includes/db/loadbalancer/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         /** @var array LBFactory information */
  44         private $mParentInfo;
  45
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50         /** @var BagOStuff */
  51         private $srvCache;
  52
  53         /** @var bool|DatabaseBase Database connection that caused a problem */
  54         private $mErrorConnection;
  55         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  56         private $mReadIndex;
  57         /** @var bool|DBMasterPos False if not set */
  58         private $mWaitForPos;
  59         /** @var bool Whether the generic reader fell back to a lagged slave */
  60         private $laggedSlaveMode = false;
  61         /** @var bool Whether the generic reader fell back to a lagged slave */
  62         private $slavesDownMode = false;
  63         /** @var string The last DB selection or connection error */
  64         private $mLastError = 'Unknown error';
  65         /** @var string|bool Reason the LB is read-only or false if not */
  66         private $readOnlyReason = false;
  67         /** @var integer Total connections opened */
  68         private $connsOpened = 0;
  69
  70         /** @var TransactionProfiler */
  71         protected $trxProfiler;
  72
  73         /** @var integer Warn when this many connection are held */
  74         const CONN_HELD_WARN_THRESHOLD = 10;
  75         /** @var integer Default 'max lag' when unspecified */
  76         const MAX_LAG = 10;
  77         /** @var integer Max time to wait for a slave to catch up (e.g. ChronologyProtector) */
  78         const POS_WAIT_TIMEOUT = 10;
  79
  80         /**
  81          * @param array $params Array with keys:
  82          *  - servers : Required. Array of server info structures.
  83          *  - loadMonitor : Name of a class used to fetch server lag and load.
  84          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  85          * @throws MWException
  86          */
  87         public function __construct( array $params ) {
  88                 if ( !isset( $params['servers'] ) ) {
  89                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  90                 }
  91                 $this->mServers = $params['servers'];
  92                 $this->mWaitTimeout = self::POS_WAIT_TIMEOUT;
  93
  94                 $this->mReadIndex = -1;
  95                 $this->mWriteIndex = -1;
  96                 $this->mConns = array(
  97                         'local' => array(),
  98                         'foreignUsed' => array(),
  99                         'foreignFree' => array() );
 100                 $this->mLoads = array();
 101                 $this->mWaitForPos = false;
 102                 $this->mErrorConnection = false;
 103                 $this->mAllowLagged = false;
 104
 105                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 106                         $this->readOnlyReason = $params['readOnlyReason'];
 107                 }
 108
 109                 if ( isset( $params['loadMonitor'] ) ) {
 110                         $this->mLoadMonitorClass = $params['loadMonitor'];
 111                 } else {
 112                         $master = reset( $params['servers'] );
 113                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 114                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 115                         } else {
 116                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 117                         }
 118                 }
 119
 120                 foreach ( $params['servers'] as $i => $server ) {
 121                         $this->mLoads[$i] = $server['load'];
 122                         if ( isset( $server['groupLoads'] ) ) {
 123                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 124                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 125                                                 $this->mGroupLoads[$group] = array();
 126                                         }
 127                                         $this->mGroupLoads[$group][$i] = $ratio;
 128                                 }
 129                         }
 130                 }
 131
 132                 $this->srvCache = ObjectCache::getLocalServerInstance();
 133
 134                 if ( isset( $params['trxProfiler'] ) ) {
 135                         $this->trxProfiler = $params['trxProfiler'];
 136                 } else {
 137                         $this->trxProfiler = new TransactionProfiler();
 138                 }
 139         }
 140
 141         /**
 142          * Get a LoadMonitor instance
 143          *
 144          * @return LoadMonitor
 145          */
 146         private function getLoadMonitor() {
 147                 if ( !isset( $this->mLoadMonitor ) ) {
 148                         $class = $this->mLoadMonitorClass;
 149                         $this->mLoadMonitor = new $class( $this );
 150                 }
 151
 152                 return $this->mLoadMonitor;
 153         }
 154
 155         /**
 156          * Get or set arbitrary data used by the parent object, usually an LBFactory
 157          * @param mixed $x
 158          * @return mixed
 159          */
 160         public function parentInfo( $x = null ) {
 161                 return wfSetVar( $this->mParentInfo, $x );
 162         }
 163
 164         /**
 165          * Given an array of non-normalised probabilities, this function will select
 166          * an element and return the appropriate key
 167          *
 168          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 169          *
 170          * @param array $weights
 171          * @return bool|int|string
 172          */
 173         public function pickRandom( array $weights ) {
 174                 return ArrayUtils::pickRandom( $weights );
 175         }
 176
 177         /**
 178          * @param array $loads
 179          * @param bool|string $wiki Wiki to get non-lagged for
 180          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 181          * @return bool|int|string
 182          */
 183         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) {
 184                 $lags = $this->getLagTimes( $wiki );
 185
 186                 # Unset excessively lagged servers
 187                 foreach ( $lags as $i => $lag ) {
 188                         if ( $i != 0 ) {
 189                                 $maxServerLag = $maxLag;
 190                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 191                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 192                                 }
 193
 194                                 $host = $this->getServerName( $i );
 195                                 if ( $lag === false ) {
 196                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 197                                         unset( $loads[$i] );
 198                                 } elseif ( $lag > $maxServerLag ) {
 199                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 200                                         unset( $loads[$i] );
 201                                 }
 202                         }
 203                 }
 204
 205                 # Find out if all the slaves with non-zero load are lagged
 206                 $sum = 0;
 207                 foreach ( $loads as $load ) {
 208                         $sum += $load;
 209                 }
 210                 if ( $sum == 0 ) {
 211                         # No appropriate DB servers except maybe the master and some slaves with zero load
 212                         # Do NOT use the master
 213                         # Instead, this function will return false, triggering read-only mode,
 214                         # and a lagged slave will be used instead.
