 516                         $trxProf = Profiler::instance()->getTransactionProfiler();
 517                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 518                 }
 519
 520                 return $conn;
 521         }
 522
 523         /**
 524          * Mark a foreign connection as being available for reuse under a different
 525          * DB name or prefix. This mechanism is reference-counted, and must be called
 526          * the same number of times as getConnection() to work.
 527          *
 528          * @param DatabaseBase $conn
 529          * @throws MWException
 530          */
 531         public function reuseConnection( $conn ) {
 532                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 533                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 534                 if ( $serverIndex === null || $refCount === null ) {
 535                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 536
 537                         /**
 538                          * This can happen in code like:
 539                          *   foreach ( $dbs as $db ) {
 540                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 541                          *     ...
 542                          *     $lb->reuseConnection( $conn );
 543                          *   }
 544                          * When a connection to the local DB is opened in this way, reuseConnection()
 545                          * should be ignored
 546                          */
 547
 548                         return;
 549                 }
 550
 551                 $dbName = $conn->getDBname();
 552                 $prefix = $conn->tablePrefix();
 553                 if ( strval( $prefix ) !== '' ) {
 554                         $wiki = "$dbName-$prefix";
 555                 } else {
 556                         $wiki = $dbName;
 557                 }
 558                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 559                         throw new MWException( __METHOD__ . ": connection not found, has " .
 560                                 "the connection been freed already?" );
 561                 }
 562                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 563                 if ( $refCount <= 0 ) {
 564                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 565                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 566                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 567                 } else {
 568                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 569                 }
 570         }
 571
 572         /**
 573          * Get a database connection handle reference
 574          *
 575          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 576          *
 577          * @see LoadBalancer::getConnection() for parameter information
 578          *
 579          * @param int $db
 580          * @param array|string|bool $groups Query group(s), or false for the generic reader
 581          * @param string|bool $wiki Wiki ID, or false for the current wiki
 582          * @return DBConnRef
 583          */
 584         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 585                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 586         }
 587
 588         /**
 589          * Get a database connection handle reference without connecting yet
 590          *
 591          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 592          *
 593          * @see LoadBalancer::getConnection() for parameter information
 594          *
 595          * @param int $db
 596          * @param array|string|bool $groups Query group(s), or false for the generic reader
 597          * @param string|bool $wiki Wiki ID, or false for the current wiki
 598          * @return DBConnRef
 599          */
 600         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 601                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 602         }
 603
 604         /**
 605          * Open a connection to the server given by the specified index
 606          * Index must be an actual index into the array.
 607          * If the server is already open, returns it.
 608          *
 609          * On error, returns false, and the connection which caused the
 610          * error will be available via $this->mErrorConnection.
 611          *
 612          * @param int $i Server index
 613          * @param string|bool $wiki Wiki ID, or false for the current wiki
 614          * @return DatabaseBase
 615          *
 616          * @access private
 617          */
 618         public function openConnection( $i, $wiki = false ) {
 619                 if ( $wiki !== false ) {
 620                         $conn = $this->openForeignConnection( $i, $wiki );
 621
 622                         return $conn;
 623                 }
 624                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 625                         $conn = $this->mConns['local'][$i][0];
 626                 } else {
 627                         $server = $this->mServers[$i];
 628                         $server['serverIndex'] = $i;
 629                         $conn = $this->reallyOpenConnection( $server, false );
 630                         if ( $conn->isOpen() ) {
 631                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 632                                 $this->mConns['local'][$i][0] = $conn;
 633                         } else {
 634                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 635                                 $this->mErrorConnection = $conn;
 636                                 $conn = false;
 637                         }
 638                 }
 639
 640                 return $conn;
 641         }
 642
 643         /**
 644          * Open a connection to a foreign DB, or return one if it is already open.
 645          *
 646          * Increments a reference count on the returned connection which locks the
 647          * connection to the requested wiki. This reference count can be
 648          * decremented by calling reuseConnection().
 649          *
 650          * If a connection is open to the appropriate server already, but with the wrong
 651          * database, it will be switched to the right database and returned, as long as
 652          * it has been freed first with reuseConnection().
 653          *
 654          * On error, returns false, and the connection which caused the
 655          * error will be available via $this->mErrorConnection.
 656          *
 657          * @param int $i Server index
 658          * @param string $wiki Wiki ID to open
 659          * @return DatabaseBase
 660          */
 661         private function openForeignConnection( $i, $wiki ) {
 662                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 663                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 664                         // Reuse an already-used connection
 665                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 666                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 667                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 668                         // Reuse a free connection for the same wiki
 669                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 670                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 671                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 672                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 673                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 674                         // Reuse a connection from another wiki
 675                         $conn = reset( $this->mConns['foreignFree'][$i] );
 676                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 677
 678                         // The empty string as a DB name means "don't care".
