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         /** @var WANObjectCache */
  53         private $wanCache;
  54         /** @var TransactionProfiler */
  55         protected $trxProfiler;
  56
  57         /** @var bool|DatabaseBase Database connection that caused a problem */
  58         private $mErrorConnection;
  59         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  60         private $mReadIndex;
  61         /** @var bool|DBMasterPos False if not set */
  62         private $mWaitForPos;
  63         /** @var bool Whether the generic reader fell back to a lagged slave */
  64         private $laggedSlaveMode = false;
  65         /** @var bool Whether the generic reader fell back to a lagged slave */
  66         private $slavesDownMode = false;
  67         /** @var string The last DB selection or connection error */
  68         private $mLastError = 'Unknown error';
  69         /** @var string|bool Reason the LB is read-only or false if not */
  70         private $readOnlyReason = false;
  71         /** @var integer Total connections opened */
  72         private $connsOpened = 0;
  73         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  74         private $trxRoundId = false;
  75
  76         /** @var integer Warn when this many connection are held */
  77         const CONN_HELD_WARN_THRESHOLD = 10;
  78         /** @var integer Default 'max lag' when unspecified */
  79         const MAX_LAG = 10;
  80         /** @var integer Max time to wait for a slave to catch up (e.g. ChronologyProtector) */
  81         const POS_WAIT_TIMEOUT = 10;
  82         /** @var integer Seconds to cache master server read-only status */
  83         const TTL_CACHE_READONLY = 5;
  84
  85         /**
  86          * @var boolean
  87          */
  88         private $disabled = false;
  89
  90         /**
  91          * @param array $params Array with keys:
  92          *  - servers : Required. Array of server info structures.
  93          *  - loadMonitor : Name of a class used to fetch server lag and load.
  94          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  95          *  - srvCache : BagOStuff object [optional]
  96          *  - wanCache : WANObjectCache object [optional]
  97          * @throws MWException
  98          */
  99         public function __construct( array $params ) {
 100                 if ( !isset( $params['servers'] ) ) {
 101                         throw new MWException( __CLASS__ . ': missing servers parameter' );
 102                 }
 103                 $this->mServers = $params['servers'];
 104                 $this->mWaitTimeout = self::POS_WAIT_TIMEOUT;
 105
 106                 $this->mReadIndex = -1;
 107                 $this->mWriteIndex = -1;
 108                 $this->mConns = [
 109                         'local' => [],
 110                         'foreignUsed' => [],
 111                         'foreignFree' => [] ];
 112                 $this->mLoads = [];
 113                 $this->mWaitForPos = false;
 114                 $this->mErrorConnection = false;
 115                 $this->mAllowLagged = false;
 116
 117                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 118                         $this->readOnlyReason = $params['readOnlyReason'];
 119                 }
 120
 121                 if ( isset( $params['loadMonitor'] ) ) {
 122                         $this->mLoadMonitorClass = $params['loadMonitor'];
 123                 } else {
 124                         $master = reset( $params['servers'] );
 125                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 126                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 127                         } else {
 128                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 129                         }
 130                 }
 131
 132                 foreach ( $params['servers'] as $i => $server ) {
 133                         $this->mLoads[$i] = $server['load'];
 134                         if ( isset( $server['groupLoads'] ) ) {
 135                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 136                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 137                                                 $this->mGroupLoads[$group] = [];
 138                                         }
 139                                         $this->mGroupLoads[$group][$i] = $ratio;
 140                                 }
 141                         }
 142                 }
 143
 144                 if ( isset( $params['srvCache'] ) ) {
 145                         $this->srvCache = $params['srvCache'];
 146                 } else {
 147                         $this->srvCache = new EmptyBagOStuff();
 148                 }
 149                 if ( isset( $params['wanCache'] ) ) {
 150                         $this->wanCache = $params['wanCache'];
 151                 } else {
 152                         $this->wanCache = WANObjectCache::newEmpty();
 153                 }
 154                 if ( isset( $params['trxProfiler'] ) ) {
 155                         $this->trxProfiler = $params['trxProfiler'];
 156                 } else {
 157                         $this->trxProfiler = new TransactionProfiler();
 158                 }
 159         }
 160
 161         /**
 162          * Get a LoadMonitor instance
 163          *
 164          * @return LoadMonitor
 165          */
 166         private function getLoadMonitor() {
 167                 if ( !isset( $this->mLoadMonitor ) ) {
 168                         $class = $this->mLoadMonitorClass;
 169                         $this->mLoadMonitor = new $class( $this );
 170                 }
 171
 172                 return $this->mLoadMonitor;
 173         }
 174
 175         /**
 176          * Get or set arbitrary data used by the parent object, usually an LBFactory
 177          * @param mixed $x
 178          * @return mixed
 179          */
 180         public function parentInfo( $x = null ) {
 181                 return wfSetVar( $this->mParentInfo, $x );
 182         }
 183
 184         /**
 185          * @param array $loads
 186          * @param bool|string $wiki Wiki to get non-lagged for
 187          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 188          * @return bool|int|string
 189          */
 190         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) {
 191                 $lags = $this->getLagTimes( $wiki );
 192
 193                 # Unset excessively lagged servers
 194                 foreach ( $lags as $i => $lag ) {
 195                         if ( $i != 0 ) {
 196                                 $maxServerLag = $maxLag;
 197                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 198                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 199                                 }
 200
 201                                 $host = $this->getServerName( $i );
 202                                 if ( $lag === false ) {
 203                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 204                                         unset( $loads[$i] );
 205                                 } elseif ( $lag > $maxServerLag ) {
 206                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 207                                         unset( $loads[$i] );
 208                                 }
 209                         }
 210                 }
 211
 212                 # Find out if all the slaves with non-zero load are lagged
 213                 $sum = 0;
 214                 foreach ( $loads as $load ) {
 215                         $sum += $load;
 216                 }
 217                 if ( $sum == 0 ) {
 218                         # No appropriate DB servers except maybe the master and some slaves with zero load
 219                         # Do NOT use the master
 220                         # Instead, this function will return false, triggering read-only mode,
 221                         # and a lagged slave will be used instead.
