includes/db/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23
  24 /**
  25  * Database load balancing object
  26  *
  27  * @todo document
  28  * @ingroup Database
  29  */
  30 class LoadBalancer {
  31         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  42         private $mWaitTimeout;
  43         /** @var array LBFactory information */
  44         private $mParentInfo;
  45
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50         /** @var BagOStuff */
  51         private $srvCache;
  52         /** @var WANObjectCache */
  53         private $wanCache;
  54         /** @var TransactionProfiler */
  55         protected $trxProfiler;
  56
  57         /** @var bool|DatabaseBase Database connection that caused a problem */
  58         private $mErrorConnection;
  59         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  60         private $mReadIndex;
  61         /** @var bool|DBMasterPos False if not set */
  62         private $mWaitForPos;
  63         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  64         private $laggedReplicaMode = false;
  65         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  66         private $allReplicasDownMode = false;
  67         /** @var string The last DB selection or connection error */
  68         private $mLastError = 'Unknown error';
  69         /** @var string|bool Reason the LB is read-only or false if not */
  70         private $readOnlyReason = false;
  71         /** @var integer Total connections opened */
  72         private $connsOpened = 0;
  73         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  74         private $trxRoundId = false;
  75         /** @var array[] Map of (name => callable) */
  76         private $trxRecurringCallbacks = [];
  77
  78         /** @var integer Warn when this many connection are held */
  79         const CONN_HELD_WARN_THRESHOLD = 10;
  80         /** @var integer Default 'max lag' when unspecified */
  81         const MAX_LAG = 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                 $laggedReplicaMode = false;
 284
 285                 # No server found yet
 286                 $i = false;
 287                 # First try quickly looking through the available servers for a server that
 288                 # meets our criteria
 289                 $currentLoads = $nonErrorLoads;
 290                 while ( count( $currentLoads ) ) {
 291                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 292                                 $i = ArrayUtils::pickRandom( $currentLoads );
 293                         } else {
 294                                 $i = false;
 295                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 296                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 297                                         # This triggers doWait() after connect, so it's especially good to
 298                                         # avoid lagged servers so as to avoid just blocking in that method.
 299                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 300                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 301                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 302                                 }
 303                                 if ( $i === false ) {
 304                                         # Any server with less lag than it's 'max lag' param is preferable
 305                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 306                                 }
 307                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 308                                         # All replica DBs lagged. Switch to read-only mode
 309                                         wfDebugLog( 'replication', "All replica DBs lagged. Switch to read-only mode" );
 310                                         $i = ArrayUtils::pickRandom( $currentLoads );
 311                                         $laggedReplicaMode = true;
 312                                 }
 313                         }
 314
 315                         if ( $i === false ) {
 316                                 # pickRandom() returned false
 317                                 # This is permanent and means the configuration or the load monitor
 318                                 # wants us to return false.
 319                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 320
 321                                 return false;
 322                         }
 323
 324                         $serverName = $this->getServerName( $i );
 325                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 326
 327                         $conn = $this->openConnection( $i, $wiki );
 328                         if ( !$conn ) {
 329                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 330                                 unset( $nonErrorLoads[$i] );
 331                                 unset( $currentLoads[$i] );
 332                                 $i = false;
 333                                 continue;
 334                         }
 335
 336                         // Decrement reference counter, we are finished with this connection.
 337                         // It will be incremented for the caller later.
 338                         if ( $wiki !== false ) {
 339                                 $this->reuseConnection( $conn );
 340                         }
 341
 342                         # Return this server
 343                         break;
 344                 }
 345
 346                 # If all servers were down, quit now
 347                 if ( !count( $nonErrorLoads ) ) {
 348                         wfDebugLog( 'connect', "All servers down" );
 349                 }
 350
 351                 if ( $i !== false ) {
 352                         # Replica DB connection successful.
 353                         # Wait for the session master pos for a short time.
 354                         if ( $this->mWaitForPos && $i > 0 ) {
 355                                 $this->doWait( $i );
 356                         }
 357                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 358                                 $this->mReadIndex = $i;
 359                                 # Record if the generic reader index is in "lagged replica DB" mode
 360                                 if ( $laggedReplicaMode ) {
 361                                         $this->laggedReplicaMode = true;
 362                                 }
 363                         }
 364                         $serverName = $this->getServerName( $i );
 365                         wfDebugLog( 'connect', __METHOD__ .
