includes/db/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23
  24 /**
  25  * Database load balancing object
  26  *
  27  * @todo document
  28  * @ingroup Database
  29  */
  30 class LoadBalancer {
  31         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  42         private $mWaitTimeout;
  43         /** @var array LBFactory information */
  44         private $mParentInfo;
  45
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50         /** @var BagOStuff */
  51         private $srvCache;
  52         /** @var WANObjectCache */
  53         private $wanCache;
  54         /** @var TransactionProfiler */
  55         protected $trxProfiler;
  56
  57         /** @var bool|DatabaseBase Database connection that caused a problem */
  58         private $mErrorConnection;
  59         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  60         private $mReadIndex;
  61         /** @var bool|DBMasterPos False if not set */
  62         private $mWaitForPos;
  63         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  64         private $laggedReplicaMode = false;
  65         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  66         private $allReplicasDownMode = false;
  67         /** @var string The last DB selection or connection error */
  68         private $mLastError = 'Unknown error';
  69         /** @var string|bool Reason the LB is read-only or false if not */
  70         private $readOnlyReason = false;
  71         /** @var integer Total connections opened */
  72         private $connsOpened = 0;
  73         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  74         private $trxRoundId = false;
  75         /** @var array[] Map of (name => callable) */
  76         private $trxRecurringCallbacks = [];
  77
  78         /** @var integer Warn when this many connection are held */
  79         const CONN_HELD_WARN_THRESHOLD = 10;
  80         /** @var integer Default 'max lag' when unspecified */
  81         const MAX_LAG_DEFAULT = 10;
  82         /** @var integer Max time to wait for a replica DB to catch up (e.g. ChronologyProtector) */
  83         const POS_WAIT_TIMEOUT = 10;
  84         /** @var integer Seconds to cache master server read-only status */
  85         const TTL_CACHE_READONLY = 5;
  86
  87         /**
  88          * @var boolean
  89          */
  90         private $disabled = false;
  91
  92         /**
  93          * @param array $params Array with keys:
  94          *  - servers : Required. Array of server info structures.
  95          *  - loadMonitor : Name of a class used to fetch server lag and load.
  96          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  97          *  - waitTimeout : Maximum time to wait for replicas for consistency [optional]
  98          *  - srvCache : BagOStuff object [optional]
  99          *  - wanCache : WANObjectCache object [optional]
 100          * @throws MWException
 101          */
 102         public function __construct( array $params ) {
 103                 if ( !isset( $params['servers'] ) ) {
 104                         throw new MWException( __CLASS__ . ': missing servers parameter' );
 105                 }
 106                 $this->mServers = $params['servers'];
 107                 $this->mWaitTimeout = isset( $params['waitTimeout'] )
 108                         ? $params['waitTimeout']
 109                         : self::POS_WAIT_TIMEOUT;
 110
 111                 $this->mReadIndex = -1;
 112                 $this->mWriteIndex = -1;
 113                 $this->mConns = [
 114                         'local' => [],
 115                         'foreignUsed' => [],
 116                         'foreignFree' => [] ];
 117                 $this->mLoads = [];
 118                 $this->mWaitForPos = false;
 119                 $this->mErrorConnection = false;
 120                 $this->mAllowLagged = false;
 121
 122                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 123                         $this->readOnlyReason = $params['readOnlyReason'];
 124                 }
 125
 126                 if ( isset( $params['loadMonitor'] ) ) {
 127                         $this->mLoadMonitorClass = $params['loadMonitor'];
 128                 } else {
 129                         $master = reset( $params['servers'] );
 130                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 131                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 132                         } else {
 133                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 134                         }
 135                 }
 136
 137                 foreach ( $params['servers'] as $i => $server ) {
 138                         $this->mLoads[$i] = $server['load'];
 139                         if ( isset( $server['groupLoads'] ) ) {
 140                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 141                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 142                                                 $this->mGroupLoads[$group] = [];
 143                                         }
 144                                         $this->mGroupLoads[$group][$i] = $ratio;
 145                                 }
 146                         }
 147                 }
 148
 149                 if ( isset( $params['srvCache'] ) ) {
 150                         $this->srvCache = $params['srvCache'];
 151                 } else {
 152                         $this->srvCache = new EmptyBagOStuff();
 153                 }
 154                 if ( isset( $params['wanCache'] ) ) {
 155                         $this->wanCache = $params['wanCache'];
 156                 } else {
 157                         $this->wanCache = WANObjectCache::newEmpty();
 158                 }
 159                 if ( isset( $params['trxProfiler'] ) ) {
 160                         $this->trxProfiler = $params['trxProfiler'];
 161                 } else {
 162                         $this->trxProfiler = new TransactionProfiler();
 163                 }
 164         }
 165
 166         /**
 167          * Get a LoadMonitor instance
 168          *
 169          * @return LoadMonitor
 170          */
 171         private function getLoadMonitor() {
 172                 if ( !isset( $this->mLoadMonitor ) ) {
 173                         $class = $this->mLoadMonitorClass;
