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         /** @var string Local Wiki ID and default for selectDB() calls */
  78         private $localDomain;
  79         /** @var callable Exception logger */
  80         private $errorLogger;
  81
  82         /** @var integer Warn when this many connection are held */
  83         const CONN_HELD_WARN_THRESHOLD = 10;
  84         /** @var integer Default 'max lag' when unspecified */
  85         const MAX_LAG_DEFAULT = 10;
  86         /** @var integer Max time to wait for a replica DB to catch up (e.g. ChronologyProtector) */
  87         const POS_WAIT_TIMEOUT = 10;
  88         /** @var integer Seconds to cache master server read-only status */
  89         const TTL_CACHE_READONLY = 5;
  90
  91         /**
  92          * @var boolean
  93          */
  94         private $disabled = false;
  95
  96         /**
  97          * @param array $params Array with keys:
  98          *  - servers : Required. Array of server info structures.
  99          *  - loadMonitor : Name of a class used to fetch server lag and load.
 100          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
 101          *  - waitTimeout : Maximum time to wait for replicas for consistency [optional]
 102          *  - srvCache : BagOStuff object [optional]
 103          *  - wanCache : WANObjectCache object [optional]
 104          *  - localDomain: The wiki ID of the "local"/"current" wiki [optional]
 105          *  - errorLogger: Callback that takes an Exception and logs it [optional]
 106          * @throws MWException
 107          */
 108         public function __construct( array $params ) {
 109                 if ( !isset( $params['servers'] ) ) {
 110                         throw new MWException( __CLASS__ . ': missing servers parameter' );
 111                 }
 112                 $this->mServers = $params['servers'];
 113                 $this->mWaitTimeout = isset( $params['waitTimeout'] )
 114                         ? $params['waitTimeout']
 115                         : self::POS_WAIT_TIMEOUT;
 116                 $this->localDomain = isset( $params['localDomain'] ) ? $params['localDomain'] : '';
 117
 118                 $this->mReadIndex = -1;
 119                 $this->mWriteIndex = -1;
 120                 $this->mConns = [
 121                         'local' => [],
 122                         'foreignUsed' => [],
 123                         'foreignFree' => [] ];
 124                 $this->mLoads = [];
 125                 $this->mWaitForPos = false;
 126                 $this->mErrorConnection = false;
 127                 $this->mAllowLagged = false;
 128
 129                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 130                         $this->readOnlyReason = $params['readOnlyReason'];
 131                 }
 132
 133                 if ( isset( $params['loadMonitor'] ) ) {
 134                         $this->mLoadMonitorClass = $params['loadMonitor'];
 135                 } else {
 136                         $master = reset( $params['servers'] );
 137                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 138                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 139                         } else {
 140                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 141                         }
 142                 }
 143
 144                 foreach ( $params['servers'] as $i => $server ) {
 145                         $this->mLoads[$i] = $server['load'];
 146                         if ( isset( $server['groupLoads'] ) ) {
 147                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 148                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 149                                                 $this->mGroupLoads[$group] = [];
 150                                         }
 151                                         $this->mGroupLoads[$group][$i] = $ratio;
 152                                 }
 153                         }
 154                 }
 155
 156                 if ( isset( $params['srvCache'] ) ) {
 157                         $this->srvCache = $params['srvCache'];
 158                 } else {
 159                         $this->srvCache = new EmptyBagOStuff();
 160                 }
 161                 if ( isset( $params['wanCache'] ) ) {
 162                         $this->wanCache = $params['wanCache'];
 163                 } else {
 164                         $this->wanCache = WANObjectCache::newEmpty();
 165                 }
 166                 if ( isset( $params['trxProfiler'] ) ) {
 167                         $this->trxProfiler = $params['trxProfiler'];
 168                 } else {
 169                         $this->trxProfiler = new TransactionProfiler();
 170                 }
 171
 172                 $this->errorLogger = isset( $params['errorLogger'] )
 173                         ? $params['errorLogger']
 174                         : function ( Exception $e ) {
 175                                 trigger_error( E_WARNING, $e->getMessage() );
 176                         };
 177         }
 178
 179         /**
 180          * Get a LoadMonitor instance
 181          *
 182          * @return LoadMonitor
 183          */
 184         private function getLoadMonitor() {
 185                 if ( !isset( $this->mLoadMonitor ) ) {
 186                         $class = $this->mLoadMonitorClass;
 187                         $this->mLoadMonitor = new $class( $this );
 188                 }
 189
 190                 return $this->mLoadMonitor;
 191         }
 192
 193         /**
 194          * @param array $loads
 195          * @param bool|string $wiki Wiki to get non-lagged for
 196          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 197          * @return bool|int|string
 198          */
 199         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 200                 $lags = $this->getLagTimes( $wiki );
 201
 202                 # Unset excessively lagged servers
 203                 foreach ( $lags as $i => $lag ) {
 204                         if ( $i != 0 ) {
 205                                 # How much lag this server nominally is allowed to have
 206                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 207                                         ? $this->mServers[$i]['max lag']
 208                                         : self::MAX_LAG_DEFAULT; // default
 209                                 # Constrain that futher by $maxLag argument
 210                                 $maxServerLag = min( $maxServerLag, $maxLag );
 211
 212                                 $host = $this->getServerName( $i );
 213                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 214                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 215                                         unset( $loads[$i] );
 216                                 } elseif ( $lag > $maxServerLag ) {
 217                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 218                                         unset( $loads[$i] );
 219                                 }
 220                         }
 221                 }
 222
 223                 # Find out if all the replica DBs with non-zero load are lagged
 224                 $sum = 0;
 225                 foreach ( $loads as $load ) {
 226                         $sum += $load;
 227                 }
 228                 if ( $sum == 0 ) {
 229                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 230                         # Do NOT use the master
 231                         # Instead, this function will return false, triggering read-only mode,
 232                         # and a lagged replica DB will be used instead.
