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 $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 ( $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                                         $i = ArrayUtils::pickRandom( $currentLoads );
 281                                         $laggedSlaveMode = true;
 282                                 }
 283                         }
 284
 285                         if ( $i === false ) {
 286                                 # pickRandom() returned false
 287                                 # This is permanent and means the configuration or the load monitor
 288                                 # wants us to return false.
 289                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 290
 291                                 return false;
 292                         }
 293
 294                         wfDebugLog( 'connect', __METHOD__ .
 295                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 296
 297                         $conn = $this->openConnection( $i, $wiki );
 298                         if ( !$conn ) {
 299                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 300                                 unset( $nonErrorLoads[$i] );
 301                                 unset( $currentLoads[$i] );
 302                                 $i = false;
 303                                 continue;
 304                         }
 305
 306                         // Decrement reference counter, we are finished with this connection.
 307                         // It will be incremented for the caller later.
 308                         if ( $wiki !== false ) {
 309                                 $this->reuseConnection( $conn );
 310                         }
 311
 312                         # Return this server
 313                         break;
 314                 }
 315
 316                 # If all servers were down, quit now
 317                 if ( !count( $nonErrorLoads ) ) {
 318                         wfDebugLog( 'connect', "All servers down" );
 319                 }
 320
 321                 if ( $i !== false ) {
 322                         # Slave connection successful
 323                         # Wait for the session master pos for a short time
 324                         if ( $this->mWaitForPos && $i > 0 ) {
 325                                 if ( !$this->doWait( $i ) ) {
 326                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 327                                 }
 328                         }
 329                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 330                                 $this->mReadIndex = $i;
 331                                 # Record if the generic reader index is in "lagged slave" mode
 332                                 if ( $laggedSlaveMode ) {
 333                                         $this->mLaggedSlaveMode = true;
 334                                 }
 335                         }
 336                         $serverName = $this->getServerName( $i );
 337                         wfDebug( __METHOD__ . ": using server $serverName for group '$group'\n" );
 338                 }
 339
 340                 return $i;
 341         }
 342
 343         /**
 344          * Set the master wait position
 345          * If a DB_SLAVE connection has been opened already, waits
 346          * Otherwise sets a variable telling it to wait if such a connection is opened
 347          * @param DBMasterPos $pos
 348          */
 349         public function waitFor( $pos ) {
 350                 $this->mWaitForPos = $pos;
 351                 $i = $this->mReadIndex;
 352
 353                 if ( $i > 0 ) {
 354                         if ( !$this->doWait( $i ) ) {
 355                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 356                                 $this->mLaggedSlaveMode = true;
 357                         }
 358                 }
 359         }
 360
 361         /**
 362          * Set the master wait position and wait for ALL slaves to catch up to it
 363          * @param DBMasterPos $pos
 364          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 365          * @return bool Success (able to connect and no timeouts reached)
 366          */
 367         public function waitForAll( $pos, $timeout = null ) {
 368                 $this->mWaitForPos = $pos;
 369                 $serverCount = count( $this->mServers );
 370
 371                 $ok = true;
 372                 for ( $i = 1; $i < $serverCount; $i++ ) {
 373                         if ( $this->mLoads[$i] > 0 ) {
 374                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 375                         }
 376                 }
 377
 378                 return $ok;
 379         }
 380
 381         /**
 382          * Get any open connection to a given server index, local or foreign
 383          * Returns false if there is no connection open
 384          *
 385          * @param int $i
 386          * @return DatabaseBase|bool False on failure
 387          */
 388         public function getAnyOpenConnection( $i ) {
 389                 foreach ( $this->mConns as $conns ) {
 390                         if ( !empty( $conns[$i] ) ) {
 391                                 return reset( $conns[$i] );
 392                         }
 393                 }
 394
 395                 return false;
 396         }
 397
 398         /**
 399          * Wait for a given slave to catch up to the master pos stored in $this
 400          * @param int $index Server index
 401          * @param bool $open Check the server even if a new connection has to be made
 402          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 403          * @return bool
 404          */
 405         protected function doWait( $index, $open = false, $timeout = null ) {
 406                 $close = false; // close the connection afterwards
 407
 408                 # Find a connection to wait on, creating one if needed and allowed
 409                 $conn = $this->getAnyOpenConnection( $index );
 410                 if ( !$conn ) {
 411                         if ( !$open ) {
 412                                 wfDebug( __METHOD__ . ": no connection open\n" );
 413
 414                                 return false;
 415                         } else {
 416                                 $conn = $this->openConnection( $index, '' );
 417                                 if ( !$conn ) {
 418                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 419
 420                                         return false;
 421                                 }
 422                                 // Avoid connection spam in waitForAll() when connections
 423                                 // are made just for the sake of doing this lag check.
