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 $laggedSlaveMode = false;
  65         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  66         private $slavesDownMode = false;
  67         /** @var string The last DB selection or connection error */
  68         private $mLastError = 'Unknown error';
  69         /** @var string|bool Reason the LB is read-only or false if not */
  70         private $readOnlyReason = false;
  71         /** @var integer Total connections opened */
  72         private $connsOpened = 0;
  73         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  74         private $trxRoundId = false;
  75         /** @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 = 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 = self::MAX_LAG ) {
 193                 $lags = $this->getLagTimes( $wiki );
 194
 195                 # Unset excessively lagged servers
 196                 foreach ( $lags as $i => $lag ) {
 197                         if ( $i != 0 ) {
 198                                 $maxServerLag = $maxLag;
 199                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 200                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 201                                 }
 202
 203                                 $host = $this->getServerName( $i );
 204                                 if ( $lag === false ) {
 205                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 206                                         unset( $loads[$i] );
 207                                 } elseif ( $lag > $maxServerLag ) {
 208                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 209                                         unset( $loads[$i] );
 210                                 }
 211                         }
 212                 }
 213
 214                 # Find out if all the replica DBs with non-zero load are lagged
 215                 $sum = 0;
 216                 foreach ( $loads as $load ) {
 217                         $sum += $load;
 218                 }
 219                 if ( $sum == 0 ) {
 220                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 221                         # Do NOT use the master
 222                         # Instead, this function will return false, triggering read-only mode,
 223                         # and a lagged replica DB will be used instead.
 224                         return false;
 225                 }
 226
 227                 if ( count( $loads ) == 0 ) {
 228                         return false;
 229                 }
 230
 231                 # Return a random representative of the remainder
 232                 return ArrayUtils::pickRandom( $loads );
 233         }
 234
 235         /**
 236          * Get the index of the reader connection, which may be a replica DB
 237          * This takes into account load ratios and lag times. It should
 238          * always return a consistent index during a given invocation
 239          *
 240          * Side effect: opens connections to databases
 241          * @param string|bool $group Query group, or false for the generic reader
 242          * @param string|bool $wiki Wiki ID, or false for the current wiki
 243          * @throws MWException
 244          * @return bool|int|string
 245          */
 246         public function getReaderIndex( $group = false, $wiki = false ) {
 247                 global $wgDBtype;
 248
 249                 # @todo FIXME: For now, only go through all this for mysql databases
 250                 if ( $wgDBtype != 'mysql' ) {
 251                         return $this->getWriterIndex();
 252                 }
 253
 254                 if ( count( $this->mServers ) == 1 ) {
 255                         # Skip the load balancing if there's only one server
 256                         return 0;
 257                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 258                         # Shortcut if generic reader exists already
 259                         return $this->mReadIndex;
 260                 }
 261
 262                 # Find the relevant load array
 263                 if ( $group !== false ) {
 264                         if ( isset( $this->mGroupLoads[$group] ) ) {
 265                                 $nonErrorLoads = $this->mGroupLoads[$group];
 266                         } else {
 267                                 # No loads for this group, return false and the caller can use some other group
 268                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 269
 270                                 return false;
 271                         }
 272                 } else {
 273                         $nonErrorLoads = $this->mLoads;
 274                 }
 275
 276                 if ( !count( $nonErrorLoads ) ) {
 277                         throw new MWException( "Empty server array given to LoadBalancer" );
 278                 }
 279
 280                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 281                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 282
 283                 $laggedSlaveMode = false;
 284
 285                 # No server found yet
 286                 $i = false;
 287                 $conn = false;
 288                 # First try quickly looking through the available servers for a server that
 289                 # meets our criteria
 290                 $currentLoads = $nonErrorLoads;
 291                 while ( count( $currentLoads ) ) {
 292                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 293                                 $i = ArrayUtils::pickRandom( $currentLoads );
 294                         } else {
 295                                 $i = false;
 296                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 297                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 298                                         # This triggers doWait() after connect, so it's especially good to
 299                                         # avoid lagged servers so as to avoid just blocking in that method.
 300                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 301                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 302                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 303                                 }
 304                                 if ( $i === false ) {
 305                                         # Any server with less lag than it's 'max lag' param is preferable
 306                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 307                                 }
 308                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 309                                         # All replica DBs lagged. Switch to read-only mode
 310                                         wfDebugLog( 'replication', "All replica DBs lagged. Switch to read-only mode" );
 311                                         $i = ArrayUtils::pickRandom( $currentLoads );
 312                                         $laggedSlaveMode = true;
 313                                 }
 314                         }
 315
 316                         if ( $i === false ) {
 317                                 # pickRandom() returned false
 318                                 # This is permanent and means the configuration or the load monitor
 319                                 # wants us to return false.
 320                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 321
 322                                 return false;
 323                         }
 324
 325                         $serverName = $this->getServerName( $i );
 326                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 327
 328                         $conn = $this->openConnection( $i, $wiki );
 329                         if ( !$conn ) {
 330                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 331                                 unset( $nonErrorLoads[$i] );
 332                                 unset( $currentLoads[$i] );
 333                                 $i = false;
 334                                 continue;
 335                         }
 336
 337                         // Decrement reference counter, we are finished with this connection.
 338                         // It will be incremented for the caller later.
 339                         if ( $wiki !== false ) {
 340                                 $this->reuseConnection( $conn );
 341                         }
 342
 343                         # Return this server
 344                         break;
 345                 }
 346
 347                 # If all servers were down, quit now
 348                 if ( !count( $nonErrorLoads ) ) {
 349                         wfDebugLog( 'connect', "All servers down" );
 350                 }
 351
 352                 if ( $i !== false ) {
 353                         # replica DB connection successful
 354                         # Wait for the session master pos for a short time
 355                         if ( $this->mWaitForPos && $i > 0 ) {
 356                                 if ( !$this->doWait( $i ) ) {
 357                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 358                                 }
 359                         }
 360                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 361                                 $this->mReadIndex = $i;
 362                                 # Record if the generic reader index is in "lagged replica DB" mode
 363                                 if ( $laggedSlaveMode ) {
 364                                         $this->laggedSlaveMode = true;
 365                                 }
 366                         }
 367                         $serverName = $this->getServerName( $i );
 368                         wfDebugLog( 'connect', __METHOD__ .