 233                         return false;
 234                 }
 235
 236                 if ( count( $loads ) == 0 ) {
 237                         return false;
 238                 }
 239
 240                 # Return a random representative of the remainder
 241                 return ArrayUtils::pickRandom( $loads );
 242         }
 243
 244         /**
 245          * Get the index of the reader connection, which may be a replica DB
 246          * This takes into account load ratios and lag times. It should
 247          * always return a consistent index during a given invocation
 248          *
 249          * Side effect: opens connections to databases
 250          * @param string|bool $group Query group, or false for the generic reader
 251          * @param string|bool $wiki Wiki ID, or false for the current wiki
 252          * @throws MWException
 253          * @return bool|int|string
 254          */
 255         public function getReaderIndex( $group = false, $wiki = false ) {
 256                 if ( count( $this->mServers ) == 1 ) {
 257                         # Skip the load balancing if there's only one server
 258                         return $this->getWriterIndex();
 259                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 260                         # Shortcut if generic reader exists already
 261                         return $this->mReadIndex;
 262                 }
 263
 264                 # Find the relevant load array
 265                 if ( $group !== false ) {
 266                         if ( isset( $this->mGroupLoads[$group] ) ) {
 267                                 $nonErrorLoads = $this->mGroupLoads[$group];
 268                         } else {
 269                                 # No loads for this group, return false and the caller can use some other group
 270                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 271
 272                                 return false;
 273                         }
 274                 } else {
 275                         $nonErrorLoads = $this->mLoads;
 276                 }
 277
 278                 if ( !count( $nonErrorLoads ) ) {
 279                         throw new MWException( "Empty server array given to LoadBalancer" );
 280                 }
 281
 282                 # Scale the configured load ratios according to the dynamic load if supported
 283                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 284
 285                 $laggedReplicaMode = false;
 286
 287                 # No server found yet
 288                 $i = false;
 289                 # First try quickly looking through the available servers for a server that
 290                 # meets our criteria
 291                 $currentLoads = $nonErrorLoads;
 292                 while ( count( $currentLoads ) ) {
 293                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 294                                 $i = ArrayUtils::pickRandom( $currentLoads );
 295                         } else {
 296                                 $i = false;
 297                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 298                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 299                                         # This triggers doWait() after connect, so it's especially good to
 300                                         # avoid lagged servers so as to avoid just blocking in that method.
 301                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 302                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 303                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 304                                 }
 305                                 if ( $i === false ) {
 306                                         # Any server with less lag than it's 'max lag' param is preferable
 307                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 308                                 }
 309                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 310                                         # All replica DBs lagged. Switch to read-only mode
 311                                         wfDebugLog( 'replication', "All replica DBs lagged. Switch to read-only mode" );
 312                                         $i = ArrayUtils::pickRandom( $currentLoads );
 313                                         $laggedReplicaMode = true;
 314                                 }
 315                         }
 316
 317                         if ( $i === false ) {
 318                                 # pickRandom() returned false
 319                                 # This is permanent and means the configuration or the load monitor
 320                                 # wants us to return false.
 321                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 322
 323                                 return false;
 324                         }
 325
 326                         $serverName = $this->getServerName( $i );
 327                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 328
 329                         $conn = $this->openConnection( $i, $wiki );
 330                         if ( !$conn ) {
 331                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 332                                 unset( $nonErrorLoads[$i] );
 333                                 unset( $currentLoads[$i] );
 334                                 $i = false;
 335                                 continue;
 336                         }
 337
 338                         // Decrement reference counter, we are finished with this connection.
 339                         // It will be incremented for the caller later.
 340                         if ( $wiki !== false ) {
 341                                 $this->reuseConnection( $conn );
 342                         }
 343
 344                         # Return this server
 345                         break;
 346                 }
 347
 348                 # If all servers were down, quit now
 349                 if ( !count( $nonErrorLoads ) ) {
 350                         wfDebugLog( 'connect', "All servers down" );
 351                 }
 352
 353                 if ( $i !== false ) {
 354                         # Replica DB connection successful.
 355                         # Wait for the session master pos for a short time.
 356                         if ( $this->mWaitForPos && $i > 0 ) {
 357                                 $this->doWait( $i );
 358                         }
 359                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 360                                 $this->mReadIndex = $i;
 361                                 # Record if the generic reader index is in "lagged replica DB" mode
 362                                 if ( $laggedReplicaMode ) {
 363                                         $this->laggedReplicaMode = true;
 364                                 }
 365                         }
 366                         $serverName = $this->getServerName( $i );
 367                         wfDebugLog( 'connect', __METHOD__ .
