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 replica DB lag as a factor in replica DB selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on replica DB 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) replica DB 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 replica DB */
  64         private $laggedReplicaMode = false;
  65         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  66         private $allReplicasDownMode = 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         /** @var array[] Map of (name => callable) */
  76         private $trxRecurringCallbacks = [];
  77
  78         /** @var integer Warn when this many connection are held */
  79         const CONN_HELD_WARN_THRESHOLD = 10;
  80         /** @var integer Default 'max lag' when unspecified */
  81         const MAX_LAG_DEFAULT = 10;
  82         /** @var integer Max time to wait for a replica DB to catch up (e.g. ChronologyProtector) */
  83         const POS_WAIT_TIMEOUT = 10;
  84         /** @var integer Seconds to cache master server read-only status */
  85         const TTL_CACHE_READONLY = 5;
  86
  87         /**
  88          * @var boolean
  89          */
  90         private $disabled = false;
  91
  92         /**
  93          * @param array $params Array with keys:
  94          *  - servers : Required. Array of server info structures.
  95          *  - loadMonitor : Name of a class used to fetch server lag and load.
  96          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  97          *  - srvCache : BagOStuff object [optional]
  98          *  - wanCache : WANObjectCache object [optional]
  99          * @throws MWException
 100          */
 101         public function __construct( array $params ) {
 102                 if ( !isset( $params['servers'] ) ) {
 103                         throw new MWException( __CLASS__ . ': missing servers parameter' );
 104                 }
 105                 $this->mServers = $params['servers'];
 106                 $this->mWaitTimeout = self::POS_WAIT_TIMEOUT;
 107
 108                 $this->mReadIndex = -1;
 109                 $this->mWriteIndex = -1;
 110                 $this->mConns = [
 111                         'local' => [],
 112                         'foreignUsed' => [],
 113                         'foreignFree' => [] ];
 114                 $this->mLoads = [];
 115                 $this->mWaitForPos = false;
 116                 $this->mErrorConnection = false;
 117                 $this->mAllowLagged = false;
 118
 119                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 120                         $this->readOnlyReason = $params['readOnlyReason'];
 121                 }
 122
 123                 if ( isset( $params['loadMonitor'] ) ) {
 124                         $this->mLoadMonitorClass = $params['loadMonitor'];
 125                 } else {
 126                         $master = reset( $params['servers'] );
 127                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 128                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 129                         } else {
 130                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 131                         }
 132                 }
 133
 134                 foreach ( $params['servers'] as $i => $server ) {
 135                         $this->mLoads[$i] = $server['load'];
 136                         if ( isset( $server['groupLoads'] ) ) {
 137                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 138                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 139                                                 $this->mGroupLoads[$group] = [];
 140                                         }
 141                                         $this->mGroupLoads[$group][$i] = $ratio;
 142                                 }
 143                         }
 144                 }
 145
 146                 if ( isset( $params['srvCache'] ) ) {
 147                         $this->srvCache = $params['srvCache'];
 148                 } else {
 149                         $this->srvCache = new EmptyBagOStuff();
 150                 }
 151                 if ( isset( $params['wanCache'] ) ) {
 152                         $this->wanCache = $params['wanCache'];
 153                 } else {
 154                         $this->wanCache = WANObjectCache::newEmpty();
 155                 }
 156                 if ( isset( $params['trxProfiler'] ) ) {
 157                         $this->trxProfiler = $params['trxProfiler'];
 158                 } else {
 159                         $this->trxProfiler = new TransactionProfiler();
 160                 }
 161         }
 162
 163         /**
 164          * Get a LoadMonitor instance
 165          *
 166          * @return LoadMonitor
 167          */
 168         private function getLoadMonitor() {
 169                 if ( !isset( $this->mLoadMonitor ) ) {
 170                         $class = $this->mLoadMonitorClass;
 171                         $this->mLoadMonitor = new $class( $this );
 172                 }
 173
 174                 return $this->mLoadMonitor;
 175         }
 176
 177         /**
 178          * Get or set arbitrary data used by the parent object, usually an LBFactory
 179          * @param mixed $x
 180          * @return mixed
 181          */
 182         public function parentInfo( $x = null ) {
 183                 return wfSetVar( $this->mParentInfo, $x );
 184         }
 185
 186         /**
 187          * @param array $loads
 188          * @param bool|string $wiki Wiki to get non-lagged for
 189          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 190          * @return bool|int|string
 191          */
 192         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 193                 $lags = $this->getLagTimes( $wiki );
 194
 195                 # Unset excessively lagged servers
 196                 foreach ( $lags as $i => $lag ) {
 197                         if ( $i != 0 ) {
 198                                 # How much lag this server nominally is allowed to have
 199                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 200                                         ? $this->mServers[$i]['max lag']
 201                                         : self::MAX_LAG_DEFAULT; // default
 202                                 # Constrain that futher by $maxLag argument
 203                                 $maxServerLag = min( $maxServerLag, $maxLag );
 204
 205                                 $host = $this->getServerName( $i );
 206                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 207                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 208                                         unset( $loads[$i] );
 209                                 } elseif ( $lag > $maxServerLag ) {
 210                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 211                                         unset( $loads[$i] );
 212                                 }
 213                         }
 214                 }
 215
 216                 # Find out if all the replica DBs with non-zero load are lagged
 217                 $sum = 0;
 218                 foreach ( $loads as $load ) {
 219                         $sum += $load;
 220                 }
 221                 if ( $sum == 0 ) {
 222                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 223                         # Do NOT use the master
 224                         # Instead, this function will return false, triggering read-only mode,
 225                         # and a lagged replica DB will be used instead.