 366                                 ": using server $serverName for group '$group'\n" );
 367                 }
 368
 369                 return $i;
 370         }
 371
 372         /**
 373          * Set the master wait position
 374          * If a DB_SLAVE connection has been opened already, waits
 375          * Otherwise sets a variable telling it to wait if such a connection is opened
 376          * @param DBMasterPos $pos
 377          */
 378         public function waitFor( $pos ) {
 379                 $this->mWaitForPos = $pos;
 380                 $i = $this->mReadIndex;
 381
 382                 if ( $i > 0 ) {
 383                         if ( !$this->doWait( $i ) ) {
 384                                 $this->laggedReplicaMode = true;
 385                         }
 386                 }
 387         }
 388
 389         /**
 390          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 391          *
 392          * This can be used a faster proxy for waitForAll()
 393          *
 394          * @param DBMasterPos $pos
 395          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 396          * @return bool Success (able to connect and no timeouts reached)
 397          * @since 1.26
 398          */
 399         public function waitForOne( $pos, $timeout = null ) {
 400                 $this->mWaitForPos = $pos;
 401
 402                 $i = $this->mReadIndex;
 403                 if ( $i <= 0 ) {
 404                         // Pick a generic replica DB if there isn't one yet
 405                         $readLoads = $this->mLoads;
 406                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 407                         $readLoads = array_filter( $readLoads ); // with non-zero load
 408                         $i = ArrayUtils::pickRandom( $readLoads );
 409                 }
 410
 411                 if ( $i > 0 ) {
 412                         $ok = $this->doWait( $i, true, $timeout );
 413                 } else {
 414                         $ok = true; // no applicable loads
 415                 }
 416
 417                 return $ok;
 418         }
 419
 420         /**
 421          * Set the master wait position and wait for ALL replica DBs to catch up to it
 422          * @param DBMasterPos $pos
 423          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 424          * @return bool Success (able to connect and no timeouts reached)
 425          */
 426         public function waitForAll( $pos, $timeout = null ) {
 427                 $this->mWaitForPos = $pos;
 428                 $serverCount = count( $this->mServers );
 429
 430                 $ok = true;
 431                 for ( $i = 1; $i < $serverCount; $i++ ) {
 432                         if ( $this->mLoads[$i] > 0 ) {
 433                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 434                         }
 435                 }
 436
 437                 return $ok;
 438         }
 439
 440         /**
 441          * Get any open connection to a given server index, local or foreign
 442          * Returns false if there is no connection open
 443          *
 444          * @param int $i
 445          * @return DatabaseBase|bool False on failure
 446          */
 447         public function getAnyOpenConnection( $i ) {
 448                 foreach ( $this->mConns as $conns ) {
 449                         if ( !empty( $conns[$i] ) ) {
 450                                 return reset( $conns[$i] );
 451                         }
 452                 }
 453
 454                 return false;
 455         }
 456
 457         /**
 458          * Wait for a given replica DB to catch up to the master pos stored in $this
 459          * @param int $index Server index
 460          * @param bool $open Check the server even if a new connection has to be made
 461          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 462          * @return bool
 463          */
 464         protected function doWait( $index, $open = false, $timeout = null ) {
 465                 $close = false; // close the connection afterwards
 466
 467                 // Check if we already know that the DB has reached this point
 468                 $server = $this->getServerName( $index );
 469                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 470                 /** @var DBMasterPos $knownReachedPos */
 471                 $knownReachedPos = $this->srvCache->get( $key );
 472                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 473                         wfDebugLog( 'replication', __METHOD__ .
 474                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos).\n" );
 475                         return true;
 476                 }
 477
 478                 // Find a connection to wait on, creating one if needed and allowed
 479                 $conn = $this->getAnyOpenConnection( $index );
 480                 if ( !$conn ) {
 481                         if ( !$open ) {
 482                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 483
 484                                 return false;
 485                         } else {
 486                                 $conn = $this->openConnection( $index, '' );
 487                                 if ( !$conn ) {
 488                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 489
 490                                         return false;
 491                                 }
 492                                 // Avoid connection spam in waitForAll() when connections
 493                                 // are made just for the sake of doing this lag check.
 494                                 $close = true;
 495                         }
 496                 }
 497
 498                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for replica DB $server to catch up...\n" );
 499                 $timeout = $timeout ?: $this->mWaitTimeout;
 500                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 501
 502                 if ( $result == -1 || is_null( $result ) ) {
 503                         // Timed out waiting for replica DB, use master instead
 504                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 505                         wfDebugLog( 'replication', "$msg\n" );
 506                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 507                         $ok = false;
 508                 } else {
 509                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 510                         $ok = true;
 511                         // Remember that the DB reached this point
 512                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 513                 }
 514
 515                 if ( $close ) {
 516                         $this->closeConnection( $conn );
 517                 }
 518
 519                 return $ok;
 520         }
 521
 522         /**
 523          * Get a connection by index
 524          * This is the main entry point for this class.
 525          *
 526          * @param int $i Server index
 527          * @param array|string|bool $groups Query group(s), or false for the generic reader
 528          * @param string|bool $wiki Wiki ID, or false for the current wiki
 529          *
 530          * @throws MWException
 531          * @return DatabaseBase
 532          */
 533         public function getConnection( $i, $groups = [], $wiki = false ) {
 534                 if ( $i === null || $i === false ) {
 535                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 536                                 ' with invalid server index' );
 537                 }
 538
 539                 if ( $wiki === wfWikiID() ) {
 540                         $wiki = false;
 541                 }
 542
 543                 $groups = ( $groups === false || $groups === [] )
 544                         ? [ false ] // check one "group": the generic pool
 545                         : (array)$groups;
 546
 547                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 548                 $oldConnsOpened = $this->connsOpened; // connections open now
 549
 550                 if ( $i == DB_MASTER ) {
 551                         $i = $this->getWriterIndex();
 552                 } else {
 553                         # Try to find an available server in any the query groups (in order)
 554                         foreach ( $groups as $group ) {
 555                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 556                                 if ( $groupIndex !== false ) {
 557                                         $i = $groupIndex;
 558                                         break;
 559                                 }
 560                         }
 561                 }
 562
 563                 # Operation-based index
 564                 if ( $i == DB_SLAVE ) {
 565                         $this->mLastError = 'Unknown error'; // reset error string
 566                         # Try the general server pool if $groups are unavailable.
 567                         $i = in_array( false, $groups, true )
 568                                 ? false // don't bother with this if that is what was tried above
 569                                 : $this->getReaderIndex( false, $wiki );
 570                         # Couldn't find a working server in getReaderIndex()?
 571                         if ( $i === false ) {
 572                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 573
 574                                 return $this->reportConnectionError();
 575                         }
 576                 }
 577
 578                 # Now we have an explicit index into the servers array
 579                 $conn = $this->openConnection( $i, $wiki );
 580                 if ( !$conn ) {
 581                         return $this->reportConnectionError();
 582                 }
 583
 584                 # Profile any new connections that happen
 585                 if ( $this->connsOpened > $oldConnsOpened ) {
 586                         $host = $conn->getServer();
 587                         $dbname = $conn->getDBname();
 588                         $trxProf = Profiler::instance()->getTransactionProfiler();
 589                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 590                 }
 591
 592                 if ( $masterOnly ) {
 593                         # Make master-requested DB handles inherit any read-only mode setting
 594                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
 595                 }
 596
 597                 return $conn;
 598         }
 599
 600         /**
 601          * Mark a foreign connection as being available for reuse under a different
 602          * DB name or prefix. This mechanism is reference-counted, and must be called
 603          * the same number of times as getConnection() to work.