 222                         return false;
 223                 }
 224
 225                 if ( count( $loads ) == 0 ) {
 226                         return false;
 227                 }
 228
 229                 # Return a random representative of the remainder
 230                 return ArrayUtils::pickRandom( $loads );
 231         }
 232
 233         /**
 234          * Get the index of the reader connection, which may be a slave
 235          * This takes into account load ratios and lag times. It should
 236          * always return a consistent index during a given invocation
 237          *
 238          * Side effect: opens connections to databases
 239          * @param string|bool $group Query group, or false for the generic reader
 240          * @param string|bool $wiki Wiki ID, or false for the current wiki
 241          * @throws MWException
 242          * @return bool|int|string
 243          */
 244         public function getReaderIndex( $group = false, $wiki = false ) {
 245                 global $wgDBtype;
 246
 247                 # @todo FIXME: For now, only go through all this for mysql databases
 248                 if ( $wgDBtype != 'mysql' ) {
 249                         return $this->getWriterIndex();
 250                 }
 251
 252                 if ( count( $this->mServers ) == 1 ) {
 253                         # Skip the load balancing if there's only one server
 254                         return 0;
 255                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 256                         # Shortcut if generic reader exists already
 257                         return $this->mReadIndex;
 258                 }
 259
 260                 # Find the relevant load array
 261                 if ( $group !== false ) {
 262                         if ( isset( $this->mGroupLoads[$group] ) ) {
 263                                 $nonErrorLoads = $this->mGroupLoads[$group];
 264                         } else {
 265                                 # No loads for this group, return false and the caller can use some other group
 266                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 267
 268                                 return false;
 269                         }
 270                 } else {
 271                         $nonErrorLoads = $this->mLoads;
 272                 }
 273
 274                 if ( !count( $nonErrorLoads ) ) {
 275                         throw new MWException( "Empty server array given to LoadBalancer" );
 276                 }
 277
 278                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 279                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 280
 281                 $laggedSlaveMode = false;
 282
 283                 # No server found yet
 284                 $i = false;
 285                 $conn = false;
 286                 # First try quickly looking through the available servers for a server that
 287                 # meets our criteria
 288                 $currentLoads = $nonErrorLoads;
 289                 while ( count( $currentLoads ) ) {
 290                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 291                                 $i = ArrayUtils::pickRandom( $currentLoads );
 292                         } else {
 293                                 $i = false;
 294                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 295                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 296                                         # This triggers doWait() after connect, so it's especially good to
 297                                         # avoid lagged servers so as to avoid just blocking in that method.
 298                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 299                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 300                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 301                                 }
 302                                 if ( $i === false ) {
 303                                         # Any server with less lag than it's 'max lag' param is preferable
 304                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 305                                 }
 306                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 307                                         # All slaves lagged. Switch to read-only mode
 308                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 309                                         $i = ArrayUtils::pickRandom( $currentLoads );
 310                                         $laggedSlaveMode = true;
 311                                 }
 312                         }
 313
 314                         if ( $i === false ) {
 315                                 # pickRandom() returned false
 316                                 # This is permanent and means the configuration or the load monitor
 317                                 # wants us to return false.
 318                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 319
 320                                 return false;
 321                         }
 322
 323                         $serverName = $this->getServerName( $i );
 324                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 325
 326                         $conn = $this->openConnection( $i, $wiki );
 327                         if ( !$conn ) {
 328                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 329                                 unset( $nonErrorLoads[$i] );
 330                                 unset( $currentLoads[$i] );
 331                                 $i = false;
 332                                 continue;
 333                         }
 334
 335                         // Decrement reference counter, we are finished with this connection.
 336                         // It will be incremented for the caller later.
 337                         if ( $wiki !== false ) {
 338                                 $this->reuseConnection( $conn );
 339                         }
 340
 341                         # Return this server
 342                         break;
 343                 }
 344
 345                 # If all servers were down, quit now
 346                 if ( !count( $nonErrorLoads ) ) {
 347                         wfDebugLog( 'connect', "All servers down" );
 348                 }
 349
 350                 if ( $i !== false ) {
 351                         # Slave connection successful
 352                         # Wait for the session master pos for a short time
 353                         if ( $this->mWaitForPos && $i > 0 ) {
 354                                 if ( !$this->doWait( $i ) ) {
 355                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 356                                 }
 357                         }
 358                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 359                                 $this->mReadIndex = $i;
 360                                 # Record if the generic reader index is in "lagged slave" mode
 361                                 if ( $laggedSlaveMode ) {
 362                                         $this->laggedSlaveMode = true;
 363                                 }
 364                         }
 365                         $serverName = $this->getServerName( $i );
 366                         wfDebugLog( 'connect', __METHOD__ .
 367                                 ": using server $serverName for group '$group'\n" );
 368                 }
 369
 370                 return $i;
 371         }
 372
 373         /**
 374          * Set the master wait position
 375          * If a DB_SLAVE connection has been opened already, waits
 376          * Otherwise sets a variable telling it to wait if such a connection is opened
 377          * @param DBMasterPos $pos
 378          */
 379         public function waitFor( $pos ) {
 380                 $this->mWaitForPos = $pos;
 381                 $i = $this->mReadIndex;
 382
 383                 if ( $i > 0 ) {
 384                         if ( !$this->doWait( $i ) ) {
 385                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 386                                 $this->laggedSlaveMode = true;
 387                         }
 388                 }
 389         }
 390
 391         /**
 392          * Set the master wait position and wait for a "generic" slave to catch up to it
 393          *
 394          * This can be used a faster proxy for waitForAll()
 395          *
 396          * @param DBMasterPos $pos
 397          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 398          * @return bool Success (able to connect and no timeouts reached)
 399          * @since 1.26
 400          */
 401         public function waitForOne( $pos, $timeout = null ) {
 402                 $this->mWaitForPos = $pos;
 403
 404                 $i = $this->mReadIndex;
 405                 if ( $i <= 0 ) {
 406                         // Pick a generic slave if there isn't one yet
 407                         $readLoads = $this->mLoads;
 408                         unset( $readLoads[$this->getWriterIndex()] ); // slaves only
 409                         $readLoads = array_filter( $readLoads ); // with non-zero load
 410                         $i = ArrayUtils::pickRandom( $readLoads );
 411                 }
 412
 413                 if ( $i > 0 ) {
 414                         $ok = $this->doWait( $i, true, $timeout );
 415                 } else {
 416                         $ok = true; // no applicable loads
 417                 }
 418
 419                 return $ok;
 420         }
 421
 422         /**
 423          * Set the master wait position and wait for ALL slaves to catch up to it
 424          * @param DBMasterPos $pos
 425          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 426          * @return bool Success (able to connect and no timeouts reached)
 427          */
 428         public function waitForAll( $pos, $timeout = null ) {
 429                 $this->mWaitForPos = $pos;
 430                 $serverCount = count( $this->mServers );
 431
 432                 $ok = true;
 433                 for ( $i = 1; $i < $serverCount; $i++ ) {
 434                         if ( $this->mLoads[$i] > 0 ) {
 435                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 436                         }
 437                 }
 438
 439                 return $ok;
 440         }
 441
 442         /**
 443          * Get any open connection to a given server index, local or foreign
 444          * Returns false if there is no connection open
 445          *
 446          * @param int $i
 447          * @return DatabaseBase|bool False on failure
 448          */
 449         public function getAnyOpenConnection( $i ) {
 450                 foreach ( $this->mConns as $conns ) {
 451                         if ( !empty( $conns[$i] ) ) {
 452                                 return reset( $conns[$i] );
 453                         }
 454                 }
 455
 456                 return false;
 457         }
 458
 459         /**
 460          * Wait for a given slave to catch up to the master pos stored in $this
 461          * @param int $index Server index
 462          * @param bool $open Check the server even if a new connection has to be made
 463          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 464          * @return bool
 465          */
 466         protected function doWait( $index, $open = false, $timeout = null ) {
 467                 $close = false; // close the connection afterwards
 468
 469                 // Check if we already know that the DB has reached this point
 470                 $server = $this->getServerName( $index );
 471                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 472                 /** @var DBMasterPos $knownReachedPos */
 473                 $knownReachedPos = $this->srvCache->get( $key );
 474                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 475                         wfDebugLog( 'replication', __METHOD__ .