 226                         return false;
 227                 }
 228
 229                 if ( count( $loads ) == 0 ) {
 230                         return false;
 231                 }
 232
 233                 # Return a random representative of the remainder
 234                 return ArrayUtils::pickRandom( $loads );
 235         }
 236
 237         /**
 238          * Get the index of the reader connection, which may be a replica DB
 239          * This takes into account load ratios and lag times. It should
 240          * always return a consistent index during a given invocation
 241          *
 242          * Side effect: opens connections to databases
 243          * @param string|bool $group Query group, or false for the generic reader
 244          * @param string|bool $wiki Wiki ID, or false for the current wiki
 245          * @throws MWException
 246          * @return bool|int|string
 247          */
 248         public function getReaderIndex( $group = false, $wiki = false ) {
 249                 global $wgDBtype;
 250
 251                 # @todo FIXME: For now, only go through all this for mysql databases
 252                 if ( $wgDBtype != 'mysql' ) {
 253                         return $this->getWriterIndex();
 254                 }
 255
 256                 if ( count( $this->mServers ) == 1 ) {
 257                         # Skip the load balancing if there's only one server
 258                         return 0;
 259                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 260                         # Shortcut if generic reader exists already
 261                         return $this->mReadIndex;
 262                 }
 263
 264                 # Find the relevant load array
 265                 if ( $group !== false ) {
 266                         if ( isset( $this->mGroupLoads[$group] ) ) {
 267                                 $nonErrorLoads = $this->mGroupLoads[$group];
 268                         } else {
 269                                 # No loads for this group, return false and the caller can use some other group
 270                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 271
 272                                 return false;
 273                         }
 274                 } else {
 275                         $nonErrorLoads = $this->mLoads;
 276                 }
 277
 278                 if ( !count( $nonErrorLoads ) ) {
 279                         throw new MWException( "Empty server array given to LoadBalancer" );
 280                 }
 281
 282                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 283                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 284
 285                 $laggedReplicaMode = false;
 286
 287                 # No server found yet
 288                 $i = false;
 289                 # First try quickly looking through the available servers for a server that
 290                 # meets our criteria
 291                 $currentLoads = $nonErrorLoads;
 292                 while ( count( $currentLoads ) ) {
 293                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 294                                 $i = ArrayUtils::pickRandom( $currentLoads );
 295                         } else {
 296                                 $i = false;
 297                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 298                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 299                                         # This triggers doWait() after connect, so it's especially good to
 300                                         # avoid lagged servers so as to avoid just blocking in that method.
 301                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 302                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 303                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 304                                 }
 305                                 if ( $i === false ) {
 306                                         # Any server with less lag than it's 'max lag' param is preferable
 307                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 308                                 }
 309                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 310                                         # All replica DBs lagged. Switch to read-only mode
 311                                         wfDebugLog( 'replication', "All replica DBs lagged. Switch to read-only mode" );
 312                                         $i = ArrayUtils::pickRandom( $currentLoads );
 313                                         $laggedReplicaMode = true;
 314                                 }
 315                         }
 316
 317                         if ( $i === false ) {
 318                                 # pickRandom() returned false
 319                                 # This is permanent and means the configuration or the load monitor
 320                                 # wants us to return false.
 321                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 322
 323                                 return false;
 324                         }
 325
 326                         $serverName = $this->getServerName( $i );
 327                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 328
 329                         $conn = $this->openConnection( $i, $wiki );
 330                         if ( !$conn ) {
 331                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 332                                 unset( $nonErrorLoads[$i] );
 333                                 unset( $currentLoads[$i] );
 334                                 $i = false;
 335                                 continue;
 336                         }
 337
 338                         // Decrement reference counter, we are finished with this connection.
 339                         // It will be incremented for the caller later.
 340                         if ( $wiki !== false ) {
 341                                 $this->reuseConnection( $conn );
 342                         }
 343
 344                         # Return this server
 345                         break;
 346                 }
 347
 348                 # If all servers were down, quit now
 349                 if ( !count( $nonErrorLoads ) ) {
 350                         wfDebugLog( 'connect', "All servers down" );
 351                 }
 352
 353                 if ( $i !== false ) {
 354                         # Replica DB connection successful.
 355                         # Wait for the session master pos for a short time.
 356                         if ( $this->mWaitForPos && $i > 0 ) {
 357                                 $this->doWait( $i );
 358                         }
 359                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 360                                 $this->mReadIndex = $i;
 361                                 # Record if the generic reader index is in "lagged replica DB" mode
 362                                 if ( $laggedReplicaMode ) {
 363                                         $this->laggedReplicaMode = true;
 364                                 }
 365                         }
 366                         $serverName = $this->getServerName( $i );
 367                         wfDebugLog( 'connect', __METHOD__ .
 368                                 ": using server $serverName for group '$group'\n" );
 369                 }
 370
 371                 return $i;
 372         }
 373
 374         /**
 375          * Set the master wait position
 376          * If a DB_REPLICA connection has been opened already, waits
 377          * Otherwise sets a variable telling it to wait if such a connection is opened
 378          * @param DBMasterPos $pos
 379          */
 380         public function waitFor( $pos ) {
 381                 $this->mWaitForPos = $pos;
 382                 $i = $this->mReadIndex;
 383
 384                 if ( $i > 0 ) {
 385                         if ( !$this->doWait( $i ) ) {
 386                                 $this->laggedReplicaMode = true;
 387                         }
 388                 }
 389         }
 390
 391         /**
 392          * Set the master wait position and wait for a "generic" replica DB 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 replica DB if there isn't one yet
 407                         $readLoads = $this->mLoads;
 408                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs 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 replica DBs 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 replica DB 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                                 ": replica DB $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 replica DB $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 replica DB, 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_REPLICA ) {
 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 replica DB 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                         /**
 615                          * This can happen in code like:
 616                          *   foreach ( $dbs as $db ) {
 617                          *     $conn = $lb->getConnection( DB_REPLICA, [], $db );
 618                          *     ...