 679                         // DatabaseMysqlBase::open() already handle this on connection.
 680                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 681                                 $this->mLastError = "Error selecting database $dbName on server " .
 682                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 683                                 $this->mErrorConnection = $conn;
 684                                 $conn = false;
 685                         } else {
 686                                 $conn->tablePrefix( $prefix );
 687                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 688                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 689                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 690                         }
 691                 } else {
 692                         // Open a new connection
 693                         $server = $this->mServers[$i];
 694                         $server['serverIndex'] = $i;
 695                         $server['foreignPoolRefCount'] = 0;
 696                         $server['foreign'] = true;
 697                         $conn = $this->reallyOpenConnection( $server, $dbName );
 698                         if ( !$conn->isOpen() ) {
 699                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 700                                 $this->mErrorConnection = $conn;
 701                                 $conn = false;
 702                         } else {
 703                                 $conn->tablePrefix( $prefix );
 704                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 705                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 706                         }
 707                 }
 708
 709                 // Increment reference count
 710                 if ( $conn ) {
 711                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 712                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 713                 }
 714
 715                 return $conn;
 716         }
 717
 718         /**
 719          * Test if the specified index represents an open connection
 720          *
 721          * @param int $index Server index
 722          * @access private
 723          * @return bool
 724          */
 725         private function isOpen( $index ) {
 726                 if ( !is_integer( $index ) ) {
 727                         return false;
 728                 }
 729
 730                 return (bool)$this->getAnyOpenConnection( $index );
 731         }
 732
 733         /**
 734          * Really opens a connection. Uncached.
 735          * Returns a Database object whether or not the connection was successful.
 736          * @access private
 737          *
 738          * @param array $server
 739          * @param bool $dbNameOverride
 740          * @throws MWException
 741          * @return DatabaseBase
 742          */
 743         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 744                 if ( !is_array( $server ) ) {
 745                         throw new MWException( 'You must update your load-balancing configuration. ' .
 746                                 'See DefaultSettings.php entry for $wgDBservers.' );
 747                 }
 748
 749                 if ( $dbNameOverride !== false ) {
 750                         $server['dbname'] = $dbNameOverride;
 751                 }
 752
 753                 // Log when many connection are made on requests
 754                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 755                         $masterAddr = $this->getServerName( 0 );
 756                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 757                                 "{$this->connsOpened}+ connections made (master=$masterAddr)\n" .
 758                                 wfBacktrace( true ) );
 759                 }
 760
 761                 # Create object
 762                 try {
 763                         $db = DatabaseBase::factory( $server['type'], $server );
 764                 } catch ( DBConnectionError $e ) {
 765                         // FIXME: This is probably the ugliest thing I have ever done to
 766                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 767                         $db = $e->db;
 768                 }
 769
 770                 $db->setLBInfo( $server );
 771                 if ( isset( $server['fakeSlaveLag'] ) ) {
 772                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 773                 }
 774                 if ( isset( $server['fakeMaster'] ) ) {
 775                         $db->setFakeMaster( true );
 776                 }
 777
 778                 return $db;
 779         }
 780
 781         /**
 782          * @throws DBConnectionError
 783          * @return bool
 784          */
 785         private function reportConnectionError() {
 786                 $conn = $this->mErrorConnection; // The connection which caused the error
 787                 $context = array(
 788                         'method' => __METHOD__,
 789                         'last_error' => $this->mLastError,
 790                 );
 791
 792                 if ( !is_object( $conn ) ) {
 793                         // No last connection, probably due to all servers being too busy
 794                         wfLogDBError(
 795                                 "LB failure with no last connection. Connection error: {last_error}",
 796                                 $context
 797                         );
 798
 799                         // If all servers were busy, mLastError will contain something sensible
 800                         throw new DBConnectionError( null, $this->mLastError );
 801                 } else {
 802                         $context['db_server'] = $conn->getProperty( 'mServer' );
 803                         wfLogDBError(
 804                                 "Connection error: {last_error} ({db_server})",
 805                                 $context
 806                         );
 807                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
 808                 }
 809
 810                 return false; /* not reached */
 811         }
 812
 813         /**
 814          * @return int
 815          */
 816         private function getWriterIndex() {
 817                 return 0;
 818         }
 819
 820         /**
 821          * Returns true if the specified index is a valid server index
 822          *
 823          * @param string $i
 824          * @return bool
 825          */
 826         public function haveIndex( $i ) {
 827                 return array_key_exists( $i, $this->mServers );
 828         }
 829
 830         /**
 831          * Returns true if the specified index is valid and has non-zero load
 832          *
 833          * @param string $i
 834          * @return bool
 835          */
 836         public function isNonZeroLoad( $i ) {
 837                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 838         }
 839
 840         /**
 841          * Get the number of defined servers (not the number of open connections)
 842          *
 843          * @return int
 844          */
 845         public function getServerCount() {
 846                 return count( $this->mServers );
 847         }
 848
 849         /**
 850          * Get the host name or IP address of the server with the specified index
 851          * Prefer a readable name if available.