 174                         $this->mLoadMonitor = new $class( $this );
 175                 }
 176
 177                 return $this->mLoadMonitor;
 178         }
 179
 180         /**
 181          * Get or set arbitrary data used by the parent object, usually an LBFactory
 182          * @param mixed $x
 183          * @return mixed
 184          */
 185         public function parentInfo( $x = null ) {
 186                 return wfSetVar( $this->mParentInfo, $x );
 187         }
 188
 189         /**
 190          * @param array $loads
 191          * @param bool|string $wiki Wiki to get non-lagged for
 192          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 193          * @return bool|int|string
 194          */
 195         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 196                 $lags = $this->getLagTimes( $wiki );
 197
 198                 # Unset excessively lagged servers
 199                 foreach ( $lags as $i => $lag ) {
 200                         if ( $i != 0 ) {
 201                                 # How much lag this server nominally is allowed to have
 202                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 203                                         ? $this->mServers[$i]['max lag']
 204                                         : self::MAX_LAG_DEFAULT; // default
 205                                 # Constrain that futher by $maxLag argument
 206                                 $maxServerLag = min( $maxServerLag, $maxLag );
 207
 208                                 $host = $this->getServerName( $i );
 209                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 210                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 211                                         unset( $loads[$i] );
 212                                 } elseif ( $lag > $maxServerLag ) {
 213                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 214                                         unset( $loads[$i] );
 215                                 }
 216                         }
 217                 }
 218
 219                 # Find out if all the replica DBs with non-zero load are lagged
 220                 $sum = 0;
 221                 foreach ( $loads as $load ) {
 222                         $sum += $load;
 223                 }
 224                 if ( $sum == 0 ) {
 225                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 226                         # Do NOT use the master
 227                         # Instead, this function will return false, triggering read-only mode,
 228                         # and a lagged replica DB will be used instead.
 229                         return false;
 230                 }
 231
 232                 if ( count( $loads ) == 0 ) {
 233                         return false;
 234                 }
 235
 236                 # Return a random representative of the remainder
 237                 return ArrayUtils::pickRandom( $loads );
 238         }
 239
 240         /**
 241          * Get the index of the reader connection, which may be a replica DB
 242          * This takes into account load ratios and lag times. It should
 243          * always return a consistent index during a given invocation
 244          *
 245          * Side effect: opens connections to databases
 246          * @param string|bool $group Query group, or false for the generic reader
 247          * @param string|bool $wiki Wiki ID, or false for the current wiki
 248          * @throws MWException
 249          * @return bool|int|string
 250          */
 251         public function getReaderIndex( $group = false, $wiki = false ) {
 252                 global $wgDBtype;
 253
 254                 # @todo FIXME: For now, only go through all this for mysql databases
 255                 if ( $wgDBtype != 'mysql' ) {
 256                         return $this->getWriterIndex();
 257                 }
 258
 259                 if ( count( $this->mServers ) == 1 ) {
 260                         # Skip the load balancing if there's only one server
 261                         return 0;
 262                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 263                         # Shortcut if generic reader exists already
 264                         return $this->mReadIndex;
 265                 }
 266
 267                 # Find the relevant load array
 268                 if ( $group !== false ) {
 269                         if ( isset( $this->mGroupLoads[$group] ) ) {
 270                                 $nonErrorLoads = $this->mGroupLoads[$group];
 271                         } else {
 272                                 # No loads for this group, return false and the caller can use some other group
 273                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 274
 275                                 return false;
 276                         }
 277                 } else {
 278                         $nonErrorLoads = $this->mLoads;
 279                 }
 280
 281                 if ( !count( $nonErrorLoads ) ) {
 282                         throw new MWException( "Empty server array given to LoadBalancer" );
 283                 }
 284
 285                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 286                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 287
 288                 $laggedReplicaMode = false;
 289
 290                 # No server found yet
 291                 $i = false;
 292                 # First try quickly looking through the available servers for a server that
 293                 # meets our criteria
 294                 $currentLoads = $nonErrorLoads;
 295                 while ( count( $currentLoads ) ) {
 296                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 297                                 $i = ArrayUtils::pickRandom( $currentLoads );
 298                         } else {
 299                                 $i = false;
 300                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 301                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 302                                         # This triggers doWait() after connect, so it's especially good to
 303                                         # avoid lagged servers so as to avoid just blocking in that method.