 619                          *     $lb->reuseConnection( $conn );
 620                          *   }
 621                          * When a connection to the local DB is opened in this way, reuseConnection()
 622                          * should be ignored
 623                          */
 624                         return;
 625                 }
 626
 627                 $dbName = $conn->getDBname();
 628                 $prefix = $conn->tablePrefix();
 629                 if ( strval( $prefix ) !== '' ) {
 630                         $wiki = "$dbName-$prefix";
 631                 } else {
 632                         $wiki = $dbName;
 633                 }
 634                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 635                         throw new MWException( __METHOD__ . ": connection not found, has " .
 636                                 "the connection been freed already?" );
 637                 }
 638                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 639                 if ( $refCount <= 0 ) {
 640                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 641                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 642                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 643                 } else {
 644                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 645                 }
 646         }
 647
 648         /**
 649          * Get a database connection handle reference
 650          *
 651          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 652          *
 653          * @see LoadBalancer::getConnection() for parameter information
 654          *
 655          * @param int $db
 656          * @param array|string|bool $groups Query group(s), or false for the generic reader
 657          * @param string|bool $wiki Wiki ID, or false for the current wiki
 658          * @return DBConnRef
 659          */
 660         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 661                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 662         }
 663
 664         /**
 665          * Get a database connection handle reference without connecting yet
 666          *
 667          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 668          *
 669          * @see LoadBalancer::getConnection() for parameter information
 670          *
 671          * @param int $db
 672          * @param array|string|bool $groups Query group(s), or false for the generic reader
 673          * @param string|bool $wiki Wiki ID, or false for the current wiki
 674          * @return DBConnRef
 675          */
 676         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 677                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 678         }
 679
 680         /**
 681          * Open a connection to the server given by the specified index
 682          * Index must be an actual index into the array.
 683          * If the server is already open, returns it.
 684          *
 685          * On error, returns false, and the connection which caused the
 686          * error will be available via $this->mErrorConnection.
 687          *
 688          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 689          *
 690          * @param int $i Server index
 691          * @param string|bool $wiki Wiki ID, or false for the current wiki
 692          * @return DatabaseBase|bool Returns false on errors
 693          */
 694         public function openConnection( $i, $wiki = false ) {
 695                 if ( $wiki !== false ) {
 696                         $conn = $this->openForeignConnection( $i, $wiki );
 697                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 698                         $conn = $this->mConns['local'][$i][0];
 699                 } else {
 700                         $server = $this->mServers[$i];
 701                         $server['serverIndex'] = $i;
 702                         $conn = $this->reallyOpenConnection( $server, false );
 703                         $serverName = $this->getServerName( $i );
 704                         if ( $conn->isOpen() ) {
 705                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 706                                 $this->mConns['local'][$i][0] = $conn;
 707                         } else {
 708                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 709                                 $this->mErrorConnection = $conn;
 710                                 $conn = false;
 711                         }
 712                 }
 713
 714                 if ( $conn && !$conn->isOpen() ) {
 715                         // Connection was made but later unrecoverably lost for some reason.
 716                         // Do not return a handle that will just throw exceptions on use,
 717                         // but let the calling code (e.g. getReaderIndex) try another server.
 718                         // See DatabaseMyslBase::ping() for how this can happen.
 719                         $this->mErrorConnection = $conn;
 720                         $conn = false;
 721                 }
 722
 723                 return $conn;
 724         }
 725
 726         /**
 727          * Open a connection to a foreign DB, or return one if it is already open.
 728          *
 729          * Increments a reference count on the returned connection which locks the
 730          * connection to the requested wiki. This reference count can be
 731          * decremented by calling reuseConnection().
 732          *
 733          * If a connection is open to the appropriate server already, but with the wrong
 734          * database, it will be switched to the right database and returned, as long as
 735          * it has been freed first with reuseConnection().
 736          *
 737          * On error, returns false, and the connection which caused the
 738          * error will be available via $this->mErrorConnection.
 739          *
 740          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 741          *
 742          * @param int $i Server index
 743          * @param string $wiki Wiki ID to open
 744          * @return DatabaseBase
 745          */
 746         private function openForeignConnection( $i, $wiki ) {
 747                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 748                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 749                         // Reuse an already-used connection
 750                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 751                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 752                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 753                         // Reuse a free connection for the same wiki
 754                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 755                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 756                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 757                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 758                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 759                         // Reuse a connection from another wiki
 760                         $conn = reset( $this->mConns['foreignFree'][$i] );
 761                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 762
 763                         // The empty string as a DB name means "don't care".
 764                         // DatabaseMysqlBase::open() already handle this on connection.
 765                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 766                                 $this->mLastError = "Error selecting database $dbName on server " .
 767                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 768                                 $this->mErrorConnection = $conn;
 769                                 $conn = false;
 770                         } else {
 771                                 $conn->tablePrefix( $prefix );
 772                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 773                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 774                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 775                         }
 776                 } else {
 777                         // Open a new connection
 778                         $server = $this->mServers[$i];
 779                         $server['serverIndex'] = $i;
 780                         $server['foreignPoolRefCount'] = 0;
 781                         $server['foreign'] = true;
 782                         $conn = $this->reallyOpenConnection( $server, $dbName );
 783                         if ( !$conn->isOpen() ) {
 784                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 785                                 $this->mErrorConnection = $conn;
 786                                 $conn = false;
 787                         } else {
 788                                 $conn->tablePrefix( $prefix );
 789                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 790                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 791                         }
 792                 }
 793
 794                 // Increment reference count
 795                 if ( $conn ) {
 796                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 797                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 798                 }
 799
 800                 return $conn;
 801         }
 802
 803         /**
 804          * Test if the specified index represents an open connection
 805          *
 806          * @param int $index Server index
 807          * @access private
 808          * @return bool
 809          */
 810         private function isOpen( $index ) {
 811                 if ( !is_integer( $index ) ) {
 812                         return false;
 813                 }
 814
 815                 return (bool)$this->getAnyOpenConnection( $index );
 816         }
 817
 818         /**
 819          * Really opens a connection. Uncached.