 368                                 ": using server $serverName for group '$group'\n" );
 369                 }
 370
 371                 return $i;
 372         }
 373
 374         /**
 375          * Set the master wait position
 376          * If a DB_REPLICA connection has been opened already, waits
 377          * Otherwise sets a variable telling it to wait if such a connection is opened
 378          * @param DBMasterPos $pos
 379          */
 380         public function waitFor( $pos ) {
 381                 $this->mWaitForPos = $pos;
 382                 $i = $this->mReadIndex;
 383
 384                 if ( $i > 0 ) {
 385                         if ( !$this->doWait( $i ) ) {
 386                                 $this->laggedReplicaMode = true;
 387                         }
 388                 }
 389         }
 390
 391         /**
 392          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 393          *
 394          * This can be used a faster proxy for waitForAll()
 395          *
 396          * @param DBMasterPos $pos
 397          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 398          * @return bool Success (able to connect and no timeouts reached)
 399          * @since 1.26
 400          */
 401         public function waitForOne( $pos, $timeout = null ) {
 402                 $this->mWaitForPos = $pos;
 403
 404                 $i = $this->mReadIndex;
 405                 if ( $i <= 0 ) {
 406                         // Pick a generic replica DB if there isn't one yet
 407                         $readLoads = $this->mLoads;
 408                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 409                         $readLoads = array_filter( $readLoads ); // with non-zero load
 410                         $i = ArrayUtils::pickRandom( $readLoads );
 411                 }
 412
 413                 if ( $i > 0 ) {
 414                         $ok = $this->doWait( $i, true, $timeout );
 415                 } else {
 416                         $ok = true; // no applicable loads
 417                 }
 418
 419                 return $ok;
 420         }
 421
 422         /**
 423          * Set the master wait position and wait for ALL replica DBs to catch up to it
 424          * @param DBMasterPos $pos
 425          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 426          * @return bool Success (able to connect and no timeouts reached)
 427          */
 428         public function waitForAll( $pos, $timeout = null ) {
 429                 $this->mWaitForPos = $pos;
 430                 $serverCount = count( $this->mServers );
 431
 432                 $ok = true;
 433                 for ( $i = 1; $i < $serverCount; $i++ ) {
 434                         if ( $this->mLoads[$i] > 0 ) {
 435                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 436                         }
 437                 }
 438
 439                 return $ok;
 440         }
 441
 442         /**
 443          * Get any open connection to a given server index, local or foreign
 444          * Returns false if there is no connection open
 445          *
 446          * @param int $i Server index
 447          * @return DatabaseBase|bool False on failure
 448          */
 449         public function getAnyOpenConnection( $i ) {
 450                 foreach ( $this->mConns as $connsByServer ) {
 451                         if ( !empty( $connsByServer[$i] ) ) {
 452                                 return reset( $connsByServer[$i] );
 453                         }
 454                 }
 455
 456                 return false;
 457         }
 458
 459         /**
 460          * Wait for a given replica DB to catch up to the master pos stored in $this
 461          * @param int $index Server index
 462          * @param bool $open Check the server even if a new connection has to be made
 463          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 464          * @return bool
 465          */
 466         protected function doWait( $index, $open = false, $timeout = null ) {
 467                 $close = false; // close the connection afterwards
 468
 469                 // Check if we already know that the DB has reached this point
 470                 $server = $this->getServerName( $index );
 471                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 472                 /** @var DBMasterPos $knownReachedPos */
 473                 $knownReachedPos = $this->srvCache->get( $key );
 474                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 475                         wfDebugLog( 'replication', __METHOD__ .
 476                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos).\n" );
 477                         return true;
 478                 }
 479
 480                 // Find a connection to wait on, creating one if needed and allowed
 481                 $conn = $this->getAnyOpenConnection( $index );
 482                 if ( !$conn ) {
 483                         if ( !$open ) {
 484                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 485
 486                                 return false;
 487                         } else {
 488                                 $conn = $this->openConnection( $index, '' );
 489                                 if ( !$conn ) {
 490                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 491
 492                                         return false;
 493                                 }
 494                                 // Avoid connection spam in waitForAll() when connections
 495                                 // are made just for the sake of doing this lag check.
 496                                 $close = true;
 497                         }
 498                 }
 499
 500                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for replica DB $server to catch up...\n" );
 501                 $timeout = $timeout ?: $this->mWaitTimeout;
 502                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 503
 504                 if ( $result == -1 || is_null( $result ) ) {
 505                         // Timed out waiting for replica DB, use master instead
 506                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 507                         wfDebugLog( 'replication', "$msg\n" );
 508                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 509                         $ok = false;
 510                 } else {
 511                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 512                         $ok = true;
 513                         // Remember that the DB reached this point
 514                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 515                 }
 516
 517                 if ( $close ) {
 518                         $this->closeConnection( $conn );
 519                 }
 520
 521                 return $ok;
 522         }
 523
 524         /**
 525          * Get a connection by index
 526          * This is the main entry point for this class.
 527          *
 528          * @param int $i Server index
 529          * @param array|string|bool $groups Query group(s), or false for the generic reader
 530          * @param string|bool $wiki Wiki ID, or false for the current wiki
 531          *
 532          * @throws MWException
 533          * @return DatabaseBase
 534          */
 535         public function getConnection( $i, $groups = [], $wiki = false ) {
 536                 if ( $i === null || $i === false ) {
 537                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 538                                 ' with invalid server index' );
 539                 }
 540
 541                 if ( $wiki === $this->localDomain ) {
 542                         $wiki = false;
 543                 }
 544
 545                 $groups = ( $groups === false || $groups === [] )
 546                         ? [ false ] // check one "group": the generic pool
 547                         : (array)$groups;
 548
 549                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 550                 $oldConnsOpened = $this->connsOpened; // connections open now
 551
 552                 if ( $i == DB_MASTER ) {
 553                         $i = $this->getWriterIndex();
 554                 } else {
 555                         # Try to find an available server in any the query groups (in order)
 556                         foreach ( $groups as $group ) {
 557                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 558                                 if ( $groupIndex !== false ) {
 559                                         $i = $groupIndex;
 560                                         break;
 561                                 }
 562                         }
 563                 }
 564
 565                 # Operation-based index
 566                 if ( $i == DB_REPLICA ) {
 567                         $this->mLastError = 'Unknown error'; // reset error string
 568                         # Try the general server pool if $groups are unavailable.
 569                         $i = in_array( false, $groups, true )
 570                                 ? false // don't bother with this if that is what was tried above
 571                                 : $this->getReaderIndex( false, $wiki );
 572                         # Couldn't find a working server in getReaderIndex()?
 573                         if ( $i === false ) {
 574                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 575
 576                                 return $this->reportConnectionError();
 577                         }
 578                 }
 579
 580                 # Now we have an explicit index into the servers array
 581                 $conn = $this->openConnection( $i, $wiki );
 582                 if ( !$conn ) {
 583                         return $this->reportConnectionError();
 584                 }
 585
 586                 # Profile any new connections that happen
 587                 if ( $this->connsOpened > $oldConnsOpened ) {
 588                         $host = $conn->getServer();
 589                         $dbname = $conn->getDBname();
 590                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 591                 }
 592
 593                 if ( $masterOnly ) {
 594                         # Make master-requested DB handles inherit any read-only mode setting
 595                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
 596                 }
 597
 598                 return $conn;
 599         }
 600
 601         /**
 602          * Mark a foreign connection as being available for reuse under a different
 603          * DB name or prefix. This mechanism is reference-counted, and must be called
 604          * the same number of times as getConnection() to work.