 215                         return false;
 216                 }
 217
 218                 if ( count( $loads ) == 0 ) {
 219                         return false;
 220                 }
 221
 222                 # Return a random representative of the remainder
 223                 return ArrayUtils::pickRandom( $loads );
 224         }
 225
 226         /**
 227          * Get the index of the reader connection, which may be a slave
 228          * This takes into account load ratios and lag times. It should
 229          * always return a consistent index during a given invocation
 230          *
 231          * Side effect: opens connections to databases
 232          * @param string|bool $group Query group, or false for the generic reader
 233          * @param string|bool $wiki Wiki ID, or false for the current wiki
 234          * @throws MWException
 235          * @return bool|int|string
 236          */
 237         public function getReaderIndex( $group = false, $wiki = false ) {
 238                 global $wgDBtype;
 239
 240                 # @todo FIXME: For now, only go through all this for mysql databases
 241                 if ( $wgDBtype != 'mysql' ) {
 242                         return $this->getWriterIndex();
 243                 }
 244
 245                 if ( count( $this->mServers ) == 1 ) {
 246                         # Skip the load balancing if there's only one server
 247                         return 0;
 248                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 249                         # Shortcut if generic reader exists already
 250                         return $this->mReadIndex;
 251                 }
 252
 253                 # Find the relevant load array
 254                 if ( $group !== false ) {
 255                         if ( isset( $this->mGroupLoads[$group] ) ) {
 256                                 $nonErrorLoads = $this->mGroupLoads[$group];
 257                         } else {
 258                                 # No loads for this group, return false and the caller can use some other group
 259                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 260
 261                                 return false;
 262                         }
 263                 } else {
 264                         $nonErrorLoads = $this->mLoads;
 265                 }
 266
 267                 if ( !count( $nonErrorLoads ) ) {
 268                         throw new MWException( "Empty server array given to LoadBalancer" );
 269                 }
 270
 271                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 272                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 273
 274                 $laggedSlaveMode = false;
 275
 276                 # No server found yet
 277                 $i = false;
 278                 $conn = false;
 279                 # First try quickly looking through the available servers for a server that
 280                 # meets our criteria
 281                 $currentLoads = $nonErrorLoads;
 282                 while ( count( $currentLoads ) ) {
 283                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 284                                 $i = ArrayUtils::pickRandom( $currentLoads );
 285                         } else {
 286                                 $i = false;
 287                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 288                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 289                                         # This triggers doWait() after connect, so it's especially good to
 290                                         # avoid lagged servers so as to avoid just blocking in that method.
 291                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 292                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 293                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 294                                 }
 295                                 if ( $i === false ) {
 296                                         # Any server with less lag than it's 'max lag' param is preferable
 297                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 298                                 }
 299                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 300                                         # All slaves lagged. Switch to read-only mode
 301                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 302                                         $i = ArrayUtils::pickRandom( $currentLoads );
 303                                         $laggedSlaveMode = true;
 304                                 }
 305                         }
 306
 307                         if ( $i === false ) {
 308                                 # pickRandom() returned false
 309                                 # This is permanent and means the configuration or the load monitor
 310                                 # wants us to return false.
 311                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 312
 313                                 return false;
 314                         }
 315
 316                         $serverName = $this->getServerName( $i );
 317                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 318
 319                         $conn = $this->openConnection( $i, $wiki );
 320                         if ( !$conn ) {
 321                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 322                                 unset( $nonErrorLoads[$i] );
 323                                 unset( $currentLoads[$i] );
 324                                 $i = false;
 325                                 continue;
 326                         }
 327
 328                         // Decrement reference counter, we are finished with this connection.
 329                         // It will be incremented for the caller later.
 330                         if ( $wiki !== false ) {
 331                                 $this->reuseConnection( $conn );
 332                         }
 333
 334                         # Return this server
 335                         break;
 336                 }
 337
 338                 # If all servers were down, quit now
 339                 if ( !count( $nonErrorLoads ) ) {
 340                         wfDebugLog( 'connect', "All servers down" );
 341                 }
 342
 343                 if ( $i !== false ) {
 344                         # Slave connection successful
 345                         # Wait for the session master pos for a short time
 346                         if ( $this->mWaitForPos && $i > 0 ) {
 347                                 if ( !$this->doWait( $i ) ) {
 348                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 349                                 }
 350                         }
 351                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 352                                 $this->mReadIndex = $i;
 353                                 # Record if the generic reader index is in "lagged slave" mode
 354                                 if ( $laggedSlaveMode ) {
 355                                         $this->laggedSlaveMode = true;
 356                                 }
 357                         }
 358                         $serverName = $this->getServerName( $i );
 359                         wfDebugLog( 'connect', __METHOD__ .