 369                                 ": using server $serverName for group '$group'\n" );
 370                 }
 371
 372                 return $i;
 373         }
 374
 375         /**
 376          * Set the master wait position
 377          * If a DB_SLAVE connection has been opened already, waits
 378          * Otherwise sets a variable telling it to wait if such a connection is opened
 379          * @param DBMasterPos $pos
 380          */
 381         public function waitFor( $pos ) {
 382                 $this->mWaitForPos = $pos;
 383                 $i = $this->mReadIndex;
 384
 385                 if ( $i > 0 ) {
 386                         if ( !$this->doWait( $i ) ) {
 387                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 388                                 $this->laggedSlaveMode = true;
 389                         }
 390                 }
 391         }
 392
 393         /**
 394          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 395          *
 396          * This can be used a faster proxy for waitForAll()
 397          *
 398          * @param DBMasterPos $pos
 399          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 400          * @return bool Success (able to connect and no timeouts reached)
 401          * @since 1.26
 402          */
 403         public function waitForOne( $pos, $timeout = null ) {
 404                 $this->mWaitForPos = $pos;
 405
 406                 $i = $this->mReadIndex;
 407                 if ( $i <= 0 ) {
 408                         // Pick a generic replica DB if there isn't one yet
 409                         $readLoads = $this->mLoads;
 410                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 411                         $readLoads = array_filter( $readLoads ); // with non-zero load
 412                         $i = ArrayUtils::pickRandom( $readLoads );
 413                 }
 414
 415                 if ( $i > 0 ) {
 416                         $ok = $this->doWait( $i, true, $timeout );
 417                 } else {
 418                         $ok = true; // no applicable loads
 419                 }
 420
 421                 return $ok;
 422         }
 423
 424         /**
 425          * Set the master wait position and wait for ALL replica DBs to catch up to it
 426          * @param DBMasterPos $pos
 427          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 428          * @return bool Success (able to connect and no timeouts reached)
 429          */
 430         public function waitForAll( $pos, $timeout = null ) {
 431                 $this->mWaitForPos = $pos;
 432                 $serverCount = count( $this->mServers );
 433
 434                 $ok = true;
 435                 for ( $i = 1; $i < $serverCount; $i++ ) {
 436                         if ( $this->mLoads[$i] > 0 ) {
 437                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 438                         }
 439                 }
 440
 441                 return $ok;
 442         }
 443
 444         /**
 445          * Get any open connection to a given server index, local or foreign
 446          * Returns false if there is no connection open
 447          *
 448          * @param int $i
 449          * @return DatabaseBase|bool False on failure
 450          */
 451         public function getAnyOpenConnection( $i ) {
 452                 foreach ( $this->mConns as $conns ) {
 453                         if ( !empty( $conns[$i] ) ) {
 454                                 return reset( $conns[$i] );
 455                         }
 456                 }
 457
 458                 return false;
 459         }
 460
 461         /**
 462          * Wait for a given replica DB to catch up to the master pos stored in $this
 463          * @param int $index Server index
 464          * @param bool $open Check the server even if a new connection has to be made
 465          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 466          * @return bool
 467          */
 468         protected function doWait( $index, $open = false, $timeout = null ) {
 469                 $close = false; // close the connection afterwards
 470
 471                 // Check if we already know that the DB has reached this point
 472                 $server = $this->getServerName( $index );
 473                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 474                 /** @var DBMasterPos $knownReachedPos */
 475                 $knownReachedPos = $this->srvCache->get( $key );
 476                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 477                         wfDebugLog( 'replication', __METHOD__ .
 478                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos).\n" );
 479                         return true;
 480                 }
 481
 482                 // Find a connection to wait on, creating one if needed and allowed
 483                 $conn = $this->getAnyOpenConnection( $index );
 484                 if ( !$conn ) {
 485                         if ( !$open ) {
 486                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 487
 488                                 return false;
 489                         } else {
 490                                 $conn = $this->openConnection( $index, '' );
 491                                 if ( !$conn ) {
 492                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 493
 494                                         return false;
 495                                 }
 496                                 // Avoid connection spam in waitForAll() when connections
 497                                 // are made just for the sake of doing this lag check.
 498                                 $close = true;
 499                         }
 500                 }
 501
 502                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for replica DB $server to catch up...\n" );
 503                 $timeout = $timeout ?: $this->mWaitTimeout;
 504                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 505
 506                 if ( $result == -1 || is_null( $result ) ) {
 507                         // Timed out waiting for replica DB, use master instead
 508                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 509                         wfDebugLog( 'replication', "$msg\n" );
 510                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 511                         $ok = false;
 512                 } else {
 513                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 514                         $ok = true;
 515                         // Remember that the DB reached this point
 516                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 517                 }
 518
 519                 if ( $close ) {
 520                         $this->closeConnection( $conn );
 521                 }
 522
 523                 return $ok;
 524         }
 525
 526         /**
 527          * Get a connection by index
 528          * This is the main entry point for this class.
 529          *
 530          * @param int $i Server index
 531          * @param array|string|bool $groups Query group(s), or false for the generic reader
 532          * @param string|bool $wiki Wiki ID, or false for the current wiki
 533          *
 534          * @throws MWException
 535          * @return DatabaseBase
 536          */
 537         public function getConnection( $i, $groups = [], $wiki = false ) {
 538                 if ( $i === null || $i === false ) {
 539                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 540                                 ' with invalid server index' );
 541                 }
 542
 543                 if ( $wiki === wfWikiID() ) {
 544                         $wiki = false;
 545                 }
 546
 547                 $groups = ( $groups === false || $groups === [] )
 548                         ? [ false ] // check one "group": the generic pool
 549                         : (array)$groups;
 550
 551                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 552                 $oldConnsOpened = $this->connsOpened; // connections open now
 553
 554                 if ( $i == DB_MASTER ) {
 555                         $i = $this->getWriterIndex();
 556                 } else {
 557                         # Try to find an available server in any the query groups (in order)
 558                         foreach ( $groups as $group ) {
 559                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 560                                 if ( $groupIndex !== false ) {
 561                                         $i = $groupIndex;
 562                                         break;
 563                                 }
 564                         }
 565                 }
 566
 567                 # Operation-based index
 568                 if ( $i == DB_SLAVE ) {
 569                         $this->mLastError = 'Unknown error'; // reset error string
 570                         # Try the general server pool if $groups are unavailable.