 304                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 305                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 306                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 307                                 }
 308                                 if ( $i === false ) {
 309                                         # Any server with less lag than it's 'max lag' param is preferable
 310                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 311                                 }
 312                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 313                                         # All replica DBs lagged. Switch to read-only mode
 314                                         wfDebugLog( 'replication', "All replica DBs lagged. Switch to read-only mode" );
 315                                         $i = ArrayUtils::pickRandom( $currentLoads );
 316                                         $laggedReplicaMode = true;
 317                                 }
 318                         }
 319
 320                         if ( $i === false ) {
 321                                 # pickRandom() returned false
 322                                 # This is permanent and means the configuration or the load monitor
 323                                 # wants us to return false.
 324                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 325
 326                                 return false;
 327                         }
 328
 329                         $serverName = $this->getServerName( $i );
 330                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 331
 332                         $conn = $this->openConnection( $i, $wiki );
 333                         if ( !$conn ) {
 334                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 335                                 unset( $nonErrorLoads[$i] );
 336                                 unset( $currentLoads[$i] );
 337                                 $i = false;
 338                                 continue;
 339                         }
 340
 341                         // Decrement reference counter, we are finished with this connection.
 342                         // It will be incremented for the caller later.
 343                         if ( $wiki !== false ) {
 344                                 $this->reuseConnection( $conn );
 345                         }
 346
 347                         # Return this server
 348                         break;
 349                 }
 350
 351                 # If all servers were down, quit now
 352                 if ( !count( $nonErrorLoads ) ) {
 353                         wfDebugLog( 'connect', "All servers down" );
 354                 }
 355
 356                 if ( $i !== false ) {
 357                         # Replica DB connection successful.
 358                         # Wait for the session master pos for a short time.
 359                         if ( $this->mWaitForPos && $i > 0 ) {
 360                                 $this->doWait( $i );
 361                         }
 362                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 363                                 $this->mReadIndex = $i;
 364                                 # Record if the generic reader index is in "lagged replica DB" mode
 365                                 if ( $laggedReplicaMode ) {
 366                                         $this->laggedReplicaMode = true;
 367                                 }
 368                         }
 369                         $serverName = $this->getServerName( $i );
 370                         wfDebugLog( 'connect', __METHOD__ .