 476                                 ": slave $server known to be caught up (pos >= $knownReachedPos).\n" );
 477                         return true;
 478                 }
 479
 480                 // Find a connection to wait on, creating one if needed and allowed
 481                 $conn = $this->getAnyOpenConnection( $index );
 482                 if ( !$conn ) {
 483                         if ( !$open ) {
 484                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 485
 486                                 return false;
 487                         } else {
 488                                 $conn = $this->openConnection( $index, '' );
 489                                 if ( !$conn ) {
 490                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 491
 492                                         return false;
 493                                 }
 494                                 // Avoid connection spam in waitForAll() when connections
 495                                 // are made just for the sake of doing this lag check.
 496                                 $close = true;
 497                         }
 498                 }
 499
 500                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for slave $server to catch up...\n" );
 501                 $timeout = $timeout ?: $this->mWaitTimeout;
 502                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 503
 504                 if ( $result == -1 || is_null( $result ) ) {
 505                         // Timed out waiting for slave, use master instead
 506                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 507                         wfDebugLog( 'replication', "$msg\n" );
 508                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 509                         $ok = false;
 510                 } else {
 511                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 512                         $ok = true;
 513                         // Remember that the DB reached this point
 514                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 515                 }
 516
 517                 if ( $close ) {
 518                         $this->closeConnection( $conn );
 519                 }
 520
 521                 return $ok;
 522         }
 523
 524         /**
 525          * Get a connection by index
 526          * This is the main entry point for this class.
 527          *
 528          * @param int $i Server index
 529          * @param array|string|bool $groups Query group(s), or false for the generic reader
 530          * @param string|bool $wiki Wiki ID, or false for the current wiki
 531          *
 532          * @throws MWException
 533          * @return DatabaseBase
 534          */
 535         public function getConnection( $i, $groups = [], $wiki = false ) {
 536                 if ( $i === null || $i === false ) {
 537                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 538                                 ' with invalid server index' );
 539                 }
 540
 541                 if ( $wiki === wfWikiID() ) {
 542                         $wiki = false;
 543                 }
 544
 545                 $groups = ( $groups === false || $groups === [] )
 546                         ? [ false ] // check one "group": the generic pool
 547                         : (array)$groups;
 548
 549                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 550                 $oldConnsOpened = $this->connsOpened; // connections open now
 551
 552                 if ( $i == DB_MASTER ) {
 553                         $i = $this->getWriterIndex();
 554                 } else {
 555                         # Try to find an available server in any the query groups (in order)
 556                         foreach ( $groups as $group ) {
 557                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 558                                 if ( $groupIndex !== false ) {
 559                                         $i = $groupIndex;
 560                                         break;
 561                                 }
 562                         }
 563                 }
 564
 565                 # Operation-based index
 566                 if ( $i == DB_SLAVE ) {
 567                         $this->mLastError = 'Unknown error'; // reset error string
 568                         # Try the general server pool if $groups are unavailable.
 569                         $i = in_array( false, $groups, true )
 570                                 ? false // don't bother with this if that is what was tried above
 571                                 : $this->getReaderIndex( false, $wiki );
 572                         # Couldn't find a working server in getReaderIndex()?
 573                         if ( $i === false ) {
 574                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 575
 576                                 return $this->reportConnectionError();
 577                         }
 578                 }
 579
 580                 # Now we have an explicit index into the servers array
 581                 $conn = $this->openConnection( $i, $wiki );
 582                 if ( !$conn ) {
 583                         return $this->reportConnectionError();
 584                 }
 585
 586                 # Profile any new connections that happen
 587                 if ( $this->connsOpened > $oldConnsOpened ) {
 588                         $host = $conn->getServer();
 589                         $dbname = $conn->getDBname();
 590                         $trxProf = Profiler::instance()->getTransactionProfiler();
 591                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 592                 }
 593
 594                 if ( $masterOnly ) {
 595                         # Make master-requested DB handles inherit any read-only mode setting
 596                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
 597                 }
 598
 599                 return $conn;
 600         }
 601
 602         /**
 603          * Mark a foreign connection as being available for reuse under a different
 604          * DB name or prefix. This mechanism is reference-counted, and must be called
 605          * the same number of times as getConnection() to work.
 606          *
 607          * @param DatabaseBase $conn
 608          * @throws MWException
 609          */
 610         public function reuseConnection( $conn ) {
 611                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 612                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 613                 if ( $serverIndex === null || $refCount === null ) {
 614                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 615                         /**
 616                          * This can happen in code like:
 617                          *   foreach ( $dbs as $db ) {
 618                          *     $conn = $lb->getConnection( DB_SLAVE, [], $db );
 619                          *     ...