 360                                 ": using server $serverName for group '$group'\n" );
 361                 }
 362
 363                 return $i;
 364         }
 365
 366         /**
 367          * Set the master wait position
 368          * If a DB_SLAVE connection has been opened already, waits
 369          * Otherwise sets a variable telling it to wait if such a connection is opened
 370          * @param DBMasterPos $pos
 371          */
 372         public function waitFor( $pos ) {
 373                 $this->mWaitForPos = $pos;
 374                 $i = $this->mReadIndex;
 375
 376                 if ( $i > 0 ) {
 377                         if ( !$this->doWait( $i ) ) {
 378                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 379                                 $this->laggedSlaveMode = true;
 380                         }
 381                 }
 382         }
 383
 384         /**
 385          * Set the master wait position and wait for a "generic" slave to catch up to it
 386          *
 387          * This can be used a faster proxy for waitForAll()
 388          *
 389          * @param DBMasterPos $pos
 390          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 391          * @return bool Success (able to connect and no timeouts reached)
 392          * @since 1.26
 393          */
 394         public function waitForOne( $pos, $timeout = null ) {
 395                 $this->mWaitForPos = $pos;
 396
 397                 $i = $this->mReadIndex;
 398                 if ( $i <= 0 ) {
 399                         // Pick a generic slave if there isn't one yet
 400                         $readLoads = $this->mLoads;
 401                         unset( $readLoads[$this->getWriterIndex()] ); // slaves only
 402                         $readLoads = array_filter( $readLoads ); // with non-zero load
 403                         $i = ArrayUtils::pickRandom( $readLoads );
 404                 }
 405
 406                 if ( $i > 0 ) {
 407                         $ok = $this->doWait( $i, true, $timeout );
 408                 } else {
 409                         $ok = true; // no applicable loads
 410                 }
 411
 412                 return $ok;
 413         }
 414
 415         /**
 416          * Set the master wait position and wait for ALL slaves to catch up to it
 417          * @param DBMasterPos $pos
 418          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 419          * @return bool Success (able to connect and no timeouts reached)
 420          */
 421         public function waitForAll( $pos, $timeout = null ) {
 422                 $this->mWaitForPos = $pos;
 423                 $serverCount = count( $this->mServers );
 424
 425                 $ok = true;
 426                 for ( $i = 1; $i < $serverCount; $i++ ) {
 427                         if ( $this->mLoads[$i] > 0 ) {
 428                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 429                         }
 430                 }
 431
 432                 return $ok;
 433         }
 434
 435         /**
 436          * Get any open connection to a given server index, local or foreign
 437          * Returns false if there is no connection open
 438          *
 439          * @param int $i
 440          * @return DatabaseBase|bool False on failure
 441          */
 442         public function getAnyOpenConnection( $i ) {
 443                 foreach ( $this->mConns as $conns ) {
 444                         if ( !empty( $conns[$i] ) ) {
 445                                 return reset( $conns[$i] );
 446                         }
 447                 }
 448
 449                 return false;
 450         }
 451
 452         /**
 453          * Wait for a given slave to catch up to the master pos stored in $this
 454          * @param int $index Server index
 455          * @param bool $open Check the server even if a new connection has to be made
 456          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 457          * @return bool
 458          */
 459         protected function doWait( $index, $open = false, $timeout = null ) {
 460                 $close = false; // close the connection afterwards
 461
 462                 // Check if we already know that the DB has reached this point
 463                 $server = $this->getServerName( $index );
 464                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 465                 /** @var DBMasterPos $knownReachedPos */
 466                 $knownReachedPos = $this->srvCache->get( $key );
 467                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 468                         wfDebugLog( 'replication', __METHOD__ .
 469                                 ": slave $server known to be caught up (pos >= $knownReachedPos).\n" );
 470                         return true;
 471                 }
 472
 473                 // Find a connection to wait on, creating one if needed and allowed
 474                 $conn = $this->getAnyOpenConnection( $index );
 475                 if ( !$conn ) {
 476                         if ( !$open ) {
 477                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 478
 479                                 return false;
 480                         } else {
 481                                 $conn = $this->openConnection( $index, '' );
 482                                 if ( !$conn ) {
 483                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 484
 485                                         return false;
 486                                 }
 487                                 // Avoid connection spam in waitForAll() when connections
 488                                 // are made just for the sake of doing this lag check.
 489                                 $close = true;
 490                         }
 491                 }
 492
 493                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for slave $server to catch up...\n" );
 494                 $timeout = $timeout ?: $this->mWaitTimeout;
 495                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 496
 497                 if ( $result == -1 || is_null( $result ) ) {
 498                         // Timed out waiting for slave, use master instead
 499                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 500                         wfDebugLog( 'replication', "$msg\n" );
 501                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 502                         $ok = false;
 503                 } else {
 504                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 505                         $ok = true;
 506                         // Remember that the DB reached this point
 507                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 508                 }
 509
 510                 if ( $close ) {
 511                         $this->closeConnection( $conn );
 512                 }
 513
 514                 return $ok;
 515         }
 516
 517         /**
 518          * Get a connection by index
 519          * This is the main entry point for this class.
 520          *
 521          * @param int $i Server index
 522          * @param array|string|bool $groups Query group(s), or false for the generic reader
 523          * @param string|bool $wiki Wiki ID, or false for the current wiki
 524          *
 525          * @throws MWException
 526          * @return DatabaseBase
 527          */
 528         public function getConnection( $i, $groups = array(), $wiki = false ) {
 529                 if ( $i === null || $i === false ) {
 530                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 531                                 ' with invalid server index' );
 532                 }
 533
 534                 if ( $wiki === wfWikiID() ) {
 535                         $wiki = false;
 536                 }
 537
 538                 $groups = ( $groups === false || $groups === array() )
 539                         ? array( false ) // check one "group": the generic pool
 540                         : (array)$groups;
 541
 542                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 543                 $oldConnsOpened = $this->connsOpened; // connections open now
 544
 545                 if ( $i == DB_MASTER ) {
 546                         $i = $this->getWriterIndex();
 547                 } else {
 548                         # Try to find an available server in any the query groups (in order)
 549                         foreach ( $groups as $group ) {
 550                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 551                                 if ( $groupIndex !== false ) {
 552                                         $i = $groupIndex;
 553                                         break;
 554                                 }
 555                         }
 556                 }
 557
 558                 # Operation-based index
 559                 if ( $i == DB_SLAVE ) {
 560                         $this->mLastError = 'Unknown error'; // reset error string
 561                         # Try the general server pool if $groups are unavailable.