 820          * Returns a Database object whether or not the connection was successful.
 821          * @access private
 822          *
 823          * @param array $server
 824          * @param bool $dbNameOverride
 825          * @throws MWException
 826          * @return DatabaseBase
 827          */
 828         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 829                 if ( $this->disabled ) {
 830                         throw new DBAccessError();
 831                 }
 832
 833                 if ( !is_array( $server ) ) {
 834                         throw new MWException( 'You must update your load-balancing configuration. ' .
 835                                 'See DefaultSettings.php entry for $wgDBservers.' );
 836                 }
 837
 838                 if ( $dbNameOverride !== false ) {
 839                         $server['dbname'] = $dbNameOverride;
 840                 }
 841
 842                 // Let the handle know what the cluster master is (e.g. "db1052")
 843                 $masterName = $this->getServerName( 0 );
 844                 $server['clusterMasterHost'] = $masterName;
 845
 846                 // Log when many connection are made on requests
 847                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 848                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 849                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 850                                 wfBacktrace( true ) );
 851                 }
 852
 853                 # Create object
 854                 try {
 855                         $db = DatabaseBase::factory( $server['type'], $server );
 856                 } catch ( DBConnectionError $e ) {
 857                         // FIXME: This is probably the ugliest thing I have ever done to
 858                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 859                         $db = $e->db;
 860                 }
 861
 862                 $db->setLBInfo( $server );
 863                 $db->setLazyMasterHandle(
 864                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 865                 );
 866                 $db->setTransactionProfiler( $this->trxProfiler );
 867                 if ( $this->trxRoundId !== false ) {
 868                         $this->applyTransactionRoundFlags( $db );
 869                 }
 870
 871                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 872                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 873                                 $db->setTransactionListener( $name, $callback );
 874                         }
 875                 }
 876
 877                 return $db;
 878         }
 879
 880         /**
 881          * @throws DBConnectionError
 882          * @return bool
 883          */
 884         private function reportConnectionError() {
 885                 $conn = $this->mErrorConnection; // The connection which caused the error
 886                 $context = [
 887                         'method' => __METHOD__,
 888                         'last_error' => $this->mLastError,
 889                 ];
 890
 891                 if ( !is_object( $conn ) ) {
 892                         // No last connection, probably due to all servers being too busy
 893                         wfLogDBError(
 894                                 "LB failure with no last connection. Connection error: {last_error}",
 895                                 $context
 896                         );
 897
 898                         // If all servers were busy, mLastError will contain something sensible
 899                         throw new DBConnectionError( null, $this->mLastError );
 900                 } else {
 901                         $context['db_server'] = $conn->getProperty( 'mServer' );
 902                         wfLogDBError(
 903                                 "Connection error: {last_error} ({db_server})",
 904                                 $context
 905                         );
 906
 907                         // throws DBConnectionError
 908                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 909                 }
 910
 911                 return false; /* not reached */
 912         }
 913
 914         /**
 915          * @return int
 916          * @since 1.26
 917          */
 918         public function getWriterIndex() {
 919                 return 0;
 920         }
 921
 922         /**
 923          * Returns true if the specified index is a valid server index
 924          *
 925          * @param string $i
 926          * @return bool
 927          */
 928         public function haveIndex( $i ) {
 929                 return array_key_exists( $i, $this->mServers );
 930         }
 931
 932         /**
 933          * Returns true if the specified index is valid and has non-zero load
 934          *
 935          * @param string $i
 936          * @return bool
 937          */
 938         public function isNonZeroLoad( $i ) {
 939                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 940         }
 941
 942         /**
 943          * Get the number of defined servers (not the number of open connections)
 944          *
 945          * @return int
 946          */
 947         public function getServerCount() {
 948                 return count( $this->mServers );
 949         }
 950
 951         /**
 952          * Get the host name or IP address of the server with the specified index
 953          * Prefer a readable name if available.
 954          * @param string $i
 955          * @return string
 956          */
 957         public function getServerName( $i ) {
 958                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 959                         $name = $this->mServers[$i]['hostName'];
 960                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 961                         $name = $this->mServers[$i]['host'];
 962                 } else {
 963                         $name = '';
 964                 }
 965
 966                 return ( $name != '' ) ? $name : 'localhost';
 967         }
 968
 969         /**
 970          * Return the server info structure for a given index, or false if the index is invalid.
 971          * @param int $i
 972          * @return array|bool
 973          */
 974         public function getServerInfo( $i ) {
 975                 if ( isset( $this->mServers[$i] ) ) {
 976                         return $this->mServers[$i];
 977                 } else {
 978                         return false;
 979                 }
 980         }
 981
 982         /**
 983          * Sets the server info structure for the given index. Entry at index $i
 984          * is created if it doesn't exist
 985          * @param int $i
 986          * @param array $serverInfo
 987          */
 988         public function setServerInfo( $i, array $serverInfo ) {
 989                 $this->mServers[$i] = $serverInfo;
 990         }
 991
 992         /**
 993          * Get the current master position for chronology control purposes
 994          * @return mixed
 995          */
 996         public function getMasterPos() {
 997                 # If this entire request was served from a replica DB without opening a connection to the
 998                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 999                 $masterConn = $this->getAnyOpenConnection( 0 );
1000                 if ( !$masterConn ) {
1001                         $serverCount = count( $this->mServers );
1002                         for ( $i = 1; $i < $serverCount; $i++ ) {
1003                                 $conn = $this->getAnyOpenConnection( $i );
1004                                 if ( $conn ) {
1005                                         return $conn->getSlavePos();
1006                                 }
1007                         }
1008                 } else {
1009                         return $masterConn->getMasterPos();
1010                 }
1011
1012                 return false;
1013         }
1014
1015         /**
1016          * Disable this load balancer. All connections are closed, and any attempt to
1017          * open a new connection will result in a DBAccessError.
