includes/db/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23
  24 /**
  25  * Database load balancing object
  26  *
  27  * @todo document
  28  * @ingroup Database
  29  */
  30 class LoadBalancer {
  31         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard slave lag as a factor in slave selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on slave lag to resolve */
  42         private $mWaitTimeout;
  43         /** @var array LBFactory information */
  44         private $mParentInfo;
  45
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50         /** @var BagOStuff */
  51         private $srvCache;
  52         /** @var WANObjectCache */
  53         private $wanCache;
  54         /** @var TransactionProfiler */
  55         protected $trxProfiler;
  56
  57         /** @var bool|DatabaseBase Database connection that caused a problem */
  58         private $mErrorConnection;
  59         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  60         private $mReadIndex;
  61         /** @var bool|DBMasterPos False if not set */
  62         private $mWaitForPos;
  63         /** @var bool Whether the generic reader fell back to a lagged slave */
  64         private $laggedSlaveMode = false;
  65         /** @var bool Whether the generic reader fell back to a lagged slave */
  66         private $slavesDownMode = false;
  67         /** @var string The last DB selection or connection error */
  68         private $mLastError = 'Unknown error';
  69         /** @var string|bool Reason the LB is read-only or false if not */
  70         private $readOnlyReason = false;
  71         /** @var integer Total connections opened */
  72         private $connsOpened = 0;
  73         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  74         private $trxRoundId = false;
  75         /** @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 slave 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 slaves 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 slaves with zero load
 221                         # Do NOT use the master
 222                         # Instead, this function will return false, triggering read-only mode,
 223                         # and a lagged slave 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 slave
 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 slaves lagged. Switch to read-only mode
 310                                         wfDebugLog( 'replication', "All slaves 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                         # Slave 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 slave" 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" slave 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 slave if there isn't one yet
 409                         $readLoads = $this->mLoads;
 410                         unset( $readLoads[$this->getWriterIndex()] ); // slaves 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 slaves 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 slave 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                                 ": slave $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 slave $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 slave, 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 slave 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                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 617                         /**
 618                          * This can happen in code like:
 619                          *   foreach ( $dbs as $db ) {
 620                          *     $conn = $lb->getConnection( DB_SLAVE, [], $db );
 621                          *     ...
 622                          *     $lb->reuseConnection( $conn );
 623                          *   }
 624                          * When a connection to the local DB is opened in this way, reuseConnection()
 625                          * should be ignored
 626                          */
 627                         return;
 628                 }
 629
 630                 $dbName = $conn->getDBname();
 631                 $prefix = $conn->tablePrefix();
 632                 if ( strval( $prefix ) !== '' ) {
 633                         $wiki = "$dbName-$prefix";
 634                 } else {
 635                         $wiki = $dbName;
 636                 }
 637                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 638                         throw new MWException( __METHOD__ . ": connection not found, has " .
 639                                 "the connection been freed already?" );
 640                 }
 641                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 642                 if ( $refCount <= 0 ) {
 643                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 644                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 645                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 646                 } else {
 647                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 648                 }
 649         }
 650
 651         /**
 652          * Get a database connection handle reference
 653          *
 654          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 655          *
 656          * @see LoadBalancer::getConnection() for parameter information
 657          *
 658          * @param int $db
 659          * @param array|string|bool $groups Query group(s), or false for the generic reader
 660          * @param string|bool $wiki Wiki ID, or false for the current wiki
 661          * @return DBConnRef
 662          */
 663         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 664                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 665         }
 666
 667         /**
 668          * Get a database connection handle reference without connecting yet
 669          *
 670          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 671          *
 672          * @see LoadBalancer::getConnection() for parameter information
 673          *
 674          * @param int $db
 675          * @param array|string|bool $groups Query group(s), or false for the generic reader
 676          * @param string|bool $wiki Wiki ID, or false for the current wiki
 677          * @return DBConnRef
 678          */
 679         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 680                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 681         }
 682
 683         /**
 684          * Open a connection to the server given by the specified index
 685          * Index must be an actual index into the array.
 686          * If the server is already open, returns it.
 687          *
 688          * On error, returns false, and the connection which caused the
 689          * error will be available via $this->mErrorConnection.