 562                         $i = in_array( false, $groups, true )
 563                                 ? false // don't bother with this if that is what was tried above
 564                                 : $this->getReaderIndex( false, $wiki );
 565                         # Couldn't find a working server in getReaderIndex()?
 566                         if ( $i === false ) {
 567                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 568
 569                                 return $this->reportConnectionError();
 570                         }
 571                 }
 572
 573                 # Now we have an explicit index into the servers array
 574                 $conn = $this->openConnection( $i, $wiki );
 575                 if ( !$conn ) {
 576                         return $this->reportConnectionError();
 577                 }
 578
 579                 # Profile any new connections that happen
 580                 if ( $this->connsOpened > $oldConnsOpened ) {
 581                         $host = $conn->getServer();
 582                         $dbname = $conn->getDBname();
 583                         $trxProf = Profiler::instance()->getTransactionProfiler();
 584                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 585                 }
 586
 587                 if ( $masterOnly ) {
 588                         # Make master-requested DB handles inherit any read-only mode setting
 589                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki ) );
 590                 }
 591
 592                 return $conn;
 593         }
 594
 595         /**
 596          * Mark a foreign connection as being available for reuse under a different
 597          * DB name or prefix. This mechanism is reference-counted, and must be called
 598          * the same number of times as getConnection() to work.
 599          *
 600          * @param DatabaseBase $conn
 601          * @throws MWException
 602          */
 603         public function reuseConnection( $conn ) {
 604                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 605                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 606                 if ( $serverIndex === null || $refCount === null ) {
 607                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 608                         /**
 609                          * This can happen in code like:
 610                          *   foreach ( $dbs as $db ) {
 611                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 612                          *     ...
 613                          *     $lb->reuseConnection( $conn );
 614                          *   }
 615                          * When a connection to the local DB is opened in this way, reuseConnection()
 616                          * should be ignored
 617                          */
 618                         return;
 619                 }
 620
 621                 $dbName = $conn->getDBname();
 622                 $prefix = $conn->tablePrefix();
 623                 if ( strval( $prefix ) !== '' ) {
 624                         $wiki = "$dbName-$prefix";
 625                 } else {
 626                         $wiki = $dbName;
 627                 }
 628                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 629                         throw new MWException( __METHOD__ . ": connection not found, has " .
 630                                 "the connection been freed already?" );
 631                 }
 632                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 633                 if ( $refCount <= 0 ) {
 634                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 635                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 636                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 637                 } else {
 638                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 639                 }
 640         }
 641
 642         /**
 643          * Get a database connection handle reference
 644          *
 645          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 646          *
 647          * @see LoadBalancer::getConnection() for parameter information
 648          *
 649          * @param int $db
 650          * @param array|string|bool $groups Query group(s), or false for the generic reader
 651          * @param string|bool $wiki Wiki ID, or false for the current wiki
 652          * @return DBConnRef
 653          */
 654         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 655                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 656         }
 657
 658         /**
 659          * Get a database connection handle reference without connecting yet
 660          *
 661          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 662          *
 663          * @see LoadBalancer::getConnection() for parameter information
 664          *
 665          * @param int $db
 666          * @param array|string|bool $groups Query group(s), or false for the generic reader
 667          * @param string|bool $wiki Wiki ID, or false for the current wiki
 668          * @return DBConnRef
 669          */
 670         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 671                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 672         }
 673
 674         /**
 675          * Open a connection to the server given by the specified index
 676          * Index must be an actual index into the array.
 677          * If the server is already open, returns it.
 678          *
 679          * On error, returns false, and the connection which caused the
 680          * error will be available via $this->mErrorConnection.
 681          *
 682          * @param int $i Server index
 683          * @param string|bool $wiki Wiki ID, or false for the current wiki
 684          * @return DatabaseBase|bool Returns false on errors
 685          */
 686         public function openConnection( $i, $wiki = false ) {
 687                 if ( $wiki !== false ) {
 688                         $conn = $this->openForeignConnection( $i, $wiki );
 689                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 690                         $conn = $this->mConns['local'][$i][0];
 691                 } else {
 692                         $server = $this->mServers[$i];
 693                         $server['serverIndex'] = $i;
 694                         $conn = $this->reallyOpenConnection( $server, false );
 695                         $serverName = $this->getServerName( $i );
 696                         if ( $conn->isOpen() ) {
 697                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 698                                 $this->mConns['local'][$i][0] = $conn;
 699                         } else {
 700                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 701                                 $this->mErrorConnection = $conn;
 702                                 $conn = false;
 703                         }
 704                 }
 705
 706                 if ( $conn && !$conn->isOpen() ) {
 707                         // Connection was made but later unrecoverably lost for some reason.
 708                         // Do not return a handle that will just throw exceptions on use,
 709                         // but let the calling code (e.g. getReaderIndex) try another server.
 710                         // See DatabaseMyslBase::ping() for how this can happen.
 711                         $this->mErrorConnection = $conn;
 712                         $conn = false;
 713                 }
 714
 715                 return $conn;
 716         }
 717
 718         /**
 719          * Open a connection to a foreign DB, or return one if it is already open.