1018          *
1019          * @since 1.27
1020          */
1021         public function disable() {
1022                 $this->closeAll();
1023                 $this->disabled = true;
1024         }
1025
1026         /**
1027          * Close all open connections
1028          */
1029         public function closeAll() {
1030                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1031                         $conn->close();
1032                 } );
1033
1034                 $this->mConns = [
1035                         'local' => [],
1036                         'foreignFree' => [],
1037                         'foreignUsed' => [],
1038                 ];
1039                 $this->connsOpened = 0;
1040         }
1041
1042         /**
1043          * Close a connection
1044          * Using this function makes sure the LoadBalancer knows the connection is closed.
1045          * If you use $conn->close() directly, the load balancer won't update its state.
1046          * @param DatabaseBase $conn
1047          */
1048         public function closeConnection( $conn ) {
1049                 $done = false;
1050                 foreach ( $this->mConns as $i1 => $conns2 ) {
1051                         foreach ( $conns2 as $i2 => $conns3 ) {
1052                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1053                                         if ( $conn === $candidateConn ) {
1054                                                 $conn->close();
1055                                                 unset( $this->mConns[$i1][$i2][$i3] );
1056                                                 --$this->connsOpened;
1057                                                 $done = true;
1058                                                 break;
1059                                         }
1060                                 }
1061                         }
1062                 }
1063                 if ( !$done ) {
1064                         $conn->close();
1065                 }
1066         }
1067
1068         /**
1069          * Commit transactions on all open connections
1070          * @param string $fname Caller name
1071          * @throws DBExpectedError
1072          */
1073         public function commitAll( $fname = __METHOD__ ) {
1074                 $failures = [];
1075
1076                 $restore = ( $this->trxRoundId !== false );
1077                 $this->trxRoundId = false;
1078                 $this->forEachOpenConnection(
1079                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1080                                 try {
1081                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1082                                 } catch ( DBError $e ) {
1083                                         MWExceptionHandler::logException( $e );
1084                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1085                                 }
1086                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1087                                         $this->undoTransactionRoundFlags( $conn );
1088                                 }
1089                         }
1090                 );
1091
1092                 if ( $failures ) {
1093                         throw new DBExpectedError(
1094                                 null,
1095                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1096                         );
1097                 }
1098         }
1099
1100         /**
1101          * Perform all pre-commit callbacks that remain part of the atomic transactions
1102          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
1103          * @since 1.28
1104          */
1105         public function finalizeMasterChanges() {
1106                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1107                         // Any error should cause all DB transactions to be rolled back together
1108                         $conn->setTrxEndCallbackSuppression( false );
1109                         $conn->runOnTransactionPreCommitCallbacks();
1110                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1111                         $conn->setTrxEndCallbackSuppression( true );
1112                 } );
1113         }
1114
1115         /**
1116          * Perform all pre-commit checks for things like replication safety
1117          * @param array $options Includes:
1118          *   - maxWriteDuration : max write query duration time in seconds
1119          * @throws DBTransactionError
1120          * @since 1.28
1121          */
1122         public function approveMasterChanges( array $options ) {
1123                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1124                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1125                         // If atomic sections or explicit transactions are still open, some caller must have
1126                         // caught an exception but failed to properly rollback any changes. Detect that and
1127                         // throw and error (causing rollback).
1128                         if ( $conn->explicitTrxActive() ) {
1129                                 throw new DBTransactionError(
1130                                         $conn,
1131                                         "Explicit transaction still active. A caller may have caught an error."
1132                                 );
1133                         }
1134                         // Assert that the time to replicate the transaction will be sane.
1135                         // If this fails, then all DB transactions will be rollback back together.
1136                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1137                         if ( $limit > 0 && $time > $limit ) {
1138                                 throw new DBTransactionError(
1139                                         $conn,
1140                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1141                                 );
1142                         }
1143                         // If a connection sits idle while slow queries execute on another, that connection
1144                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1145                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1146                                 throw new DBTransactionError(
1147                                         $conn,
1148                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1149                                 );
1150                         }
1151                 } );
1152         }
1153
1154         /**
1155          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
1156          *
1157          * The DBO_TRX setting will be reverted to the default in each of these methods:
1158          *   - commitMasterChanges()
1159          *   - rollbackMasterChanges()
1160          *   - commitAll()
1161          * This allows for custom transaction rounds from any outer transaction scope.