 690          *
 691          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 692          *
 693          * @param int $i Server index
 694          * @param string|bool $wiki Wiki ID, or false for the current wiki
 695          * @return DatabaseBase|bool Returns false on errors
 696          */
 697         public function openConnection( $i, $wiki = false ) {
 698                 if ( $wiki !== false ) {
 699                         $conn = $this->openForeignConnection( $i, $wiki );
 700                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 701                         $conn = $this->mConns['local'][$i][0];
 702                 } else {
 703                         $server = $this->mServers[$i];
 704                         $server['serverIndex'] = $i;
 705                         $conn = $this->reallyOpenConnection( $server, false );
 706                         $serverName = $this->getServerName( $i );
 707                         if ( $conn->isOpen() ) {
 708                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 709                                 $this->mConns['local'][$i][0] = $conn;
 710                         } else {
 711                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 712                                 $this->mErrorConnection = $conn;
 713                                 $conn = false;
 714                         }
 715                 }
 716
 717                 if ( $conn && !$conn->isOpen() ) {
 718                         // Connection was made but later unrecoverably lost for some reason.
 719                         // Do not return a handle that will just throw exceptions on use,
 720                         // but let the calling code (e.g. getReaderIndex) try another server.
 721                         // See DatabaseMyslBase::ping() for how this can happen.
 722                         $this->mErrorConnection = $conn;
 723                         $conn = false;
 724                 }
 725
 726                 return $conn;
 727         }
 728
 729         /**
 730          * Open a connection to a foreign DB, or return one if it is already open.
 731          *
 732          * Increments a reference count on the returned connection which locks the
 733          * connection to the requested wiki. This reference count can be
 734          * decremented by calling reuseConnection().
 735          *
 736          * If a connection is open to the appropriate server already, but with the wrong
 737          * database, it will be switched to the right database and returned, as long as
 738          * it has been freed first with reuseConnection().
 739          *
 740          * On error, returns false, and the connection which caused the
 741          * error will be available via $this->mErrorConnection.
 742          *
 743          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 744          *
 745          * @param int $i Server index
 746          * @param string $wiki Wiki ID to open
 747          * @return DatabaseBase
 748          */
 749         private function openForeignConnection( $i, $wiki ) {
 750                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 751                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 752                         // Reuse an already-used connection
 753                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 754                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 755                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 756                         // Reuse a free connection for the same wiki
 757                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 758                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 759                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 760                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 761                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 762                         // Reuse a connection from another wiki
 763                         $conn = reset( $this->mConns['foreignFree'][$i] );
 764                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 765
 766                         // The empty string as a DB name means "don't care".
 767                         // DatabaseMysqlBase::open() already handle this on connection.
 768                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 769                                 $this->mLastError = "Error selecting database $dbName on server " .
 770                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 771                                 $this->mErrorConnection = $conn;
 772                                 $conn = false;
 773                         } else {
 774                                 $conn->tablePrefix( $prefix );
 775                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 776                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 777                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 778                         }
 779                 } else {
 780                         // Open a new connection
 781                         $server = $this->mServers[$i];
 782                         $server['serverIndex'] = $i;
 783                         $server['foreignPoolRefCount'] = 0;
 784                         $server['foreign'] = true;
 785                         $conn = $this->reallyOpenConnection( $server, $dbName );
 786                         if ( !$conn->isOpen() ) {
 787                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 788                                 $this->mErrorConnection = $conn;
 789                                 $conn = false;
 790                         } else {
 791                                 $conn->tablePrefix( $prefix );
 792                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 793                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 794                         }
 795                 }
 796
 797                 // Increment reference count
 798                 if ( $conn ) {
 799                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 800                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 801                 }
 802
 803                 return $conn;
 804         }
 805
 806         /**
 807          * Test if the specified index represents an open connection
 808          *
 809          * @param int $index Server index
 810          * @access private
 811          * @return bool
 812          */
 813         private function isOpen( $index ) {
 814                 if ( !is_integer( $index ) ) {
 815                         return false;
 816                 }
 817
 818                 return (bool)$this->getAnyOpenConnection( $index );
 819         }
 820
 821         /**
 822          * Really opens a connection. Uncached.
 823          * Returns a Database object whether or not the connection was successful.
 824          * @access private
 825          *
 826          * @param array $server
 827          * @param bool $dbNameOverride
 828          * @throws MWException
 829          * @return DatabaseBase
 830          */
 831         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 832                 if ( $this->disabled ) {
 833                         throw new DBAccessError();
 834                 }
 835
 836                 if ( !is_array( $server ) ) {
 837                         throw new MWException( 'You must update your load-balancing configuration. ' .
