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          *  - waitTimeout : Maximum time to wait for replicas for consistency [optional]
  98          *  - srvCache : BagOStuff object [optional]
  99          *  - wanCache : WANObjectCache object [optional]
 100          * @throws MWException
 101          */
 102         public function __construct( array $params ) {
 103                 if ( !isset( $params['servers'] ) ) {
 104                         throw new MWException( __CLASS__ . ': missing servers parameter' );
 105                 }
 106                 $this->mServers = $params['servers'];
 107                 $this->mWaitTimeout = isset( $params['waitTimeout'] )
 108                         ? $params['waitTimeout']
 109                         : self::POS_WAIT_TIMEOUT;
 110
 111                 $this->mReadIndex = -1;
 112                 $this->mWriteIndex = -1;
 113                 $this->mConns = [
 114                         'local' => [],
 115                         'foreignUsed' => [],
 116                         'foreignFree' => [] ];
 117                 $this->mLoads = [];
 118                 $this->mWaitForPos = false;
 119                 $this->mErrorConnection = false;
 120                 $this->mAllowLagged = false;
 121
 122                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 123                         $this->readOnlyReason = $params['readOnlyReason'];
 124                 }
 125
 126                 if ( isset( $params['loadMonitor'] ) ) {
 127                         $this->mLoadMonitorClass = $params['loadMonitor'];
 128                 } else {
 129                         $master = reset( $params['servers'] );
 130                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 131                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 132                         } else {
 133                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 134                         }
 135                 }
 136
 137                 foreach ( $params['servers'] as $i => $server ) {
 138                         $this->mLoads[$i] = $server['load'];
 139                         if ( isset( $server['groupLoads'] ) ) {
 140                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 141                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 142                                                 $this->mGroupLoads[$group] = [];
 143                                         }
 144                                         $this->mGroupLoads[$group][$i] = $ratio;
 145                                 }
 146                         }
 147                 }
 148
 149                 if ( isset( $params['srvCache'] ) ) {
 150                         $this->srvCache = $params['srvCache'];
 151                 } else {
 152                         $this->srvCache = new EmptyBagOStuff();
 153                 }
 154                 if ( isset( $params['wanCache'] ) ) {
 155                         $this->wanCache = $params['wanCache'];
 156                 } else {
 157                         $this->wanCache = WANObjectCache::newEmpty();
 158                 }
 159                 if ( isset( $params['trxProfiler'] ) ) {
 160                         $this->trxProfiler = $params['trxProfiler'];
 161                 } else {
 162                         $this->trxProfiler = new TransactionProfiler();
 163                 }
 164         }
 165
 166         /**
 167          * Get a LoadMonitor instance
 168          *
 169          * @return LoadMonitor
 170          */
 171         private function getLoadMonitor() {
 172                 if ( !isset( $this->mLoadMonitor ) ) {
 173                         $class = $this->mLoadMonitorClass;
 174                         $this->mLoadMonitor = new $class( $this );
 175                 }
 176
 177                 return $this->mLoadMonitor;
 178         }
 179
 180         /**
 181          * @param array $loads
 182          * @param bool|string $wiki Wiki to get non-lagged for
 183          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 184          * @return bool|int|string
 185          */
 186         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 187                 $lags = $this->getLagTimes( $wiki );
 188
 189                 # Unset excessively lagged servers
 190                 foreach ( $lags as $i => $lag ) {
 191                         if ( $i != 0 ) {
 192                                 # How much lag this server nominally is allowed to have
 193                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 194                                         ? $this->mServers[$i]['max lag']
 195                                         : self::MAX_LAG_DEFAULT; // default
 196                                 # Constrain that futher by $maxLag argument
 197                                 $maxServerLag = min( $maxServerLag, $maxLag );
 198
 199                                 $host = $this->getServerName( $i );
 200                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 201                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 202                                         unset( $loads[$i] );
 203                                 } elseif ( $lag > $maxServerLag ) {
 204                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 205                                         unset( $loads[$i] );
 206                                 }
 207                         }
 208                 }
 209
 210                 # Find out if all the replica DBs with non-zero load are lagged
 211                 $sum = 0;
 212                 foreach ( $loads as $load ) {
 213                         $sum += $load;
 214                 }
 215                 if ( $sum == 0 ) {
 216                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 217                         # Do NOT use the master
 218                         # Instead, this function will return false, triggering read-only mode,
 219                         # and a lagged replica DB will be used instead.