 620                          *     $lb->reuseConnection( $conn );
 621                          *   }
 622                          * When a connection to the local DB is opened in this way, reuseConnection()
 623                          * should be ignored
 624                          */
 625                         return;
 626                 }
 627
 628                 $dbName = $conn->getDBname();
 629                 $prefix = $conn->tablePrefix();
 630                 if ( strval( $prefix ) !== '' ) {
 631                         $wiki = "$dbName-$prefix";
 632                 } else {
 633                         $wiki = $dbName;
 634                 }
 635                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 636                         throw new MWException( __METHOD__ . ": connection not found, has " .
 637                                 "the connection been freed already?" );
 638                 }
 639                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 640                 if ( $refCount <= 0 ) {
 641                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 642                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 643                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 644                 } else {
 645                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 646                 }
 647         }
 648
 649         /**
 650          * Get a database connection handle reference
 651          *
 652          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 653          *
 654          * @see LoadBalancer::getConnection() for parameter information
 655          *
 656          * @param int $db
 657          * @param array|string|bool $groups Query group(s), or false for the generic reader
 658          * @param string|bool $wiki Wiki ID, or false for the current wiki
 659          * @return DBConnRef
 660          */
 661         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 662                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 663         }
 664
 665         /**
 666          * Get a database connection handle reference without connecting yet
 667          *
 668          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 669          *
 670          * @see LoadBalancer::getConnection() for parameter information
 671          *
 672          * @param int $db
 673          * @param array|string|bool $groups Query group(s), or false for the generic reader
 674          * @param string|bool $wiki Wiki ID, or false for the current wiki
 675          * @return DBConnRef
 676          */
 677         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 678                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 679         }
 680
 681         /**
 682          * Open a connection to the server given by the specified index
 683          * Index must be an actual index into the array.
 684          * If the server is already open, returns it.
 685          *
 686          * On error, returns false, and the connection which caused the
 687          * error will be available via $this->mErrorConnection.
 688          *
 689          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 690          *
 691          * @param int $i Server index
 692          * @param string|bool $wiki Wiki ID, or false for the current wiki
 693          * @return DatabaseBase|bool Returns false on errors
 694          */
 695         public function openConnection( $i, $wiki = false ) {
 696                 if ( $wiki !== false ) {
 697                         $conn = $this->openForeignConnection( $i, $wiki );
 698                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 699                         $conn = $this->mConns['local'][$i][0];
 700                 } else {
 701                         $server = $this->mServers[$i];
 702                         $server['serverIndex'] = $i;
 703                         $conn = $this->reallyOpenConnection( $server, false );
 704                         $serverName = $this->getServerName( $i );
 705                         if ( $conn->isOpen() ) {
 706                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 707                                 $this->mConns['local'][$i][0] = $conn;
 708                         } else {
 709                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 710                                 $this->mErrorConnection = $conn;
 711                                 $conn = false;
 712                         }
 713                 }
 714
 715                 if ( $conn && !$conn->isOpen() ) {
 716                         // Connection was made but later unrecoverably lost for some reason.
 717                         // Do not return a handle that will just throw exceptions on use,
 718                         // but let the calling code (e.g. getReaderIndex) try another server.
 719                         // See DatabaseMyslBase::ping() for how this can happen.
 720                         $this->mErrorConnection = $conn;
 721                         $conn = false;
 722                 }
 723
 724                 return $conn;
 725         }
 726
 727         /**
 728          * Open a connection to a foreign DB, or return one if it is already open.
 729          *
 730          * Increments a reference count on the returned connection which locks the
 731          * connection to the requested wiki. This reference count can be
 732          * decremented by calling reuseConnection().
 733          *
 734          * If a connection is open to the appropriate server already, but with the wrong
 735          * database, it will be switched to the right database and returned, as long as
 736          * it has been freed first with reuseConnection().
 737          *
 738          * On error, returns false, and the connection which caused the
 739          * error will be available via $this->mErrorConnection.
 740          *
 741          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 742          *
 743          * @param int $i Server index
 744          * @param string $wiki Wiki ID to open
 745          * @return DatabaseBase
 746          */
 747         private function openForeignConnection( $i, $wiki ) {
 748                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 749                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 750                         // Reuse an already-used connection
 751                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 752                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 753                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 754                         // Reuse a free connection for the same wiki
 755                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 756                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 757                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 758                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 759                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 760                         // Reuse a connection from another wiki
 761                         $conn = reset( $this->mConns['foreignFree'][$i] );
 762                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 763
 764                         // The empty string as a DB name means "don't care".
 765                         // DatabaseMysqlBase::open() already handle this on connection.
 766                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 767                                 $this->mLastError = "Error selecting database $dbName on server " .
 768                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 769                                 $this->mErrorConnection = $conn;
 770                                 $conn = false;
 771                         } else {
 772                                 $conn->tablePrefix( $prefix );
 773                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 774                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 775                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 776                         }
 777                 } else {
 778                         // Open a new connection
 779                         $server = $this->mServers[$i];
 780                         $server['serverIndex'] = $i;
 781                         $server['foreignPoolRefCount'] = 0;
 782                         $server['foreign'] = true;
 783                         $conn = $this->reallyOpenConnection( $server, $dbName );
 784                         if ( !$conn->isOpen() ) {
 785                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 786                                 $this->mErrorConnection = $conn;
 787                                 $conn = false;
 788                         } else {
 789                                 $conn->tablePrefix( $prefix );
 790                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 791                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 792                         }
 793                 }
 794
 795                 // Increment reference count
 796                 if ( $conn ) {
 797                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 798                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 799                 }
 800
 801                 return $conn;
 802         }
 803
 804         /**
 805          * Test if the specified index represents an open connection
 806          *
 807          * @param int $index Server index
 808          * @access private
 809          * @return bool
 810          */
 811         private function isOpen( $index ) {
 812                 if ( !is_integer( $index ) ) {
 813                         return false;
 814                 }
 815
 816                 return (bool)$this->getAnyOpenConnection( $index );
 817         }
 818
 819         /**
 820          * Really opens a connection. Uncached.
 821          * Returns a Database object whether or not the connection was successful.
 822          * @access private
 823          *
 824          * @param array $server
 825          * @param bool $dbNameOverride
 826          * @throws MWException
 827          * @return DatabaseBase
 828          */
 829         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 830                 if ( $this->disabled ) {
 831                         throw new DBAccessError();
 832                 }
 833
 834                 if ( !is_array( $server ) ) {
 835                         throw new MWException( 'You must update your load-balancing configuration. ' .