 604          *
 605          * @param DatabaseBase $conn
 606          * @throws MWException
 607          */
 608         public function reuseConnection( $conn ) {
 609                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 610                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 611                 if ( $serverIndex === null || $refCount === null ) {
 612                         /**
 613                          * This can happen in code like:
 614                          *   foreach ( $dbs as $db ) {
 615                          *     $conn = $lb->getConnection( DB_SLAVE, [], $db );
 616                          *     ...
 617                          *     $lb->reuseConnection( $conn );
 618                          *   }
 619                          * When a connection to the local DB is opened in this way, reuseConnection()
 620                          * should be ignored
 621                          */
 622                         return;
 623                 }
 624
 625                 $dbName = $conn->getDBname();
 626                 $prefix = $conn->tablePrefix();
 627                 if ( strval( $prefix ) !== '' ) {
 628                         $wiki = "$dbName-$prefix";
 629                 } else {
 630                         $wiki = $dbName;
 631                 }
 632                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 633                         throw new MWException( __METHOD__ . ": connection not found, has " .
 634                                 "the connection been freed already?" );
 635                 }
 636                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 637                 if ( $refCount <= 0 ) {
 638                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 639                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 640                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 641                 } else {
 642                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 643                 }
 644         }
 645
 646         /**
 647          * Get a database connection handle reference
 648          *
 649          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 650          *
 651          * @see LoadBalancer::getConnection() for parameter information
 652          *
 653          * @param int $db
 654          * @param array|string|bool $groups Query group(s), or false for the generic reader
 655          * @param string|bool $wiki Wiki ID, or false for the current wiki
 656          * @return DBConnRef
 657          */
 658         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 659                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 660         }
 661
 662         /**
 663          * Get a database connection handle reference without connecting yet
 664          *
 665          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 666          *
 667          * @see LoadBalancer::getConnection() for parameter information
 668          *
 669          * @param int $db
 670          * @param array|string|bool $groups Query group(s), or false for the generic reader
 671          * @param string|bool $wiki Wiki ID, or false for the current wiki
 672          * @return DBConnRef
 673          */
 674         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 675                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 676         }
 677
 678         /**
 679          * Open a connection to the server given by the specified index
 680          * Index must be an actual index into the array.
 681          * If the server is already open, returns it.
 682          *
 683          * On error, returns false, and the connection which caused the
 684          * error will be available via $this->mErrorConnection.
 685          *
 686          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 687          *
 688          * @param int $i Server index
 689          * @param string|bool $wiki Wiki ID, or false for the current wiki
 690          * @return DatabaseBase|bool Returns false on errors
 691          */
 692         public function openConnection( $i, $wiki = false ) {
 693                 if ( $wiki !== false ) {
 694                         $conn = $this->openForeignConnection( $i, $wiki );
 695                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 696                         $conn = $this->mConns['local'][$i][0];
 697                 } else {
 698                         $server = $this->mServers[$i];
 699                         $server['serverIndex'] = $i;
 700                         $conn = $this->reallyOpenConnection( $server, false );
 701                         $serverName = $this->getServerName( $i );
 702                         if ( $conn->isOpen() ) {
 703                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 704                                 $this->mConns['local'][$i][0] = $conn;
 705                         } else {
 706                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 707                                 $this->mErrorConnection = $conn;
 708                                 $conn = false;
 709                         }
 710                 }
 711
 712                 if ( $conn && !$conn->isOpen() ) {
 713                         // Connection was made but later unrecoverably lost for some reason.
 714                         // Do not return a handle that will just throw exceptions on use,
 715                         // but let the calling code (e.g. getReaderIndex) try another server.
 716                         // See DatabaseMyslBase::ping() for how this can happen.
 717                         $this->mErrorConnection = $conn;
 718                         $conn = false;
 719                 }
 720
 721                 return $conn;
 722         }
 723
 724         /**
 725          * Open a connection to a foreign DB, or return one if it is already open.
 726          *
 727          * Increments a reference count on the returned connection which locks the
 728          * connection to the requested wiki. This reference count can be
 729          * decremented by calling reuseConnection().
 730          *
 731          * If a connection is open to the appropriate server already, but with the wrong
 732          * database, it will be switched to the right database and returned, as long as
 733          * it has been freed first with reuseConnection().
 734          *
 735          * On error, returns false, and the connection which caused the
 736          * error will be available via $this->mErrorConnection.
 737          *
 738          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 739          *
 740          * @param int $i Server index
 741          * @param string $wiki Wiki ID to open
 742          * @return DatabaseBase
 743          */
 744         private function openForeignConnection( $i, $wiki ) {
 745                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 746                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 747                         // Reuse an already-used connection
 748                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 749                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 750                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 751                         // Reuse a free connection for the same wiki
 752                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 753                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 754                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 755                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 756                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 757                         // Reuse a connection from another wiki
 758                         $conn = reset( $this->mConns['foreignFree'][$i] );
 759                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 760
 761                         // The empty string as a DB name means "don't care".
 762                         // DatabaseMysqlBase::open() already handle this on connection.
 763                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 764                                 $this->mLastError = "Error selecting database $dbName on server " .