 720          *
 721          * Increments a reference count on the returned connection which locks the
 722          * connection to the requested wiki. This reference count can be
 723          * decremented by calling reuseConnection().
 724          *
 725          * If a connection is open to the appropriate server already, but with the wrong
 726          * database, it will be switched to the right database and returned, as long as
 727          * it has been freed first with reuseConnection().
 728          *
 729          * On error, returns false, and the connection which caused the
 730          * error will be available via $this->mErrorConnection.
 731          *
 732          * @param int $i Server index
 733          * @param string $wiki Wiki ID to open
 734          * @return DatabaseBase
 735          */
 736         private function openForeignConnection( $i, $wiki ) {
 737                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 738                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 739                         // Reuse an already-used connection
 740                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 741                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 742                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 743                         // Reuse a free connection for the same wiki
 744                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 745                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 746                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 747                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 748                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 749                         // Reuse a connection from another wiki
 750                         $conn = reset( $this->mConns['foreignFree'][$i] );
 751                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 752
 753                         // The empty string as a DB name means "don't care".
 754                         // DatabaseMysqlBase::open() already handle this on connection.
 755                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 756                                 $this->mLastError = "Error selecting database $dbName on server " .
 757                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 758                                 $this->mErrorConnection = $conn;
 759                                 $conn = false;
 760                         } else {
 761                                 $conn->tablePrefix( $prefix );
 762                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 763                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 764                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 765                         }
 766                 } else {
 767                         // Open a new connection
 768                         $server = $this->mServers[$i];
 769                         $server['serverIndex'] = $i;
 770                         $server['foreignPoolRefCount'] = 0;
 771                         $server['foreign'] = true;
 772                         $conn = $this->reallyOpenConnection( $server, $dbName );
 773                         if ( !$conn->isOpen() ) {
 774                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 775                                 $this->mErrorConnection = $conn;
 776                                 $conn = false;
 777                         } else {
 778                                 $conn->tablePrefix( $prefix );
 779                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 780                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 781                         }
 782                 }
 783
 784                 // Increment reference count
 785                 if ( $conn ) {
 786                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 787                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 788                 }
 789
 790                 return $conn;
 791         }
 792
 793         /**
 794          * Test if the specified index represents an open connection
 795          *
 796          * @param int $index Server index
 797          * @access private
 798          * @return bool
 799          */
 800         private function isOpen( $index ) {
 801                 if ( !is_integer( $index ) ) {
 802                         return false;
 803                 }
 804
 805                 return (bool)$this->getAnyOpenConnection( $index );
 806         }
 807
 808         /**
 809          * Really opens a connection. Uncached.
 810          * Returns a Database object whether or not the connection was successful.
 811          * @access private
 812          *
 813          * @param array $server
 814          * @param bool $dbNameOverride
 815          * @throws MWException
 816          * @return DatabaseBase
 817          */
 818         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 819                 if ( !is_array( $server ) ) {
 820                         throw new MWException( 'You must update your load-balancing configuration. ' .
 821                                 'See DefaultSettings.php entry for $wgDBservers.' );
 822                 }
 823
 824                 if ( $dbNameOverride !== false ) {
 825                         $server['dbname'] = $dbNameOverride;
 826                 }
 827
 828                 // Let the handle know what the cluster master is (e.g. "db1052")
 829                 $masterName = $this->getServerName( 0 );
 830                 $server['clusterMasterHost'] = $masterName;
 831
 832                 // Log when many connection are made on requests
 833                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 834                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 835                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 836                                 wfBacktrace( true ) );
 837                 }
 838
 839                 # Create object
 840                 try {
 841                         $db = DatabaseBase::factory( $server['type'], $server );
 842                 } catch ( DBConnectionError $e ) {
 843                         // FIXME: This is probably the ugliest thing I have ever done to
 844                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 845                         $db = $e->db;
 846                 }
 847
 848                 $db->setLBInfo( $server );
 849                 $db->setLazyMasterHandle(
 850                         $this->getLazyConnectionRef( DB_MASTER, array(), $db->getWikiID() )
 851                 );
 852                 $db->setTransactionProfiler( $this->trxProfiler );
 853
 854                 return $db;
 855         }
 856
 857         /**
 858          * @throws DBConnectionError
 859          * @return bool
 860          */
 861         private function reportConnectionError() {
 862                 $conn = $this->mErrorConnection; // The connection which caused the error
 863                 $context = array(
 864                         'method' => __METHOD__,
 865                         'last_error' => $this->mLastError,
 866                 );
 867
 868                 if ( !is_object( $conn ) ) {
 869                         // No last connection, probably due to all servers being too busy
 870                         wfLogDBError(
 871                                 "LB failure with no last connection. Connection error: {last_error}",
 872                                 $context
 873                         );
 874
 875                         // If all servers were busy, mLastError will contain something sensible
 876                         throw new DBConnectionError( null, $this->mLastError );
 877                 } else {
 878                         $context['db_server'] = $conn->getProperty( 'mServer' );
 879                         wfLogDBError(
 880                                 "Connection error: {last_error} ({db_server})",
 881                                 $context
 882                         );
 883
 884                         // throws DBConnectionError
 885                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 886                 }
 887
 888                 return false; /* not reached */
 889         }
 890
 891         /**
 892          * @return int
 893          * @since 1.26
 894          */
 895         public function getWriterIndex() {
 896                 return 0;
 897         }
 898
 899         /**
 900          * Returns true if the specified index is a valid server index
 901          *
 902          * @param string $i
 903          * @return bool
 904          */
 905         public function haveIndex( $i ) {
 906                 return array_key_exists( $i, $this->mServers );
 907         }
 908
 909         /**
 910          * Returns true if the specified index is valid and has non-zero load
 911          *
 912          * @param string $i
 913          * @return bool
 914          */
 915         public function isNonZeroLoad( $i ) {
 916                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 917         }
 918
 919         /**
 920          * Get the number of defined servers (not the number of open connections)
 921          *
 922          * @return int
 923          */
 924         public function getServerCount() {
 925                 return count( $this->mServers );
 926         }
 927
 928         /**
 929          * Get the host name or IP address of the server with the specified index
 930          * Prefer a readable name if available.