 836                                 'See DefaultSettings.php entry for $wgDBservers.' );
 837                 }
 838
 839                 if ( $dbNameOverride !== false ) {
 840                         $server['dbname'] = $dbNameOverride;
 841                 }
 842
 843                 // Let the handle know what the cluster master is (e.g. "db1052")
 844                 $masterName = $this->getServerName( 0 );
 845                 $server['clusterMasterHost'] = $masterName;
 846
 847                 // Log when many connection are made on requests
 848                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 849                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 850                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 851                                 wfBacktrace( true ) );
 852                 }
 853
 854                 # Create object
 855                 try {
 856                         $db = DatabaseBase::factory( $server['type'], $server );
 857                 } catch ( DBConnectionError $e ) {
 858                         // FIXME: This is probably the ugliest thing I have ever done to
 859                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 860                         $db = $e->db;
 861                 }
 862
 863                 $db->setLBInfo( $server );
 864                 $db->setLazyMasterHandle(
 865                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 866                 );
 867                 $db->setTransactionProfiler( $this->trxProfiler );
 868                 if ( $this->trxRoundId !== false ) {
 869                         $this->applyTransactionRoundFlags( $db );
 870                 }
 871
 872                 return $db;
 873         }
 874
 875         /**
 876          * @throws DBConnectionError
 877          * @return bool
 878          */
 879         private function reportConnectionError() {
 880                 $conn = $this->mErrorConnection; // The connection which caused the error
 881                 $context = [
 882                         'method' => __METHOD__,
 883                         'last_error' => $this->mLastError,
 884                 ];
 885
 886                 if ( !is_object( $conn ) ) {
 887                         // No last connection, probably due to all servers being too busy
 888                         wfLogDBError(
 889                                 "LB failure with no last connection. Connection error: {last_error}",
 890                                 $context
 891                         );
 892
 893                         // If all servers were busy, mLastError will contain something sensible
 894                         throw new DBConnectionError( null, $this->mLastError );
 895                 } else {
 896                         $context['db_server'] = $conn->getProperty( 'mServer' );
 897                         wfLogDBError(
 898                                 "Connection error: {last_error} ({db_server})",
 899                                 $context
 900                         );
 901
 902                         // throws DBConnectionError
 903                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 904                 }
 905
 906                 return false; /* not reached */
 907         }
 908
 909         /**
 910          * @return int
 911          * @since 1.26
 912          */
 913         public function getWriterIndex() {
 914                 return 0;
 915         }
 916
 917         /**
 918          * Returns true if the specified index is a valid server index
 919          *
 920          * @param string $i
 921          * @return bool
 922          */
 923         public function haveIndex( $i ) {
 924                 return array_key_exists( $i, $this->mServers );
 925         }
 926
 927         /**
 928          * Returns true if the specified index is valid and has non-zero load
 929          *
 930          * @param string $i
 931          * @return bool
 932          */
 933         public function isNonZeroLoad( $i ) {
 934                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 935         }
 936
 937         /**
 938          * Get the number of defined servers (not the number of open connections)
 939          *
 940          * @return int
 941          */
 942         public function getServerCount() {
 943                 return count( $this->mServers );
 944         }
 945
 946         /**
 947          * Get the host name or IP address of the server with the specified index
 948          * Prefer a readable name if available.
 949          * @param string $i
 950          * @return string
 951          */
 952         public function getServerName( $i ) {
 953                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 954                         $name = $this->mServers[$i]['hostName'];
 955                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 956                         $name = $this->mServers[$i]['host'];
 957                 } else {
 958                         $name = '';
 959                 }
 960
 961                 return ( $name != '' ) ? $name : 'localhost';
 962         }
 963
 964         /**
 965          * Return the server info structure for a given index, or false if the index is invalid.
 966          * @param int $i
 967          * @return array|bool
 968          */
 969         public function getServerInfo( $i ) {
 970                 if ( isset( $this->mServers[$i] ) ) {
 971                         return $this->mServers[$i];
 972                 } else {
 973                         return false;
 974                 }
 975         }
 976
 977         /**
 978          * Sets the server info structure for the given index. Entry at index $i
 979          * is created if it doesn't exist
 980          * @param int $i
 981          * @param array $serverInfo
 982          */
 983         public function setServerInfo( $i, array $serverInfo ) {
 984                 $this->mServers[$i] = $serverInfo;
 985         }
 986
 987         /**
 988          * Get the current master position for chronology control purposes
 989          * @return mixed
 990          */
 991         public function getMasterPos() {
 992                 # If this entire request was served from a slave without opening a connection to the
 993                 # master (however unlikely that may be), then we can fetch the position from the slave.
 994                 $masterConn = $this->getAnyOpenConnection( 0 );
 995                 if ( !$masterConn ) {
 996                         $serverCount = count( $this->mServers );
 997                         for ( $i = 1; $i < $serverCount; $i++ ) {
 998                                 $conn = $this->getAnyOpenConnection( $i );
 999                                 if ( $conn ) {
1000                                         return $conn->getSlavePos();
1001                                 }
1002                         }
1003                 } else {
1004                         return $masterConn->getMasterPos();
1005                 }
1006
1007                 return false;
1008         }
1009
1010         /**
1011          * Disable this load balancer. All connections are closed, and any attempt to
1012          * open a new connection will result in a DBAccessError.
1013          *
1014          * @since 1.27
1015          */
1016         public function disable() {
1017                 $this->closeAll();
1018                 $this->disabled = true;
1019         }
1020
1021         /**
1022          * Close all open connections
1023          */
1024         public function closeAll() {
1025                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1026                         $conn->close();
1027                 } );
1028
1029                 $this->mConns = [
1030                         'local' => [],
1031                         'foreignFree' => [],
1032                         'foreignUsed' => [],
1033                 ];
1034                 $this->connsOpened = 0;
1035         }
1036
1037         /**
1038          * Close a connection
1039          * Using this function makes sure the LoadBalancer knows the connection is closed.
1040          * If you use $conn->close() directly, the load balancer won't update its state.