1162          *
1163          * @param string $fname
1164          * @throws DBExpectedError
1165          * @since 1.28
1166          */
1167         public function beginMasterChanges( $fname = __METHOD__ ) {
1168                 if ( $this->trxRoundId !== false ) {
1169                         throw new DBTransactionError(
1170                                 null,
1171                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1172                         );
1173                 }
1174                 $this->trxRoundId = $fname;
1175
1176                 $failures = [];
1177                 $this->forEachOpenMasterConnection(
1178                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1179                                 $conn->setTrxEndCallbackSuppression( true );
1180                                 try {
1181                                         $conn->clearSnapshot( $fname );
1182                                 } catch ( DBError $e ) {
1183                                         MWExceptionHandler::logException( $e );
1184                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1185                                 }
1186                                 $conn->setTrxEndCallbackSuppression( false );
1187                                 $this->applyTransactionRoundFlags( $conn );
1188                         }
1189                 );
1190
1191                 if ( $failures ) {
1192                         throw new DBExpectedError(
1193                                 null,
1194                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1195                         );
1196                 }
1197         }
1198
1199         /**
1200          * Issue COMMIT on all master connections where writes where done
1201          * @param string $fname Caller name
1202          * @throws DBExpectedError
1203          */
1204         public function commitMasterChanges( $fname = __METHOD__ ) {
1205                 $failures = [];
1206
1207                 $restore = ( $this->trxRoundId !== false );
1208                 $this->trxRoundId = false;
1209                 $this->forEachOpenMasterConnection(
1210                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1211                                 try {
1212                                         if ( $conn->writesOrCallbacksPending() ) {
1213                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1214                                         } elseif ( $restore ) {
1215                                                 $conn->clearSnapshot( $fname );
1216                                         }
1217                                 } catch ( DBError $e ) {
1218                                         MWExceptionHandler::logException( $e );
1219                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1220                                 }
1221                                 if ( $restore ) {
1222                                         $this->undoTransactionRoundFlags( $conn );
1223                                 }
1224                         }
1225                 );
1226
1227                 if ( $failures ) {
1228                         throw new DBExpectedError(
1229                                 null,
1230                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1231                         );
1232                 }
1233         }
1234
1235         /**
1236          * Issue all pending post-COMMIT/ROLLBACK callbacks
1237          * @param integer $type IDatabase::TRIGGER_* constant
1238          * @return Exception|null The first exception or null if there were none
1239          * @since 1.28
1240          */
1241         public function runMasterPostTrxCallbacks( $type ) {
1242                 $e = null; // first exception
1243                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1244                         $conn->clearSnapshot( __METHOD__ ); // clear no-op transactions
1245
1246                         $conn->setTrxEndCallbackSuppression( false );
1247                         try {
1248                                 $conn->runOnTransactionIdleCallbacks( $type );
1249                         } catch ( Exception $ex ) {
1250                                 $e = $e ?: $ex;
1251                         }
1252                         try {
1253                                 $conn->runTransactionListenerCallbacks( $type );
1254                         } catch ( Exception $ex ) {
1255                                 $e = $e ?: $ex;
1256                         }
1257                 } );
1258
1259                 return $e;
1260         }
1261
1262         /**
1263          * Issue ROLLBACK only on master, only if queries were done on connection
1264          * @param string $fname Caller name
1265          * @throws DBExpectedError
1266          * @since 1.23
1267          */
1268         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1269                 $restore = ( $this->trxRoundId !== false );
1270                 $this->trxRoundId = false;
1271                 $this->forEachOpenMasterConnection(
1272                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1273                                 if ( $conn->writesOrCallbacksPending() ) {
1274                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1275                                 }
1276                                 if ( $restore ) {
1277                                         $this->undoTransactionRoundFlags( $conn );
1278                                 }
1279                         }
1280                 );
1281         }
1282
1283         /**
1284          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1285          * @return Exception|null The first exception or null if there were none
1286          * @since 1.28
1287          */
1288         public function suppressTransactionEndCallbacks() {
1289                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1290                         $conn->setTrxEndCallbackSuppression( true );
1291                 } );
1292         }
1293
1294         /**
1295          * @param DatabaseBase $conn
1296          */
1297         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1298                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1299                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1300                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1301                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1302                         // If config has explicitly requested DBO_TRX be either on or off by not
1303                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1304                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1305                 }
1306         }
1307
1308         /**
1309          * @param DatabaseBase $conn
1310          */
1311         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1312                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1313                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1314                 }
1315         }
1316
1317         /**
1318          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
1319          *
1320          * @param string $fname Caller name
1321          * @since 1.28
1322          */
1323         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1324                 $this->forEachOpenReplicaConnection( function ( DatabaseBase $conn ) {
1325                         $conn->clearSnapshot( __METHOD__ );
1326                 } );
1327         }
1328
1329         /**
1330          * @return bool Whether a master connection is already open
1331          * @since 1.24
1332          */
1333         public function hasMasterConnection() {
1334                 return $this->isOpen( $this->getWriterIndex() );
1335         }
1336
1337         /**
1338          * Determine if there are pending changes in a transaction by this thread
1339          * @since 1.23
1340          * @return bool
1341          */
1342         public function hasMasterChanges() {
1343                 $masterIndex = $this->getWriterIndex();
1344                 foreach ( $this->mConns as $conns2 ) {
1345                         if ( empty( $conns2[$masterIndex] ) ) {
1346                                 continue;
1347                         }
1348                         /** @var DatabaseBase $conn */
1349                         foreach ( $conns2[$masterIndex] as $conn ) {
1350                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1351                                         return true;
1352                                 }
1353                         }
1354                 }
1355                 return false;
1356         }
1357
1358         /**
1359          * Get the timestamp of the latest write query done by this thread
1360          * @since 1.25
1361          * @return float|bool UNIX timestamp or false
1362          */
1363         public function lastMasterChangeTimestamp() {
1364                 $lastTime = false;
1365                 $masterIndex = $this->getWriterIndex();
1366                 foreach ( $this->mConns as $conns2 ) {
1367                         if ( empty( $conns2[$masterIndex] ) ) {
1368                                 continue;
1369                         }
1370                         /** @var DatabaseBase $conn */
1371                         foreach ( $conns2[$masterIndex] as $conn ) {
1372                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1373                         }
1374                 }
1375                 return $lastTime;
1376         }
1377
1378         /**
1379          * Check if this load balancer object had any recent or still
1380          * pending writes issued against it by this PHP thread
1381          *
1382          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1383          * @return bool
1384          * @since 1.25
1385          */
1386         public function hasOrMadeRecentMasterChanges( $age = null ) {