 424                                 $close = true;
 425                         }
 426                 }
 427
 428                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 429                 $timeout = $timeout ?: $this->mWaitTimeout;
 430                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 431
 432                 if ( $result == -1 || is_null( $result ) ) {
 433                         # Timed out waiting for slave, use master instead
 434                         $server = $this->mServers[$index]['host'];
 435                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 436                         wfDebug( "$msg\n" );
 437                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 438                         $ok = false;
 439                 } else {
 440                         wfDebug( __METHOD__ . ": Done\n" );
 441                         $ok = true;
 442                 }
 443
 444                 if ( $close ) {
 445                         $this->closeConnection( $conn );
 446                 }
 447
 448                 return $ok;
 449         }
 450
 451         /**
 452          * Get a connection by index
 453          * This is the main entry point for this class.
 454          *
 455          * @param int $i Server index
 456          * @param array|string|bool $groups Query group(s), or false for the generic reader
 457          * @param string|bool $wiki Wiki ID, or false for the current wiki
 458          *
 459          * @throws MWException
 460          * @return DatabaseBase
 461          */
 462         public function getConnection( $i, $groups = array(), $wiki = false ) {
 463                 if ( $i === null || $i === false ) {
 464                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 465                                 ' with invalid server index' );
 466                 }
 467
 468                 if ( $wiki === wfWikiID() ) {
 469                         $wiki = false;
 470                 }
 471
 472                 $groups = ( $groups === false || $groups === array() )
 473                         ? array( false ) // check one "group": the generic pool
 474                         : (array)$groups;
 475
 476                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 477                 $oldConnsOpened = $this->connsOpened; // connections open now
 478
 479                 if ( $i == DB_MASTER ) {
 480                         $i = $this->getWriterIndex();
 481                 } else {
 482                         # Try to find an available server in any the query groups (in order)
 483                         foreach ( $groups as $group ) {
 484                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 485                                 if ( $groupIndex !== false ) {
 486                                         $i = $groupIndex;
 487                                         break;
 488                                 }
 489                         }
 490                 }
 491
 492                 # Operation-based index
 493                 if ( $i == DB_SLAVE ) {
 494                         $this->mLastError = 'Unknown error'; // reset error string
 495                         # Try the general server pool if $groups are unavailable.
 496                         $i = in_array( false, $groups, true )
 497                                 ? false // don't bother with this if that is what was tried above
 498                                 : $this->getReaderIndex( false, $wiki );
 499                         # Couldn't find a working server in getReaderIndex()?
 500                         if ( $i === false ) {
 501                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 502
 503                                 return $this->reportConnectionError();
 504                         }
 505                 }
 506
 507                 # Now we have an explicit index into the servers array
 508                 $conn = $this->openConnection( $i, $wiki );
 509                 if ( !$conn ) {
 510
 511                         return $this->reportConnectionError();
 512                 }
 513
 514                 # Profile any new connections that happen
 515                 if ( $this->connsOpened > $oldConnsOpened ) {
 516                         $host = $conn->getServer();
 517                         $dbname = $conn->getDBname();
 518                         $trxProf = Profiler::instance()->getTransactionProfiler();
 519                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 520                 }
 521
 522                 return $conn;
 523         }
 524
 525         /**
 526          * Mark a foreign connection as being available for reuse under a different
 527          * DB name or prefix. This mechanism is reference-counted, and must be called
 528          * the same number of times as getConnection() to work.