 571                         $i = in_array( false, $groups, true )
 572                                 ? false // don't bother with this if that is what was tried above
 573                                 : $this->getReaderIndex( false, $wiki );
 574                         # Couldn't find a working server in getReaderIndex()?
 575                         if ( $i === false ) {
 576                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 577
 578                                 return $this->reportConnectionError();
 579                         }
 580                 }
 581
 582                 # Now we have an explicit index into the servers array
 583                 $conn = $this->openConnection( $i, $wiki );
 584                 if ( !$conn ) {
 585                         return $this->reportConnectionError();
 586                 }
 587
 588                 # Profile any new connections that happen
 589                 if ( $this->connsOpened > $oldConnsOpened ) {
 590                         $host = $conn->getServer();
 591                         $dbname = $conn->getDBname();
 592                         $trxProf = Profiler::instance()->getTransactionProfiler();
 593                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 594                 }
 595
 596                 if ( $masterOnly ) {
 597                         # Make master-requested DB handles inherit any read-only mode setting
 598                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
 599                 }
 600
 601                 return $conn;
 602         }
 603
 604         /**
 605          * Mark a foreign connection as being available for reuse under a different
 606          * DB name or prefix. This mechanism is reference-counted, and must be called
 607          * the same number of times as getConnection() to work.
 608          *
 609          * @param DatabaseBase $conn
 610          * @throws MWException
 611          */
 612         public function reuseConnection( $conn ) {
 613                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 614                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 615                 if ( $serverIndex === null || $refCount === null ) {
 616                         /**
 617                          * This can happen in code like:
 618                          *   foreach ( $dbs as $db ) {
 619                          *     $conn = $lb->getConnection( DB_SLAVE, [], $db );
 620                          *     ...
 621                          *     $lb->reuseConnection( $conn );
 622                          *   }
 623                          * When a connection to the local DB is opened in this way, reuseConnection()
 624                          * should be ignored
 625                          */
 626                         return;
 627                 }
 628
 629                 $dbName = $conn->getDBname();
 630                 $prefix = $conn->tablePrefix();
 631                 if ( strval( $prefix ) !== '' ) {
 632                         $wiki = "$dbName-$prefix";
 633                 } else {
 634                         $wiki = $dbName;
 635                 }
 636                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 637                         throw new MWException( __METHOD__ . ": connection not found, has " .
 638                                 "the connection been freed already?" );
 639                 }
 640                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 641                 if ( $refCount <= 0 ) {
 642                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 643                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 644                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 645                 } else {
 646                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 647                 }
 648         }
 649
 650         /**
 651          * Get a database connection handle reference
 652          *
 653          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 654          *
 655          * @see LoadBalancer::getConnection() for parameter information
 656          *
 657          * @param int $db
 658          * @param array|string|bool $groups Query group(s), or false for the generic reader
 659          * @param string|bool $wiki Wiki ID, or false for the current wiki
 660          * @return DBConnRef
 661          */
 662         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 663                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 664         }
 665
 666         /**
 667          * Get a database connection handle reference without connecting yet
 668          *
 669          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 670          *
 671          * @see LoadBalancer::getConnection() for parameter information
 672          *
 673          * @param int $db
 674          * @param array|string|bool $groups Query group(s), or false for the generic reader
 675          * @param string|bool $wiki Wiki ID, or false for the current wiki
 676          * @return DBConnRef
 677          */
 678         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 679                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 680         }
 681
 682         /**
 683          * Open a connection to the server given by the specified index
 684          * Index must be an actual index into the array.
 685          * If the server is already open, returns it.
 686          *
 687          * On error, returns false, and the connection which caused the
 688          * error will be available via $this->mErrorConnection.
 689          *
 690          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 691          *
 692          * @param int $i Server index
 693          * @param string|bool $wiki Wiki ID, or false for the current wiki
 694          * @return DatabaseBase|bool Returns false on errors
 695          */
 696         public function openConnection( $i, $wiki = false ) {
 697                 if ( $wiki !== false ) {
 698                         $conn = $this->openForeignConnection( $i, $wiki );
 699                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 700                         $conn = $this->mConns['local'][$i][0];
 701                 } else {
 702                         $server = $this->mServers[$i];
 703                         $server['serverIndex'] = $i;
 704                         $conn = $this->reallyOpenConnection( $server, false );
 705                         $serverName = $this->getServerName( $i );
 706                         if ( $conn->isOpen() ) {
 707                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 708                                 $this->mConns['local'][$i][0] = $conn;
 709                         } else {
 710                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 711                                 $this->mErrorConnection = $conn;
 712                                 $conn = false;
 713                         }
 714                 }
 715
 716                 if ( $conn && !$conn->isOpen() ) {
 717                         // Connection was made but later unrecoverably lost for some reason.
 718                         // Do not return a handle that will just throw exceptions on use,
 719                         // but let the calling code (e.g. getReaderIndex) try another server.
 720                         // See DatabaseMyslBase::ping() for how this can happen.
 721                         $this->mErrorConnection = $conn;
 722                         $conn = false;
 723                 }
 724
 725                 return $conn;
 726         }
 727
 728         /**
 729          * Open a connection to a foreign DB, or return one if it is already open.
 730          *
 731          * Increments a reference count on the returned connection which locks the
 732          * connection to the requested wiki. This reference count can be
 733          * decremented by calling reuseConnection().