 220                         return false;
 221                 }
 222
 223                 if ( count( $loads ) == 0 ) {
 224                         return false;
 225                 }
 226
 227                 # Return a random representative of the remainder
 228                 return ArrayUtils::pickRandom( $loads );
 229         }
 230
 231         /**
 232          * Get the index of the reader connection, which may be a replica DB
 233          * This takes into account load ratios and lag times. It should
 234          * always return a consistent index during a given invocation
 235          *
 236          * Side effect: opens connections to databases
 237          * @param string|bool $group Query group, or false for the generic reader
 238          * @param string|bool $wiki Wiki ID, or false for the current wiki
 239          * @throws MWException
 240          * @return bool|int|string
 241          */
 242         public function getReaderIndex( $group = false, $wiki = false ) {
 243                 global $wgDBtype;
 244
 245                 # @todo FIXME: For now, only go through all this for mysql databases
 246                 if ( $wgDBtype != 'mysql' ) {
 247                         return $this->getWriterIndex();
 248                 }
 249
 250                 if ( count( $this->mServers ) == 1 ) {
 251                         # Skip the load balancing if there's only one server
 252                         return 0;
 253                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 254                         # Shortcut if generic reader exists already
 255                         return $this->mReadIndex;
 256                 }
 257
 258                 # Find the relevant load array
 259                 if ( $group !== false ) {
 260                         if ( isset( $this->mGroupLoads[$group] ) ) {
 261                                 $nonErrorLoads = $this->mGroupLoads[$group];
 262                         } else {
 263                                 # No loads for this group, return false and the caller can use some other group
 264                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 265
 266                                 return false;
 267                         }
 268                 } else {
 269                         $nonErrorLoads = $this->mLoads;
 270                 }
 271
 272                 if ( !count( $nonErrorLoads ) ) {
 273                         throw new MWException( "Empty server array given to LoadBalancer" );
 274                 }
 275
 276                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 277                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 278
 279                 $laggedReplicaMode = false;
 280
 281                 # No server found yet
 282                 $i = false;
 283                 # First try quickly looking through the available servers for a server that
 284                 # meets our criteria
 285                 $currentLoads = $nonErrorLoads;
 286                 while ( count( $currentLoads ) ) {
 287                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 288                                 $i = ArrayUtils::pickRandom( $currentLoads );
 289                         } else {
 290                                 $i = false;
 291                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 292                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 293                                         # This triggers doWait() after connect, so it's especially good to
 294                                         # avoid lagged servers so as to avoid just blocking in that method.
 295                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 296                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 297                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 298                                 }
 299                                 if ( $i === false ) {
 300                                         # Any server with less lag than it's 'max lag' param is preferable
 301                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 302                                 }
 303                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 304                                         # All replica DBs lagged. Switch to read-only mode
 305                                         wfDebugLog( 'replication', "All replica DBs lagged. Switch to read-only mode" );
 306                                         $i = ArrayUtils::pickRandom( $currentLoads );
 307                                         $laggedReplicaMode = true;
 308                                 }
 309                         }
 310
 311                         if ( $i === false ) {
 312                                 # pickRandom() returned false
 313                                 # This is permanent and means the configuration or the load monitor
 314                                 # wants us to return false.
 315                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 316
 317                                 return false;
 318                         }
 319
 320                         $serverName = $this->getServerName( $i );
 321                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 322
 323                         $conn = $this->openConnection( $i, $wiki );
 324                         if ( !$conn ) {
 325                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 326                                 unset( $nonErrorLoads[$i] );
 327                                 unset( $currentLoads[$i] );
 328                                 $i = false;
 329                                 continue;
 330                         }
 331
 332                         // Decrement reference counter, we are finished with this connection.
 333                         // It will be incremented for the caller later.
 334                         if ( $wiki !== false ) {
 335                                 $this->reuseConnection( $conn );
 336                         }
 337
 338                         # Return this server
 339                         break;
 340                 }
 341
 342                 # If all servers were down, quit now
 343                 if ( !count( $nonErrorLoads ) ) {
 344                         wfDebugLog( 'connect', "All servers down" );
 345                 }
 346
 347                 if ( $i !== false ) {
 348                         # Replica DB connection successful.
 349                         # Wait for the session master pos for a short time.
 350                         if ( $this->mWaitForPos && $i > 0 ) {
 351                                 $this->doWait( $i );
 352                         }
 353                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 354                                 $this->mReadIndex = $i;
 355                                 # Record if the generic reader index is in "lagged replica DB" mode
 356                                 if ( $laggedReplicaMode ) {
 357                                         $this->laggedReplicaMode = true;
 358                                 }
 359                         }
 360                         $serverName = $this->getServerName( $i );
 361                         wfDebugLog( 'connect', __METHOD__ .
 362                                 ": using server $serverName for group '$group'\n" );
 363                 }
 364
 365                 return $i;
 366         }
 367
 368         /**
 369          * Set the master wait position
 370          * If a DB_REPLICA connection has been opened already, waits
 371          * Otherwise sets a variable telling it to wait if such a connection is opened
 372          * @param DBMasterPos $pos
 373          */
 374         public function waitFor( $pos ) {
 375                 $this->mWaitForPos = $pos;
 376                 $i = $this->mReadIndex;
 377
 378                 if ( $i > 0 ) {
 379                         if ( !$this->doWait( $i ) ) {
 380                                 $this->laggedReplicaMode = true;
 381                         }
 382                 }
 383         }
 384
 385         /**
 386          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 387          *
 388          * This can be used a faster proxy for waitForAll()
 389          *
 390          * @param DBMasterPos $pos
 391          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 392          * @return bool Success (able to connect and no timeouts reached)
 393          * @since 1.26
 394          */
 395         public function waitForOne( $pos, $timeout = null ) {
 396                 $this->mWaitForPos = $pos;
 397
 398                 $i = $this->mReadIndex;
 399                 if ( $i <= 0 ) {
 400                         // Pick a generic replica DB if there isn't one yet
 401                         $readLoads = $this->mLoads;
 402                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 403                         $readLoads = array_filter( $readLoads ); // with non-zero load
 404                         $i = ArrayUtils::pickRandom( $readLoads );
 405                 }
 406
 407                 if ( $i > 0 ) {
 408                         $ok = $this->doWait( $i, true, $timeout );
 409                 } else {
 410                         $ok = true; // no applicable loads
 411                 }
 412
 413                 return $ok;
 414         }
 415
 416         /**
 417          * Set the master wait position and wait for ALL replica DBs to catch up to it
 418          * @param DBMasterPos $pos
 419          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 420          * @return bool Success (able to connect and no timeouts reached)
 421          */
 422         public function waitForAll( $pos, $timeout = null ) {
 423                 $this->mWaitForPos = $pos;
 424                 $serverCount = count( $this->mServers );
 425
 426                 $ok = true;
 427                 for ( $i = 1; $i < $serverCount; $i++ ) {
 428                         if ( $this->mLoads[$i] > 0 ) {
 429                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 430                         }
 431                 }
 432
 433                 return $ok;
 434         }
 435
 436         /**
 437          * Get any open connection to a given server index, local or foreign
 438          * Returns false if there is no connection open
 439          *
 440          * @param int $i Server index
 441          * @return DatabaseBase|bool False on failure
 442          */
 443         public function getAnyOpenConnection( $i ) {
 444                 foreach ( $this->mConns as $connsByServer ) {
 445                         if ( !empty( $connsByServer[$i] ) ) {
 446                                 return reset( $connsByServer[$i] );
 447                         }
 448                 }
 449
 450                 return false;
 451         }
 452
 453         /**
 454          * Wait for a given replica DB to catch up to the master pos stored in $this
 455          * @param int $index Server index
 456          * @param bool $open Check the server even if a new connection has to be made
 457          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 458          * @return bool
 459          */
 460         protected function doWait( $index, $open = false, $timeout = null ) {
 461                 $close = false; // close the connection afterwards
 462
 463                 // Check if we already know that the DB has reached this point
 464                 $server = $this->getServerName( $index );
 465                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 466                 /** @var DBMasterPos $knownReachedPos */
 467                 $knownReachedPos = $this->srvCache->get( $key );
 468                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 469                         wfDebugLog( 'replication', __METHOD__ .