 605          *
 606          * @param DatabaseBase $conn
 607          * @throws MWException
 608          */
 609         public function reuseConnection( $conn ) {
 610                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 611                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 612                 if ( $serverIndex === null || $refCount === null ) {
 613                         /**
 614                          * This can happen in code like:
 615                          *   foreach ( $dbs as $db ) {
 616                          *     $conn = $lb->getConnection( DB_REPLICA, [], $db );
 617                          *     ...
 618                          *     $lb->reuseConnection( $conn );
 619                          *   }
 620                          * When a connection to the local DB is opened in this way, reuseConnection()
 621                          * should be ignored
 622                          */
 623                         return;
 624                 }
 625
 626                 $dbName = $conn->getDBname();
 627                 $prefix = $conn->tablePrefix();
 628                 if ( strval( $prefix ) !== '' ) {
 629                         $wiki = "$dbName-$prefix";
 630                 } else {
 631                         $wiki = $dbName;
 632                 }
 633                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 634                         throw new MWException( __METHOD__ . ": connection not found, has " .
 635                                 "the connection been freed already?" );
 636                 }
 637                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 638                 if ( $refCount <= 0 ) {
 639                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 640                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 641                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 642                 } else {
 643                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 644                 }
 645         }
 646
 647         /**
 648          * Get a database connection handle reference
 649          *
 650          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 651          *
 652          * @see LoadBalancer::getConnection() for parameter information
 653          *
 654          * @param int $db
 655          * @param array|string|bool $groups Query group(s), or false for the generic reader
 656          * @param string|bool $wiki Wiki ID, or false for the current wiki
 657          * @return DBConnRef
 658          */
 659         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 660                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 661         }
 662
 663         /**
 664          * Get a database connection handle reference without connecting yet
 665          *
 666          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 667          *
 668          * @see LoadBalancer::getConnection() for parameter information
 669          *
 670          * @param int $db
 671          * @param array|string|bool $groups Query group(s), or false for the generic reader
 672          * @param string|bool $wiki Wiki ID, or false for the current wiki
 673          * @return DBConnRef
 674          */
 675         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 676                 $wiki = ( $wiki !== false ) ? $wiki : $this->localDomain;
 677
 678                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 679         }
 680
 681         /**
 682          * Open a connection to the server given by the specified index
 683          * Index must be an actual index into the array.
 684          * If the server is already open, returns it.
 685          *
 686          * On error, returns false, and the connection which caused the
 687          * error will be available via $this->mErrorConnection.
 688          *
 689          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 690          *
 691          * @param int $i Server index
 692          * @param string|bool $wiki Wiki ID, or false for the current wiki
 693          * @return DatabaseBase|bool Returns false on errors
 694          */
 695         public function openConnection( $i, $wiki = false ) {
 696                 if ( $wiki !== false ) {
 697                         $conn = $this->openForeignConnection( $i, $wiki );
 698                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 699                         $conn = $this->mConns['local'][$i][0];
 700                 } else {
 701                         $server = $this->mServers[$i];
 702                         $server['serverIndex'] = $i;
 703                         $conn = $this->reallyOpenConnection( $server, false );
 704                         $serverName = $this->getServerName( $i );
 705                         if ( $conn->isOpen() ) {
 706                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 707                                 $this->mConns['local'][$i][0] = $conn;
 708                         } else {
 709                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 710                                 $this->mErrorConnection = $conn;
 711                                 $conn = false;
 712                         }
 713                 }
 714
 715                 if ( $conn && !$conn->isOpen() ) {
 716                         // Connection was made but later unrecoverably lost for some reason.
 717                         // Do not return a handle that will just throw exceptions on use,
 718                         // but let the calling code (e.g. getReaderIndex) try another server.
 719                         // See DatabaseMyslBase::ping() for how this can happen.
 720                         $this->mErrorConnection = $conn;
 721                         $conn = false;
 722                 }
 723
 724                 return $conn;
 725         }
 726
 727         /**
 728          * Open a connection to a foreign DB, or return one if it is already open.
 729          *
 730          * Increments a reference count on the returned connection which locks the
 731          * connection to the requested wiki. This reference count can be
 732          * decremented by calling reuseConnection().
 733          *
 734          * If a connection is open to the appropriate server already, but with the wrong
 735          * database, it will be switched to the right database and returned, as long as
 736          * it has been freed first with reuseConnection().
 737          *
 738          * On error, returns false, and the connection which caused the
 739          * error will be available via $this->mErrorConnection.
 740          *
 741          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 742          *
 743          * @param int $i Server index
 744          * @param string $wiki Wiki ID to open
 745          * @return DatabaseBase
 746          */
 747         private function openForeignConnection( $i, $wiki ) {
 748                 list( $dbName, $prefix ) = explode( '-', $wiki, 2 ) + [ '', '' ];
 749
 750                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 751                         // Reuse an already-used connection
 752                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 753                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 754                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 755                         // Reuse a free connection for the same wiki
 756                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 757                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 758                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 759                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 760                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 761                         // Reuse a connection from another wiki
 762                         $conn = reset( $this->mConns['foreignFree'][$i] );
 763                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 764
 765                         // The empty string as a DB name means "don't care".
 766                         // DatabaseMysqlBase::open() already handle this on connection.
 767                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 768                                 $this->mLastError = "Error selecting database $dbName on server " .