 734          *
 735          * If a connection is open to the appropriate server already, but with the wrong
 736          * database, it will be switched to the right database and returned, as long as
 737          * it has been freed first with reuseConnection().
 738          *
 739          * On error, returns false, and the connection which caused the
 740          * error will be available via $this->mErrorConnection.
 741          *
 742          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 743          *
 744          * @param int $i Server index
 745          * @param string $wiki Wiki ID to open
 746          * @return DatabaseBase
 747          */
 748         private function openForeignConnection( $i, $wiki ) {
 749                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 750                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 751                         // Reuse an already-used connection
 752                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 753                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 754                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 755                         // Reuse a free connection for the same wiki
 756                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 757                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 758                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 759                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 760                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 761                         // Reuse a connection from another wiki
 762                         $conn = reset( $this->mConns['foreignFree'][$i] );
 763                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 764
 765                         // The empty string as a DB name means "don't care".
 766                         // DatabaseMysqlBase::open() already handle this on connection.
 767                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 768                                 $this->mLastError = "Error selecting database $dbName on server " .
 769                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 770                                 $this->mErrorConnection = $conn;
 771                                 $conn = false;
 772                         } else {
 773                                 $conn->tablePrefix( $prefix );
 774                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 775                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 776                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 777                         }
 778                 } else {
 779                         // Open a new connection
 780                         $server = $this->mServers[$i];
 781                         $server['serverIndex'] = $i;
 782                         $server['foreignPoolRefCount'] = 0;
 783                         $server['foreign'] = true;
 784                         $conn = $this->reallyOpenConnection( $server, $dbName );
 785                         if ( !$conn->isOpen() ) {
 786                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 787                                 $this->mErrorConnection = $conn;
 788                                 $conn = false;
 789                         } else {
 790                                 $conn->tablePrefix( $prefix );
 791                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 792                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 793                         }
 794                 }
 795
 796                 // Increment reference count
 797                 if ( $conn ) {
 798                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 799                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 800                 }
 801
 802                 return $conn;
 803         }
 804
 805         /**
 806          * Test if the specified index represents an open connection
 807          *
 808          * @param int $index Server index
 809          * @access private
 810          * @return bool
 811          */
 812         private function isOpen( $index ) {
 813                 if ( !is_integer( $index ) ) {
 814                         return false;
 815                 }
 816
 817                 return (bool)$this->getAnyOpenConnection( $index );
 818         }
 819
 820         /**
 821          * Really opens a connection. Uncached.
 822          * Returns a Database object whether or not the connection was successful.
 823          * @access private
 824          *
 825          * @param array $server
 826          * @param bool $dbNameOverride
 827          * @throws MWException
 828          * @return DatabaseBase
 829          */
 830         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 831                 if ( $this->disabled ) {
 832                         throw new DBAccessError();
 833                 }
 834
 835                 if ( !is_array( $server ) ) {
 836                         throw new MWException( 'You must update your load-balancing configuration. ' .
 837                                 'See DefaultSettings.php entry for $wgDBservers.' );
 838                 }
 839
 840                 if ( $dbNameOverride !== false ) {
 841                         $server['dbname'] = $dbNameOverride;
 842                 }
 843
 844                 // Let the handle know what the cluster master is (e.g. "db1052")
 845                 $masterName = $this->getServerName( 0 );
 846                 $server['clusterMasterHost'] = $masterName;
 847
 848                 // Log when many connection are made on requests
 849                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 850                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 851                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 852                                 wfBacktrace( true ) );
 853                 }
 854
 855                 # Create object
 856                 try {
 857                         $db = DatabaseBase::factory( $server['type'], $server );
 858                 } catch ( DBConnectionError $e ) {
 859                         // FIXME: This is probably the ugliest thing I have ever done to
 860                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 861                         $db = $e->db;
 862                 }
 863
 864                 $db->setLBInfo( $server );
 865                 $db->setLazyMasterHandle(
 866                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 867                 );
 868                 $db->setTransactionProfiler( $this->trxProfiler );
 869                 if ( $this->trxRoundId !== false ) {
 870                         $this->applyTransactionRoundFlags( $db );
 871                 }
 872
 873                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 874                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 875                                 $db->setTransactionListener( $name, $callback );
 876                         }
 877                 }
 878
 879                 return $db;
 880         }
 881
 882         /**
 883          * @throws DBConnectionError
 884          * @return bool
 885          */
 886         private function reportConnectionError() {
 887                 $conn = $this->mErrorConnection; // The connection which caused the error
 888                 $context = [
 889                         'method' => __METHOD__,
 890                         'last_error' => $this->mLastError,
 891                 ];
 892
 893                 if ( !is_object( $conn ) ) {
 894                         // No last connection, probably due to all servers being too busy
 895                         wfLogDBError(
 896                                 "LB failure with no last connection. Connection error: {last_error}",
 897                                 $context
 898                         );
 899
 900                         // If all servers were busy, mLastError will contain something sensible
 901                         throw new DBConnectionError( null, $this->mLastError );
 902                 } else {
 903                         $context['db_server'] = $conn->getProperty( 'mServer' );
 904                         wfLogDBError(
 905                                 "Connection error: {last_error} ({db_server})",
 906                                 $context
 907                         );
 908
 909                         // throws DBConnectionError
 910                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 911                 }
 912
 913                 return false; /* not reached */
 914         }
 915
 916         /**
 917          * @return int
 918          * @since 1.26
 919          */
 920         public function getWriterIndex() {
 921                 return 0;
 922         }
 923
 924         /**
 925          * Returns true if the specified index is a valid server index
 926          *
 927          * @param string $i
 928          * @return bool
 929          */
 930         public function haveIndex( $i ) {
 931                 return array_key_exists( $i, $this->mServers );
 932         }
 933
 934         /**
 935          * Returns true if the specified index is valid and has non-zero load
 936          *
 937          * @param string $i
 938          * @return bool
 939          */
 940         public function isNonZeroLoad( $i ) {
 941                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 942         }
 943
 944         /**
 945          * Get the number of defined servers (not the number of open connections)
 946          *
 947          * @return int
 948          */
 949         public function getServerCount() {
 950                 return count( $this->mServers );
 951         }
 952
 953         /**
 954          * Get the host name or IP address of the server with the specified index
 955          * Prefer a readable name if available.