 931          * @param string $i
 932          * @return string
 933          */
 934         public function getServerName( $i ) {
 935                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 936                         $name = $this->mServers[$i]['hostName'];
 937                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 938                         $name = $this->mServers[$i]['host'];
 939                 } else {
 940                         $name = '';
 941                 }
 942
 943                 return ( $name != '' ) ? $name : 'localhost';
 944         }
 945
 946         /**
 947          * Return the server info structure for a given index, or false if the index is invalid.
 948          * @param int $i
 949          * @return array|bool
 950          */
 951         public function getServerInfo( $i ) {
 952                 if ( isset( $this->mServers[$i] ) ) {
 953                         return $this->mServers[$i];
 954                 } else {
 955                         return false;
 956                 }
 957         }
 958
 959         /**
 960          * Sets the server info structure for the given index. Entry at index $i
 961          * is created if it doesn't exist
 962          * @param int $i
 963          * @param array $serverInfo
 964          */
 965         public function setServerInfo( $i, array $serverInfo ) {
 966                 $this->mServers[$i] = $serverInfo;
 967         }
 968
 969         /**
 970          * Get the current master position for chronology control purposes
 971          * @return mixed
 972          */
 973         public function getMasterPos() {
 974                 # If this entire request was served from a slave without opening a connection to the
 975                 # master (however unlikely that may be), then we can fetch the position from the slave.
 976                 $masterConn = $this->getAnyOpenConnection( 0 );
 977                 if ( !$masterConn ) {
 978                         $serverCount = count( $this->mServers );
 979                         for ( $i = 1; $i < $serverCount; $i++ ) {
 980                                 $conn = $this->getAnyOpenConnection( $i );
 981                                 if ( $conn ) {
 982                                         return $conn->getSlavePos();
 983                                 }
 984                         }
 985                 } else {
 986                         return $masterConn->getMasterPos();
 987                 }
 988
 989                 return false;
 990         }
 991
 992         /**
 993          * Close all open connections
 994          */
 995         public function closeAll() {
 996                 foreach ( $this->mConns as $conns2 ) {
 997                         foreach ( $conns2 as $conns3 ) {
 998                                 /** @var DatabaseBase $conn */
 999                                 foreach ( $conns3 as $conn ) {
1000                                         $conn->close();
1001                                 }
1002                         }
1003                 }
1004                 $this->mConns = array(
1005                         'local' => array(),
1006                         'foreignFree' => array(),
1007                         'foreignUsed' => array(),
1008                 );
1009                 $this->connsOpened = 0;
1010         }
1011
1012         /**
1013          * Close a connection
1014          * Using this function makes sure the LoadBalancer knows the connection is closed.
1015          * If you use $conn->close() directly, the load balancer won't update its state.
1016          * @param DatabaseBase $conn
1017          */
1018         public function closeConnection( $conn ) {
1019                 $done = false;
1020                 foreach ( $this->mConns as $i1 => $conns2 ) {
1021                         foreach ( $conns2 as $i2 => $conns3 ) {
1022                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1023                                         if ( $conn === $candidateConn ) {
1024                                                 $conn->close();
1025                                                 unset( $this->mConns[$i1][$i2][$i3] );
1026                                                 --$this->connsOpened;
1027                                                 $done = true;
1028                                                 break;
1029                                         }
1030                                 }
1031                         }
1032                 }
1033                 if ( !$done ) {
1034                         $conn->close();
1035                 }
1036         }
1037
1038         /**
1039          * Commit transactions on all open connections
1040          * @param string $fname Caller name
1041          */
1042         public function commitAll( $fname = __METHOD__ ) {
1043                 foreach ( $this->mConns as $conns2 ) {
1044                         foreach ( $conns2 as $conns3 ) {
1045                                 /** @var DatabaseBase[] $conns3 */
1046                                 foreach ( $conns3 as $conn ) {
1047                                         if ( $conn->trxLevel() ) {
1048                                                 $conn->commit( $fname, 'flush' );
1049                                         }
1050                                 }
1051                         }
1052                 }
1053         }
1054
1055         /**
1056          * Issue COMMIT only on master, only if queries were done on connection
1057          * @param string $fname Caller name
1058          */
1059         public function commitMasterChanges( $fname = __METHOD__ ) {
1060                 $masterIndex = $this->getWriterIndex();
1061                 foreach ( $this->mConns as $conns2 ) {
1062                         if ( empty( $conns2[$masterIndex] ) ) {
1063                                 continue;
1064                         }
1065                         /** @var DatabaseBase $conn */
1066                         foreach ( $conns2[$masterIndex] as $conn ) {
1067                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1068                                         $conn->commit( $fname, 'flush' );
1069                                 }
1070                         }
1071                 }
1072         }
1073
1074         /**
1075          * Issue ROLLBACK only on master, only if queries were done on connection
1076          * @param string $fname Caller name
1077          * @throws DBExpectedError
1078          * @since 1.23
1079          */
1080         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1081                 $failedServers = array();
1082
1083                 $masterIndex = $this->getWriterIndex();
1084                 foreach ( $this->mConns as $conns2 ) {
1085                         if ( empty( $conns2[$masterIndex] ) ) {
1086                                 continue;
1087                         }
1088                         /** @var DatabaseBase $conn */
1089                         foreach ( $conns2[$masterIndex] as $conn ) {
1090                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1091                                         try {
1092                                                 $conn->rollback( $fname, 'flush' );
1093                                         } catch ( DBError $e ) {
1094                                                 MWExceptionHandler::logException( $e );
1095                                                 $failedServers[] = $conn->getServer();
1096                                         }
1097                                 }
1098                         }
1099                 }
1100
1101                 if ( $failedServers ) {
1102                         throw new DBExpectedError( null, "Rollback failed on server(s) " .