1041          * @param DatabaseBase $conn
1042          */
1043         public function closeConnection( $conn ) {
1044                 $done = false;
1045                 foreach ( $this->mConns as $i1 => $conns2 ) {
1046                         foreach ( $conns2 as $i2 => $conns3 ) {
1047                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1048                                         if ( $conn === $candidateConn ) {
1049                                                 $conn->close();
1050                                                 unset( $this->mConns[$i1][$i2][$i3] );
1051                                                 --$this->connsOpened;
1052                                                 $done = true;
1053                                                 break;
1054                                         }
1055                                 }
1056                         }
1057                 }
1058                 if ( !$done ) {
1059                         $conn->close();
1060                 }
1061         }
1062
1063         /**
1064          * Commit transactions on all open connections
1065          * @param string $fname Caller name
1066          * @throws DBExpectedError
1067          */
1068         public function commitAll( $fname = __METHOD__ ) {
1069                 $failures = [];
1070
1071                 $restore = ( $this->trxRoundId !== false );
1072                 $this->trxRoundId = false;
1073                 $this->forEachOpenConnection(
1074                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1075                                 try {
1076                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1077                                 } catch ( DBError $e ) {
1078                                         MWExceptionHandler::logException( $e );
1079                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1080                                 }
1081                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1082                                         $this->undoTransactionRoundFlags( $conn );
1083                                 }
1084                         }
1085                 );
1086
1087                 if ( $failures ) {
1088                         throw new DBExpectedError(
1089                                 null,
1090                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1091                         );
1092                 }
1093         }
1094
1095         /**
1096          * Perform all pre-commit callbacks that remain part of the atomic transactions
1097          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
1098          * @since 1.28
1099          */
1100         public function finalizeMasterChanges() {
1101                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1102                         // Any error should cause all DB transactions to be rolled back together
1103                         $conn->setTrxEndCallbackSuppression( false );
1104                         $conn->runOnTransactionPreCommitCallbacks();
1105                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1106                         $conn->setTrxEndCallbackSuppression( true );
1107                 } );
1108         }
1109
1110         /**
1111          * Perform all pre-commit checks for things like replication safety
1112          * @param array $options Includes:
1113          *   - maxWriteDuration : max write query duration time in seconds
1114          * @throws DBTransactionError
1115          * @since 1.28
1116          */
1117         public function approveMasterChanges( array $options ) {
1118                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1119                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1120                         // If atomic sections or explicit transactions are still open, some caller must have
1121                         // caught an exception but failed to properly rollback any changes. Detect that and
1122                         // throw and error (causing rollback).
1123                         if ( $conn->explicitTrxActive() ) {
1124                                 throw new DBTransactionError(
1125                                         $conn,
1126                                         "Explicit transaction still active. A caller may have caught an error."
1127                                 );
1128                         }
1129                         // Assert that the time to replicate the transaction will be sane.
1130                         // If this fails, then all DB transactions will be rollback back together.
1131                         $time = $conn->pendingWriteQueryDuration();
1132                         if ( $limit > 0 && $time > $limit ) {
1133                                 throw new DBTransactionError(
1134                                         $conn,
1135                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1136                                 );
1137                         }
1138                         // If a connection sits idle while slow queries execute on another, that connection
1139                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1140                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1141                                 throw new DBTransactionError(
1142                                         $conn,
1143                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1144                                 );
1145                         }
1146                 } );
1147         }
1148
1149         /**
1150          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
1151          *
1152          * The DBO_TRX setting will be reverted to the default in each of these methods:
1153          *   - commitMasterChanges()
1154          *   - rollbackMasterChanges()
1155          *   - commitAll()
1156          * This allows for custom transaction rounds from any outer transaction scope.
1157          *
1158          * @param string $fname
1159          * @throws DBExpectedError
1160          * @since 1.28
1161          */
1162         public function beginMasterChanges( $fname = __METHOD__ ) {
1163                 if ( $this->trxRoundId !== false ) {
1164                         throw new DBTransactionError(
1165                                 null,
1166                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1167                         );
1168                 }
1169                 $this->trxRoundId = $fname;
1170
1171                 $failures = [];
1172                 $this->forEachOpenMasterConnection(
1173                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1174                                 $conn->setTrxEndCallbackSuppression( true );
1175                                 try {
1176                                         $conn->clearSnapshot( $fname );
1177                                 } catch ( DBError $e ) {
1178                                         MWExceptionHandler::logException( $e );
1179                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1180                                 }
1181                                 $conn->setTrxEndCallbackSuppression( false );
1182                                 $this->applyTransactionRoundFlags( $conn );
1183                         }
1184                 );
1185
1186                 if ( $failures ) {
1187                         throw new DBExpectedError(
1188                                 null,
1189                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1190                         );
1191                 }
1192         }
1193
1194         /**
1195          * Issue COMMIT on all master connections where writes where done
1196          * @param string $fname Caller name
1197          * @throws DBExpectedError
1198          */
1199         public function commitMasterChanges( $fname = __METHOD__ ) {
1200                 $failures = [];
1201
1202                 $restore = ( $this->trxRoundId !== false );
1203                 $this->trxRoundId = false;
1204                 $this->forEachOpenMasterConnection(
1205                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1206                                 try {
1207                                         if ( $conn->writesOrCallbacksPending() ) {
1208                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1209                                         } elseif ( $restore ) {
1210                                                 $conn->clearSnapshot( $fname );
1211                                         }
1212                                 } catch ( DBError $e ) {
1213                                         MWExceptionHandler::logException( $e );
1214                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1215                                 }
1216                                 if ( $restore ) {
1217                                         $this->undoTransactionRoundFlags( $conn );
1218                                 }
1219                         }
1220                 );
1221
1222                 if ( $failures ) {
1223                         throw new DBExpectedError(
1224                                 null,
1225                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1226                         );
1227                 }
1228         }
1229
1230         /**
1231          * Issue all pending post-COMMIT/ROLLBACK callbacks
1232          * @param integer $type IDatabase::TRIGGER_* constant
1233          * @return Exception|null The first exception or null if there were none
1234          * @since 1.28
1235          */
1236         public function runMasterPostTrxCallbacks( $type ) {