 956          * @param string $i
 957          * @return string
 958          */
 959         public function getServerName( $i ) {
 960                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 961                         $name = $this->mServers[$i]['hostName'];
 962                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 963                         $name = $this->mServers[$i]['host'];
 964                 } else {
 965                         $name = '';
 966                 }
 967
 968                 return ( $name != '' ) ? $name : 'localhost';
 969         }
 970
 971         /**
 972          * Return the server info structure for a given index, or false if the index is invalid.
 973          * @param int $i
 974          * @return array|bool
 975          */
 976         public function getServerInfo( $i ) {
 977                 if ( isset( $this->mServers[$i] ) ) {
 978                         return $this->mServers[$i];
 979                 } else {
 980                         return false;
 981                 }
 982         }
 983
 984         /**
 985          * Sets the server info structure for the given index. Entry at index $i
 986          * is created if it doesn't exist
 987          * @param int $i
 988          * @param array $serverInfo
 989          */
 990         public function setServerInfo( $i, array $serverInfo ) {
 991                 $this->mServers[$i] = $serverInfo;
 992         }
 993
 994         /**
 995          * Get the current master position for chronology control purposes
 996          * @return mixed
 997          */
 998         public function getMasterPos() {
 999                 # If this entire request was served from a replica DB without opening a connection to the
1000                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1001                 $masterConn = $this->getAnyOpenConnection( 0 );
1002                 if ( !$masterConn ) {
1003                         $serverCount = count( $this->mServers );
1004                         for ( $i = 1; $i < $serverCount; $i++ ) {
1005                                 $conn = $this->getAnyOpenConnection( $i );
1006                                 if ( $conn ) {
1007                                         return $conn->getSlavePos();
1008                                 }
1009                         }
1010                 } else {
1011                         return $masterConn->getMasterPos();
1012                 }
1013
1014                 return false;
1015         }
1016
1017         /**
1018          * Disable this load balancer. All connections are closed, and any attempt to
1019          * open a new connection will result in a DBAccessError.
1020          *
1021          * @since 1.27
1022          */
1023         public function disable() {
1024                 $this->closeAll();
1025                 $this->disabled = true;
1026         }
1027
1028         /**
1029          * Close all open connections
1030          */
1031         public function closeAll() {
1032                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1033                         $conn->close();
1034                 } );
1035
1036                 $this->mConns = [
1037                         'local' => [],
1038                         'foreignFree' => [],
1039                         'foreignUsed' => [],
1040                 ];
1041                 $this->connsOpened = 0;
1042         }
1043
1044         /**
1045          * Close a connection
1046          * Using this function makes sure the LoadBalancer knows the connection is closed.
1047          * If you use $conn->close() directly, the load balancer won't update its state.
1048          * @param DatabaseBase $conn
1049          */
1050         public function closeConnection( $conn ) {
1051                 $done = false;
1052                 foreach ( $this->mConns as $i1 => $conns2 ) {
1053                         foreach ( $conns2 as $i2 => $conns3 ) {
1054                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1055                                         if ( $conn === $candidateConn ) {
1056                                                 $conn->close();
1057                                                 unset( $this->mConns[$i1][$i2][$i3] );
1058                                                 --$this->connsOpened;
1059                                                 $done = true;
1060                                                 break;
1061                                         }
1062                                 }
1063                         }
1064                 }
1065                 if ( !$done ) {
1066                         $conn->close();
1067                 }
1068         }
1069
1070         /**
1071          * Commit transactions on all open connections
1072          * @param string $fname Caller name
1073          * @throws DBExpectedError
1074          */
1075         public function commitAll( $fname = __METHOD__ ) {
1076                 $failures = [];
1077
1078                 $restore = ( $this->trxRoundId !== false );
1079                 $this->trxRoundId = false;
1080                 $this->forEachOpenConnection(
1081                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1082                                 try {
1083                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1084                                 } catch ( DBError $e ) {
1085                                         MWExceptionHandler::logException( $e );
1086                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1087                                 }
1088                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1089                                         $this->undoTransactionRoundFlags( $conn );
1090                                 }
1091                         }
1092                 );
1093
1094                 if ( $failures ) {
1095                         throw new DBExpectedError(
1096                                 null,
1097                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1098                         );
1099                 }
1100         }
1101
1102         /**
1103          * Perform all pre-commit callbacks that remain part of the atomic transactions
1104          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
1105          * @since 1.28
1106          */
1107         public function finalizeMasterChanges() {
1108                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1109                         // Any error should cause all DB transactions to be rolled back together
1110                         $conn->setTrxEndCallbackSuppression( false );
1111                         $conn->runOnTransactionPreCommitCallbacks();
1112                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1113                         $conn->setTrxEndCallbackSuppression( true );
1114                 } );
1115         }
1116
1117         /**
1118          * Perform all pre-commit checks for things like replication safety
1119          * @param array $options Includes:
1120          *   - maxWriteDuration : max write query duration time in seconds
1121          * @throws DBTransactionError
1122          * @since 1.28
1123          */
1124         public function approveMasterChanges( array $options ) {
1125                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1126                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1127                         // If atomic sections or explicit transactions are still open, some caller must have
1128                         // caught an exception but failed to properly rollback any changes. Detect that and
1129                         // throw and error (causing rollback).
1130                         if ( $conn->explicitTrxActive() ) {
1131                                 throw new DBTransactionError(
1132                                         $conn,
1133                                         "Explicit transaction still active. A caller may have caught an error."
1134                                 );
1135                         }
1136                         // Assert that the time to replicate the transaction will be sane.
1137                         // If this fails, then all DB transactions will be rollback back together.