 852          * @param string $i
 853          * @return string
 854          */
 855         public function getServerName( $i ) {
 856                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 857                         return $this->mServers[$i]['hostName'];
 858                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 859                         return $this->mServers[$i]['host'];
 860                 } else {
 861                         return '';
 862                 }
 863         }
 864
 865         /**
 866          * Return the server info structure for a given index, or false if the index is invalid.
 867          * @param int $i
 868          * @return array|bool
 869          */
 870         public function getServerInfo( $i ) {
 871                 if ( isset( $this->mServers[$i] ) ) {
 872                         return $this->mServers[$i];
 873                 } else {
 874                         return false;
 875                 }
 876         }
 877
 878         /**
 879          * Sets the server info structure for the given index. Entry at index $i
 880          * is created if it doesn't exist
 881          * @param int $i
 882          * @param array $serverInfo
 883          */
 884         public function setServerInfo( $i, array $serverInfo ) {
 885                 $this->mServers[$i] = $serverInfo;
 886         }
 887
 888         /**
 889          * Get the current master position for chronology control purposes
 890          * @return mixed
 891          */
 892         public function getMasterPos() {
 893                 # If this entire request was served from a slave without opening a connection to the
 894                 # master (however unlikely that may be), then we can fetch the position from the slave.
 895                 $masterConn = $this->getAnyOpenConnection( 0 );
 896                 if ( !$masterConn ) {
 897                         $serverCount = count( $this->mServers );
 898                         for ( $i = 1; $i < $serverCount; $i++ ) {
 899                                 $conn = $this->getAnyOpenConnection( $i );
 900                                 if ( $conn ) {
 901                                         wfDebug( "Master pos fetched from slave\n" );
 902
 903                                         return $conn->getSlavePos();
 904                                 }
 905                         }
 906                 } else {
 907                         wfDebug( "Master pos fetched from master\n" );
 908
 909                         return $masterConn->getMasterPos();
 910                 }
 911
 912                 return false;
 913         }
 914
 915         /**
 916          * Close all open connections
 917          */
 918         public function closeAll() {
 919                 foreach ( $this->mConns as $conns2 ) {
 920                         foreach ( $conns2 as $conns3 ) {
 921                                 /** @var DatabaseBase $conn */
 922                                 foreach ( $conns3 as $conn ) {
 923                                         $conn->close();
 924                                 }
 925                         }
 926                 }
 927                 $this->mConns = array(
 928                         'local' => array(),
 929                         'foreignFree' => array(),
 930                         'foreignUsed' => array(),
 931                 );
 932                 $this->connsOpened = 0;
 933         }
 934
 935         /**
 936          * Close a connection
 937          * Using this function makes sure the LoadBalancer knows the connection is closed.
 938          * If you use $conn->close() directly, the load balancer won't update its state.