 529          *
 530          * @param DatabaseBase $conn
 531          * @throws MWException
 532          */
 533         public function reuseConnection( $conn ) {
 534                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 535                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 536                 if ( $serverIndex === null || $refCount === null ) {
 537                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 538
 539                         /**
 540                          * This can happen in code like:
 541                          *   foreach ( $dbs as $db ) {
 542                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 543                          *     ...
 544                          *     $lb->reuseConnection( $conn );
 545                          *   }
 546                          * When a connection to the local DB is opened in this way, reuseConnection()
 547                          * should be ignored
 548                          */
 549
 550                         return;
 551                 }
 552
 553                 $dbName = $conn->getDBname();
 554                 $prefix = $conn->tablePrefix();
 555                 if ( strval( $prefix ) !== '' ) {
 556                         $wiki = "$dbName-$prefix";
 557                 } else {
 558                         $wiki = $dbName;
 559                 }
 560                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 561                         throw new MWException( __METHOD__ . ": connection not found, has " .
 562                                 "the connection been freed already?" );
 563                 }
 564                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 565                 if ( $refCount <= 0 ) {
 566                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 567                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 568                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 569                 } else {
 570                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 571                 }
 572         }
 573
 574         /**
 575          * Get a database connection handle reference
 576          *
 577          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 578          *
 579          * @see LoadBalancer::getConnection() for parameter information
 580          *
 581          * @param int $db
 582          * @param array|string|bool $groups Query group(s), or false for the generic reader
 583          * @param string|bool $wiki Wiki ID, or false for the current wiki
 584          * @return DBConnRef
 585          */
 586         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 587                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 588         }
 589
 590         /**
 591          * Get a database connection handle reference without connecting yet
 592          *
 593          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 594          *
 595          * @see LoadBalancer::getConnection() for parameter information
 596          *
 597          * @param int $db
 598          * @param array|string|bool $groups Query group(s), or false for the generic reader
 599          * @param string|bool $wiki Wiki ID, or false for the current wiki
 600          * @return DBConnRef
 601          */
 602         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 603                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 604         }
 605
 606         /**
 607          * Open a connection to the server given by the specified index
 608          * Index must be an actual index into the array.
 609          * If the server is already open, returns it.
 610          *
 611          * On error, returns false, and the connection which caused the
 612          * error will be available via $this->mErrorConnection.
 613          *
 614          * @param int $i Server index
 615          * @param string|bool $wiki Wiki ID, or false for the current wiki
 616          * @return DatabaseBase
 617          *
 618          * @access private
 619          */
 620         public function openConnection( $i, $wiki = false ) {
 621                 if ( $wiki !== false ) {
 622                         $conn = $this->openForeignConnection( $i, $wiki );
 623
 624                         return $conn;
 625                 }
 626                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 627                         $conn = $this->mConns['local'][$i][0];
 628                 } else {
 629                         $server = $this->mServers[$i];
 630                         $server['serverIndex'] = $i;
 631                         $conn = $this->reallyOpenConnection( $server, false );
 632                         if ( $conn->isOpen() ) {
 633                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 634                                 $this->mConns['local'][$i][0] = $conn;
 635                         } else {
 636                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 637                                 $this->mErrorConnection = $conn;
 638                                 $conn = false;
 639                         }
 640                 }
 641
 642                 return $conn;
 643         }
 644
 645         /**
 646          * Open a connection to a foreign DB, or return one if it is already open.
 647          *
 648          * Increments a reference count on the returned connection which locks the
 649          * connection to the requested wiki. This reference count can be
 650          * decremented by calling reuseConnection().