1138                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1139                         if ( $limit > 0 && $time > $limit ) {
1140                                 throw new DBTransactionError(
1141                                         $conn,
1142                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1143                                 );
1144                         }
1145                         // If a connection sits idle while slow queries execute on another, that connection
1146                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1147                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1148                                 throw new DBTransactionError(
1149                                         $conn,
1150                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1151                                 );
1152                         }
1153                 } );
1154         }
1155
1156         /**
1157          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
1158          *
1159          * The DBO_TRX setting will be reverted to the default in each of these methods:
1160          *   - commitMasterChanges()
1161          *   - rollbackMasterChanges()
1162          *   - commitAll()
1163          * This allows for custom transaction rounds from any outer transaction scope.
1164          *
1165          * @param string $fname
1166          * @throws DBExpectedError
1167          * @since 1.28
1168          */
1169         public function beginMasterChanges( $fname = __METHOD__ ) {
1170                 if ( $this->trxRoundId !== false ) {
1171                         throw new DBTransactionError(
1172                                 null,
1173                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1174                         );
1175                 }
1176                 $this->trxRoundId = $fname;
1177
1178                 $failures = [];
1179                 $this->forEachOpenMasterConnection(
1180                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1181                                 $conn->setTrxEndCallbackSuppression( true );
1182                                 try {
1183                                         $conn->clearSnapshot( $fname );
1184                                 } catch ( DBError $e ) {
1185                                         MWExceptionHandler::logException( $e );
1186                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1187                                 }
1188                                 $conn->setTrxEndCallbackSuppression( false );
1189                                 $this->applyTransactionRoundFlags( $conn );
1190                         }
1191                 );
1192
1193                 if ( $failures ) {
1194                         throw new DBExpectedError(
1195                                 null,
1196                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1197                         );
1198                 }
1199         }
1200
1201         /**
1202          * Issue COMMIT on all master connections where writes where done
1203          * @param string $fname Caller name
1204          * @throws DBExpectedError
1205          */
1206         public function commitMasterChanges( $fname = __METHOD__ ) {
1207                 $failures = [];
1208
1209                 $restore = ( $this->trxRoundId !== false );
1210                 $this->trxRoundId = false;
1211                 $this->forEachOpenMasterConnection(
1212                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1213                                 try {
1214                                         if ( $conn->writesOrCallbacksPending() ) {
1215                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1216                                         } elseif ( $restore ) {
1217                                                 $conn->clearSnapshot( $fname );
1218                                         }
1219                                 } catch ( DBError $e ) {
1220                                         MWExceptionHandler::logException( $e );
1221                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1222                                 }
1223                                 if ( $restore ) {
1224                                         $this->undoTransactionRoundFlags( $conn );
1225                                 }
1226                         }
1227                 );
1228
1229                 if ( $failures ) {
1230                         throw new DBExpectedError(
1231                                 null,
1232                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1233                         );
1234                 }
1235         }
1236
1237         /**
1238          * Issue all pending post-COMMIT/ROLLBACK callbacks
1239          * @param integer $type IDatabase::TRIGGER_* constant
1240          * @return Exception|null The first exception or null if there were none
1241          * @since 1.28
1242          */
1243         public function runMasterPostTrxCallbacks( $type ) {
1244                 $e = null; // first exception
1245                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1246                         $conn->clearSnapshot( __METHOD__ ); // clear no-op transactions
1247
1248                         $conn->setTrxEndCallbackSuppression( false );
1249                         try {
1250                                 $conn->runOnTransactionIdleCallbacks( $type );
1251                         } catch ( Exception $ex ) {
1252                                 $e = $e ?: $ex;
1253                         }
1254                         try {
1255                                 $conn->runTransactionListenerCallbacks( $type );
1256                         } catch ( Exception $ex ) {
1257                                 $e = $e ?: $ex;
1258                         }
1259                 } );
1260
1261                 return $e;
1262         }
1263
1264         /**
1265          * Issue ROLLBACK only on master, only if queries were done on connection
1266          * @param string $fname Caller name
1267          * @throws DBExpectedError
1268          * @since 1.23
1269          */
1270         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1271                 $restore = ( $this->trxRoundId !== false );
1272                 $this->trxRoundId = false;
1273                 $this->forEachOpenMasterConnection(
1274                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1275                                 if ( $conn->writesOrCallbacksPending() ) {
1276                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1277                                 }
1278                                 if ( $restore ) {
1279                                         $this->undoTransactionRoundFlags( $conn );
1280                                 }
1281                         }
1282                 );
1283         }
1284
1285         /**
1286          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1287          * @return Exception|null The first exception or null if there were none
1288          * @since 1.28
1289          */
1290         public function suppressTransactionEndCallbacks() {
1291                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1292                         $conn->setTrxEndCallbackSuppression( true );
1293                 } );
1294         }
1295
1296         /**
1297          * @param DatabaseBase $conn
1298          */
1299         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1300                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1301                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1302                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1303                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1304                         // If config has explicitly requested DBO_TRX be either on or off by not
1305                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1306                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1307                 }
1308         }
1309
1310         /**
1311          * @param DatabaseBase $conn
1312          */
1313         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1314                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1315                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1316                 }
1317         }
1318
1319         /**
1320          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
1321          *
1322          * @param string $fname Caller name
1323          * @since 1.28
1324          */
1325         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1326                 $this->forEachOpenReplicaConnection( function ( DatabaseBase $conn ) {
1327                         $conn->clearSnapshot( __METHOD__ );
1328                 } );
1329         }
1330
1331         /**
1332          * @return bool Whether a master connection is already open
1333          * @since 1.24
1334          */
1335         public function hasMasterConnection() {
1336                 return $this->isOpen( $this->getWriterIndex() );
1337         }
1338
1339         /**
1340          * Determine if there are pending changes in a transaction by this thread
1341          * @since 1.23
1342          * @return bool
1343          */
1344         public function hasMasterChanges() {
1345                 $masterIndex = $this->getWriterIndex();
1346                 foreach ( $this->mConns as $conns2 ) {
1347                         if ( empty( $conns2[$masterIndex] ) ) {
1348                                 continue;
1349                         }
1350                         /** @var DatabaseBase $conn */
1351                         foreach ( $conns2[$masterIndex] as $conn ) {
1352                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1353                                         return true;
1354                                 }
1355                         }
1356                 }
1357                 return false;
1358         }
1359
1360         /**
1361          * Get the timestamp of the latest write query done by this thread
1362          * @since 1.25
1363          * @return float|bool UNIX timestamp or false
1364          */
1365         public function lastMasterChangeTimestamp() {