1103                                 implode( ', ', array_unique( $failedServers ) ) );
1104                 }
1105         }
1106
1107         /**
1108          * @return bool Whether a master connection is already open
1109          * @since 1.24
1110          */
1111         public function hasMasterConnection() {
1112                 return $this->isOpen( $this->getWriterIndex() );
1113         }
1114
1115         /**
1116          * Determine if there are pending changes in a transaction by this thread
1117          * @since 1.23
1118          * @return bool
1119          */
1120         public function hasMasterChanges() {
1121                 $masterIndex = $this->getWriterIndex();
1122                 foreach ( $this->mConns as $conns2 ) {
1123                         if ( empty( $conns2[$masterIndex] ) ) {
1124                                 continue;
1125                         }
1126                         /** @var DatabaseBase $conn */
1127                         foreach ( $conns2[$masterIndex] as $conn ) {
1128                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1129                                         return true;
1130                                 }
1131                         }
1132                 }
1133                 return false;
1134         }
1135
1136         /**
1137          * Get the timestamp of the latest write query done by this thread
1138          * @since 1.25
1139          * @return float|bool UNIX timestamp or false
1140          */
1141         public function lastMasterChangeTimestamp() {
1142                 $lastTime = false;
1143                 $masterIndex = $this->getWriterIndex();
1144                 foreach ( $this->mConns as $conns2 ) {
1145                         if ( empty( $conns2[$masterIndex] ) ) {
1146                                 continue;
1147                         }
1148                         /** @var DatabaseBase $conn */
1149                         foreach ( $conns2[$masterIndex] as $conn ) {
1150                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1151                         }
1152                 }
1153                 return $lastTime;
1154         }
1155
1156         /**
1157          * Check if this load balancer object had any recent or still
1158          * pending writes issued against it by this PHP thread
1159          *
1160          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1161          * @return bool
1162          * @since 1.25
1163          */
1164         public function hasOrMadeRecentMasterChanges( $age = null ) {
1165                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1166
1167                 return ( $this->hasMasterChanges()
1168                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1169         }
1170
1171         /**
1172          * Get the list of callers that have pending master changes
1173          *
1174          * @return array
1175          * @since 1.27
1176          */
1177         public function pendingMasterChangeCallers() {
1178                 $fnames = array();
1179
1180                 $masterIndex = $this->getWriterIndex();
1181                 foreach ( $this->mConns as $conns2 ) {
1182                         if ( empty( $conns2[$masterIndex] ) ) {
1183                                 continue;
1184                         }
1185                         /** @var DatabaseBase $conn */
1186                         foreach ( $conns2[$masterIndex] as $conn ) {
1187                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1188                         }
1189                 }
1190
1191                 return $fnames;
1192         }
1193
1194         /**
1195          * @param mixed $value
1196          * @return mixed
1197          */
1198         public function waitTimeout( $value = null ) {
1199                 return wfSetVar( $this->mWaitTimeout, $value );
1200         }
1201
1202         /**
1203          * @note This method will trigger a DB connection if not yet done
1204          *
1205          * @param string|bool $wiki Wiki ID, or false for the current wiki
1206          * @return bool Whether the generic connection for reads is highly "lagged"
1207          */
1208         public function getLaggedSlaveMode( $wiki = false ) {
1209                 // No-op if there is only one DB (also avoids recursion)
1210                 if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
1211                         try {
1212                                 // See if laggedSlaveMode gets set
1213                                 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1214                                 $this->reuseConnection( $conn );
1215                         } catch ( DBConnectionError $e ) {
1216                                 // Avoid expensive re-connect attempts and failures
1217                                 $this->slavesDownMode = true;
1218                                 $this->laggedSlaveMode = true;
1219                         }
1220                 }
1221
1222                 return $this->laggedSlaveMode;
1223         }
1224
1225         /**
1226          * @note This method will never cause a new DB connection
1227          * @return bool Whether any generic connection used for reads was highly "lagged"
1228          * @since 1.27
1229          */
1230         public function laggedSlaveUsed() {
1231                 return $this->laggedSlaveMode;
1232         }
1233
1234         /**
1235          * @note This method may trigger a DB connection if not yet done
1236          * @param string|bool $wiki Wiki ID, or false for the current wiki
1237          * @return string|bool Reason the master is read-only or false if it is not
1238          * @since 1.27
1239          */
1240         public function getReadOnlyReason( $wiki = false ) {
1241                 if ( $this->readOnlyReason !== false ) {
1242                         return $this->readOnlyReason;
1243                 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1244                         if ( $this->slavesDownMode ) {
1245                                 return 'The database has been automatically locked ' .