 651          *
 652          * If a connection is open to the appropriate server already, but with the wrong
 653          * database, it will be switched to the right database and returned, as long as
 654          * it has been freed first with reuseConnection().
 655          *
 656          * On error, returns false, and the connection which caused the
 657          * error will be available via $this->mErrorConnection.
 658          *
 659          * @param int $i Server index
 660          * @param string $wiki Wiki ID to open
 661          * @return DatabaseBase
 662          */
 663         private function openForeignConnection( $i, $wiki ) {
 664                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 665                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 666                         // Reuse an already-used connection
 667                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 668                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 669                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 670                         // Reuse a free connection for the same wiki
 671                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 672                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 673                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 674                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 675                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 676                         // Reuse a connection from another wiki
 677                         $conn = reset( $this->mConns['foreignFree'][$i] );
 678                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 679
 680                         // The empty string as a DB name means "don't care".
 681                         // DatabaseMysqlBase::open() already handle this on connection.
 682                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 683                                 $this->mLastError = "Error selecting database $dbName on server " .
 684                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 685                                 $this->mErrorConnection = $conn;
 686                                 $conn = false;
 687                         } else {
 688                                 $conn->tablePrefix( $prefix );
 689                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 690                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 691                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 692                         }
 693                 } else {
 694                         // Open a new connection
 695                         $server = $this->mServers[$i];
 696                         $server['serverIndex'] = $i;
 697                         $server['foreignPoolRefCount'] = 0;
 698                         $server['foreign'] = true;
 699                         $conn = $this->reallyOpenConnection( $server, $dbName );
 700                         if ( !$conn->isOpen() ) {
 701                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 702                                 $this->mErrorConnection = $conn;
 703                                 $conn = false;
 704                         } else {
 705                                 $conn->tablePrefix( $prefix );
 706                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 707                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 708                         }
 709                 }
 710
 711                 // Increment reference count
 712                 if ( $conn ) {
 713                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 714                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 715                 }
 716
 717                 return $conn;
 718         }
 719
 720         /**
 721          * Test if the specified index represents an open connection
 722          *
 723          * @param int $index Server index
 724          * @access private
 725          * @return bool
 726          */
 727         private function isOpen( $index ) {
 728                 if ( !is_integer( $index ) ) {
 729                         return false;
 730                 }
 731
 732                 return (bool)$this->getAnyOpenConnection( $index );
 733         }
 734
 735         /**
 736          * Really opens a connection. Uncached.
 737          * Returns a Database object whether or not the connection was successful.
 738          * @access private
 739          *
 740          * @param array $server
 741          * @param bool $dbNameOverride
 742          * @throws MWException
 743          * @return DatabaseBase
 744          */
 745         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 746                 if ( !is_array( $server ) ) {
 747                         throw new MWException( 'You must update your load-balancing configuration. ' .
 748                                 'See DefaultSettings.php entry for $wgDBservers.' );
 749                 }
 750
 751                 if ( $dbNameOverride !== false ) {
 752                         $server['dbname'] = $dbNameOverride;
 753                 }
 754
 755                 // Log when many connection are made on requests
 756                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 757                         $masterAddr = $this->getServerName( 0 );
 758                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 759                                 "{$this->connsOpened}+ connections made (master=$masterAddr)\n" .