1237                 $e = null; // first exception
1238                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1239                         $conn->clearSnapshot( __METHOD__ ); // clear no-op transactions
1240
1241                         $conn->setTrxEndCallbackSuppression( false );
1242                         try {
1243                                 $conn->runOnTransactionIdleCallbacks( $type );
1244                         } catch ( Exception $ex ) {
1245                                 $e = $e ?: $ex;
1246                         }
1247                         try {
1248                                 $conn->runTransactionListenerCallbacks( $type );
1249                         } catch ( Exception $ex ) {
1250                                 $e = $e ?: $ex;
1251                         }
1252                 } );
1253
1254                 return $e;
1255         }
1256
1257         /**
1258          * Issue ROLLBACK only on master, only if queries were done on connection
1259          * @param string $fname Caller name
1260          * @throws DBExpectedError
1261          * @since 1.23
1262          */
1263         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1264                 $restore = ( $this->trxRoundId !== false );
1265                 $this->trxRoundId = false;
1266                 $this->forEachOpenMasterConnection(
1267                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1268                                 if ( $conn->writesOrCallbacksPending() ) {
1269                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1270                                 }
1271                                 if ( $restore ) {
1272                                         $this->undoTransactionRoundFlags( $conn );
1273                                 }
1274                         }
1275                 );
1276         }
1277
1278         /**
1279          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1280          * @return Exception|null The first exception or null if there were none
1281          * @since 1.28
1282          */
1283         public function suppressTransactionEndCallbacks() {
1284                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1285                         $conn->setTrxEndCallbackSuppression( true );
1286                 } );
1287         }
1288
1289         /**
1290          * @param DatabaseBase $conn
1291          */
1292         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1293                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1294                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1295                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1296                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1297                         // If config has explicitly requested DBO_TRX be either on or off by not
1298                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1299                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1300                 }
1301         }
1302
1303         /**
1304          * @param DatabaseBase $conn
1305          */
1306         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1307                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1308                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1309                 }
1310         }
1311
1312         /**
1313          * @return bool Whether a master connection is already open
1314          * @since 1.24
1315          */
1316         public function hasMasterConnection() {
1317                 return $this->isOpen( $this->getWriterIndex() );
1318         }
1319
1320         /**
1321          * Determine if there are pending changes in a transaction by this thread
1322          * @since 1.23
1323          * @return bool
1324          */
1325         public function hasMasterChanges() {
1326                 $masterIndex = $this->getWriterIndex();
1327                 foreach ( $this->mConns as $conns2 ) {
1328                         if ( empty( $conns2[$masterIndex] ) ) {
1329                                 continue;
1330                         }
1331                         /** @var DatabaseBase $conn */
1332                         foreach ( $conns2[$masterIndex] as $conn ) {
1333                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1334                                         return true;
1335                                 }
1336                         }
1337                 }
1338                 return false;
1339         }
1340
1341         /**
1342          * Get the timestamp of the latest write query done by this thread
1343          * @since 1.25
1344          * @return float|bool UNIX timestamp or false
1345          */
1346         public function lastMasterChangeTimestamp() {
1347                 $lastTime = false;
1348                 $masterIndex = $this->getWriterIndex();
1349                 foreach ( $this->mConns as $conns2 ) {
1350                         if ( empty( $conns2[$masterIndex] ) ) {
1351                                 continue;
1352                         }
1353                         /** @var DatabaseBase $conn */
1354                         foreach ( $conns2[$masterIndex] as $conn ) {
1355                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1356                         }
1357                 }
1358                 return $lastTime;
1359         }
1360
1361         /**
1362          * Check if this load balancer object had any recent or still
1363          * pending writes issued against it by this PHP thread
1364          *
1365          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1366          * @return bool
1367          * @since 1.25
1368          */
1369         public function hasOrMadeRecentMasterChanges( $age = null ) {
1370                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1371
1372                 return ( $this->hasMasterChanges()
1373                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1374         }
1375
1376         /**
1377          * Get the list of callers that have pending master changes
1378          *
1379          * @return array
1380          * @since 1.27
1381          */
1382         public function pendingMasterChangeCallers() {
1383                 $fnames = [];
1384
1385                 $masterIndex = $this->getWriterIndex();
1386                 foreach ( $this->mConns as $conns2 ) {
1387                         if ( empty( $conns2[$masterIndex] ) ) {
1388                                 continue;
1389                         }
1390                         /** @var DatabaseBase $conn */
1391                         foreach ( $conns2[$masterIndex] as $conn ) {
1392                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1393                         }
1394                 }
1395
1396                 return $fnames;
1397         }
1398
1399         /**
1400          * @param mixed $value
1401          * @return mixed
1402          */
1403         public function waitTimeout( $value = null ) {
1404                 return wfSetVar( $this->mWaitTimeout, $value );
1405         }
1406
1407         /**
1408          * @note This method will trigger a DB connection if not yet done
1409          *
1410          * @param string|bool $wiki Wiki ID, or false for the current wiki
1411          * @return bool Whether the generic connection for reads is highly "lagged"
1412          */
1413         public function getLaggedSlaveMode( $wiki = false ) {
1414                 // No-op if there is only one DB (also avoids recursion)
1415                 if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
1416                         try {
1417                                 // See if laggedSlaveMode gets set
1418                                 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1419                                 $this->reuseConnection( $conn );
1420                         } catch ( DBConnectionError $e ) {
1421                                 // Avoid expensive re-connect attempts and failures
1422                                 $this->slavesDownMode = true;
1423                                 $this->laggedSlaveMode = true;
1424                         }
1425                 }
1426
1427                 return $this->laggedSlaveMode;
1428         }
1429
1430         /**
1431          * @note This method will never cause a new DB connection
1432          * @return bool Whether any generic connection used for reads was highly "lagged"
1433          * @since 1.27
1434          */
1435         public function laggedSlaveUsed() {
1436                 return $this->laggedSlaveMode;
1437         }
1438
1439         /**
1440          * @note This method may trigger a DB connection if not yet done
1441          * @param string|bool $wiki Wiki ID, or false for the current wiki
1442          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1443          * @return string|bool Reason the master is read-only or false if it is not
1444          * @since 1.27
1445          */
1446         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1447                 if ( $this->readOnlyReason !== false ) {
1448                         return $this->readOnlyReason;
1449                 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1450                         if ( $this->slavesDownMode ) {
1451                                 return 'The database has been automatically locked ' .
1452                                         'until the slave database servers become available';
1453                         } else {
1454                                 return 'The database has been automatically locked ' .