1246                                         'until the slave database servers become available';
1247                         } else {
1248                                 return 'The database has been automatically locked ' .
1249                                         'while the slave database servers catch up to the master.';
1250                         }
1251                 }
1252
1253                 return false;
1254         }
1255
1256         /**
1257          * Disables/enables lag checks
1258          * @param null|bool $mode
1259          * @return bool
1260          */
1261         public function allowLagged( $mode = null ) {
1262                 if ( $mode === null ) {
1263                         return $this->mAllowLagged;
1264                 }
1265                 $this->mAllowLagged = $mode;
1266
1267                 return $this->mAllowLagged;
1268         }
1269
1270         /**
1271          * @return bool
1272          */
1273         public function pingAll() {
1274                 $success = true;
1275                 foreach ( $this->mConns as $conns2 ) {
1276                         foreach ( $conns2 as $conns3 ) {
1277                                 /** @var DatabaseBase[] $conns3 */
1278                                 foreach ( $conns3 as $conn ) {
1279                                         if ( !$conn->ping() ) {
1280                                                 $success = false;
1281                                         }
1282                                 }
1283                         }
1284                 }
1285
1286                 return $success;
1287         }
1288
1289         /**
1290          * Call a function with each open connection object
1291          * @param callable $callback
1292          * @param array $params
1293          */
1294         public function forEachOpenConnection( $callback, array $params = array() ) {
1295                 foreach ( $this->mConns as $conns2 ) {
1296                         foreach ( $conns2 as $conns3 ) {
1297                                 foreach ( $conns3 as $conn ) {
1298                                         $mergedParams = array_merge( array( $conn ), $params );
1299                                         call_user_func_array( $callback, $mergedParams );
1300                                 }
1301                         }
1302                 }
1303         }
1304
1305         /**
1306          * Get the hostname and lag time of the most-lagged slave
1307          *
1308          * This is useful for maintenance scripts that need to throttle their updates.
1309          * May attempt to open connections to slaves on the default DB. If there is
1310          * no lag, the maximum lag will be reported as -1.
1311          *
1312          * @param bool|string $wiki Wiki ID, or false for the default database
1313          * @return array ( host, max lag, index of max lagged host )
1314          */
1315         public function getMaxLag( $wiki = false ) {
1316                 $maxLag = -1;
1317                 $host = '';
1318                 $maxIndex = 0;
1319
1320                 if ( $this->getServerCount() <= 1 ) {
1321                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1322                 }
1323
1324                 $lagTimes = $this->getLagTimes( $wiki );
1325                 foreach ( $lagTimes as $i => $lag ) {
1326                         if ( $lag > $maxLag ) {
1327                                 $maxLag = $lag;
1328                                 $host = $this->mServers[$i]['host'];
1329                                 $maxIndex = $i;
1330                         }
1331                 }
1332
1333                 return array( $host, $maxLag, $maxIndex );
1334         }
1335
1336         /**
1337          * Get an estimate of replication lag (in seconds) for each server
1338          *
1339          * Results are cached for a short time in memcached/process cache
1340          *
1341          * Values may be "false" if replication is too broken to estimate
1342          *
1343          * @param string|bool $wiki
1344          * @return int[] Map of (server index => float|int|bool)
1345          */
1346         public function getLagTimes( $wiki = false ) {
1347                 if ( $this->getServerCount() <= 1 ) {
1348                         return array( 0 => 0 ); // no replication = no lag
1349                 }
1350
1351                 # Send the request to the load monitor
1352                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1353         }
1354
1355         /**
1356          * Get the lag in seconds for a given connection, or zero if this load
1357          * balancer does not have replication enabled.
1358          *
1359          * This should be used in preference to Database::getLag() in cases where
1360          * replication may not be in use, since there is no way to determine if
1361          * replication is in use at the connection level without running
1362          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1363          * function instead of Database::getLag() avoids a fatal error in this
1364          * case on many installations.
1365          *
1366          * @param IDatabase $conn
1367          * @return int|bool Returns false on error
1368          */
1369         public function safeGetLag( IDatabase $conn ) {
1370                 if ( $this->getServerCount() == 1 ) {
1371                         return 0;
1372                 } else {
1373                         return $conn->getLag();
1374                 }
1375         }
1376
1377         /**
1378          * Wait for a slave DB to reach a specified master position
1379          *
1380          * This will connect to the master to get an accurate position if $pos is not given
1381          *
1382          * @param IDatabase $conn Slave DB
1383          * @param DBMasterPos|bool $pos Master position; default: current position
1384          * @param integer $timeout Timeout in seconds
1385          * @return bool Success
1386          * @since 1.27
1387          */
1388         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1389                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
1390                         return true; // server is not a slave DB
1391                 }
1392
1393                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1394                 if ( !$pos ) {
1395                         return false; // something is misconfigured
1396                 }
1397
1398                 $result = $conn->masterPosWait( $pos, $timeout );
1399                 if ( $result == -1 || is_null( $result ) ) {
1400                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1401                         wfDebugLog( 'replication', "$msg\n" );
1402                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1403                         $ok = false;
1404                 } else {
1405                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1406                         $ok = true;
1407                 }
1408
1409                 return $ok;
1410         }
1411
1412         /**
1413          * Clear the cache for slag lag delay times
1414          *
1415          * This is only used for testing
1416          */
1417         public function clearLagTimeCache() {
1418                 $this->getLoadMonitor()->clearCaches();
1419         }
1420 }