 470                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos).\n" );
 471                         return true;
 472                 }
 473
 474                 // Find a connection to wait on, creating one if needed and allowed
 475                 $conn = $this->getAnyOpenConnection( $index );
 476                 if ( !$conn ) {
 477                         if ( !$open ) {
 478                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 479
 480                                 return false;
 481                         } else {
 482                                 $conn = $this->openConnection( $index, '' );
 483                                 if ( !$conn ) {
 484                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 485
 486                                         return false;
 487                                 }
 488                                 // Avoid connection spam in waitForAll() when connections
 489                                 // are made just for the sake of doing this lag check.
 490                                 $close = true;
 491                         }
 492                 }
 493
 494                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for replica DB $server to catch up...\n" );
 495                 $timeout = $timeout ?: $this->mWaitTimeout;
 496                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 497
 498                 if ( $result == -1 || is_null( $result ) ) {
 499                         // Timed out waiting for replica DB, use master instead
 500                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 501                         wfDebugLog( 'replication', "$msg\n" );
 502                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 503                         $ok = false;
 504                 } else {
 505                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 506                         $ok = true;
 507                         // Remember that the DB reached this point
 508                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 509                 }
 510
 511                 if ( $close ) {
 512                         $this->closeConnection( $conn );
 513                 }
 514
 515                 return $ok;
 516         }
 517
 518         /**
 519          * Get a connection by index
 520          * This is the main entry point for this class.
 521          *
 522          * @param int $i Server index
 523          * @param array|string|bool $groups Query group(s), or false for the generic reader
 524          * @param string|bool $wiki Wiki ID, or false for the current wiki
 525          *
 526          * @throws MWException
 527          * @return DatabaseBase
 528          */
 529         public function getConnection( $i, $groups = [], $wiki = false ) {
 530                 if ( $i === null || $i === false ) {
 531                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 532                                 ' with invalid server index' );
 533                 }
 534
 535                 if ( $wiki === wfWikiID() ) {
 536                         $wiki = false;
 537                 }
 538
 539                 $groups = ( $groups === false || $groups === [] )
 540                         ? [ false ] // check one "group": the generic pool
 541                         : (array)$groups;
 542
 543                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 544                 $oldConnsOpened = $this->connsOpened; // connections open now
 545
 546                 if ( $i == DB_MASTER ) {
 547                         $i = $this->getWriterIndex();
 548                 } else {
 549                         # Try to find an available server in any the query groups (in order)
 550                         foreach ( $groups as $group ) {
 551                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 552                                 if ( $groupIndex !== false ) {
 553                                         $i = $groupIndex;
 554                                         break;
 555                                 }
 556                         }
 557                 }
 558
 559                 # Operation-based index
 560                 if ( $i == DB_REPLICA ) {
 561                         $this->mLastError = 'Unknown error'; // reset error string
 562                         # Try the general server pool if $groups are unavailable.
 563                         $i = in_array( false, $groups, true )
 564                                 ? false // don't bother with this if that is what was tried above
 565                                 : $this->getReaderIndex( false, $wiki );
 566                         # Couldn't find a working server in getReaderIndex()?
 567                         if ( $i === false ) {
 568                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 569
 570                                 return $this->reportConnectionError();
 571                         }
 572                 }
 573
 574                 # Now we have an explicit index into the servers array
 575                 $conn = $this->openConnection( $i, $wiki );
 576                 if ( !$conn ) {
 577                         return $this->reportConnectionError();
 578                 }
 579
 580                 # Profile any new connections that happen
 581                 if ( $this->connsOpened > $oldConnsOpened ) {
 582                         $host = $conn->getServer();
 583                         $dbname = $conn->getDBname();
 584                         $trxProf = Profiler::instance()->getTransactionProfiler();
 585                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 586                 }
 587
 588                 if ( $masterOnly ) {
 589                         # Make master-requested DB handles inherit any read-only mode setting
 590                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
 591                 }
 592
 593                 return $conn;
 594         }
 595
 596         /**
 597          * Mark a foreign connection as being available for reuse under a different
 598          * DB name or prefix. This mechanism is reference-counted, and must be called
 599          * the same number of times as getConnection() to work.