 769                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 770                                 $this->mErrorConnection = $conn;
 771                                 $conn = false;
 772                         } else {
 773                                 $conn->tablePrefix( $prefix );
 774                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 775                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 776                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 777                         }
 778                 } else {
 779                         // Open a new connection
 780                         $server = $this->mServers[$i];
 781                         $server['serverIndex'] = $i;
 782                         $server['foreignPoolRefCount'] = 0;
 783                         $server['foreign'] = true;
 784                         $conn = $this->reallyOpenConnection( $server, $dbName );
 785                         if ( !$conn->isOpen() ) {
 786                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 787                                 $this->mErrorConnection = $conn;
 788                                 $conn = false;
 789                         } else {
 790                                 $conn->tablePrefix( $prefix );
 791                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 792                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 793                         }
 794                 }
 795
 796                 // Increment reference count
 797                 if ( $conn ) {
 798                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 799                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 800                 }
 801
 802                 return $conn;
 803         }
 804
 805         /**
 806          * Test if the specified index represents an open connection
 807          *
 808          * @param int $index Server index
 809          * @access private
 810          * @return bool
 811          */
 812         private function isOpen( $index ) {
 813                 if ( !is_integer( $index ) ) {
 814                         return false;
 815                 }
 816
 817                 return (bool)$this->getAnyOpenConnection( $index );
 818         }
 819
 820         /**
 821          * Really opens a connection. Uncached.
 822          * Returns a Database object whether or not the connection was successful.
 823          * @access private
 824          *
 825          * @param array $server
 826          * @param bool $dbNameOverride
 827          * @throws MWException
 828          * @return DatabaseBase
 829          */
 830         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 831                 if ( $this->disabled ) {
 832                         throw new DBAccessError();
 833                 }
 834
 835                 if ( !is_array( $server ) ) {
 836                         throw new MWException( 'You must update your load-balancing configuration. ' .
 837                                 'See DefaultSettings.php entry for $wgDBservers.' );
 838                 }
 839
 840                 if ( $dbNameOverride !== false ) {
 841                         $server['dbname'] = $dbNameOverride;
 842                 }
 843
 844                 // Let the handle know what the cluster master is (e.g. "db1052")
 845                 $masterName = $this->getServerName( $this->getWriterIndex() );
 846                 $server['clusterMasterHost'] = $masterName;
 847
 848                 // Log when many connection are made on requests
 849                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 850                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 851                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 852                                 wfBacktrace( true ) );
 853                 }
 854
 855                 # Create object
 856                 try {
 857                         $db = DatabaseBase::factory( $server['type'], $server );
 858                 } catch ( DBConnectionError $e ) {
 859                         // FIXME: This is probably the ugliest thing I have ever done to
 860                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 861                         $db = $e->db;
 862                 }
 863
 864                 $db->setLBInfo( $server );
 865                 $db->setLazyMasterHandle(
 866                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 867                 );
 868                 $db->setTransactionProfiler( $this->trxProfiler );
 869
 870                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 871                         if ( $this->trxRoundId !== false ) {
 872                                 $this->applyTransactionRoundFlags( $db );
 873                         }
 874                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 875                                 $db->setTransactionListener( $name, $callback );
 876                         }
 877                 }
 878
 879                 return $db;
 880         }
 881
 882         /**
 883          * @throws DBConnectionError
 884          * @return bool
 885          */
 886         private function reportConnectionError() {
 887                 $conn = $this->mErrorConnection; // The connection which caused the error
 888                 $context = [
 889                         'method' => __METHOD__,
 890                         'last_error' => $this->mLastError,
 891                 ];
 892
 893                 if ( !is_object( $conn ) ) {
 894                         // No last connection, probably due to all servers being too busy
 895                         wfLogDBError(
 896                                 "LB failure with no last connection. Connection error: {last_error}",
 897                                 $context
 898                         );
 899
 900                         // If all servers were busy, mLastError will contain something sensible
 901                         throw new DBConnectionError( null, $this->mLastError );
 902                 } else {
 903                         $context['db_server'] = $conn->getProperty( 'mServer' );
 904                         wfLogDBError(
 905                                 "Connection error: {last_error} ({db_server})",
 906                                 $context
 907                         );
 908
 909                         // throws DBConnectionError
 910                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 911                 }
 912
 913                 return false; /* not reached */
 914         }
 915
 916         /**
 917          * @return int
 918          * @since 1.26
 919          */
 920         public function getWriterIndex() {
 921                 return 0;
 922         }
 923
 924         /**
 925          * Returns true if the specified index is a valid server index
 926          *
 927          * @param string $i
 928          * @return bool
 929          */
 930         public function haveIndex( $i ) {
 931                 return array_key_exists( $i, $this->mServers );
 932         }
 933
 934         /**
 935          * Returns true if the specified index is valid and has non-zero load
 936          *
 937          * @param string $i
 938          * @return bool
 939          */
 940         public function isNonZeroLoad( $i ) {
 941                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 942         }
 943
 944         /**
 945          * Get the number of defined servers (not the number of open connections)
 946          *
 947          * @return int
 948          */
 949         public function getServerCount() {
 950                 return count( $this->mServers );
 951         }
 952
 953         /**
 954          * Get the host name or IP address of the server with the specified index
 955          * Prefer a readable name if available.
 956          * @param string $i
 957          * @return string
 958          */
 959         public function getServerName( $i ) {
 960                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 961                         $name = $this->mServers[$i]['hostName'];
 962                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 963                         $name = $this->mServers[$i]['host'];
 964                 } else {
 965                         $name = '';
 966                 }
 967
 968                 return ( $name != '' ) ? $name : 'localhost';
 969         }
 970
 971         /**
 972          * Return the server info structure for a given index, or false if the index is invalid.