 838                                 'See DefaultSettings.php entry for $wgDBservers.' );
 839                 }
 840
 841                 if ( $dbNameOverride !== false ) {
 842                         $server['dbname'] = $dbNameOverride;
 843                 }
 844
 845                 // Let the handle know what the cluster master is (e.g. "db1052")
 846                 $masterName = $this->getServerName( 0 );
 847                 $server['clusterMasterHost'] = $masterName;
 848
 849                 // Log when many connection are made on requests
 850                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 851                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 852                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 853                                 wfBacktrace( true ) );
 854                 }
 855
 856                 # Create object
 857                 try {
 858                         $db = DatabaseBase::factory( $server['type'], $server );
 859                 } catch ( DBConnectionError $e ) {
 860                         // FIXME: This is probably the ugliest thing I have ever done to
 861                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 862                         $db = $e->db;
 863                 }
 864
 865                 $db->setLBInfo( $server );
 866                 $db->setLazyMasterHandle(
 867                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 868                 );
 869                 $db->setTransactionProfiler( $this->trxProfiler );
 870                 if ( $this->trxRoundId !== false ) {
 871                         $this->applyTransactionRoundFlags( $db );
 872                 }
 873
 874                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 875                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 876                                 $db->setTransactionListener( $name, $callback );
 877                         }
 878                 }
 879
 880                 return $db;
 881         }
 882
 883         /**
 884          * @throws DBConnectionError
 885          * @return bool
 886          */
 887         private function reportConnectionError() {
 888                 $conn = $this->mErrorConnection; // The connection which caused the error
 889                 $context = [
 890                         'method' => __METHOD__,
 891                         'last_error' => $this->mLastError,
 892                 ];
 893
 894                 if ( !is_object( $conn ) ) {
 895                         // No last connection, probably due to all servers being too busy
 896                         wfLogDBError(
 897                                 "LB failure with no last connection. Connection error: {last_error}",
 898                                 $context
 899                         );
 900
 901                         // If all servers were busy, mLastError will contain something sensible
 902                         throw new DBConnectionError( null, $this->mLastError );
 903                 } else {
 904                         $context['db_server'] = $conn->getProperty( 'mServer' );
 905                         wfLogDBError(
 906                                 "Connection error: {last_error} ({db_server})",
 907                                 $context
 908                         );
 909
 910                         // throws DBConnectionError
 911                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 912                 }
 913
 914                 return false; /* not reached */
 915         }
 916
 917         /**
 918          * @return int
 919          * @since 1.26
 920          */
 921         public function getWriterIndex() {
 922                 return 0;
 923         }
 924
 925         /**
 926          * Returns true if the specified index is a valid server index
 927          *
 928          * @param string $i
 929          * @return bool
 930          */
 931         public function haveIndex( $i ) {
 932                 return array_key_exists( $i, $this->mServers );
 933         }
 934
 935         /**
 936          * Returns true if the specified index is valid and has non-zero load
 937          *
 938          * @param string $i
 939          * @return bool
 940          */
 941         public function isNonZeroLoad( $i ) {
 942                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 943         }
 944
 945         /**
 946          * Get the number of defined servers (not the number of open connections)
 947          *
 948          * @return int
 949          */
 950         public function getServerCount() {
 951                 return count( $this->mServers );
 952         }
 953
 954         /**
 955          * Get the host name or IP address of the server with the specified index
 956          * Prefer a readable name if available.
 957          * @param string $i
 958          * @return string
 959          */
 960         public function getServerName( $i ) {
 961                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 962                         $name = $this->mServers[$i]['hostName'];
 963                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 964                         $name = $this->mServers[$i]['host'];
 965                 } else {
 966                         $name = '';
 967                 }
 968
 969                 return ( $name != '' ) ? $name : 'localhost';
 970         }
 971
 972         /**
 973          * Return the server info structure for a given index, or false if the index is invalid.
 974          * @param int $i
 975          * @return array|bool
 976          */
 977         public function getServerInfo( $i ) {
 978                 if ( isset( $this->mServers[$i] ) ) {
 979                         return $this->mServers[$i];
 980                 } else {
 981                         return false;
 982                 }
 983         }
 984
 985         /**
 986          * Sets the server info structure for the given index. Entry at index $i
 987          * is created if it doesn't exist
 988          * @param int $i
 989          * @param array $serverInfo
 990          */
 991         public function setServerInfo( $i, array $serverInfo ) {
 992                 $this->mServers[$i] = $serverInfo;
 993         }
 994
 995         /**
 996          * Get the current master position for chronology control purposes
 997          * @return mixed
 998          */
 999         public function getMasterPos() {
1000                 # If this entire request was served from a slave without opening a connection to the
1001                 # master (however unlikely that may be), then we can fetch the position from the slave.