 600          *
 601          * @param DatabaseBase $conn
 602          * @throws MWException
 603          */
 604         public function reuseConnection( $conn ) {
 605                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 606                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 607                 if ( $serverIndex === null || $refCount === null ) {
 608                         /**
 609                          * This can happen in code like:
 610                          *   foreach ( $dbs as $db ) {
 611                          *     $conn = $lb->getConnection( DB_REPLICA, [], $db );
 612                          *     ...
 613                          *     $lb->reuseConnection( $conn );
 614                          *   }
 615                          * When a connection to the local DB is opened in this way, reuseConnection()
 616                          * should be ignored
 617                          */
 618                         return;
 619                 }
 620
 621                 $dbName = $conn->getDBname();
 622                 $prefix = $conn->tablePrefix();
 623                 if ( strval( $prefix ) !== '' ) {
 624                         $wiki = "$dbName-$prefix";
 625                 } else {
 626                         $wiki = $dbName;
 627                 }
 628                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 629                         throw new MWException( __METHOD__ . ": connection not found, has " .
 630                                 "the connection been freed already?" );
 631                 }
 632                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 633                 if ( $refCount <= 0 ) {
 634                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 635                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 636                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 637                 } else {
 638                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 639                 }
 640         }
 641
 642         /**
 643          * Get a database connection handle reference
 644          *
 645          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 646          *
 647          * @see LoadBalancer::getConnection() for parameter information
 648          *
 649          * @param int $db
 650          * @param array|string|bool $groups Query group(s), or false for the generic reader
 651          * @param string|bool $wiki Wiki ID, or false for the current wiki
 652          * @return DBConnRef
 653          */
 654         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 655                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 656         }
 657
 658         /**
 659          * Get a database connection handle reference without connecting yet
 660          *
 661          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 662          *
 663          * @see LoadBalancer::getConnection() for parameter information
 664          *
 665          * @param int $db
 666          * @param array|string|bool $groups Query group(s), or false for the generic reader
 667          * @param string|bool $wiki Wiki ID, or false for the current wiki
 668          * @return DBConnRef
 669          */
 670         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 671                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 672         }
 673
 674         /**
 675          * Open a connection to the server given by the specified index
 676          * Index must be an actual index into the array.
 677          * If the server is already open, returns it.
 678          *
 679          * On error, returns false, and the connection which caused the
 680          * error will be available via $this->mErrorConnection.
 681          *
 682          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 683          *
 684          * @param int $i Server index
 685          * @param string|bool $wiki Wiki ID, or false for the current wiki
 686          * @return DatabaseBase|bool Returns false on errors
 687          */
 688         public function openConnection( $i, $wiki = false ) {
 689                 if ( $wiki !== false ) {
 690                         $conn = $this->openForeignConnection( $i, $wiki );
 691                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 692                         $conn = $this->mConns['local'][$i][0];
 693                 } else {
 694                         $server = $this->mServers[$i];
 695                         $server['serverIndex'] = $i;
 696                         $conn = $this->reallyOpenConnection( $server, false );
 697                         $serverName = $this->getServerName( $i );
 698                         if ( $conn->isOpen() ) {
 699                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 700                                 $this->mConns['local'][$i][0] = $conn;
 701                         } else {
 702                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 703                                 $this->mErrorConnection = $conn;
 704                                 $conn = false;
 705                         }
 706                 }
 707
 708                 if ( $conn && !$conn->isOpen() ) {
 709                         // Connection was made but later unrecoverably lost for some reason.
 710                         // Do not return a handle that will just throw exceptions on use,
 711                         // but let the calling code (e.g. getReaderIndex) try another server.
 712                         // See DatabaseMyslBase::ping() for how this can happen.
 713                         $this->mErrorConnection = $conn;
 714                         $conn = false;
 715                 }
 716
 717                 return $conn;
 718         }
 719
 720         /**
 721          * Open a connection to a foreign DB, or return one if it is already open.
 722          *
 723          * Increments a reference count on the returned connection which locks the
 724          * connection to the requested wiki. This reference count can be
 725          * decremented by calling reuseConnection().
 726          *
 727          * If a connection is open to the appropriate server already, but with the wrong
 728          * database, it will be switched to the right database and returned, as long as
 729          * it has been freed first with reuseConnection().
 730          *
 731          * On error, returns false, and the connection which caused the
 732          * error will be available via $this->mErrorConnection.
 733          *
 734          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 735          *
 736          * @param int $i Server index
 737          * @param string $wiki Wiki ID to open
 738          * @return DatabaseBase
 739          */
 740         private function openForeignConnection( $i, $wiki ) {
 741                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 742                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 743                         // Reuse an already-used connection
 744                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 745                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 746                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 747                         // Reuse a free connection for the same wiki
 748                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 749                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 750                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 751                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 752                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 753                         // Reuse a connection from another wiki
 754                         $conn = reset( $this->mConns['foreignFree'][$i] );
 755                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 756
 757                         // The empty string as a DB name means "don't care".
 758                         // DatabaseMysqlBase::open() already handle this on connection.
 759                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 760                                 $this->mLastError = "Error selecting database $dbName on server " .