 765                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 766                                 $this->mErrorConnection = $conn;
 767                                 $conn = false;
 768                         } else {
 769                                 $conn->tablePrefix( $prefix );
 770                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 771                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 772                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 773                         }
 774                 } else {
 775                         // Open a new connection
 776                         $server = $this->mServers[$i];
 777                         $server['serverIndex'] = $i;
 778                         $server['foreignPoolRefCount'] = 0;
 779                         $server['foreign'] = true;
 780                         $conn = $this->reallyOpenConnection( $server, $dbName );
 781                         if ( !$conn->isOpen() ) {
 782                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 783                                 $this->mErrorConnection = $conn;
 784                                 $conn = false;
 785                         } else {
 786                                 $conn->tablePrefix( $prefix );
 787                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 788                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 789                         }
 790                 }
 791
 792                 // Increment reference count
 793                 if ( $conn ) {
 794                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 795                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 796                 }
 797
 798                 return $conn;
 799         }
 800
 801         /**
 802          * Test if the specified index represents an open connection
 803          *
 804          * @param int $index Server index
 805          * @access private
 806          * @return bool
 807          */
 808         private function isOpen( $index ) {
 809                 if ( !is_integer( $index ) ) {
 810                         return false;
 811                 }
 812
 813                 return (bool)$this->getAnyOpenConnection( $index );
 814         }
 815
 816         /**
 817          * Really opens a connection. Uncached.
 818          * Returns a Database object whether or not the connection was successful.
 819          * @access private
 820          *
 821          * @param array $server
 822          * @param bool $dbNameOverride
 823          * @throws MWException
 824          * @return DatabaseBase
 825          */
 826         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 827                 if ( $this->disabled ) {
 828                         throw new DBAccessError();
 829                 }
 830
 831                 if ( !is_array( $server ) ) {
 832                         throw new MWException( 'You must update your load-balancing configuration. ' .
 833                                 'See DefaultSettings.php entry for $wgDBservers.' );
 834                 }
 835
 836                 if ( $dbNameOverride !== false ) {
 837                         $server['dbname'] = $dbNameOverride;
 838                 }
 839
 840                 // Let the handle know what the cluster master is (e.g. "db1052")
 841                 $masterName = $this->getServerName( 0 );
 842                 $server['clusterMasterHost'] = $masterName;
 843
 844                 // Log when many connection are made on requests
 845                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 846                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 847                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 848                                 wfBacktrace( true ) );
 849                 }
 850
 851                 # Create object
 852                 try {
 853                         $db = DatabaseBase::factory( $server['type'], $server );
 854                 } catch ( DBConnectionError $e ) {
 855                         // FIXME: This is probably the ugliest thing I have ever done to
 856                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 857                         $db = $e->db;
 858                 }
 859
 860                 $db->setLBInfo( $server );
 861                 $db->setLazyMasterHandle(
 862                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 863                 );
 864                 $db->setTransactionProfiler( $this->trxProfiler );
 865                 if ( $this->trxRoundId !== false ) {
 866                         $this->applyTransactionRoundFlags( $db );
 867                 }
 868
 869                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 870                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 871                                 $db->setTransactionListener( $name, $callback );
 872                         }
 873                 }
 874
 875                 return $db;
 876         }
 877
 878         /**
 879          * @throws DBConnectionError
 880          * @return bool
 881          */
 882         private function reportConnectionError() {
 883                 $conn = $this->mErrorConnection; // The connection which caused the error
 884                 $context = [
 885                         'method' => __METHOD__,
 886                         'last_error' => $this->mLastError,
 887                 ];
 888
 889                 if ( !is_object( $conn ) ) {
 890                         // No last connection, probably due to all servers being too busy
 891                         wfLogDBError(
 892                                 "LB failure with no last connection. Connection error: {last_error}",
 893                                 $context
 894                         );
 895
 896                         // If all servers were busy, mLastError will contain something sensible
 897                         throw new DBConnectionError( null, $this->mLastError );
 898                 } else {
 899                         $context['db_server'] = $conn->getProperty( 'mServer' );
 900                         wfLogDBError(
 901                                 "Connection error: {last_error} ({db_server})",
 902                                 $context
 903                         );
 904
 905                         // throws DBConnectionError
 906                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 907                 }
 908
 909                 return false; /* not reached */
 910         }
 911
 912         /**
 913          * @return int
 914          * @since 1.26
 915          */
 916         public function getWriterIndex() {
 917                 return 0;
 918         }
 919
 920         /**
 921          * Returns true if the specified index is a valid server index
 922          *
 923          * @param string $i
 924          * @return bool
 925          */
 926         public function haveIndex( $i ) {
 927                 return array_key_exists( $i, $this->mServers );
 928         }
 929
 930         /**
 931          * Returns true if the specified index is valid and has non-zero load
 932          *
 933          * @param string $i
 934          * @return bool
 935          */
 936         public function isNonZeroLoad( $i ) {
 937                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 938         }
 939
 940         /**
 941          * Get the number of defined servers (not the number of open connections)
 942          *
 943          * @return int
 944          */
 945         public function getServerCount() {
 946                 return count( $this->mServers );
 947         }
 948
 949         /**
 950          * Get the host name or IP address of the server with the specified index
 951          * Prefer a readable name if available.
 952          * @param string $i
 953          * @return string
 954          */
 955         public function getServerName( $i ) {
 956                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 957                         $name = $this->mServers[$i]['hostName'];
 958                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 959                         $name = $this->mServers[$i]['host'];
 960                 } else {
 961                         $name = '';
 962                 }
 963
 964                 return ( $name != '' ) ? $name : 'localhost';
 965         }
 966
 967         /**
 968          * Return the server info structure for a given index, or false if the index is invalid.