1002                 $masterConn = $this->getAnyOpenConnection( 0 );
1003                 if ( !$masterConn ) {
1004                         $serverCount = count( $this->mServers );
1005                         for ( $i = 1; $i < $serverCount; $i++ ) {
1006                                 $conn = $this->getAnyOpenConnection( $i );
1007                                 if ( $conn ) {
1008                                         return $conn->getSlavePos();
1009                                 }
1010                         }
1011                 } else {
1012                         return $masterConn->getMasterPos();
1013                 }
1014
1015                 return false;
1016         }
1017
1018         /**
1019          * Disable this load balancer. All connections are closed, and any attempt to
1020          * open a new connection will result in a DBAccessError.
1021          *
1022          * @since 1.27
1023          */
1024         public function disable() {
1025                 $this->closeAll();
1026                 $this->disabled = true;
1027         }
1028
1029         /**
1030          * Close all open connections
1031          */
1032         public function closeAll() {
1033                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1034                         $conn->close();
1035                 } );
1036
1037                 $this->mConns = [
1038                         'local' => [],
1039                         'foreignFree' => [],
1040                         'foreignUsed' => [],
1041                 ];
1042                 $this->connsOpened = 0;
1043         }
1044
1045         /**
1046          * Close a connection
1047          * Using this function makes sure the LoadBalancer knows the connection is closed.
1048          * If you use $conn->close() directly, the load balancer won't update its state.
1049          * @param DatabaseBase $conn
1050          */
1051         public function closeConnection( $conn ) {
1052                 $done = false;
1053                 foreach ( $this->mConns as $i1 => $conns2 ) {
1054                         foreach ( $conns2 as $i2 => $conns3 ) {
1055                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1056                                         if ( $conn === $candidateConn ) {
1057                                                 $conn->close();
1058                                                 unset( $this->mConns[$i1][$i2][$i3] );
1059                                                 --$this->connsOpened;
1060                                                 $done = true;
1061                                                 break;
1062                                         }
1063                                 }
1064                         }
1065                 }
1066                 if ( !$done ) {
1067                         $conn->close();
1068                 }
1069         }
1070
1071         /**
1072          * Commit transactions on all open connections
1073          * @param string $fname Caller name
1074          * @throws DBExpectedError
1075          */
1076         public function commitAll( $fname = __METHOD__ ) {
1077                 $failures = [];
1078
1079                 $restore = ( $this->trxRoundId !== false );
1080                 $this->trxRoundId = false;
1081                 $this->forEachOpenConnection(
1082                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1083                                 try {
1084                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1085                                 } catch ( DBError $e ) {
1086                                         MWExceptionHandler::logException( $e );
1087                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1088                                 }
1089                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1090                                         $this->undoTransactionRoundFlags( $conn );
1091                                 }
1092                         }
1093                 );
1094
1095                 if ( $failures ) {
1096                         throw new DBExpectedError(
1097                                 null,
1098                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1099                         );
1100                 }
1101         }
1102
1103         /**
1104          * Perform all pre-commit callbacks that remain part of the atomic transactions
1105          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
1106          * @since 1.28
1107          */
1108         public function finalizeMasterChanges() {
1109                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1110                         // Any error should cause all DB transactions to be rolled back together
1111                         $conn->setTrxEndCallbackSuppression( false );
1112                         $conn->runOnTransactionPreCommitCallbacks();
1113                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1114                         $conn->setTrxEndCallbackSuppression( true );
1115                 } );
1116         }
1117
1118         /**
1119          * Perform all pre-commit checks for things like replication safety
1120          * @param array $options Includes:
1121          *   - maxWriteDuration : max write query duration time in seconds
1122          * @throws DBTransactionError
1123          * @since 1.28
1124          */
1125         public function approveMasterChanges( array $options ) {
1126                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1127                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1128                         // If atomic sections or explicit transactions are still open, some caller must have
1129                         // caught an exception but failed to properly rollback any changes. Detect that and
1130                         // throw and error (causing rollback).