 761                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 762                                 $this->mErrorConnection = $conn;
 763                                 $conn = false;
 764                         } else {
 765                                 $conn->tablePrefix( $prefix );
 766                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 767                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 768                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 769                         }
 770                 } else {
 771                         // Open a new connection
 772                         $server = $this->mServers[$i];
 773                         $server['serverIndex'] = $i;
 774                         $server['foreignPoolRefCount'] = 0;
 775                         $server['foreign'] = true;
 776                         $conn = $this->reallyOpenConnection( $server, $dbName );
 777                         if ( !$conn->isOpen() ) {
 778                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 779                                 $this->mErrorConnection = $conn;
 780                                 $conn = false;
 781                         } else {
 782                                 $conn->tablePrefix( $prefix );
 783                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 784                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 785                         }
 786                 }
 787
 788                 // Increment reference count
 789                 if ( $conn ) {
 790                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 791                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 792                 }
 793
 794                 return $conn;
 795         }
 796
 797         /**
 798          * Test if the specified index represents an open connection
 799          *
 800          * @param int $index Server index
 801          * @access private
 802          * @return bool
 803          */
 804         private function isOpen( $index ) {
 805                 if ( !is_integer( $index ) ) {
 806                         return false;
 807                 }
 808
 809                 return (bool)$this->getAnyOpenConnection( $index );
 810         }
 811
 812         /**
 813          * Really opens a connection. Uncached.
 814          * Returns a Database object whether or not the connection was successful.
 815          * @access private
 816          *
 817          * @param array $server
 818          * @param bool $dbNameOverride
 819          * @throws MWException
 820          * @return DatabaseBase
 821          */
 822         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 823                 if ( $this->disabled ) {
 824                         throw new DBAccessError();
 825                 }
 826
 827                 if ( !is_array( $server ) ) {
 828                         throw new MWException( 'You must update your load-balancing configuration. ' .
 829                                 'See DefaultSettings.php entry for $wgDBservers.' );
 830                 }
 831
 832                 if ( $dbNameOverride !== false ) {
 833                         $server['dbname'] = $dbNameOverride;
 834                 }
 835
 836                 // Let the handle know what the cluster master is (e.g. "db1052")
 837                 $masterName = $this->getServerName( $this->getWriterIndex() );
 838                 $server['clusterMasterHost'] = $masterName;
 839
 840                 // Log when many connection are made on requests
 841                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 842                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 843                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 844                                 wfBacktrace( true ) );
 845                 }
 846
 847                 # Create object
 848                 try {
 849                         $db = DatabaseBase::factory( $server['type'], $server );
 850                 } catch ( DBConnectionError $e ) {
 851                         // FIXME: This is probably the ugliest thing I have ever done to
 852                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 853                         $db = $e->db;
 854                 }
 855
 856                 $db->setLBInfo( $server );
 857                 $db->setLazyMasterHandle(
 858                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 859                 );
 860                 $db->setTransactionProfiler( $this->trxProfiler );
 861
 862                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 863                         if ( $this->trxRoundId !== false ) {
 864                                 $this->applyTransactionRoundFlags( $db );
 865                         }
 866                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 867                                 $db->setTransactionListener( $name, $callback );
 868                         }
 869                 }
 870
 871                 return $db;
 872         }
 873
 874         /**
 875          * @throws DBConnectionError
 876          * @return bool
 877          */
 878         private function reportConnectionError() {
 879                 $conn = $this->mErrorConnection; // The connection which caused the error
 880                 $context = [
 881                         'method' => __METHOD__,
 882                         'last_error' => $this->mLastError,
 883                 ];
 884
 885                 if ( !is_object( $conn ) ) {
 886                         // No last connection, probably due to all servers being too busy
 887                         wfLogDBError(
 888                                 "LB failure with no last connection. Connection error: {last_error}",
 889                                 $context
 890                         );
 891
 892                         // If all servers were busy, mLastError will contain something sensible
 893                         throw new DBConnectionError( null, $this->mLastError );
 894                 } else {
 895                         $context['db_server'] = $conn->getProperty( 'mServer' );
 896                         wfLogDBError(
 897                                 "Connection error: {last_error} ({db_server})",
 898                                 $context
 899                         );
 900
 901                         // throws DBConnectionError
 902                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 903                 }
 904
 905                 return false; /* not reached */
 906         }
 907
 908         /**
 909          * @return int
 910          * @since 1.26
 911          */
 912         public function getWriterIndex() {
 913                 return 0;
 914         }
 915
 916         /**
 917          * Returns true if the specified index is a valid server index
 918          *
 919          * @param string $i
 920          * @return bool
 921          */
 922         public function haveIndex( $i ) {
 923                 return array_key_exists( $i, $this->mServers );
 924         }
 925
 926         /**
 927          * Returns true if the specified index is valid and has non-zero load
 928          *
 929          * @param string $i
 930          * @return bool
 931          */
 932         public function isNonZeroLoad( $i ) {
 933                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 934         }
 935
 936         /**
 937          * Get the number of defined servers (not the number of open connections)
 938          *
 939          * @return int
 940          */
 941         public function getServerCount() {
 942                 return count( $this->mServers );
 943         }
 944
 945         /**
 946          * Get the host name or IP address of the server with the specified index
 947          * Prefer a readable name if available.
 948          * @param string $i
 949          * @return string
 950          */
 951         public function getServerName( $i ) {
 952                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 953                         $name = $this->mServers[$i]['hostName'];
 954                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 955                         $name = $this->mServers[$i]['host'];
 956                 } else {
 957                         $name = '';
 958                 }
 959
 960                 return ( $name != '' ) ? $name : 'localhost';
 961         }
 962
 963         /**
 964          * Return the server info structure for a given index, or false if the index is invalid.