 973          * @param int $i
 974          * @return array|bool
 975          */
 976         public function getServerInfo( $i ) {
 977                 if ( isset( $this->mServers[$i] ) ) {
 978                         return $this->mServers[$i];
 979                 } else {
 980                         return false;
 981                 }
 982         }
 983
 984         /**
 985          * Sets the server info structure for the given index. Entry at index $i
 986          * is created if it doesn't exist
 987          * @param int $i
 988          * @param array $serverInfo
 989          */
 990         public function setServerInfo( $i, array $serverInfo ) {
 991                 $this->mServers[$i] = $serverInfo;
 992         }
 993
 994         /**
 995          * Get the current master position for chronology control purposes
 996          * @return DBMasterPos|bool Returns false if not applicable
 997          */
 998         public function getMasterPos() {
 999                 # If this entire request was served from a replica DB without opening a connection to the
1000                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1001                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1002                 if ( !$masterConn ) {
1003                         $serverCount = count( $this->mServers );
1004                         for ( $i = 1; $i < $serverCount; $i++ ) {
1005                                 $conn = $this->getAnyOpenConnection( $i );
1006                                 if ( $conn ) {
1007                                         return $conn->getSlavePos();
1008                                 }
1009                         }
1010                 } else {
1011                         return $masterConn->getMasterPos();
1012                 }
1013
1014                 return false;
1015         }
1016
1017         /**
1018          * Disable this load balancer. All connections are closed, and any attempt to
1019          * open a new connection will result in a DBAccessError.
1020          *
1021          * @since 1.27
1022          */
1023         public function disable() {
1024                 $this->closeAll();
1025                 $this->disabled = true;
1026         }
1027
1028         /**
1029          * Close all open connections
1030          */
1031         public function closeAll() {
1032                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1033                         $conn->close();
1034                 } );
1035
1036                 $this->mConns = [
1037                         'local' => [],
1038                         'foreignFree' => [],
1039                         'foreignUsed' => [],
1040                 ];
1041                 $this->connsOpened = 0;
1042         }
1043
1044         /**
1045          * Close a connection
1046          *
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          *
1050          * @param DatabaseBase $conn
1051          */
1052         public function closeConnection( DatabaseBase $conn ) {
1053                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1054                 foreach ( $this->mConns as $type => $connsByServer ) {
1055                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1056                                 continue;
1057                         }
1058
1059                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1060                                 if ( $conn === $trackedConn ) {
1061                                         unset( $this->mConns[$type][$serverIndex][$i] );
1062                                         --$this->connsOpened;
1063                                         break 2;
1064                                 }
1065                         }
1066                 }
1067
1068                 $conn->close();
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                                         call_user_func( $this->errorLogger, $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->flushSnapshot( $fname );
1185                                 } catch ( DBError $e ) {
1186                                         call_user_func( $this->errorLogger, $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->flushSnapshot( $fname );
1219                                         }
1220                                 } catch ( DBError $e ) {
1221                                         call_user_func( $this->errorLogger, $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->setTrxEndCallbackSuppression( false );
1248                         if ( $conn->writesOrCallbacksPending() ) {
1249                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1250                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1251                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1252                                 wfWarn( __METHOD__ . ": did not expect writes/callbacks pending." );
1253                                 return;
1254                         } elseif ( $conn->trxLevel() ) {
1255                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1256                                 // thus leaving an implicit read-only transaction open at this point. It
1257                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1258                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1259                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1260                                 return;
1261                         }
1262                         try {
1263                                 $conn->runOnTransactionIdleCallbacks( $type );
1264                         } catch ( Exception $ex ) {
1265                                 $e = $e ?: $ex;
1266                         }
1267                         try {
1268                                 $conn->runTransactionListenerCallbacks( $type );
1269                         } catch ( Exception $ex ) {
1270                                 $e = $e ?: $ex;
1271                         }
1272                 } );
1273
1274                 return $e;
1275         }
1276
1277         /**
1278          * Issue ROLLBACK only on master, only if queries were done on connection
1279          * @param string $fname Caller name
1280          * @throws DBExpectedError
1281          * @since 1.23
1282          */
1283         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1284                 $restore = ( $this->trxRoundId !== false );
1285                 $this->trxRoundId = false;
1286                 $this->forEachOpenMasterConnection(
1287                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1288                                 if ( $conn->writesOrCallbacksPending() ) {
1289                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1290                                 }
1291                                 if ( $restore ) {
1292                                         $this->undoTransactionRoundFlags( $conn );
1293                                 }
1294                         }
1295                 );
1296         }
1297
1298         /**
1299          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1300          * @return Exception|null The first exception or null if there were none
1301          * @since 1.28
1302          */
1303         public function suppressTransactionEndCallbacks() {
1304                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1305                         $conn->setTrxEndCallbackSuppression( true );
1306                 } );
1307         }
1308
1309         /**
1310          * @param DatabaseBase $conn
1311          */
1312         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1313                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1314                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1315                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1316                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1317                         // If config has explicitly requested DBO_TRX be either on or off by not
1318                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1319                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1320                 }
1321         }
1322
1323         /**
1324          * @param DatabaseBase $conn
1325          */
1326         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1327                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1328                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1329                 }
1330         }
1331
1332         /**
1333          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
1334          *
1335          * @param string $fname Caller name
1336          * @since 1.28
1337          */
1338         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1339                 $this->forEachOpenReplicaConnection( function ( DatabaseBase $conn ) {
1340                         $conn->flushSnapshot( __METHOD__ );
1341                 } );
1342         }
1343
1344         /**
1345          * @return bool Whether a master connection is already open
1346          * @since 1.24
1347          */
1348         public function hasMasterConnection() {
1349                 return $this->isOpen( $this->getWriterIndex() );
1350         }
1351
1352         /**
1353          * Determine if there are pending changes in a transaction by this thread
1354          * @since 1.23
1355          * @return bool
1356          */
1357         public function hasMasterChanges() {
1358                 $pending = 0;
1359                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$pending ) {
1360                         $pending |= $conn->writesOrCallbacksPending();
1361                 } );
1362
1363                 return (bool)$pending;
1364         }
1365
1366         /**
1367          * Get the timestamp of the latest write query done by this thread
1368          * @since 1.25
1369          * @return float|bool UNIX timestamp or false
1370          */
1371         public function lastMasterChangeTimestamp() {