1131                         if ( $conn->explicitTrxActive() ) {
1132                                 throw new DBTransactionError(
1133                                         $conn,
1134                                         "Explicit transaction still active. A caller may have caught an error."
1135                                 );
1136                         }
1137                         // Assert that the time to replicate the transaction will be sane.
1138                         // If this fails, then all DB transactions will be rollback back together.
1139                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1140                         if ( $limit > 0 && $time > $limit ) {
1141                                 throw new DBTransactionError(
1142                                         $conn,
1143                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1144                                 );
1145                         }
1146                         // If a connection sits idle while slow queries execute on another, that connection
1147                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1148                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1149                                 throw new DBTransactionError(
1150                                         $conn,
1151                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1152                                 );
1153                         }
1154                 } );
1155         }
1156
1157         /**
1158          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
1159          *
1160          * The DBO_TRX setting will be reverted to the default in each of these methods:
1161          *   - commitMasterChanges()
1162          *   - rollbackMasterChanges()
1163          *   - commitAll()
1164          * This allows for custom transaction rounds from any outer transaction scope.
1165          *
1166          * @param string $fname
1167          * @throws DBExpectedError
1168          * @since 1.28
1169          */
1170         public function beginMasterChanges( $fname = __METHOD__ ) {
1171                 if ( $this->trxRoundId !== false ) {
1172                         throw new DBTransactionError(
1173                                 null,
1174                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1175                         );
1176                 }
1177                 $this->trxRoundId = $fname;
1178
1179                 $failures = [];
1180                 $this->forEachOpenMasterConnection(
1181                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1182                                 $conn->setTrxEndCallbackSuppression( true );
1183                                 try {
1184                                         $conn->clearSnapshot( $fname );
1185                                 } catch ( DBError $e ) {
1186                                         MWExceptionHandler::logException( $e );
1187                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1188                                 }
1189                                 $conn->setTrxEndCallbackSuppression( false );
1190                                 $this->applyTransactionRoundFlags( $conn );
1191                         }
1192                 );
1193
1194                 if ( $failures ) {
1195                         throw new DBExpectedError(
1196                                 null,
1197                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1198                         );
1199                 }
1200         }
1201
1202         /**
1203          * Issue COMMIT on all master connections where writes where done
1204          * @param string $fname Caller name
1205          * @throws DBExpectedError
1206          */
1207         public function commitMasterChanges( $fname = __METHOD__ ) {
1208                 $failures = [];
1209
1210                 $restore = ( $this->trxRoundId !== false );
1211                 $this->trxRoundId = false;
1212                 $this->forEachOpenMasterConnection(
1213                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1214                                 try {
1215                                         if ( $conn->writesOrCallbacksPending() ) {
1216                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1217                                         } elseif ( $restore ) {
1218                                                 $conn->clearSnapshot( $fname );
1219                                         }
1220                                 } catch ( DBError $e ) {
1221                                         MWExceptionHandler::logException( $e );
1222                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1223                                 }
1224                                 if ( $restore ) {
1225                                         $this->undoTransactionRoundFlags( $conn );
1226                                 }
1227                         }
1228                 );
1229
1230                 if ( $failures ) {
1231                         throw new DBExpectedError(
1232                                 null,
1233                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1234                         );
1235                 }
1236         }
1237
1238         /**
1239          * Issue all pending post-COMMIT/ROLLBACK callbacks
1240          * @param integer $type IDatabase::TRIGGER_* constant
1241          * @return Exception|null The first exception or null if there were none
1242          * @since 1.28
1243          */
1244         public function runMasterPostTrxCallbacks( $type ) {
1245                 $e = null; // first exception
1246                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1247                         $conn->clearSnapshot( __METHOD__ ); // clear no-op transactions
1248
1249                         $conn->setTrxEndCallbackSuppression( false );
1250                         try {
1251                                 $conn->runOnTransactionIdleCallbacks( $type );
1252                         } catch ( Exception $ex ) {
1253                                 $e = $e ?: $ex;
1254                         }
1255                         try {
1256                                 $conn->runTransactionListenerCallbacks( $type );
1257                         } catch ( Exception $ex ) {
1258                                 $e = $e ?: $ex;
1259                         }
1260                 } );
1261
1262                 return $e;
1263         }
1264
1265         /**
1266          * Issue ROLLBACK only on master, only if queries were done on connection
1267          * @param string $fname Caller name
1268          * @throws DBExpectedError
1269          * @since 1.23
1270          */
1271         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1272                 $restore = ( $this->trxRoundId !== false );
1273                 $this->trxRoundId = false;
1274                 $this->forEachOpenMasterConnection(
1275                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1276                                 if ( $conn->writesOrCallbacksPending() ) {
1277                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1278                                 }
1279                                 if ( $restore ) {
1280                                         $this->undoTransactionRoundFlags( $conn );
1281                                 }
1282                         }
1283                 );
1284         }
1285
1286         /**