 760                                 wfBacktrace( true ) );
 761                 }
 762
 763                 # Create object
 764                 try {
 765                         $db = DatabaseBase::factory( $server['type'], $server );
 766                 } catch ( DBConnectionError $e ) {
 767                         // FIXME: This is probably the ugliest thing I have ever done to
 768                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 769                         $db = $e->db;
 770                 }
 771
 772                 $db->setLBInfo( $server );
 773                 if ( isset( $server['fakeSlaveLag'] ) ) {
 774                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 775                 }
 776                 if ( isset( $server['fakeMaster'] ) ) {
 777                         $db->setFakeMaster( true );
 778                 }
 779
 780                 return $db;
 781         }
 782
 783         /**
 784          * @throws DBConnectionError
 785          * @return bool
 786          */
 787         private function reportConnectionError() {
 788                 $conn = $this->mErrorConnection; // The connection which caused the error
 789                 $context = array(
 790                         'method' => __METHOD__,
 791                         'last_error' => $this->mLastError,
 792                 );
 793
 794                 if ( !is_object( $conn ) ) {
 795                         // No last connection, probably due to all servers being too busy
 796                         wfLogDBError(
 797                                 "LB failure with no last connection. Connection error: {last_error}",
 798                                 $context
 799                         );
 800
 801                         // If all servers were busy, mLastError will contain something sensible
 802                         throw new DBConnectionError( null, $this->mLastError );
 803                 } else {
 804                         $context['db_server'] = $conn->getProperty( 'mServer' );
 805                         wfLogDBError(
 806                                 "Connection error: {last_error} ({db_server})",
 807                                 $context
 808                         );
 809                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
 810                 }
 811
 812                 return false; /* not reached */
 813         }
 814
 815         /**
 816          * @return int
 817          */
 818         private function getWriterIndex() {
 819                 return 0;
 820         }
 821
 822         /**
 823          * Returns true if the specified index is a valid server index
 824          *
 825          * @param string $i
 826          * @return bool
 827          */
 828         public function haveIndex( $i ) {
 829                 return array_key_exists( $i, $this->mServers );
 830         }
 831
 832         /**
 833          * Returns true if the specified index is valid and has non-zero load
 834          *
 835          * @param string $i
 836          * @return bool
 837          */
 838         public function isNonZeroLoad( $i ) {
 839                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 840         }
 841
 842         /**
 843          * Get the number of defined servers (not the number of open connections)
 844          *
 845          * @return int
 846          */
 847         public function getServerCount() {
 848                 return count( $this->mServers );
 849         }
 850
 851         /**
 852          * Get the host name or IP address of the server with the specified index
 853          * Prefer a readable name if available.
 854          * @param string $i
 855          * @return string
 856          */
 857         public function getServerName( $i ) {
 858                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 859                         return $this->mServers[$i]['hostName'];
 860                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 861                         return $this->mServers[$i]['host'];
 862                 } else {
 863                         return '';
 864                 }
 865         }
 866
 867         /**
 868          * Return the server info structure for a given index, or false if the index is invalid.
 869          * @param int $i
 870          * @return array|bool
 871          */
 872         public function getServerInfo( $i ) {
 873                 if ( isset( $this->mServers[$i] ) ) {
 874                         return $this->mServers[$i];
 875                 } else {
 876                         return false;
 877                 }
 878         }
 879
 880         /**
 881          * Sets the server info structure for the given index. Entry at index $i
 882          * is created if it doesn't exist
 883          * @param int $i
 884          * @param array $serverInfo
 885          */
 886         public function setServerInfo( $i, array $serverInfo ) {
 887                 $this->mServers[$i] = $serverInfo;
 888         }
 889
 890         /**
 891          * Get the current master position for chronology control purposes
 892          * @return mixed
 893          */
 894         public function getMasterPos() {
 895                 # If this entire request was served from a slave without opening a connection to the
 896                 # master (however unlikely that may be), then we can fetch the position from the slave.