 969          * @param int $i
 970          * @return array|bool
 971          */
 972         public function getServerInfo( $i ) {
 973                 if ( isset( $this->mServers[$i] ) ) {
 974                         return $this->mServers[$i];
 975                 } else {
 976                         return false;
 977                 }
 978         }
 979
 980         /**
 981          * Sets the server info structure for the given index. Entry at index $i
 982          * is created if it doesn't exist
 983          * @param int $i
 984          * @param array $serverInfo
 985          */
 986         public function setServerInfo( $i, array $serverInfo ) {
 987                 $this->mServers[$i] = $serverInfo;
 988         }
 989
 990         /**
 991          * Get the current master position for chronology control purposes
 992          * @return mixed
 993          */
 994         public function getMasterPos() {
 995                 # If this entire request was served from a replica DB without opening a connection to the
 996                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 997                 $masterConn = $this->getAnyOpenConnection( 0 );
 998                 if ( !$masterConn ) {
 999                         $serverCount = count( $this->mServers );
1000                         for ( $i = 1; $i < $serverCount; $i++ ) {
1001                                 $conn = $this->getAnyOpenConnection( $i );
1002                                 if ( $conn ) {
1003                                         return $conn->getSlavePos();
1004                                 }
1005                         }
1006                 } else {
1007                         return $masterConn->getMasterPos();
1008                 }
1009
1010                 return false;
1011         }
1012
1013         /**
1014          * Disable this load balancer. All connections are closed, and any attempt to
1015          * open a new connection will result in a DBAccessError.
1016          *
1017          * @since 1.27
1018          */
1019         public function disable() {
1020                 $this->closeAll();
1021                 $this->disabled = true;
1022         }
1023
1024         /**
1025          * Close all open connections
1026          */
1027         public function closeAll() {
1028                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1029                         $conn->close();
1030                 } );
1031
1032                 $this->mConns = [
1033                         'local' => [],
1034                         'foreignFree' => [],
1035                         'foreignUsed' => [],
1036                 ];
1037                 $this->connsOpened = 0;
1038         }
1039
1040         /**
1041          * Close a connection
1042          * Using this function makes sure the LoadBalancer knows the connection is closed.
1043          * If you use $conn->close() directly, the load balancer won't update its state.
1044          * @param DatabaseBase $conn
1045          */
1046         public function closeConnection( $conn ) {
1047                 $done = false;
1048                 foreach ( $this->mConns as $i1 => $conns2 ) {
1049                         foreach ( $conns2 as $i2 => $conns3 ) {
1050                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1051                                         if ( $conn === $candidateConn ) {
1052                                                 $conn->close();
1053                                                 unset( $this->mConns[$i1][$i2][$i3] );
1054                                                 --$this->connsOpened;
1055                                                 $done = true;
1056                                                 break;
1057                                         }
1058                                 }
1059                         }
1060                 }
1061                 if ( !$done ) {
1062                         $conn->close();
1063                 }
1064         }
1065
1066         /**
1067          * Commit transactions on all open connections
1068          * @param string $fname Caller name
1069          * @throws DBExpectedError
1070          */
1071         public function commitAll( $fname = __METHOD__ ) {
1072                 $failures = [];
1073
1074                 $restore = ( $this->trxRoundId !== false );
1075                 $this->trxRoundId = false;
1076                 $this->forEachOpenConnection(
1077                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1078                                 try {
1079                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1080                                 } catch ( DBError $e ) {
1081                                         MWExceptionHandler::logException( $e );
1082                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1083                                 }
1084                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1085                                         $this->undoTransactionRoundFlags( $conn );
1086                                 }
1087                         }
1088                 );
1089
1090                 if ( $failures ) {
1091                         throw new DBExpectedError(
1092                                 null,
1093                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1094                         );
1095                 }
1096         }
1097
1098         /**
1099          * Perform all pre-commit callbacks that remain part of the atomic transactions
1100          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
1101          * @since 1.28
1102          */
1103         public function finalizeMasterChanges() {
1104                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1105                         // Any error should cause all DB transactions to be rolled back together
1106                         $conn->setTrxEndCallbackSuppression( false );
1107                         $conn->runOnTransactionPreCommitCallbacks();
1108                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1109                         $conn->setTrxEndCallbackSuppression( true );
1110                 } );
1111         }
1112
1113         /**
1114          * Perform all pre-commit checks for things like replication safety
1115          * @param array $options Includes:
1116          *   - maxWriteDuration : max write query duration time in seconds
1117          * @throws DBTransactionError
1118          * @since 1.28
1119          */
1120         public function approveMasterChanges( array $options ) {
1121                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1122                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1123                         // If atomic sections or explicit transactions are still open, some caller must have
1124                         // caught an exception but failed to properly rollback any changes. Detect that and
1125                         // throw and error (causing rollback).
1126                         if ( $conn->explicitTrxActive() ) {
1127                                 throw new DBTransactionError(
1128                                         $conn,
1129                                         "Explicit transaction still active. A caller may have caught an error."
1130                                 );
1131                         }
1132                         // Assert that the time to replicate the transaction will be sane.
1133                         // If this fails, then all DB transactions will be rollback back together.
1134                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1135                         if ( $limit > 0 && $time > $limit ) {
1136                                 throw new DBTransactionError(
1137                                         $conn,
1138                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1139                                 );
1140                         }
1141                         // If a connection sits idle while slow queries execute on another, that connection
1142                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1143                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1144                                 throw new DBTransactionError(
1145                                         $conn,
1146                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1147                                 );
1148                         }
1149                 } );
1150         }
1151
1152         /**
1153          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
1154          *
1155          * The DBO_TRX setting will be reverted to the default in each of these methods:
1156          *   - commitMasterChanges()
1157          *   - rollbackMasterChanges()
1158          *   - commitAll()
1159          * This allows for custom transaction rounds from any outer transaction scope.