1455                                         'while the slave database servers catch up to the master.';
1456                         }
1457                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1458                         return 'The database master is running in read-only mode.';
1459                 }
1460
1461                 return false;
1462         }
1463
1464         /**
1465          * @param string $wiki Wiki ID, or false for the current wiki
1466          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1467          * @return bool
1468          */
1469         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1470                 $cache = $this->wanCache;
1471                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1472
1473                 return (bool)$cache->getWithSetCallback(
1474                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1475                         self::TTL_CACHE_READONLY,
1476                         function () use ( $wiki, $conn ) {
1477                                 $this->trxProfiler->setSilenced( true );
1478                                 try {
1479                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1480                                         $readOnly = (int)$dbw->serverIsReadOnly();
1481                                 } catch ( DBError $e ) {
1482                                         $readOnly = 0;
1483                                 }
1484                                 $this->trxProfiler->setSilenced( false );
1485                                 return $readOnly;
1486                         },
1487                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1488                 );
1489         }
1490
1491         /**
1492          * Disables/enables lag checks
1493          * @param null|bool $mode
1494          * @return bool
1495          */
1496         public function allowLagged( $mode = null ) {
1497                 if ( $mode === null ) {
1498                         return $this->mAllowLagged;
1499                 }
1500                 $this->mAllowLagged = $mode;
1501
1502                 return $this->mAllowLagged;
1503         }
1504
1505         /**
1506          * @return bool
1507          */
1508         public function pingAll() {
1509                 $success = true;
1510                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1511                         if ( !$conn->ping() ) {
1512                                 $success = false;
1513                         }
1514                 } );
1515
1516                 return $success;
1517         }
1518
1519         /**
1520          * Call a function with each open connection object
1521          * @param callable $callback
1522          * @param array $params
1523          */
1524         public function forEachOpenConnection( $callback, array $params = [] ) {
1525                 foreach ( $this->mConns as $connsByServer ) {
1526                         foreach ( $connsByServer as $serverConns ) {
1527                                 foreach ( $serverConns as $conn ) {
1528                                         $mergedParams = array_merge( [ $conn ], $params );
1529                                         call_user_func_array( $callback, $mergedParams );
1530                                 }
1531                         }
1532                 }
1533         }
1534
1535         /**
1536          * Call a function with each open connection object to a master
1537          * @param callable $callback
1538          * @param array $params
1539          * @since 1.28
1540          */
1541         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1542                 $masterIndex = $this->getWriterIndex();
1543                 foreach ( $this->mConns as $connsByServer ) {
1544                         if ( isset( $connsByServer[$masterIndex] ) ) {
1545                                 /** @var DatabaseBase $conn */
1546                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1547                                         $mergedParams = array_merge( [ $conn ], $params );
1548                                         call_user_func_array( $callback, $mergedParams );
1549                                 }
1550                         }
1551                 }
1552         }
1553
1554         /**
1555          * Get the hostname and lag time of the most-lagged slave
1556          *
1557          * This is useful for maintenance scripts that need to throttle their updates.
1558          * May attempt to open connections to slaves on the default DB. If there is
1559          * no lag, the maximum lag will be reported as -1.
1560          *
1561          * @param bool|string $wiki Wiki ID, or false for the default database
1562          * @return array ( host, max lag, index of max lagged host )
1563          */
1564         public function getMaxLag( $wiki = false ) {
1565                 $maxLag = -1;
1566                 $host = '';
1567                 $maxIndex = 0;
1568
1569                 if ( $this->getServerCount() <= 1 ) {
1570                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1571                 }
1572
1573                 $lagTimes = $this->getLagTimes( $wiki );
1574                 foreach ( $lagTimes as $i => $lag ) {
1575                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1576                                 $maxLag = $lag;
1577                                 $host = $this->mServers[$i]['host'];
1578                                 $maxIndex = $i;
1579                         }
1580                 }
1581
1582                 return [ $host, $maxLag, $maxIndex ];
1583         }
1584
1585         /**
1586          * Get an estimate of replication lag (in seconds) for each server
1587          *
1588          * Results are cached for a short time in memcached/process cache
1589          *
1590          * Values may be "false" if replication is too broken to estimate
1591          *
1592          * @param string|bool $wiki
1593          * @return int[] Map of (server index => float|int|bool)
1594          */
1595         public function getLagTimes( $wiki = false ) {
1596                 if ( $this->getServerCount() <= 1 ) {
1597                         return [ 0 => 0 ]; // no replication = no lag
1598                 }
1599
1600                 # Send the request to the load monitor
1601                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1602         }
1603
1604         /**
1605          * Get the lag in seconds for a given connection, or zero if this load
1606          * balancer does not have replication enabled.
1607          *
1608          * This should be used in preference to Database::getLag() in cases where
1609          * replication may not be in use, since there is no way to determine if
1610          * replication is in use at the connection level without running
1611          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1612          * function instead of Database::getLag() avoids a fatal error in this
1613          * case on many installations.
1614          *
1615          * @param IDatabase $conn
1616          * @return int|bool Returns false on error
1617          */
1618         public function safeGetLag( IDatabase $conn ) {
1619                 if ( $this->getServerCount() == 1 ) {
1620                         return 0;
1621                 } else {
1622                         return $conn->getLag();
1623                 }
1624         }
1625
1626         /**
1627          * Wait for a slave DB to reach a specified master position
1628          *
1629          * This will connect to the master to get an accurate position if $pos is not given
1630          *
1631          * @param IDatabase $conn Slave DB
1632          * @param DBMasterPos|bool $pos Master position; default: current position
1633          * @param integer $timeout Timeout in seconds
1634          * @return bool Success
1635          * @since 1.27
1636          */
1637         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1638                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
1639                         return true; // server is not a slave DB
1640                 }
1641
1642                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1643                 if ( !( $pos instanceof DBMasterPos ) ) {
1644                         return false; // something is misconfigured
1645                 }
1646
1647                 $result = $conn->masterPosWait( $pos, $timeout );
1648                 if ( $result == -1 || is_null( $result ) ) {
1649                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1650                         wfDebugLog( 'replication', "$msg\n" );
1651                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1652                         $ok = false;
1653                 } else {
1654                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1655                         $ok = true;
1656                 }
1657
1658                 return $ok;
1659         }
1660
1661         /**
1662          * Clear the cache for slag lag delay times
1663          *
1664          * This is only used for testing
1665          */
1666         public function clearLagTimeCache() {
1667                 $this->getLoadMonitor()->clearCaches();
1668         }
1669 }