1372                 $lastTime = false;
1373                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$lastTime ) {
1374                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1375                 } );
1376
1377                 return $lastTime;
1378         }
1379
1380         /**
1381          * Check if this load balancer object had any recent or still
1382          * pending writes issued against it by this PHP thread
1383          *
1384          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1385          * @return bool
1386          * @since 1.25
1387          */
1388         public function hasOrMadeRecentMasterChanges( $age = null ) {
1389                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1390
1391                 return ( $this->hasMasterChanges()
1392                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1393         }
1394
1395         /**
1396          * Get the list of callers that have pending master changes
1397          *
1398          * @return string[] List of method names
1399          * @since 1.27
1400          */
1401         public function pendingMasterChangeCallers() {
1402                 $fnames = [];
1403                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$fnames ) {
1404                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1405                 } );
1406
1407                 return $fnames;
1408         }
1409
1410         /**
1411          * @note This method will trigger a DB connection if not yet done
1412          * @param string|bool $wiki Wiki ID, or false for the current wiki
1413          * @return bool Whether the generic connection for reads is highly "lagged"
1414          */
1415         public function getLaggedReplicaMode( $wiki = false ) {
1416                 // No-op if there is only one DB (also avoids recursion)
1417                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1418                         try {
1419                                 // See if laggedReplicaMode gets set
1420                                 $conn = $this->getConnection( DB_REPLICA, false, $wiki );
1421                                 $this->reuseConnection( $conn );
1422                         } catch ( DBConnectionError $e ) {
1423                                 // Avoid expensive re-connect attempts and failures
1424                                 $this->allReplicasDownMode = true;
1425                                 $this->laggedReplicaMode = true;
1426                         }
1427                 }
1428
1429                 return $this->laggedReplicaMode;
1430         }
1431
1432         /**
1433          * @param bool $wiki
1434          * @return bool
1435          * @deprecated 1.28; use getLaggedReplicaMode()
1436          */
1437         public function getLaggedSlaveMode( $wiki = false ) {
1438                 return $this->getLaggedReplicaMode( $wiki );
1439         }
1440
1441         /**
1442          * @note This method will never cause a new DB connection
1443          * @return bool Whether any generic connection used for reads was highly "lagged"
1444          * @since 1.28
1445          */
1446         public function laggedReplicaUsed() {
1447                 return $this->laggedReplicaMode;
1448         }
1449
1450         /**
1451          * @return bool
1452          * @since 1.27
1453          * @deprecated Since 1.28; use laggedReplicaUsed()
1454          */
1455         public function laggedSlaveUsed() {
1456                 return $this->laggedReplicaUsed();
1457         }
1458
1459         /**
1460          * @note This method may trigger a DB connection if not yet done
1461          * @param string|bool $wiki Wiki ID, or false for the current wiki
1462          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1463          * @return string|bool Reason the master is read-only or false if it is not
1464          * @since 1.27
1465          */
1466         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1467                 if ( $this->readOnlyReason !== false ) {
1468                         return $this->readOnlyReason;
1469                 } elseif ( $this->getLaggedReplicaMode( $wiki ) ) {
1470                         if ( $this->allReplicasDownMode ) {
1471                                 return 'The database has been automatically locked ' .
1472                                         'until the replica database servers become available';
1473                         } else {
1474                                 return 'The database has been automatically locked ' .
1475                                         'while the replica database servers catch up to the master.';
1476                         }
1477                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1478                         return 'The database master is running in read-only mode.';
1479                 }
1480
1481                 return false;
1482         }
1483
1484         /**
1485          * @param string $wiki Wiki ID, or false for the current wiki
1486          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1487          * @return bool
1488          */
1489         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1490                 $cache = $this->wanCache;
1491                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1492
1493                 return (bool)$cache->getWithSetCallback(
1494                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1495                         self::TTL_CACHE_READONLY,
1496                         function () use ( $wiki, $conn ) {
1497                                 $this->trxProfiler->setSilenced( true );
1498                                 try {
1499                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1500                                         $readOnly = (int)$dbw->serverIsReadOnly();
1501                                 } catch ( DBError $e ) {
1502                                         $readOnly = 0;
1503                                 }
1504                                 $this->trxProfiler->setSilenced( false );
1505                                 return $readOnly;
1506                         },
1507                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1508                 );
1509         }
1510
1511         /**
1512          * Disables/enables lag checks
1513          * @param null|bool $mode
1514          * @return bool
1515          */
1516         public function allowLagged( $mode = null ) {
1517                 if ( $mode === null ) {
1518                         return $this->mAllowLagged;
1519                 }
1520                 $this->mAllowLagged = $mode;
1521
1522                 return $this->mAllowLagged;
1523         }
1524
1525         /**
1526          * @return bool
1527          */
1528         public function pingAll() {
1529                 $success = true;
1530                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1531                         if ( !$conn->ping() ) {
1532                                 $success = false;
1533                         }
1534                 } );
1535
1536                 return $success;
1537         }
1538
1539         /**
1540          * Call a function with each open connection object
1541          * @param callable $callback
1542          * @param array $params
1543          */
1544         public function forEachOpenConnection( $callback, array $params = [] ) {
1545                 foreach ( $this->mConns as $connsByServer ) {
1546                         foreach ( $connsByServer as $serverConns ) {
1547                                 foreach ( $serverConns as $conn ) {
1548                                         $mergedParams = array_merge( [ $conn ], $params );
1549                                         call_user_func_array( $callback, $mergedParams );
1550                                 }
1551                         }
1552                 }
1553         }
1554
1555         /**
1556          * Call a function with each open connection object to a master
1557          * @param callable $callback
1558          * @param array $params
1559          * @since 1.28
1560          */
1561         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1562                 $masterIndex = $this->getWriterIndex();
1563                 foreach ( $this->mConns as $connsByServer ) {
1564                         if ( isset( $connsByServer[$masterIndex] ) ) {
1565                                 /** @var DatabaseBase $conn */
1566                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1567                                         $mergedParams = array_merge( [ $conn ], $params );
1568                                         call_user_func_array( $callback, $mergedParams );
1569                                 }
1570                         }
1571                 }
1572         }
1573
1574         /**
1575          * Call a function with each open replica DB connection object
1576          * @param callable $callback
1577          * @param array $params
1578          * @since 1.28
1579          */
1580         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1581                 foreach ( $this->mConns as $connsByServer ) {
1582                         foreach ( $connsByServer as $i => $serverConns ) {
1583                                 if ( $i === $this->getWriterIndex() ) {
1584                                         continue; // skip master
1585                                 }
1586                                 foreach ( $serverConns as $conn ) {
1587                                         $mergedParams = array_merge( [ $conn ], $params );
1588                                         call_user_func_array( $callback, $mergedParams );
1589                                 }
1590                         }
1591                 }
1592         }
1593
1594         /**
1595          * Get the hostname and lag time of the most-lagged replica DB
1596          *
1597          * This is useful for maintenance scripts that need to throttle their updates.