1160          *
1161          * @param string $fname
1162          * @throws DBExpectedError
1163          * @since 1.28
1164          */
1165         public function beginMasterChanges( $fname = __METHOD__ ) {
1166                 if ( $this->trxRoundId !== false ) {
1167                         throw new DBTransactionError(
1168                                 null,
1169                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1170                         );
1171                 }
1172                 $this->trxRoundId = $fname;
1173
1174                 $failures = [];
1175                 $this->forEachOpenMasterConnection(
1176                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1177                                 $conn->setTrxEndCallbackSuppression( true );
1178                                 try {
1179                                         $conn->clearSnapshot( $fname );
1180                                 } catch ( DBError $e ) {
1181                                         MWExceptionHandler::logException( $e );
1182                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1183                                 }
1184                                 $conn->setTrxEndCallbackSuppression( false );
1185                                 $this->applyTransactionRoundFlags( $conn );
1186                         }
1187                 );
1188
1189                 if ( $failures ) {
1190                         throw new DBExpectedError(
1191                                 null,
1192                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1193                         );
1194                 }
1195         }
1196
1197         /**
1198          * Issue COMMIT on all master connections where writes where done
1199          * @param string $fname Caller name
1200          * @throws DBExpectedError
1201          */
1202         public function commitMasterChanges( $fname = __METHOD__ ) {
1203                 $failures = [];
1204
1205                 $restore = ( $this->trxRoundId !== false );
1206                 $this->trxRoundId = false;
1207                 $this->forEachOpenMasterConnection(
1208                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1209                                 try {
1210                                         if ( $conn->writesOrCallbacksPending() ) {
1211                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1212                                         } elseif ( $restore ) {
1213                                                 $conn->clearSnapshot( $fname );
1214                                         }
1215                                 } catch ( DBError $e ) {
1216                                         MWExceptionHandler::logException( $e );
1217                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1218                                 }
1219                                 if ( $restore ) {
1220                                         $this->undoTransactionRoundFlags( $conn );
1221                                 }
1222                         }
1223                 );
1224
1225                 if ( $failures ) {
1226                         throw new DBExpectedError(
1227                                 null,
1228                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1229                         );
1230                 }
1231         }
1232
1233         /**
1234          * Issue all pending post-COMMIT/ROLLBACK callbacks
1235          * @param integer $type IDatabase::TRIGGER_* constant
1236          * @return Exception|null The first exception or null if there were none
1237          * @since 1.28
1238          */
1239         public function runMasterPostTrxCallbacks( $type ) {
1240                 $e = null; // first exception
1241                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1242                         $conn->clearSnapshot( __METHOD__ ); // clear no-op transactions
1243
1244                         $conn->setTrxEndCallbackSuppression( false );
1245                         try {
1246                                 $conn->runOnTransactionIdleCallbacks( $type );
1247                         } catch ( Exception $ex ) {
1248                                 $e = $e ?: $ex;
1249                         }
1250                         try {
1251                                 $conn->runTransactionListenerCallbacks( $type );
1252                         } catch ( Exception $ex ) {
1253                                 $e = $e ?: $ex;
1254                         }
1255                 } );
1256
1257                 return $e;
1258         }
1259
1260         /**
1261          * Issue ROLLBACK only on master, only if queries were done on connection
1262          * @param string $fname Caller name
1263          * @throws DBExpectedError
1264          * @since 1.23
1265          */
1266         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1267                 $restore = ( $this->trxRoundId !== false );
1268                 $this->trxRoundId = false;
1269                 $this->forEachOpenMasterConnection(
1270                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1271                                 if ( $conn->writesOrCallbacksPending() ) {
1272                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1273                                 }
1274                                 if ( $restore ) {
1275                                         $this->undoTransactionRoundFlags( $conn );
1276                                 }
1277                         }
1278                 );
1279         }
1280
1281         /**
1282          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1283          * @return Exception|null The first exception or null if there were none
1284          * @since 1.28
1285          */
1286         public function suppressTransactionEndCallbacks() {
1287                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1288                         $conn->setTrxEndCallbackSuppression( true );
1289                 } );
1290         }
1291
1292         /**
1293          * @param DatabaseBase $conn
1294          */
1295         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1296                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1297                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1298                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1299                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1300                         // If config has explicitly requested DBO_TRX be either on or off by not
1301                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1302                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1303                 }
1304         }
1305
1306         /**
1307          * @param DatabaseBase $conn
1308          */
1309         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1310                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1311                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1312                 }
1313         }
1314
1315         /**
1316          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
1317          *
1318          * @param string $fname Caller name
1319          * @since 1.28
1320          */
1321         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1322                 $this->forEachOpenReplicaConnection( function ( DatabaseBase $conn ) {
1323                         $conn->clearSnapshot( __METHOD__ );
1324                 } );
1325         }
1326
1327         /**
1328          * @return bool Whether a master connection is already open
1329          * @since 1.24
1330          */
1331         public function hasMasterConnection() {
1332                 return $this->isOpen( $this->getWriterIndex() );
1333         }
1334
1335         /**
1336          * Determine if there are pending changes in a transaction by this thread
1337          * @since 1.23
1338          * @return bool
1339          */
1340         public function hasMasterChanges() {
1341                 $masterIndex = $this->getWriterIndex();
1342                 foreach ( $this->mConns as $conns2 ) {
1343                         if ( empty( $conns2[$masterIndex] ) ) {
1344                                 continue;
1345                         }
1346                         /** @var DatabaseBase $conn */
1347                         foreach ( $conns2[$masterIndex] as $conn ) {
1348                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1349                                         return true;
1350                                 }
1351                         }
1352                 }
1353                 return false;
1354         }
1355
1356         /**
1357          * Get the timestamp of the latest write query done by this thread
1358          * @since 1.25
1359          * @return float|bool UNIX timestamp or false
1360          */
1361         public function lastMasterChangeTimestamp() {
1362                 $lastTime = false;
1363                 $masterIndex = $this->getWriterIndex();
1364                 foreach ( $this->mConns as $conns2 ) {
1365                         if ( empty( $conns2[$masterIndex] ) ) {
1366                                 continue;
1367                         }
1368                         /** @var DatabaseBase $conn */
1369                         foreach ( $conns2[$masterIndex] as $conn ) {
1370                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1371                         }
1372                 }
1373                 return $lastTime;
1374         }
1375
1376         /**
1377          * Check if this load balancer object had any recent or still
1378          * pending writes issued against it by this PHP thread
1379          *
1380          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1381          * @return bool
1382          * @since 1.25
1383          */
1384         public function hasOrMadeRecentMasterChanges( $age = null ) {