1287          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1288          * @return Exception|null The first exception or null if there were none
1289          * @since 1.28
1290          */
1291         public function suppressTransactionEndCallbacks() {
1292                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1293                         $conn->setTrxEndCallbackSuppression( true );
1294                 } );
1295         }
1296
1297         /**
1298          * @param DatabaseBase $conn
1299          */
1300         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1301                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1302                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1303                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1304                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1305                         // If config has explicitly requested DBO_TRX be either on or off by not
1306                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1307                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1308                 }
1309         }
1310
1311         /**
1312          * @param DatabaseBase $conn
1313          */
1314         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1315                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1316                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1317                 }
1318         }
1319
1320         /**
1321          * @return bool Whether a master connection is already open
1322          * @since 1.24
1323          */
1324         public function hasMasterConnection() {
1325                 return $this->isOpen( $this->getWriterIndex() );
1326         }
1327
1328         /**
1329          * Determine if there are pending changes in a transaction by this thread
1330          * @since 1.23
1331          * @return bool
1332          */
1333         public function hasMasterChanges() {
1334                 $masterIndex = $this->getWriterIndex();
1335                 foreach ( $this->mConns as $conns2 ) {
1336                         if ( empty( $conns2[$masterIndex] ) ) {
1337                                 continue;
1338                         }
1339                         /** @var DatabaseBase $conn */
1340                         foreach ( $conns2[$masterIndex] as $conn ) {
1341                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1342                                         return true;
1343                                 }
1344                         }
1345                 }
1346                 return false;
1347         }
1348
1349         /**
1350          * Get the timestamp of the latest write query done by this thread
1351          * @since 1.25
1352          * @return float|bool UNIX timestamp or false
1353          */
1354         public function lastMasterChangeTimestamp() {
1355                 $lastTime = false;
1356                 $masterIndex = $this->getWriterIndex();
1357                 foreach ( $this->mConns as $conns2 ) {
1358                         if ( empty( $conns2[$masterIndex] ) ) {
1359                                 continue;
1360                         }
1361                         /** @var DatabaseBase $conn */
1362                         foreach ( $conns2[$masterIndex] as $conn ) {
1363                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1364                         }
1365                 }
1366                 return $lastTime;
1367         }
1368
1369         /**
1370          * Check if this load balancer object had any recent or still
1371          * pending writes issued against it by this PHP thread
1372          *
1373          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1374          * @return bool
1375          * @since 1.25
1376          */
1377         public function hasOrMadeRecentMasterChanges( $age = null ) {
1378                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1379
1380                 return ( $this->hasMasterChanges()
1381                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1382         }
1383
1384         /**
1385          * Get the list of callers that have pending master changes
1386          *
1387          * @return array
1388          * @since 1.27
1389          */
1390         public function pendingMasterChangeCallers() {
1391                 $fnames = [];
1392
1393                 $masterIndex = $this->getWriterIndex();
1394                 foreach ( $this->mConns as $conns2 ) {
1395                         if ( empty( $conns2[$masterIndex] ) ) {
1396                                 continue;
1397                         }
1398                         /** @var DatabaseBase $conn */
1399                         foreach ( $conns2[$masterIndex] as $conn ) {
1400                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1401                         }
1402                 }
1403
1404                 return $fnames;
1405         }
1406
1407         /**
1408          * @param mixed $value
1409          * @return mixed
1410          */
1411         public function waitTimeout( $value = null ) {
1412                 return wfSetVar( $this->mWaitTimeout, $value );
1413         }
1414
1415         /**
1416          * @note This method will trigger a DB connection if not yet done
1417          *
1418          * @param string|bool $wiki Wiki ID, or false for the current wiki
1419          * @return bool Whether the generic connection for reads is highly "lagged"
1420          */
1421         public function getLaggedSlaveMode( $wiki = false ) {
1422                 // No-op if there is only one DB (also avoids recursion)
1423                 if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
1424                         try {
1425                                 // See if laggedSlaveMode gets set
1426                                 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1427                                 $this->reuseConnection( $conn );
1428                         } catch ( DBConnectionError $e ) {
1429                                 // Avoid expensive re-connect attempts and failures
1430                                 $this->slavesDownMode = true;
1431                                 $this->laggedSlaveMode = true;
1432                         }
1433                 }
1434
1435                 return $this->laggedSlaveMode;
1436         }
1437
1438         /**
1439          * @note This method will never cause a new DB connection
1440          * @return bool Whether any generic connection used for reads was highly "lagged"
1441          * @since 1.27
1442          */
1443         public function laggedSlaveUsed() {
1444                 return $this->laggedSlaveMode;
1445         }
1446
1447         /**
1448          * @note This method may trigger a DB connection if not yet done
1449          * @param string|bool $wiki Wiki ID, or false for the current wiki
1450          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1451          * @return string|bool Reason the master is read-only or false if it is not
1452          * @since 1.27
1453          */
1454         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1455                 if ( $this->readOnlyReason !== false ) {
1456                         return $this->readOnlyReason;
1457                 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1458                         if ( $this->slavesDownMode ) {
1459                                 return 'The database has been automatically locked ' .