1366                 $lastTime = false;
1367                 $masterIndex = $this->getWriterIndex();
1368                 foreach ( $this->mConns as $conns2 ) {
1369                         if ( empty( $conns2[$masterIndex] ) ) {
1370                                 continue;
1371                         }
1372                         /** @var DatabaseBase $conn */
1373                         foreach ( $conns2[$masterIndex] as $conn ) {
1374                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1375                         }
1376                 }
1377                 return $lastTime;
1378         }
1379
1380         /**
1381          * Check if this load balancer object had any recent or still
1382          * pending writes issued against it by this PHP thread
1383          *
1384          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1385          * @return bool
1386          * @since 1.25
1387          */
1388         public function hasOrMadeRecentMasterChanges( $age = null ) {
1389                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1390
1391                 return ( $this->hasMasterChanges()
1392                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1393         }
1394
1395         /**
1396          * Get the list of callers that have pending master changes
1397          *
1398          * @return array
1399          * @since 1.27
1400          */
1401         public function pendingMasterChangeCallers() {
1402                 $fnames = [];
1403
1404                 $masterIndex = $this->getWriterIndex();
1405                 foreach ( $this->mConns as $conns2 ) {
1406                         if ( empty( $conns2[$masterIndex] ) ) {
1407                                 continue;
1408                         }
1409                         /** @var DatabaseBase $conn */
1410                         foreach ( $conns2[$masterIndex] as $conn ) {
1411                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1412                         }
1413                 }
1414
1415                 return $fnames;
1416         }
1417
1418         /**
1419          * @param mixed $value
1420          * @return mixed
1421          */
1422         public function waitTimeout( $value = null ) {
1423                 return wfSetVar( $this->mWaitTimeout, $value );
1424         }
1425
1426         /**
1427          * @note This method will trigger a DB connection if not yet done
1428          *
1429          * @param string|bool $wiki Wiki ID, or false for the current wiki
1430          * @return bool Whether the generic connection for reads is highly "lagged"
1431          */
1432         public function getLaggedSlaveMode( $wiki = false ) {
1433                 // No-op if there is only one DB (also avoids recursion)
1434                 if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
1435                         try {
1436                                 // See if laggedSlaveMode gets set
1437                                 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1438                                 $this->reuseConnection( $conn );
1439                         } catch ( DBConnectionError $e ) {
1440                                 // Avoid expensive re-connect attempts and failures
1441                                 $this->slavesDownMode = true;
1442                                 $this->laggedSlaveMode = true;
1443                         }
1444                 }
1445
1446                 return $this->laggedSlaveMode;
1447         }
1448
1449         /**
1450          * @note This method will never cause a new DB connection
1451          * @return bool Whether any generic connection used for reads was highly "lagged"
1452          * @since 1.27
1453          */
1454         public function laggedSlaveUsed() {
1455                 return $this->laggedSlaveMode;
1456         }
1457
1458         /**
1459          * @note This method may trigger a DB connection if not yet done
1460          * @param string|bool $wiki Wiki ID, or false for the current wiki
1461          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1462          * @return string|bool Reason the master is read-only or false if it is not
1463          * @since 1.27
1464          */
1465         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1466                 if ( $this->readOnlyReason !== false ) {
1467                         return $this->readOnlyReason;
1468                 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1469                         if ( $this->slavesDownMode ) {
1470                                 return 'The database has been automatically locked ' .
1471                                         'until the replica database servers become available';
1472                         } else {
1473                                 return 'The database has been automatically locked ' .
1474                                         'while the replica database servers catch up to the master.';
1475                         }
1476                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1477                         return 'The database master is running in read-only mode.';
1478                 }
1479
1480                 return false;
1481         }
1482
1483         /**
1484          * @param string $wiki Wiki ID, or false for the current wiki
1485          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1486          * @return bool
1487          */
1488         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1489                 $cache = $this->wanCache;
1490                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1491
1492                 return (bool)$cache->getWithSetCallback(
1493                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1494                         self::TTL_CACHE_READONLY,
1495                         function () use ( $wiki, $conn ) {
1496                                 $this->trxProfiler->setSilenced( true );
1497                                 try {
1498                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1499                                         $readOnly = (int)$dbw->serverIsReadOnly();
1500                                 } catch ( DBError $e ) {
1501                                         $readOnly = 0;
1502                                 }
1503                                 $this->trxProfiler->setSilenced( false );
1504                                 return $readOnly;
1505                         },
1506                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1507                 );
1508         }
1509
1510         /**
1511          * Disables/enables lag checks
1512          * @param null|bool $mode
1513          * @return bool
1514          */
1515         public function allowLagged( $mode = null ) {
1516                 if ( $mode === null ) {
1517                         return $this->mAllowLagged;
1518                 }
1519                 $this->mAllowLagged = $mode;
1520
1521                 return $this->mAllowLagged;
1522         }
1523
1524         /**
1525          * @return bool
1526          */
1527         public function pingAll() {
1528                 $success = true;
1529                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1530                         if ( !$conn->ping() ) {
1531                                 $success = false;
1532                         }
1533                 } );
1534
1535                 return $success;
1536         }
1537
1538         /**
1539          * Call a function with each open connection object
1540          * @param callable $callback
1541          * @param array $params
1542          */
1543         public function forEachOpenConnection( $callback, array $params = [] ) {
1544                 foreach ( $this->mConns as $connsByServer ) {
1545                         foreach ( $connsByServer as $serverConns ) {
1546                                 foreach ( $serverConns as $conn ) {
1547                                         $mergedParams = array_merge( [ $conn ], $params );
1548                                         call_user_func_array( $callback, $mergedParams );
1549                                 }
1550                         }
1551                 }
1552         }
1553
1554         /**
1555          * Call a function with each open connection object to a master
1556          * @param callable $callback
1557          * @param array $params
1558          * @since 1.28
1559          */
1560         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1561                 $masterIndex = $this->getWriterIndex();
1562                 foreach ( $this->mConns as $connsByServer ) {
1563                         if ( isset( $connsByServer[$masterIndex] ) ) {
1564                                 /** @var DatabaseBase $conn */
1565                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1566                                         $mergedParams = array_merge( [ $conn ], $params );
1567                                         call_user_func_array( $callback, $mergedParams );
1568                                 }
1569                         }
1570                 }
1571         }
1572
1573         /**
1574          * Call a function with each open replica DB connection object
1575          * @param callable $callback
1576          * @param array $params
1577          * @since 1.28
1578          */
1579         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1580                 foreach ( $this->mConns as $connsByServer ) {
1581                         foreach ( $connsByServer as $i => $serverConns ) {
1582                                 if ( $i === $this->getWriterIndex() ) {
1583                                         continue; // skip master
1584                                 }
1585                                 foreach ( $serverConns as $conn ) {
1586                                         $mergedParams = array_merge( [ $conn ], $params );
1587                                         call_user_func_array( $callback, $mergedParams );
1588                                 }
1589                         }
1590                 }
1591         }
1592
1593         /**
1594          * Get the hostname and lag time of the most-lagged replica DB
1595          *
1596          * This is useful for maintenance scripts that need to throttle their updates.