 965          * @param int $i
 966          * @return array|bool
 967          */
 968         public function getServerInfo( $i ) {
 969                 if ( isset( $this->mServers[$i] ) ) {
 970                         return $this->mServers[$i];
 971                 } else {
 972                         return false;
 973                 }
 974         }
 975
 976         /**
 977          * Sets the server info structure for the given index. Entry at index $i
 978          * is created if it doesn't exist
 979          * @param int $i
 980          * @param array $serverInfo
 981          */
 982         public function setServerInfo( $i, array $serverInfo ) {
 983                 $this->mServers[$i] = $serverInfo;
 984         }
 985
 986         /**
 987          * Get the current master position for chronology control purposes
 988          * @return DBMasterPos|bool Returns false if not applicable
 989          */
 990         public function getMasterPos() {
 991                 # If this entire request was served from a replica DB without opening a connection to the
 992                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 993                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 994                 if ( !$masterConn ) {
 995                         $serverCount = count( $this->mServers );
 996                         for ( $i = 1; $i < $serverCount; $i++ ) {
 997                                 $conn = $this->getAnyOpenConnection( $i );
 998                                 if ( $conn ) {
 999                                         return $conn->getSlavePos();
1000                                 }
1001                         }
1002                 } else {
1003                         return $masterConn->getMasterPos();
1004                 }
1005
1006                 return false;
1007         }
1008
1009         /**
1010          * Disable this load balancer. All connections are closed, and any attempt to
1011          * open a new connection will result in a DBAccessError.
1012          *
1013          * @since 1.27
1014          */
1015         public function disable() {
1016                 $this->closeAll();
1017                 $this->disabled = true;
1018         }
1019
1020         /**
1021          * Close all open connections
1022          */
1023         public function closeAll() {
1024                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1025                         $conn->close();
1026                 } );
1027
1028                 $this->mConns = [
1029                         'local' => [],
1030                         'foreignFree' => [],
1031                         'foreignUsed' => [],
1032                 ];
1033                 $this->connsOpened = 0;
1034         }
1035
1036         /**
1037          * Close a connection
1038          *
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          *
1042          * @param DatabaseBase $conn
1043          */
1044         public function closeConnection( DatabaseBase $conn ) {
1045                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1046                 foreach ( $this->mConns as $type => $connsByServer ) {
1047                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1048                                 continue;
1049                         }
1050
1051                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1052                                 if ( $conn === $trackedConn ) {
1053                                         unset( $this->mConns[$type][$serverIndex][$i] );
1054                                         --$this->connsOpened;
1055                                         break 2;
1056                                 }
1057                         }
1058                 }
1059
1060                 $conn->close();
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( $conn::ESTIMATE_DB_APPLY );
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->flushSnapshot( $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->flushSnapshot( $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->setTrxEndCallbackSuppression( false );
1240                         if ( $conn->writesOrCallbacksPending() ) {
1241                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1242                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1243                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1244                                 wfWarn( __METHOD__ . ": did not expect writes/callbacks pending." );
1245                                 return;
1246                         } elseif ( $conn->trxLevel() ) {
1247                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1248                                 // thus leaving an implicit read-only transaction open at this point. It
1249                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1250                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1251                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1252                                 return;
1253                         }
1254                         try {
1255                                 $conn->runOnTransactionIdleCallbacks( $type );
1256                         } catch ( Exception $ex ) {
1257                                 $e = $e ?: $ex;
1258                         }
1259                         try {
1260                                 $conn->runTransactionListenerCallbacks( $type );
1261                         } catch ( Exception $ex ) {
1262                                 $e = $e ?: $ex;
1263                         }
1264                 } );
1265
1266                 return $e;
1267         }
1268
1269         /**
1270          * Issue ROLLBACK only on master, only if queries were done on connection
1271          * @param string $fname Caller name
1272          * @throws DBExpectedError
1273          * @since 1.23
1274          */
1275         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1276                 $restore = ( $this->trxRoundId !== false );
1277                 $this->trxRoundId = false;
1278                 $this->forEachOpenMasterConnection(
1279                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1280                                 if ( $conn->writesOrCallbacksPending() ) {
1281                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1282                                 }
1283                                 if ( $restore ) {
1284                                         $this->undoTransactionRoundFlags( $conn );
1285                                 }
1286                         }
1287                 );
1288         }
1289
1290         /**
1291          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1292          * @return Exception|null The first exception or null if there were none
1293          * @since 1.28
1294          */
1295         public function suppressTransactionEndCallbacks() {
1296                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1297                         $conn->setTrxEndCallbackSuppression( true );
1298                 } );
1299         }
1300
1301         /**
1302          * @param DatabaseBase $conn
1303          */
1304         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1305                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1306                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1307                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1308                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1309                         // If config has explicitly requested DBO_TRX be either on or off by not
1310                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1311                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1312                 }
1313         }
1314
1315         /**
1316          * @param DatabaseBase $conn
1317          */
1318         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1319                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1320                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1321                 }
1322         }
1323
1324         /**
1325          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
1326          *
1327          * @param string $fname Caller name
1328          * @since 1.28
1329          */
1330         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1331                 $this->forEachOpenReplicaConnection( function ( DatabaseBase $conn ) {
1332                         $conn->flushSnapshot( __METHOD__ );
1333                 } );
1334         }
1335
1336         /**
1337          * @return bool Whether a master connection is already open
1338          * @since 1.24
1339          */
1340         public function hasMasterConnection() {
1341                 return $this->isOpen( $this->getWriterIndex() );
1342         }
1343
1344         /**
1345          * Determine if there are pending changes in a transaction by this thread
1346          * @since 1.23
1347          * @return bool
1348          */
1349         public function hasMasterChanges() {
1350                 $pending = 0;
1351                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$pending ) {
1352                         $pending |= $conn->writesOrCallbacksPending();
1353                 } );
1354
1355                 return (bool)$pending;
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                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$lastTime ) {
1366                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1367                 } );
1368
1369                 return $lastTime;
1370         }
1371
1372         /**