 897                 $masterConn = $this->getAnyOpenConnection( 0 );
 898                 if ( !$masterConn ) {
 899                         $serverCount = count( $this->mServers );
 900                         for ( $i = 1; $i < $serverCount; $i++ ) {
 901                                 $conn = $this->getAnyOpenConnection( $i );
 902                                 if ( $conn ) {
 903                                         wfDebug( "Master pos fetched from slave\n" );
 904
 905                                         return $conn->getSlavePos();
 906                                 }
 907                         }
 908                 } else {
 909                         wfDebug( "Master pos fetched from master\n" );
 910
 911                         return $masterConn->getMasterPos();
 912                 }
 913
 914                 return false;
 915         }
 916
 917         /**
 918          * Close all open connections
 919          */
 920         public function closeAll() {
 921                 foreach ( $this->mConns as $conns2 ) {
 922                         foreach ( $conns2 as $conns3 ) {
 923                                 /** @var DatabaseBase $conn */
 924                                 foreach ( $conns3 as $conn ) {
 925                                         $conn->close();
 926                                 }
 927                         }
 928                 }
 929                 $this->mConns = array(
 930                         'local' => array(),
 931                         'foreignFree' => array(),
 932                         'foreignUsed' => array(),
 933                 );
 934                 $this->connsOpened = 0;
 935         }
 936
 937         /**
 938          * Close a connection
 939          * Using this function makes sure the LoadBalancer knows the connection is closed.
 940          * If you use $conn->close() directly, the load balancer won't update its state.
 941          * @param DatabaseBase $conn
 942          */
 943         public function closeConnection( $conn ) {
 944                 $done = false;
 945                 foreach ( $this->mConns as $i1 => $conns2 ) {
 946                         foreach ( $conns2 as $i2 => $conns3 ) {
 947                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 948                                         if ( $conn === $candidateConn ) {
 949                                                 $conn->close();
 950                                                 unset( $this->mConns[$i1][$i2][$i3] );
 951                                                 --$this->connsOpened;
 952                                                 $done = true;
 953                                                 break;
 954                                         }
 955                                 }
 956                         }
 957                 }
 958                 if ( !$done ) {
 959                         $conn->close();
 960                 }
 961         }
 962
 963         /**
 964          * Commit transactions on all open connections
 965          */
 966         public function commitAll() {
 967                 foreach ( $this->mConns as $conns2 ) {
 968                         foreach ( $conns2 as $conns3 ) {
 969                                 /** @var DatabaseBase[] $conns3 */
 970                                 foreach ( $conns3 as $conn ) {
 971                                         if ( $conn->trxLevel() ) {
 972                                                 $conn->commit( __METHOD__, 'flush' );
 973                                         }
 974                                 }
 975                         }
 976                 }
 977         }
 978
 979         /**
 980          *  Issue COMMIT only on master, only if queries were done on connection
 981          */
 982         public function commitMasterChanges() {
 983                 $masterIndex = $this->getWriterIndex();
 984                 foreach ( $this->mConns as $conns2 ) {
 985                         if ( empty( $conns2[$masterIndex] ) ) {
 986                                 continue;
 987                         }
 988                         /** @var DatabaseBase $conn */
 989                         foreach ( $conns2[$masterIndex] as $conn ) {
 990                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 991                                         $conn->commit( __METHOD__, 'flush' );
 992                                 }
 993                         }
 994                 }
 995         }
 996
 997         /**
 998          * Issue ROLLBACK only on master, only if queries were done on connection
 999          * @since 1.23
1000          */
1001         public function rollbackMasterChanges() {
1002                 $failedServers = array();
1003
1004                 $masterIndex = $this->getWriterIndex();
1005                 foreach ( $this->mConns as $conns2 ) {
1006                         if ( empty( $conns2[$masterIndex] ) ) {
1007                                 continue;
1008                         }
1009                         /** @var DatabaseBase $conn */
1010                         foreach ( $conns2[$masterIndex] as $conn ) {
1011                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1012                                         try {
1013                                                 $conn->rollback( __METHOD__, 'flush' );
1014                                         } catch ( DBError $e ) {
1015                                                 MWExceptionHandler::logException( $e );
1016                                                 $failedServers[] = $conn->getServer();
1017                                         }
1018                                 }
1019                         }
1020                 }
1021
1022                 if ( $failedServers ) {
1023                         throw new DBExpectedError( null, "Rollback failed on server(s) " .