1460                                         'until the slave database servers become available';
1461                         } else {
1462                                 return 'The database has been automatically locked ' .
1463                                         'while the slave database servers catch up to the master.';
1464                         }
1465                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1466                         return 'The database master is running in read-only mode.';
1467                 }
1468
1469                 return false;
1470         }
1471
1472         /**
1473          * @param string $wiki Wiki ID, or false for the current wiki
1474          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1475          * @return bool
1476          */
1477         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1478                 $cache = $this->wanCache;
1479                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1480
1481                 return (bool)$cache->getWithSetCallback(
1482                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1483                         self::TTL_CACHE_READONLY,
1484                         function () use ( $wiki, $conn ) {
1485                                 $this->trxProfiler->setSilenced( true );
1486                                 try {
1487                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1488                                         $readOnly = (int)$dbw->serverIsReadOnly();
1489                                 } catch ( DBError $e ) {
1490                                         $readOnly = 0;
1491                                 }
1492                                 $this->trxProfiler->setSilenced( false );
1493                                 return $readOnly;
1494                         },
1495                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1496                 );
1497         }
1498
1499         /**
1500          * Disables/enables lag checks
1501          * @param null|bool $mode
1502          * @return bool
1503          */
1504         public function allowLagged( $mode = null ) {
1505                 if ( $mode === null ) {
1506                         return $this->mAllowLagged;
1507                 }
1508                 $this->mAllowLagged = $mode;
1509
1510                 return $this->mAllowLagged;
1511         }
1512
1513         /**
1514          * @return bool
1515          */
1516         public function pingAll() {
1517                 $success = true;
1518                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1519                         if ( !$conn->ping() ) {
1520                                 $success = false;
1521                         }
1522                 } );
1523
1524                 return $success;
1525         }
1526
1527         /**
1528          * Call a function with each open connection object
1529          * @param callable $callback
1530          * @param array $params
1531          */
1532         public function forEachOpenConnection( $callback, array $params = [] ) {
1533                 foreach ( $this->mConns as $connsByServer ) {
1534                         foreach ( $connsByServer as $serverConns ) {
1535                                 foreach ( $serverConns as $conn ) {
1536                                         $mergedParams = array_merge( [ $conn ], $params );
1537                                         call_user_func_array( $callback, $mergedParams );
1538                                 }
1539                         }
1540                 }
1541         }
1542
1543         /**
1544          * Call a function with each open connection object to a master
1545          * @param callable $callback
1546          * @param array $params
1547          * @since 1.28
1548          */
1549         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1550                 $masterIndex = $this->getWriterIndex();
1551                 foreach ( $this->mConns as $connsByServer ) {
1552                         if ( isset( $connsByServer[$masterIndex] ) ) {
1553                                 /** @var DatabaseBase $conn */
1554                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1555                                         $mergedParams = array_merge( [ $conn ], $params );
1556                                         call_user_func_array( $callback, $mergedParams );
1557                                 }
1558                         }
1559                 }
1560         }
1561
1562         /**
1563          * Get the hostname and lag time of the most-lagged slave
1564          *
1565          * This is useful for maintenance scripts that need to throttle their updates.