 939          * @param DatabaseBase $conn
 940          */
 941         public function closeConnection( $conn ) {
 942                 $done = false;
 943                 foreach ( $this->mConns as $i1 => $conns2 ) {
 944                         foreach ( $conns2 as $i2 => $conns3 ) {
 945                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 946                                         if ( $conn === $candidateConn ) {
 947                                                 $conn->close();
 948                                                 unset( $this->mConns[$i1][$i2][$i3] );
 949                                                 --$this->connsOpened;
 950                                                 $done = true;
 951                                                 break;
 952                                         }
 953                                 }
 954                         }
 955                 }
 956                 if ( !$done ) {
 957                         $conn->close();
 958                 }
 959         }
 960
 961         /**
 962          * Commit transactions on all open connections
 963          */
 964         public function commitAll() {
 965                 foreach ( $this->mConns as $conns2 ) {
 966                         foreach ( $conns2 as $conns3 ) {
 967                                 /** @var DatabaseBase[] $conns3 */
 968                                 foreach ( $conns3 as $conn ) {
 969                                         if ( $conn->trxLevel() ) {
 970                                                 $conn->commit( __METHOD__, 'flush' );
 971                                         }
 972                                 }
 973                         }
 974                 }
 975         }
 976
 977         /**
 978          *  Issue COMMIT only on master, only if queries were done on connection
 979          */
 980         public function commitMasterChanges() {
 981                 // Always 0, but who knows.. :)
 982                 $masterIndex = $this->getWriterIndex();
 983                 foreach ( $this->mConns as $conns2 ) {
 984                         if ( empty( $conns2[$masterIndex] ) ) {
 985                                 continue;
 986                         }
 987                         /** @var DatabaseBase $conn */
 988                         foreach ( $conns2[$masterIndex] as $conn ) {
 989                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 990                                         $conn->commit( __METHOD__, 'flush' );
 991                                 }
 992                         }
 993                 }
 994         }
 995
 996         /**
 997          * Issue ROLLBACK only on master, only if queries were done on connection
 998          * @since 1.23
 999          */
1000         public function rollbackMasterChanges() {
1001                 // Always 0, but who knows.. :)
1002                 $masterIndex = $this->getWriterIndex();
1003                 foreach ( $this->mConns as $conns2 ) {
1004                         if ( empty( $conns2[$masterIndex] ) ) {
1005                                 continue;
1006                         }
1007                         /** @var DatabaseBase $conn */
1008                         foreach ( $conns2[$masterIndex] as $conn ) {
1009                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1010                                         $conn->rollback( __METHOD__, 'flush' );
1011                                 }
1012                         }
1013                 }
1014         }
1015
1016         /**
1017          * @return bool Whether a master connection is already open
1018          * @since 1.24
1019          */
1020         public function hasMasterConnection() {
1021                 return $this->isOpen( $this->getWriterIndex() );
1022         }
1023
1024         /**
1025          * Determine if there are pending changes in a transaction by this thread
1026          * @since 1.23
1027          * @return bool
1028          */
1029         public function hasMasterChanges() {
1030                 // Always 0, but who knows.. :)
1031                 $masterIndex = $this->getWriterIndex();
1032                 foreach ( $this->mConns as $conns2 ) {
1033                         if ( empty( $conns2[$masterIndex] ) ) {
1034                                 continue;
1035                         }
1036                         /** @var DatabaseBase $conn */
1037                         foreach ( $conns2[$masterIndex] as $conn ) {
1038                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1039                                         return true;
1040                                 }
1041                         }
1042                 }
1043                 return false;
1044         }
1045
1046         /**
1047          * Get the timestamp of the latest write query done by this thread
1048          * @since 1.25
1049          * @return float|bool UNIX timestamp or false
1050          */
1051         public function lastMasterChangeTimestamp() {
1052                 $lastTime = false;
1053                 // Always 0, but who knows.. :)
1054                 $masterIndex = $this->getWriterIndex();
1055                 foreach ( $this->mConns as $conns2 ) {
1056                         if ( empty( $conns2[$masterIndex] ) ) {
1057                                 continue;
1058                         }
1059                         /** @var DatabaseBase $conn */
1060                         foreach ( $conns2[$masterIndex] as $conn ) {
1061                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1062                         }
1063                 }
1064                 return $lastTime;
1065         }
1066
1067         /**
1068          * Check if this load balancer object had any recent or still
1069          * pending writes issued against it by this PHP thread
1070          *
1071          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1072          * @return bool
1073          * @since 1.25
1074          */
1075         public function hasOrMadeRecentMasterChanges( $age = null ) {
1076                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1077
1078                 return ( $this->hasMasterChanges()
1079                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1080         }
1081
1082         /**
1083          * @param mixed $value
1084          * @return mixed
1085          */
1086         public function waitTimeout( $value = null ) {
1087                 return wfSetVar( $this->mWaitTimeout, $value );
1088         }
1089
1090         /**
1091          * @return bool
1092          */
1093         public function getLaggedSlaveMode() {
1094                 return $this->mLaggedSlaveMode;
1095         }
1096
1097         /**
1098          * Disables/enables lag checks
1099          * @param null|bool $mode
1100          * @return bool
1101          */
1102         public function allowLagged( $mode = null ) {
1103                 if ( $mode === null ) {
1104                         return $this->mAllowLagged;
1105                 }
1106                 $this->mAllowLagged = $mode;
1107
1108                 return $this->mAllowLagged;
1109         }
1110
1111         /**
1112          * @return bool
1113          */
1114         public function pingAll() {
1115                 $success = true;
1116                 foreach ( $this->mConns as $conns2 ) {
1117                         foreach ( $conns2 as $conns3 ) {
1118                                 /** @var DatabaseBase[] $conns3 */
1119                                 foreach ( $conns3 as $conn ) {
1120                                         if ( !$conn->ping() ) {
1121                                                 $success = false;
1122                                         }
1123                                 }
1124                         }
1125                 }
1126
1127                 return $success;
1128         }
1129
1130         /**
1131          * Call a function with each open connection object
1132          * @param callable $callback
1133          * @param array $params
1134          */
1135         public function forEachOpenConnection( $callback, array $params = array() ) {
1136                 foreach ( $this->mConns as $conns2 ) {
1137                         foreach ( $conns2 as $conns3 ) {
1138                                 foreach ( $conns3 as $conn ) {
1139                                         $mergedParams = array_merge( array( $conn ), $params );
1140                                         call_user_func_array( $callback, $mergedParams );
1141                                 }
1142                         }
1143                 }
1144         }
1145
1146         /**
1147          * Get the hostname and lag time of the most-lagged slave
1148          *
1149          * This is useful for maintenance scripts that need to throttle their updates.