1385                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1386
1387                 return ( $this->hasMasterChanges()
1388                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1389         }
1390
1391         /**
1392          * Get the list of callers that have pending master changes
1393          *
1394          * @return array
1395          * @since 1.27
1396          */
1397         public function pendingMasterChangeCallers() {
1398                 $fnames = [];
1399
1400                 $masterIndex = $this->getWriterIndex();
1401                 foreach ( $this->mConns as $conns2 ) {
1402                         if ( empty( $conns2[$masterIndex] ) ) {
1403                                 continue;
1404                         }
1405                         /** @var DatabaseBase $conn */
1406                         foreach ( $conns2[$masterIndex] as $conn ) {
1407                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1408                         }
1409                 }
1410
1411                 return $fnames;
1412         }
1413
1414         /**
1415          * @param mixed $value
1416          * @return mixed
1417          */
1418         public function waitTimeout( $value = null ) {
1419                 return wfSetVar( $this->mWaitTimeout, $value );
1420         }
1421
1422         /**
1423          * @note This method will trigger a DB connection if not yet done
1424          * @param string|bool $wiki Wiki ID, or false for the current wiki
1425          * @return bool Whether the generic connection for reads is highly "lagged"
1426          */
1427         public function getLaggedReplicaMode( $wiki = false ) {
1428                 // No-op if there is only one DB (also avoids recursion)
1429                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1430                         try {
1431                                 // See if laggedReplicaMode gets set
1432                                 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1433                                 $this->reuseConnection( $conn );
1434                         } catch ( DBConnectionError $e ) {
1435                                 // Avoid expensive re-connect attempts and failures
1436                                 $this->allReplicasDownMode = true;
1437                                 $this->laggedReplicaMode = true;
1438                         }
1439                 }
1440
1441                 return $this->laggedReplicaMode;
1442         }
1443
1444         /**
1445          * @param bool $wiki
1446          * @return bool
1447          * @deprecated 1.28; use getLaggedReplicaMode()
1448          */
1449         public function getLaggedSlaveMode( $wiki = false ) {
1450                 return $this->getLaggedReplicaMode( $wiki );
1451         }
1452
1453         /**
1454          * @note This method will never cause a new DB connection
1455          * @return bool Whether any generic connection used for reads was highly "lagged"
1456          * @since 1.28
1457          */
1458         public function laggedReplicaUsed() {
1459                 return $this->laggedReplicaMode;
1460         }
1461
1462         /**
1463          * @return bool
1464          * @since 1.27
1465          * @deprecated Since 1.28; use laggedReplicaUsed()
1466          */
1467         public function laggedSlaveUsed() {
1468                 return $this->laggedReplicaUsed();
1469         }
1470
1471         /**
1472          * @note This method may trigger a DB connection if not yet done
1473          * @param string|bool $wiki Wiki ID, or false for the current wiki
1474          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1475          * @return string|bool Reason the master is read-only or false if it is not
1476          * @since 1.27
1477          */
1478         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1479                 if ( $this->readOnlyReason !== false ) {
1480                         return $this->readOnlyReason;
1481                 } elseif ( $this->getLaggedReplicaMode( $wiki ) ) {
1482                         if ( $this->allReplicasDownMode ) {
1483                                 return 'The database has been automatically locked ' .
1484                                         'until the replica database servers become available';
1485                         } else {
1486                                 return 'The database has been automatically locked ' .
1487                                         'while the replica database servers catch up to the master.';
1488                         }
1489                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1490                         return 'The database master is running in read-only mode.';
1491                 }
1492
1493                 return false;
1494         }
1495
1496         /**
1497          * @param string $wiki Wiki ID, or false for the current wiki
1498          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1499          * @return bool
1500          */
1501         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1502                 $cache = $this->wanCache;
1503                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1504
1505                 return (bool)$cache->getWithSetCallback(
1506                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1507                         self::TTL_CACHE_READONLY,
1508                         function () use ( $wiki, $conn ) {
1509                                 $this->trxProfiler->setSilenced( true );
1510                                 try {
1511                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1512                                         $readOnly = (int)$dbw->serverIsReadOnly();
1513                                 } catch ( DBError $e ) {
1514                                         $readOnly = 0;
1515                                 }
1516                                 $this->trxProfiler->setSilenced( false );
1517                                 return $readOnly;
1518                         },
1519                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1520                 );
1521         }
1522
1523         /**
1524          * Disables/enables lag checks
1525          * @param null|bool $mode
1526          * @return bool
1527          */
1528         public function allowLagged( $mode = null ) {
1529                 if ( $mode === null ) {
1530                         return $this->mAllowLagged;
1531                 }
1532                 $this->mAllowLagged = $mode;
1533
1534                 return $this->mAllowLagged;
1535         }
1536
1537         /**
1538          * @return bool
1539          */
1540         public function pingAll() {
1541                 $success = true;
1542                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1543                         if ( !$conn->ping() ) {
1544                                 $success = false;
1545                         }
1546                 } );
1547
1548                 return $success;
1549         }
1550
1551         /**
1552          * Call a function with each open connection object
1553          * @param callable $callback
1554          * @param array $params
1555          */
1556         public function forEachOpenConnection( $callback, array $params = [] ) {
1557                 foreach ( $this->mConns as $connsByServer ) {
1558                         foreach ( $connsByServer as $serverConns ) {
1559                                 foreach ( $serverConns as $conn ) {
1560                                         $mergedParams = array_merge( [ $conn ], $params );
1561                                         call_user_func_array( $callback, $mergedParams );
1562                                 }
1563                         }
1564                 }
1565         }
1566
1567         /**
1568          * Call a function with each open connection object to a master
1569          * @param callable $callback
1570          * @param array $params
1571          * @since 1.28
1572          */
1573         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1574                 $masterIndex = $this->getWriterIndex();
1575                 foreach ( $this->mConns as $connsByServer ) {
1576                         if ( isset( $connsByServer[$masterIndex] ) ) {
1577                                 /** @var DatabaseBase $conn */
1578                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1579                                         $mergedParams = array_merge( [ $conn ], $params );
1580                                         call_user_func_array( $callback, $mergedParams );
1581                                 }
1582                         }
1583                 }
1584         }
1585
1586         /**
1587          * Call a function with each open replica DB connection object
1588          * @param callable $callback
1589          * @param array $params
1590          * @since 1.28
1591          */
1592         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1593                 foreach ( $this->mConns as $connsByServer ) {
1594                         foreach ( $connsByServer as $i => $serverConns ) {
1595                                 if ( $i === $this->getWriterIndex() ) {
1596                                         continue; // skip master
1597                                 }
1598                                 foreach ( $serverConns as $conn ) {
1599                                         $mergedParams = array_merge( [ $conn ], $params );
1600                                         call_user_func_array( $callback, $mergedParams );
1601                                 }
1602                         }
1603                 }
1604         }
1605
1606         /**
1607          * Get the hostname and lag time of the most-lagged replica DB
1608          *
1609          * This is useful for maintenance scripts that need to throttle their updates.