1373          * Check if this load balancer object had any recent or still
1374          * pending writes issued against it by this PHP thread
1375          *
1376          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1377          * @return bool
1378          * @since 1.25
1379          */
1380         public function hasOrMadeRecentMasterChanges( $age = null ) {
1381                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1382
1383                 return ( $this->hasMasterChanges()
1384                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1385         }
1386
1387         /**
1388          * Get the list of callers that have pending master changes
1389          *
1390          * @return string[] List of method names
1391          * @since 1.27
1392          */
1393         public function pendingMasterChangeCallers() {
1394                 $fnames = [];
1395                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$fnames ) {
1396                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1397                 } );
1398
1399                 return $fnames;
1400         }
1401
1402         /**
1403          * @note This method will trigger a DB connection if not yet done
1404          * @param string|bool $wiki Wiki ID, or false for the current wiki
1405          * @return bool Whether the generic connection for reads is highly "lagged"
1406          */
1407         public function getLaggedReplicaMode( $wiki = false ) {
1408                 // No-op if there is only one DB (also avoids recursion)
1409                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1410                         try {
1411                                 // See if laggedReplicaMode gets set
1412                                 $conn = $this->getConnection( DB_REPLICA, false, $wiki );
1413                                 $this->reuseConnection( $conn );
1414                         } catch ( DBConnectionError $e ) {
1415                                 // Avoid expensive re-connect attempts and failures
1416                                 $this->allReplicasDownMode = true;
1417                                 $this->laggedReplicaMode = true;
1418                         }
1419                 }
1420
1421                 return $this->laggedReplicaMode;
1422         }
1423
1424         /**
1425          * @param bool $wiki
1426          * @return bool
1427          * @deprecated 1.28; use getLaggedReplicaMode()
1428          */
1429         public function getLaggedSlaveMode( $wiki = false ) {
1430                 return $this->getLaggedReplicaMode( $wiki );
1431         }
1432
1433         /**
1434          * @note This method will never cause a new DB connection
1435          * @return bool Whether any generic connection used for reads was highly "lagged"
1436          * @since 1.28
1437          */
1438         public function laggedReplicaUsed() {
1439                 return $this->laggedReplicaMode;
1440         }
1441
1442         /**
1443          * @return bool
1444          * @since 1.27
1445          * @deprecated Since 1.28; use laggedReplicaUsed()
1446          */
1447         public function laggedSlaveUsed() {
1448                 return $this->laggedReplicaUsed();
1449         }
1450
1451         /**
1452          * @note This method may trigger a DB connection if not yet done
1453          * @param string|bool $wiki Wiki ID, or false for the current wiki
1454          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1455          * @return string|bool Reason the master is read-only or false if it is not
1456          * @since 1.27
1457          */
1458         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1459                 if ( $this->readOnlyReason !== false ) {
1460                         return $this->readOnlyReason;
1461                 } elseif ( $this->getLaggedReplicaMode( $wiki ) ) {
1462                         if ( $this->allReplicasDownMode ) {
1463                                 return 'The database has been automatically locked ' .
1464                                         'until the replica database servers become available';
1465                         } else {
1466                                 return 'The database has been automatically locked ' .
1467                                         'while the replica database servers catch up to the master.';
1468                         }
1469                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1470                         return 'The database master is running in read-only mode.';
1471                 }
1472
1473                 return false;
1474         }
1475
1476         /**
1477          * @param string $wiki Wiki ID, or false for the current wiki
1478          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1479          * @return bool
1480          */
1481         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1482                 $cache = $this->wanCache;
1483                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1484
1485                 return (bool)$cache->getWithSetCallback(
1486                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1487                         self::TTL_CACHE_READONLY,
1488                         function () use ( $wiki, $conn ) {
1489                                 $this->trxProfiler->setSilenced( true );
1490                                 try {
1491                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1492                                         $readOnly = (int)$dbw->serverIsReadOnly();
1493                                 } catch ( DBError $e ) {
1494                                         $readOnly = 0;
1495                                 }
1496                                 $this->trxProfiler->setSilenced( false );
1497                                 return $readOnly;
1498                         },
1499                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1500                 );
1501         }
1502
1503         /**
1504          * Disables/enables lag checks
1505          * @param null|bool $mode
1506          * @return bool
1507          */
1508         public function allowLagged( $mode = null ) {
1509                 if ( $mode === null ) {
1510                         return $this->mAllowLagged;
1511                 }
1512                 $this->mAllowLagged = $mode;
1513
1514                 return $this->mAllowLagged;
1515         }
1516
1517         /**
1518          * @return bool
1519          */
1520         public function pingAll() {
1521                 $success = true;
1522                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1523                         if ( !$conn->ping() ) {
1524                                 $success = false;
1525                         }
1526                 } );
1527
1528                 return $success;
1529         }
1530
1531         /**
1532          * Call a function with each open connection object
1533          * @param callable $callback
1534          * @param array $params
1535          */
1536         public function forEachOpenConnection( $callback, array $params = [] ) {
1537                 foreach ( $this->mConns as $connsByServer ) {
1538                         foreach ( $connsByServer as $serverConns ) {
1539                                 foreach ( $serverConns as $conn ) {
1540                                         $mergedParams = array_merge( [ $conn ], $params );
1541                                         call_user_func_array( $callback, $mergedParams );
1542                                 }
1543                         }
1544                 }
1545         }
1546
1547         /**
1548          * Call a function with each open connection object to a master
1549          * @param callable $callback
1550          * @param array $params
1551          * @since 1.28
1552          */
1553         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1554                 $masterIndex = $this->getWriterIndex();
1555                 foreach ( $this->mConns as $connsByServer ) {
1556                         if ( isset( $connsByServer[$masterIndex] ) ) {
1557                                 /** @var DatabaseBase $conn */
1558                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1559                                         $mergedParams = array_merge( [ $conn ], $params );
1560                                         call_user_func_array( $callback, $mergedParams );
1561                                 }
1562                         }
1563                 }
1564         }
1565
1566         /**
1567          * Call a function with each open replica DB connection object
1568          * @param callable $callback
1569          * @param array $params
1570          * @since 1.28
1571          */
1572         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1573                 foreach ( $this->mConns as $connsByServer ) {
1574                         foreach ( $connsByServer as $i => $serverConns ) {
1575                                 if ( $i === $this->getWriterIndex() ) {
1576                                         continue; // skip master
1577                                 }
1578                                 foreach ( $serverConns as $conn ) {
1579                                         $mergedParams = array_merge( [ $conn ], $params );
1580                                         call_user_func_array( $callback, $mergedParams );
1581                                 }
1582                         }
1583                 }
1584         }
1585
1586         /**
1587          * Get the hostname and lag time of the most-lagged replica DB
1588          *
1589          * This is useful for maintenance scripts that need to throttle their updates.