1024                                 implode( ', ', array_unique( $failedServers ) ) );
1025                 }
1026         }
1027
1028         /**
1029          * @return bool Whether a master connection is already open
1030          * @since 1.24
1031          */
1032         public function hasMasterConnection() {
1033                 return $this->isOpen( $this->getWriterIndex() );
1034         }
1035
1036         /**
1037          * Determine if there are pending changes in a transaction by this thread
1038          * @since 1.23
1039          * @return bool
1040          */
1041         public function hasMasterChanges() {
1042                 $masterIndex = $this->getWriterIndex();
1043                 foreach ( $this->mConns as $conns2 ) {
1044                         if ( empty( $conns2[$masterIndex] ) ) {
1045                                 continue;
1046                         }
1047                         /** @var DatabaseBase $conn */
1048                         foreach ( $conns2[$masterIndex] as $conn ) {
1049                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1050                                         return true;
1051                                 }
1052                         }
1053                 }
1054                 return false;
1055         }
1056
1057         /**
1058          * Get the timestamp of the latest write query done by this thread
1059          * @since 1.25
1060          * @return float|bool UNIX timestamp or false
1061          */
1062         public function lastMasterChangeTimestamp() {
1063                 $lastTime = false;
1064                 $masterIndex = $this->getWriterIndex();
1065                 foreach ( $this->mConns as $conns2 ) {
1066                         if ( empty( $conns2[$masterIndex] ) ) {
1067                                 continue;
1068                         }
1069                         /** @var DatabaseBase $conn */
1070                         foreach ( $conns2[$masterIndex] as $conn ) {
1071                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1072                         }
1073                 }
1074                 return $lastTime;
1075         }
1076
1077         /**
1078          * Check if this load balancer object had any recent or still
1079          * pending writes issued against it by this PHP thread
1080          *
1081          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1082          * @return bool
1083          * @since 1.25
1084          */
1085         public function hasOrMadeRecentMasterChanges( $age = null ) {
1086                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1087
1088                 return ( $this->hasMasterChanges()
1089                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1090         }
1091
1092         /**
1093          * @param mixed $value
1094          * @return mixed
1095          */
1096         public function waitTimeout( $value = null ) {
1097                 return wfSetVar( $this->mWaitTimeout, $value );
1098         }
1099
1100         /**
1101          * @return bool Whether the generic connection for reads is highly "lagged"
1102          */
1103         public function getLaggedSlaveMode() {
1104                 # Get a generic reader connection
1105                 $this->getConnection( DB_SLAVE );
1106
1107                 return $this->mLaggedSlaveMode;
1108         }
1109
1110         /**
1111          * Disables/enables lag checks
1112          * @param null|bool $mode
1113          * @return bool
1114          */
1115         public function allowLagged( $mode = null ) {
1116                 if ( $mode === null ) {
1117                         return $this->mAllowLagged;
1118                 }
1119                 $this->mAllowLagged = $mode;
1120
1121                 return $this->mAllowLagged;
1122         }
1123
1124         /**
1125          * @return bool
1126          */
1127         public function pingAll() {
1128                 $success = true;
1129                 foreach ( $this->mConns as $conns2 ) {
1130                         foreach ( $conns2 as $conns3 ) {
1131                                 /** @var DatabaseBase[] $conns3 */
1132                                 foreach ( $conns3 as $conn ) {
1133                                         if ( !$conn->ping() ) {
1134                                                 $success = false;
1135                                         }
1136                                 }
1137                         }
1138                 }
1139
1140                 return $success;
1141         }
1142
1143         /**
1144          * Call a function with each open connection object
1145          * @param callable $callback
1146          * @param array $params
1147          */
1148         public function forEachOpenConnection( $callback, array $params = array() ) {
1149                 foreach ( $this->mConns as $conns2 ) {
1150                         foreach ( $conns2 as $conns3 ) {
1151                                 foreach ( $conns3 as $conn ) {
1152                                         $mergedParams = array_merge( array( $conn ), $params );
1153                                         call_user_func_array( $callback, $mergedParams );
1154                                 }
1155                         }
1156                 }
1157         }
1158
1159         /**
1160          * Get the hostname and lag time of the most-lagged slave
1161          *
1162          * This is useful for maintenance scripts that need to throttle their updates.