1610          * May attempt to open connections to replica DBs on the default DB. If there is
1611          * no lag, the maximum lag will be reported as -1.
1612          *
1613          * @param bool|string $wiki Wiki ID, or false for the default database
1614          * @return array ( host, max lag, index of max lagged host )
1615          */
1616         public function getMaxLag( $wiki = false ) {
1617                 $maxLag = -1;
1618                 $host = '';
1619                 $maxIndex = 0;
1620
1621                 if ( $this->getServerCount() <= 1 ) {
1622                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1623                 }
1624
1625                 $lagTimes = $this->getLagTimes( $wiki );
1626                 foreach ( $lagTimes as $i => $lag ) {
1627                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1628                                 $maxLag = $lag;
1629                                 $host = $this->mServers[$i]['host'];
1630                                 $maxIndex = $i;
1631                         }
1632                 }
1633
1634                 return [ $host, $maxLag, $maxIndex ];
1635         }
1636
1637         /**
1638          * Get an estimate of replication lag (in seconds) for each server
1639          *
1640          * Results are cached for a short time in memcached/process cache
1641          *
1642          * Values may be "false" if replication is too broken to estimate
1643          *
1644          * @param string|bool $wiki
1645          * @return int[] Map of (server index => float|int|bool)
1646          */
1647         public function getLagTimes( $wiki = false ) {
1648                 if ( $this->getServerCount() <= 1 ) {
1649                         return [ 0 => 0 ]; // no replication = no lag
1650                 }
1651
1652                 # Send the request to the load monitor
1653                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1654         }
1655
1656         /**
1657          * Get the lag in seconds for a given connection, or zero if this load
1658          * balancer does not have replication enabled.
1659          *
1660          * This should be used in preference to Database::getLag() in cases where
1661          * replication may not be in use, since there is no way to determine if
1662          * replication is in use at the connection level without running
1663          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1664          * function instead of Database::getLag() avoids a fatal error in this
1665          * case on many installations.
1666          *
1667          * @param IDatabase $conn
1668          * @return int|bool Returns false on error
1669          */
1670         public function safeGetLag( IDatabase $conn ) {
1671                 if ( $this->getServerCount() == 1 ) {
1672                         return 0;
1673                 } else {
1674                         return $conn->getLag();
1675                 }
1676         }
1677
1678         /**
1679          * Wait for a replica DB to reach a specified master position
1680          *
1681          * This will connect to the master to get an accurate position if $pos is not given
1682          *
1683          * @param IDatabase $conn Replica DB
1684          * @param DBMasterPos|bool $pos Master position; default: current position
1685          * @param integer $timeout Timeout in seconds
1686          * @return bool Success
1687          * @since 1.27
1688          */
1689         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1690                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'replica' ) ) {
1691                         return true; // server is not a replica DB
1692                 }
1693
1694                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1695                 if ( !( $pos instanceof DBMasterPos ) ) {
1696                         return false; // something is misconfigured
1697                 }
1698
1699                 $result = $conn->masterPosWait( $pos, $timeout );
1700                 if ( $result == -1 || is_null( $result ) ) {
1701                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1702                         wfDebugLog( 'replication', "$msg\n" );
1703                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1704                         $ok = false;
1705                 } else {
1706                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1707                         $ok = true;
1708                 }
1709
1710                 return $ok;
1711         }
1712
1713         /**
1714          * Clear the cache for slag lag delay times
1715          *
1716          * This is only used for testing
1717          */
1718         public function clearLagTimeCache() {
1719                 $this->getLoadMonitor()->clearCaches();
1720         }
1721
1722         /**
1723          * Set a callback via DatabaseBase::setTransactionListener() on
1724          * all current and future master connections of this load balancer
1725          *
1726          * @param string $name Callback name
1727          * @param callable|null $callback
1728          * @since 1.28
1729          */
1730         public function setTransactionListener( $name, callable $callback = null ) {
1731                 if ( $callback ) {
1732                         $this->trxRecurringCallbacks[$name] = $callback;
1733                 } else {
1734                         unset( $this->trxRecurringCallbacks[$name] );
1735                 }
1736                 $this->forEachOpenMasterConnection(
1737                         function ( DatabaseBase $conn ) use ( $name, $callback ) {
1738                                 $conn->setTransactionListener( $name, $callback );
1739                         }
1740                 );
1741         }
1742 }