1566          * May attempt to open connections to slaves on the default DB. If there is
1567          * no lag, the maximum lag will be reported as -1.
1568          *
1569          * @param bool|string $wiki Wiki ID, or false for the default database
1570          * @return array ( host, max lag, index of max lagged host )
1571          */
1572         public function getMaxLag( $wiki = false ) {
1573                 $maxLag = -1;
1574                 $host = '';
1575                 $maxIndex = 0;
1576
1577                 if ( $this->getServerCount() <= 1 ) {
1578                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1579                 }
1580
1581                 $lagTimes = $this->getLagTimes( $wiki );
1582                 foreach ( $lagTimes as $i => $lag ) {
1583                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1584                                 $maxLag = $lag;
1585                                 $host = $this->mServers[$i]['host'];
1586                                 $maxIndex = $i;
1587                         }
1588                 }
1589
1590                 return [ $host, $maxLag, $maxIndex ];
1591         }
1592
1593         /**
1594          * Get an estimate of replication lag (in seconds) for each server
1595          *
1596          * Results are cached for a short time in memcached/process cache
1597          *
1598          * Values may be "false" if replication is too broken to estimate
1599          *
1600          * @param string|bool $wiki
1601          * @return int[] Map of (server index => float|int|bool)
1602          */
1603         public function getLagTimes( $wiki = false ) {
1604                 if ( $this->getServerCount() <= 1 ) {
1605                         return [ 0 => 0 ]; // no replication = no lag
1606                 }
1607
1608                 # Send the request to the load monitor
1609                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1610         }
1611
1612         /**
1613          * Get the lag in seconds for a given connection, or zero if this load
1614          * balancer does not have replication enabled.
1615          *
1616          * This should be used in preference to Database::getLag() in cases where
1617          * replication may not be in use, since there is no way to determine if
1618          * replication is in use at the connection level without running
1619          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1620          * function instead of Database::getLag() avoids a fatal error in this
1621          * case on many installations.
1622          *
1623          * @param IDatabase $conn
1624          * @return int|bool Returns false on error
1625          */
1626         public function safeGetLag( IDatabase $conn ) {
1627                 if ( $this->getServerCount() == 1 ) {
1628                         return 0;
1629                 } else {
1630                         return $conn->getLag();
1631                 }
1632         }
1633
1634         /**
1635          * Wait for a slave DB to reach a specified master position
1636          *
1637          * This will connect to the master to get an accurate position if $pos is not given
1638          *
1639          * @param IDatabase $conn Slave DB
1640          * @param DBMasterPos|bool $pos Master position; default: current position
1641          * @param integer $timeout Timeout in seconds
1642          * @return bool Success
1643          * @since 1.27
1644          */
1645         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1646                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
1647                         return true; // server is not a slave DB
1648                 }
1649
1650                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1651                 if ( !( $pos instanceof DBMasterPos ) ) {
1652                         return false; // something is misconfigured
1653                 }
1654
1655                 $result = $conn->masterPosWait( $pos, $timeout );
1656                 if ( $result == -1 || is_null( $result ) ) {
1657                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1658                         wfDebugLog( 'replication', "$msg\n" );
1659                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1660                         $ok = false;
1661                 } else {
1662                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1663                         $ok = true;
1664                 }
1665
1666                 return $ok;
1667         }
1668
1669         /**
1670          * Clear the cache for slag lag delay times
1671          *
1672          * This is only used for testing
1673          */
1674         public function clearLagTimeCache() {
1675                 $this->getLoadMonitor()->clearCaches();
1676         }
1677
1678         /**
1679          * Set a callback via DatabaseBase::setTransactionListener() on
1680          * all current and future master connections of this load balancer
1681          *
1682          * @param string $name Callback name
1683          * @param callable|null $callback
1684          * @since 1.28
1685          */
1686         public function setTransactionListener( $name, callable $callback = null ) {
1687                 if ( $callback ) {
1688                         $this->trxRecurringCallbacks[$name] = $callback;
1689                 } else {
1690                         unset( $this->trxRecurringCallbacks[$name] );
1691                 }
1692                 $this->forEachOpenMasterConnection(
1693                         function ( DatabaseBase $conn ) use ( $name, $callback ) {
1694                                 $conn->setTransactionListener( $name, $callback );
1695                         }
1696                 );
1697         }
1698 }