1163          * May attempt to open connections to slaves on the default DB. If there is
1164          * no lag, the maximum lag will be reported as -1.
1165          *
1166          * @param bool|string $wiki Wiki ID, or false for the default database
1167          * @return array ( host, max lag, index of max lagged host )
1168          */
1169         public function getMaxLag( $wiki = false ) {
1170                 $maxLag = -1;
1171                 $host = '';
1172                 $maxIndex = 0;
1173
1174                 if ( $this->getServerCount() <= 1 ) {
1175                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1176                 }
1177
1178                 $lagTimes = $this->getLagTimes( $wiki );
1179                 foreach ( $lagTimes as $i => $lag ) {
1180                         if ( $lag > $maxLag ) {
1181                                 $maxLag = $lag;
1182                                 $host = $this->mServers[$i]['host'];
1183                                 $maxIndex = $i;
1184                         }
1185                 }
1186
1187                 return array( $host, $maxLag, $maxIndex );
1188         }
1189
1190         /**
1191          * Get lag time for each server
1192          *
1193          * Results are cached for a short time in memcached/process cache
1194          *
1195          * @param string|bool $wiki
1196          * @return int[] Map of (server index => seconds)
1197          */
1198         public function getLagTimes( $wiki = false ) {
1199                 if ( $this->getServerCount() <= 1 ) {
1200                         return array( 0 => 0 ); // no replication = no lag
1201                 }
1202
1203                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1204                         return $this->mProcCache->get( 'slave_lag', 'times' );
1205                 }
1206
1207                 # Send the request to the load monitor
1208                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1209
1210                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1211
1212                 return $times;
1213         }
1214
1215         /**
1216          * Get the lag in seconds for a given connection, or zero if this load
1217          * balancer does not have replication enabled.
1218          *
1219          * This should be used in preference to Database::getLag() in cases where
1220          * replication may not be in use, since there is no way to determine if
1221          * replication is in use at the connection level without running
1222          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1223          * function instead of Database::getLag() avoids a fatal error in this
1224          * case on many installations.
1225          *
1226          * @param DatabaseBase $conn
1227          * @return int
1228          */
1229         public function safeGetLag( $conn ) {
1230                 if ( $this->getServerCount() == 1 ) {
1231                         return 0;
1232                 } else {
1233                         return $conn->getLag();
1234                 }
1235         }
1236
1237         /**
1238          * Clear the cache for slag lag delay times
1239          */
1240         public function clearLagTimeCache() {
1241                 $this->mProcCache->clear( 'slave_lag' );
1242         }
1243 }
1244
1245 /**
1246  * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1247  * as well handling deferring the actual network connection until the handle is used
1248  *
1249  * @ingroup Database
1250  * @since 1.22
1251  */
1252 class DBConnRef implements IDatabase {
1253         /** @var LoadBalancer */
1254         private $lb;
1255
1256         /** @var DatabaseBase|null */
1257         private $conn;
1258
1259         /** @var array|null */
1260         private $params;
1261
1262         /**
1263          * @param LoadBalancer $lb
1264          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1265          */
1266         public function __construct( LoadBalancer $lb, $conn ) {
1267                 $this->lb = $lb;
1268                 if ( $conn instanceof DatabaseBase ) {
1269                         $this->conn = $conn;
1270                 } else {
1271                         $this->params = $conn;
1272                 }
1273         }
1274
1275         public function __call( $name, $arguments ) {
1276                 if ( $this->conn === null ) {
1277                         list( $db, $groups, $wiki ) = $this->params;
1278                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1279                 }
1280
1281                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1282         }
1283
1284         public function __destruct() {
1285                 if ( $this->conn !== null ) {
1286                         $this->lb->reuseConnection( $this->conn );
1287                 }
1288         }
1289 }