1590          * May attempt to open connections to replica DBs on the default DB. If there is
1591          * no lag, the maximum lag will be reported as -1.
1592          *
1593          * @param bool|string $wiki Wiki ID, or false for the default database
1594          * @return array ( host, max lag, index of max lagged host )
1595          */
1596         public function getMaxLag( $wiki = false ) {
1597                 $maxLag = -1;
1598                 $host = '';
1599                 $maxIndex = 0;
1600
1601                 if ( $this->getServerCount() <= 1 ) {
1602                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1603                 }
1604
1605                 $lagTimes = $this->getLagTimes( $wiki );
1606                 foreach ( $lagTimes as $i => $lag ) {
1607                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1608                                 $maxLag = $lag;
1609                                 $host = $this->mServers[$i]['host'];
1610                                 $maxIndex = $i;
1611                         }
1612                 }
1613
1614                 return [ $host, $maxLag, $maxIndex ];
1615         }
1616
1617         /**
1618          * Get an estimate of replication lag (in seconds) for each server
1619          *
1620          * Results are cached for a short time in memcached/process cache
1621          *
1622          * Values may be "false" if replication is too broken to estimate
1623          *
1624          * @param string|bool $wiki
1625          * @return int[] Map of (server index => float|int|bool)
1626          */
1627         public function getLagTimes( $wiki = false ) {
1628                 if ( $this->getServerCount() <= 1 ) {
1629                         return [ 0 => 0 ]; // no replication = no lag
1630                 }
1631
1632                 # Send the request to the load monitor
1633                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1634         }
1635
1636         /**
1637          * Get the lag in seconds for a given connection, or zero if this load
1638          * balancer does not have replication enabled.
1639          *
1640          * This should be used in preference to Database::getLag() in cases where
1641          * replication may not be in use, since there is no way to determine if
1642          * replication is in use at the connection level without running
1643          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1644          * function instead of Database::getLag() avoids a fatal error in this
1645          * case on many installations.
1646          *
1647          * @param IDatabase $conn
1648          * @return int|bool Returns false on error
1649          */
1650         public function safeGetLag( IDatabase $conn ) {
1651                 if ( $this->getServerCount() == 1 ) {
1652                         return 0;
1653                 } else {
1654                         return $conn->getLag();
1655                 }
1656         }
1657
1658         /**
1659          * Wait for a replica DB to reach a specified master position
1660          *
1661          * This will connect to the master to get an accurate position if $pos is not given
1662          *
1663          * @param IDatabase $conn Replica DB
1664          * @param DBMasterPos|bool $pos Master position; default: current position
1665          * @param integer|null $timeout Timeout in seconds [optional]
1666          * @return bool Success
1667          * @since 1.27
1668          */
1669         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1670                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'replica' ) ) {
1671                         return true; // server is not a replica DB
1672                 }
1673
1674                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1675                 if ( !( $pos instanceof DBMasterPos ) ) {
1676                         return false; // something is misconfigured
1677                 }
1678
1679                 $timeout = $timeout ?: $this->mWaitTimeout;
1680                 $result = $conn->masterPosWait( $pos, $timeout );
1681                 if ( $result == -1 || is_null( $result ) ) {
1682                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1683                         wfDebugLog( 'replication', "$msg\n" );
1684                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1685                         $ok = false;
1686                 } else {
1687                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1688                         $ok = true;
1689                 }
1690
1691                 return $ok;
1692         }
1693
1694         /**
1695          * Clear the cache for slag lag delay times
1696          *
1697          * This is only used for testing
1698          */
1699         public function clearLagTimeCache() {
1700                 $this->getLoadMonitor()->clearCaches();
1701         }
1702
1703         /**
1704          * Set a callback via DatabaseBase::setTransactionListener() on
1705          * all current and future master connections of this load balancer
1706          *
1707          * @param string $name Callback name
1708          * @param callable|null $callback
1709          * @since 1.28
1710          */
1711         public function setTransactionListener( $name, callable $callback = null ) {
1712                 if ( $callback ) {
1713                         $this->trxRecurringCallbacks[$name] = $callback;
1714                 } else {
1715                         unset( $this->trxRecurringCallbacks[$name] );
1716                 }
1717                 $this->forEachOpenMasterConnection(
1718                         function ( DatabaseBase $conn ) use ( $name, $callback ) {
1719                                 $conn->setTransactionListener( $name, $callback );
1720                         }
1721                 );
1722         }
1723 }