1598          * May attempt to open connections to replica DBs on the default DB. If there is
1599          * no lag, the maximum lag will be reported as -1.
1600          *
1601          * @param bool|string $wiki Wiki ID, or false for the default database
1602          * @return array ( host, max lag, index of max lagged host )
1603          */
1604         public function getMaxLag( $wiki = false ) {
1605                 $maxLag = -1;
1606                 $host = '';
1607                 $maxIndex = 0;
1608
1609                 if ( $this->getServerCount() <= 1 ) {
1610                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1611                 }
1612
1613                 $lagTimes = $this->getLagTimes( $wiki );
1614                 foreach ( $lagTimes as $i => $lag ) {
1615                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1616                                 $maxLag = $lag;
1617                                 $host = $this->mServers[$i]['host'];
1618                                 $maxIndex = $i;
1619                         }
1620                 }
1621
1622                 return [ $host, $maxLag, $maxIndex ];
1623         }
1624
1625         /**
1626          * Get an estimate of replication lag (in seconds) for each server
1627          *
1628          * Results are cached for a short time in memcached/process cache
1629          *
1630          * Values may be "false" if replication is too broken to estimate
1631          *
1632          * @param string|bool $wiki
1633          * @return int[] Map of (server index => float|int|bool)
1634          */
1635         public function getLagTimes( $wiki = false ) {
1636                 if ( $this->getServerCount() <= 1 ) {
1637                         return [ 0 => 0 ]; // no replication = no lag
1638                 }
1639
1640                 # Send the request to the load monitor
1641                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1642         }
1643
1644         /**
1645          * Get the lag in seconds for a given connection, or zero if this load
1646          * balancer does not have replication enabled.
1647          *
1648          * This should be used in preference to Database::getLag() in cases where
1649          * replication may not be in use, since there is no way to determine if
1650          * replication is in use at the connection level without running
1651          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1652          * function instead of Database::getLag() avoids a fatal error in this
1653          * case on many installations.
1654          *
1655          * @param IDatabase $conn
1656          * @return int|bool Returns false on error
1657          */
1658         public function safeGetLag( IDatabase $conn ) {
1659                 if ( $this->getServerCount() == 1 ) {
1660                         return 0;
1661                 } else {
1662                         return $conn->getLag();
1663                 }
1664         }
1665
1666         /**
1667          * Wait for a replica DB to reach a specified master position
1668          *
1669          * This will connect to the master to get an accurate position if $pos is not given
1670          *
1671          * @param IDatabase $conn Replica DB
1672          * @param DBMasterPos|bool $pos Master position; default: current position
1673          * @param integer $timeout Timeout in seconds
1674          * @return bool Success
1675          * @since 1.27
1676          */
1677         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1678                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'replica' ) ) {
1679                         return true; // server is not a replica DB
1680                 }
1681
1682                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1683                 if ( !( $pos instanceof DBMasterPos ) ) {
1684                         return false; // something is misconfigured
1685                 }
1686
1687                 $result = $conn->masterPosWait( $pos, $timeout );
1688                 if ( $result == -1 || is_null( $result ) ) {
1689                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1690                         wfDebugLog( 'replication', "$msg\n" );
1691                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1692                         $ok = false;
1693                 } else {
1694                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1695                         $ok = true;
1696                 }
1697
1698                 return $ok;
1699         }
1700
1701         /**
1702          * Clear the cache for slag lag delay times
1703          *
1704          * This is only used for testing
1705          */
1706         public function clearLagTimeCache() {
1707                 $this->getLoadMonitor()->clearCaches();
1708         }
1709
1710         /**
1711          * Set a callback via DatabaseBase::setTransactionListener() on
1712          * all current and future master connections of this load balancer
1713          *
1714          * @param string $name Callback name
1715          * @param callable|null $callback
1716          * @since 1.28
1717          */
1718         public function setTransactionListener( $name, callable $callback = null ) {
1719                 if ( $callback ) {
1720                         $this->trxRecurringCallbacks[$name] = $callback;
1721                 } else {
1722                         unset( $this->trxRecurringCallbacks[$name] );
1723                 }
1724                 $this->forEachOpenMasterConnection(
1725                         function ( DatabaseBase $conn ) use ( $name, $callback ) {
1726                                 $conn->setTransactionListener( $name, $callback );
1727                         }
1728                 );
1729         }
1730
1731         /**
1732          * Set a new table prefix for the existing local wiki ID for testing
1733          *
1734          * @param string $prefix
1735          * @since 1.28
1736          */
1737         public function setDomainPrefix( $prefix ) {
1738                 list( $dbName, ) = explode( '-', $this->localDomain, 2 );
1739
1740                 $this->localDomain = "{$dbName}-{$prefix}";
1741         }
1742 }