1597          * May attempt to open connections to replica DBs on the default DB. If there is
1598          * no lag, the maximum lag will be reported as -1.
1599          *
1600          * @param bool|string $wiki Wiki ID, or false for the default database
1601          * @return array ( host, max lag, index of max lagged host )
1602          */
1603         public function getMaxLag( $wiki = false ) {
1604                 $maxLag = -1;
1605                 $host = '';
1606                 $maxIndex = 0;
1607
1608                 if ( $this->getServerCount() <= 1 ) {
1609                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1610                 }
1611
1612                 $lagTimes = $this->getLagTimes( $wiki );
1613                 foreach ( $lagTimes as $i => $lag ) {
1614                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1615                                 $maxLag = $lag;
1616                                 $host = $this->mServers[$i]['host'];
1617                                 $maxIndex = $i;
1618                         }
1619                 }
1620
1621                 return [ $host, $maxLag, $maxIndex ];
1622         }
1623
1624         /**
1625          * Get an estimate of replication lag (in seconds) for each server
1626          *
1627          * Results are cached for a short time in memcached/process cache
1628          *
1629          * Values may be "false" if replication is too broken to estimate
1630          *
1631          * @param string|bool $wiki
1632          * @return int[] Map of (server index => float|int|bool)
1633          */
1634         public function getLagTimes( $wiki = false ) {
1635                 if ( $this->getServerCount() <= 1 ) {
1636                         return [ 0 => 0 ]; // no replication = no lag
1637                 }
1638
1639                 # Send the request to the load monitor
1640                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1641         }
1642
1643         /**
1644          * Get the lag in seconds for a given connection, or zero if this load
1645          * balancer does not have replication enabled.
1646          *
1647          * This should be used in preference to Database::getLag() in cases where
1648          * replication may not be in use, since there is no way to determine if
1649          * replication is in use at the connection level without running
1650          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1651          * function instead of Database::getLag() avoids a fatal error in this
1652          * case on many installations.
1653          *
1654          * @param IDatabase $conn
1655          * @return int|bool Returns false on error
1656          */
1657         public function safeGetLag( IDatabase $conn ) {
1658                 if ( $this->getServerCount() == 1 ) {
1659                         return 0;
1660                 } else {
1661                         return $conn->getLag();
1662                 }
1663         }
1664
1665         /**
1666          * Wait for a replica DB to reach a specified master position
1667          *
1668          * This will connect to the master to get an accurate position if $pos is not given
1669          *
1670          * @param IDatabase $conn Replica DB
1671          * @param DBMasterPos|bool $pos Master position; default: current position
1672          * @param integer $timeout Timeout in seconds
1673          * @return bool Success
1674          * @since 1.27
1675          */
1676         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1677                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
1678                         return true; // server is not a replica DB
1679                 }
1680
1681                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1682                 if ( !( $pos instanceof DBMasterPos ) ) {
1683                         return false; // something is misconfigured
1684                 }
1685
1686                 $result = $conn->masterPosWait( $pos, $timeout );
1687                 if ( $result == -1 || is_null( $result ) ) {
1688                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1689                         wfDebugLog( 'replication', "$msg\n" );
1690                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1691                         $ok = false;
1692                 } else {
1693                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1694                         $ok = true;
1695                 }
1696
1697                 return $ok;
1698         }
1699
1700         /**
1701          * Clear the cache for slag lag delay times
1702          *
1703          * This is only used for testing
1704          */
1705         public function clearLagTimeCache() {
1706                 $this->getLoadMonitor()->clearCaches();
1707         }
1708
1709         /**
1710          * Set a callback via DatabaseBase::setTransactionListener() on
1711          * all current and future master connections of this load balancer
1712          *
1713          * @param string $name Callback name
1714          * @param callable|null $callback
1715          * @since 1.28
1716          */
1717         public function setTransactionListener( $name, callable $callback = null ) {
1718                 if ( $callback ) {
1719                         $this->trxRecurringCallbacks[$name] = $callback;
1720                 } else {
1721                         unset( $this->trxRecurringCallbacks[$name] );
1722                 }
1723                 $this->forEachOpenMasterConnection(
1724                         function ( DatabaseBase $conn ) use ( $name, $callback ) {
1725                                 $conn->setTransactionListener( $name, $callback );
1726                         }
1727                 );
1728         }
1729 }