1150          * May attempt to open connections to slaves on the default DB. If there is
1151          * no lag, the maximum lag will be reported as -1.
1152          *
1153          * @param bool|string $wiki Wiki ID, or false for the default database
1154          * @return array ( host, max lag, index of max lagged host )
1155          */
1156         public function getMaxLag( $wiki = false ) {
1157                 $maxLag = -1;
1158                 $host = '';
1159                 $maxIndex = 0;
1160
1161                 if ( $this->getServerCount() <= 1 ) {
1162                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1163                 }
1164
1165                 $lagTimes = $this->getLagTimes( $wiki );
1166                 foreach ( $lagTimes as $i => $lag ) {
1167                         if ( $lag > $maxLag ) {
1168                                 $maxLag = $lag;
1169                                 $host = $this->mServers[$i]['host'];
1170                                 $maxIndex = $i;
1171                         }
1172                 }
1173
1174                 return array( $host, $maxLag, $maxIndex );
1175         }
1176
1177         /**
1178          * Get lag time for each server
1179          *
1180          * Results are cached for a short time in memcached/process cache
1181          *
1182          * @param string|bool $wiki
1183          * @return int[] Map of (server index => seconds)
1184          */
1185         public function getLagTimes( $wiki = false ) {
1186                 if ( $this->getServerCount() <= 1 ) {
1187                         return array( 0 => 0 ); // no replication = no lag
1188                 }
1189
1190                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1191                         return $this->mProcCache->get( 'slave_lag', 'times' );
1192                 }
1193
1194                 # Send the request to the load monitor
1195                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1196
1197                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1198
1199                 return $times;
1200         }
1201
1202         /**
1203          * Get the lag in seconds for a given connection, or zero if this load
1204          * balancer does not have replication enabled.
1205          *
1206          * This should be used in preference to Database::getLag() in cases where
1207          * replication may not be in use, since there is no way to determine if
1208          * replication is in use at the connection level without running
1209          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1210          * function instead of Database::getLag() avoids a fatal error in this
1211          * case on many installations.
1212          *
1213          * @param DatabaseBase $conn
1214          * @return int
1215          */
1216         public function safeGetLag( $conn ) {
1217                 if ( $this->getServerCount() == 1 ) {
1218                         return 0;
1219                 } else {
1220                         return $conn->getLag();
1221                 }
1222         }
1223
1224         /**
1225          * Clear the cache for slag lag delay times
1226          */
1227         public function clearLagTimeCache() {
1228                 $this->mProcCache->clear( 'slave_lag' );
1229         }
1230 }
1231
1232 /**
1233  * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1234  * as well handling deferring the actual network connection until the handle is used
1235  *
1236  * @ingroup Database
1237  * @since 1.22
1238  */
1239 class DBConnRef implements IDatabase {
1240         /** @var LoadBalancer */
1241         private $lb;
1242
1243         /** @var DatabaseBase|null */
1244         private $conn;
1245
1246         /** @var array|null */
1247         private $params;
1248
1249         /**
1250          * @param LoadBalancer $lb
1251          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1252          */
1253         public function __construct( LoadBalancer $lb, $conn ) {
1254                 $this->lb = $lb;
1255                 if ( $conn instanceof DatabaseBase ) {
1256                         $this->conn = $conn;
1257                 } else {
1258                         $this->params = $conn;
1259                 }
1260         }
1261
1262         public function __call( $name, $arguments ) {
1263                 if ( $this->conn === null ) {
1264                         list( $db, $groups, $wiki ) = $this->params;
1265                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1266                 }
1267
1268                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1269         }
1270
1271         public function __destruct() {
1272                 if ( $this->conn !== null ) {
1273                         $this->lb->reuseConnection( $this->conn );
1274                 }
1275         }
1276 }