1387                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1388
1389                 return ( $this->hasMasterChanges()
1390                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1391         }
1392
1393         /**
1394          * Get the list of callers that have pending master changes
1395          *
1396          * @return array
1397          * @since 1.27
1398          */
1399         public function pendingMasterChangeCallers() {
1400                 $fnames = [];
1401
1402                 $masterIndex = $this->getWriterIndex();
1403                 foreach ( $this->mConns as $conns2 ) {
1404                         if ( empty( $conns2[$masterIndex] ) ) {
1405                                 continue;
1406                         }
1407                         /** @var DatabaseBase $conn */
1408                         foreach ( $conns2[$masterIndex] as $conn ) {
1409                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1410                         }
1411                 }
1412
1413                 return $fnames;
1414         }
1415
1416         /**
1417          * @param mixed $value
1418          * @return mixed
1419          */
1420         public function waitTimeout( $value = null ) {
1421                 return wfSetVar( $this->mWaitTimeout, $value );
1422         }
1423
1424         /**
1425          * @note This method will trigger a DB connection if not yet done
1426          * @param string|bool $wiki Wiki ID, or false for the current wiki
1427          * @return bool Whether the generic connection for reads is highly "lagged"
1428          */
1429         public function getLaggedReplicaMode( $wiki = false ) {
1430                 // No-op if there is only one DB (also avoids recursion)
1431                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1432                         try {
1433                                 // See if laggedReplicaMode gets set
1434                                 $conn = $this->getConnection( DB_REPLICA, false, $wiki );
1435                                 $this->reuseConnection( $conn );
1436                         } catch ( DBConnectionError $e ) {
1437                                 // Avoid expensive re-connect attempts and failures
1438                                 $this->allReplicasDownMode = true;
1439                                 $this->laggedReplicaMode = true;
1440                         }
1441                 }
1442
1443                 return $this->laggedReplicaMode;
1444         }
1445
1446         /**
1447          * @param bool $wiki
1448          * @return bool
1449          * @deprecated 1.28; use getLaggedReplicaMode()
1450          */
1451         public function getLaggedSlaveMode( $wiki = false ) {
1452                 return $this->getLaggedReplicaMode( $wiki );
1453         }
1454
1455         /**
1456          * @note This method will never cause a new DB connection
1457          * @return bool Whether any generic connection used for reads was highly "lagged"
1458          * @since 1.28
1459          */
1460         public function laggedReplicaUsed() {
1461                 return $this->laggedReplicaMode;
1462         }
1463
1464         /**
1465          * @return bool
1466          * @since 1.27
1467          * @deprecated Since 1.28; use laggedReplicaUsed()
1468          */
1469         public function laggedSlaveUsed() {
1470                 return $this->laggedReplicaUsed();
1471         }
1472
1473         /**
1474          * @note This method may trigger a DB connection if not yet done
1475          * @param string|bool $wiki Wiki ID, or false for the current wiki
1476          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1477          * @return string|bool Reason the master is read-only or false if it is not
1478          * @since 1.27
1479          */
1480         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1481                 if ( $this->readOnlyReason !== false ) {
1482                         return $this->readOnlyReason;
1483                 } elseif ( $this->getLaggedReplicaMode( $wiki ) ) {
1484                         if ( $this->allReplicasDownMode ) {
1485                                 return 'The database has been automatically locked ' .
1486                                         'until the replica database servers become available';
1487                         } else {
1488                                 return 'The database has been automatically locked ' .
1489                                         'while the replica database servers catch up to the master.';
1490                         }
1491                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1492                         return 'The database master is running in read-only mode.';
1493                 }
1494
1495                 return false;
1496         }
1497
1498         /**
1499          * @param string $wiki Wiki ID, or false for the current wiki
1500          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1501          * @return bool
1502          */
1503         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1504                 $cache = $this->wanCache;
1505                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1506
1507                 return (bool)$cache->getWithSetCallback(
1508                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1509                         self::TTL_CACHE_READONLY,
1510                         function () use ( $wiki, $conn ) {
1511                                 $this->trxProfiler->setSilenced( true );
1512                                 try {
1513                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1514                                         $readOnly = (int)$dbw->serverIsReadOnly();
1515                                 } catch ( DBError $e ) {
1516                                         $readOnly = 0;
1517                                 }
1518                                 $this->trxProfiler->setSilenced( false );
1519                                 return $readOnly;
1520                         },
1521                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1522                 );
1523         }
1524
1525         /**
1526          * Disables/enables lag checks
1527          * @param null|bool $mode
1528          * @return bool
1529          */
1530         public function allowLagged( $mode = null ) {
1531                 if ( $mode === null ) {
1532                         return $this->mAllowLagged;
1533                 }
1534                 $this->mAllowLagged = $mode;
1535
1536                 return $this->mAllowLagged;
1537         }
1538
1539         /**
1540          * @return bool
1541          */
1542         public function pingAll() {
1543                 $success = true;
1544                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1545                         if ( !$conn->ping() ) {
1546                                 $success = false;
1547                         }
1548                 } );
1549
1550                 return $success;
1551         }
1552
1553         /**
1554          * Call a function with each open connection object
1555          * @param callable $callback
1556          * @param array $params
1557          */
1558         public function forEachOpenConnection( $callback, array $params = [] ) {
1559                 foreach ( $this->mConns as $connsByServer ) {
1560                         foreach ( $connsByServer as $serverConns ) {
1561                                 foreach ( $serverConns as $conn ) {
1562                                         $mergedParams = array_merge( [ $conn ], $params );
1563                                         call_user_func_array( $callback, $mergedParams );
1564                                 }
1565                         }
1566                 }
1567         }
1568
1569         /**
1570          * Call a function with each open connection object to a master
1571          * @param callable $callback
1572          * @param array $params
1573          * @since 1.28
1574          */
1575         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1576                 $masterIndex = $this->getWriterIndex();
1577                 foreach ( $this->mConns as $connsByServer ) {
1578                         if ( isset( $connsByServer[$masterIndex] ) ) {
1579                                 /** @var DatabaseBase $conn */
1580                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1581                                         $mergedParams = array_merge( [ $conn ], $params );
1582                                         call_user_func_array( $callback, $mergedParams );
1583                                 }
1584                         }
1585                 }
1586         }
1587
1588         /**
1589          * Call a function with each open replica DB connection object
1590          * @param callable $callback
1591          * @param array $params
1592          * @since 1.28
1593          */
1594         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1595                 foreach ( $this->mConns as $connsByServer ) {
1596                         foreach ( $connsByServer as $i => $serverConns ) {
1597                                 if ( $i === $this->getWriterIndex() ) {
1598                                         continue; // skip master
1599                                 }
1600                                 foreach ( $serverConns as $conn ) {
1601                                         $mergedParams = array_merge( [ $conn ], $params );
1602                                         call_user_func_array( $callback, $mergedParams );
1603                                 }
1604                         }
1605                 }
1606         }
1607
1608         /**
1609          * Get the hostname and lag time of the most-lagged replica DB
1610          *
1611          * This is useful for maintenance scripts that need to throttle their updates.
1612          * May attempt to open connections to replica DBs on the default DB. If there is
1613          * no lag, the maximum lag will be reported as -1.
1614          *
1615          * @param bool|string $wiki Wiki ID, or false for the default database
1616          * @return array ( host, max lag, index of max lagged host )
1617          */
1618         public function getMaxLag( $wiki = false ) {
1619                 $maxLag = -1;
1620                 $host = '';
1621                 $maxIndex = 0;
1622
1623                 if ( $this->getServerCount() <= 1 ) {
1624                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1625                 }
1626
1627                 $lagTimes = $this->getLagTimes( $wiki );
1628                 foreach ( $lagTimes as $i => $lag ) {
1629                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1630                                 $maxLag = $lag;
1631                                 $host = $this->mServers[$i]['host'];
1632                                 $maxIndex = $i;
1633                         }
1634                 }
1635
1636                 return [ $host, $maxLag, $maxIndex ];
1637         }
1638
1639         /**
1640          * Get an estimate of replication lag (in seconds) for each server
1641          *
1642          * Results are cached for a short time in memcached/process cache
1643          *
1644          * Values may be "false" if replication is too broken to estimate
1645          *
1646          * @param string|bool $wiki
1647          * @return int[] Map of (server index => float|int|bool)
1648          */
1649         public function getLagTimes( $wiki = false ) {
1650                 if ( $this->getServerCount() <= 1 ) {
1651                         return [ 0 => 0 ]; // no replication = no lag
1652                 }
1653
1654                 # Send the request to the load monitor
1655                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1656         }
1657
1658         /**
1659          * Get the lag in seconds for a given connection, or zero if this load
1660          * balancer does not have replication enabled.
1661          *
1662          * This should be used in preference to Database::getLag() in cases where
1663          * replication may not be in use, since there is no way to determine if
1664          * replication is in use at the connection level without running
1665          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1666          * function instead of Database::getLag() avoids a fatal error in this
1667          * case on many installations.
1668          *
1669          * @param IDatabase $conn
1670          * @return int|bool Returns false on error
1671          */
1672         public function safeGetLag( IDatabase $conn ) {
1673                 if ( $this->getServerCount() == 1 ) {
1674                         return 0;
1675                 } else {
1676                         return $conn->getLag();
1677                 }
1678         }
1679
1680         /**
1681          * Wait for a replica DB to reach a specified master position
1682          *
1683          * This will connect to the master to get an accurate position if $pos is not given
1684          *
1685          * @param IDatabase $conn Replica DB
1686          * @param DBMasterPos|bool $pos Master position; default: current position
1687          * @param integer $timeout Timeout in seconds
1688          * @return bool Success
1689          * @since 1.27
1690          */
1691         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1692                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'replica' ) ) {
1693                         return true; // server is not a replica DB
1694                 }
1695
1696                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1697                 if ( !( $pos instanceof DBMasterPos ) ) {
1698                         return false; // something is misconfigured
1699                 }
1700
1701                 $result = $conn->masterPosWait( $pos, $timeout );
1702                 if ( $result == -1 || is_null( $result ) ) {
1703                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1704                         wfDebugLog( 'replication', "$msg\n" );
1705                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1706                         $ok = false;
1707                 } else {
1708                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1709                         $ok = true;
1710                 }
1711
1712                 return $ok;
1713         }
1714
1715         /**
1716          * Clear the cache for slag lag delay times
1717          *
1718          * This is only used for testing
1719          */
1720         public function clearLagTimeCache() {
1721                 $this->getLoadMonitor()->clearCaches();
1722         }
1723
1724         /**
1725          * Set a callback via DatabaseBase::setTransactionListener() on
1726          * all current and future master connections of this load balancer
1727          *
1728          * @param string $name Callback name
1729          * @param callable|null $callback
1730          * @since 1.28
1731          */
1732         public function setTransactionListener( $name, callable $callback = null ) {
1733                 if ( $callback ) {
1734                         $this->trxRecurringCallbacks[$name] = $callback;
1735                 } else {
1736                         unset( $this->trxRecurringCallbacks[$name] );
1737                 }
1738                 $this->forEachOpenMasterConnection(
1739                         function ( DatabaseBase $conn ) use ( $name, $callback ) {
1740                                 $conn->setTransactionListener( $name, $callback );
1741                         }
1742                 );
1743         }
1744 }