 371                                 ": using server $serverName for group '$group'\n" );
 372                 }
 373
 374                 return $i;
 375         }
 376
 377         /**
 378          * Set the master wait position
 379          * If a DB_REPLICA connection has been opened already, waits
 380          * Otherwise sets a variable telling it to wait if such a connection is opened
 381          * @param DBMasterPos $pos
 382          */
 383         public function waitFor( $pos ) {
 384                 $this->mWaitForPos = $pos;
 385                 $i = $this->mReadIndex;
 386
 387                 if ( $i > 0 ) {
 388                         if ( !$this->doWait( $i ) ) {
 389                                 $this->laggedReplicaMode = true;
 390                         }
 391                 }
 392         }
 393
 394         /**
 395          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 396          *
 397          * This can be used a faster proxy for waitForAll()
 398          *
 399          * @param DBMasterPos $pos
 400          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 401          * @return bool Success (able to connect and no timeouts reached)
 402          * @since 1.26
 403          */
 404         public function waitForOne( $pos, $timeout = null ) {
 405                 $this->mWaitForPos = $pos;
 406
 407                 $i = $this->mReadIndex;
 408                 if ( $i <= 0 ) {
 409                         // Pick a generic replica DB if there isn't one yet
 410                         $readLoads = $this->mLoads;
 411                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 412                         $readLoads = array_filter( $readLoads ); // with non-zero load
 413                         $i = ArrayUtils::pickRandom( $readLoads );
 414                 }
 415
 416                 if ( $i > 0 ) {
 417                         $ok = $this->doWait( $i, true, $timeout );
 418                 } else {
 419                         $ok = true; // no applicable loads
 420                 }
 421
 422                 return $ok;
 423         }
 424
 425         /**
 426          * Set the master wait position and wait for ALL replica DBs to catch up to it
 427          * @param DBMasterPos $pos
 428          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 429          * @return bool Success (able to connect and no timeouts reached)
 430          */
 431         public function waitForAll( $pos, $timeout = null ) {
 432                 $this->mWaitForPos = $pos;
 433                 $serverCount = count( $this->mServers );
 434
 435                 $ok = true;
 436                 for ( $i = 1; $i < $serverCount; $i++ ) {
 437                         if ( $this->mLoads[$i] > 0 ) {
 438                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 439                         }
 440                 }
 441
 442                 return $ok;
 443         }
 444
 445         /**
 446          * Get any open connection to a given server index, local or foreign
 447          * Returns false if there is no connection open
 448          *
 449          * @param int $i Server index
 450          * @return DatabaseBase|bool False on failure
 451          */
 452         public function getAnyOpenConnection( $i ) {
 453                 foreach ( $this->mConns as $connsByServer ) {
 454                         if ( !empty( $connsByServer[$i] ) ) {
 455                                 return reset( $connsByServer[$i] );
 456                         }
 457                 }
 458
 459                 return false;
 460         }
 461
 462         /**
 463          * Wait for a given replica DB to catch up to the master pos stored in $this
 464          * @param int $index Server index
 465          * @param bool $open Check the server even if a new connection has to be made
 466          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 467          * @return bool
 468          */
 469         protected function doWait( $index, $open = false, $timeout = null ) {
 470                 $close = false; // close the connection afterwards
 471
 472                 // Check if we already know that the DB has reached this point
 473                 $server = $this->getServerName( $index );
 474                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 475                 /** @var DBMasterPos $knownReachedPos */
 476                 $knownReachedPos = $this->srvCache->get( $key );
 477                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 478                         wfDebugLog( 'replication', __METHOD__ .
 479                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos).\n" );
 480                         return true;
 481                 }
 482
 483                 // Find a connection to wait on, creating one if needed and allowed
 484                 $conn = $this->getAnyOpenConnection( $index );
 485                 if ( !$conn ) {
 486                         if ( !$open ) {
 487                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 488
 489                                 return false;
 490                         } else {
 491                                 $conn = $this->openConnection( $index, '' );
 492                                 if ( !$conn ) {
 493                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 494
 495                                         return false;
 496                                 }
 497                                 // Avoid connection spam in waitForAll() when connections
 498                                 // are made just for the sake of doing this lag check.
 499                                 $close = true;
 500                         }
 501                 }
 502
 503                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for replica DB $server to catch up...\n" );
 504                 $timeout = $timeout ?: $this->mWaitTimeout;
 505                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 506
 507                 if ( $result == -1 || is_null( $result ) ) {
 508                         // Timed out waiting for replica DB, use master instead
 509                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 510                         wfDebugLog( 'replication', "$msg\n" );
 511                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 512                         $ok = false;
 513                 } else {
 514                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 515                         $ok = true;
 516                         // Remember that the DB reached this point
 517                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 518                 }
 519
 520                 if ( $close ) {
 521                         $this->closeConnection( $conn );
 522                 }
 523
 524                 return $ok;
 525         }
 526
 527         /**
 528          * Get a connection by index
 529          * This is the main entry point for this class.
 530          *
 531          * @param int $i Server index
 532          * @param array|string|bool $groups Query group(s), or false for the generic reader
 533          * @param string|bool $wiki Wiki ID, or false for the current wiki
 534          *
 535          * @throws MWException
 536          * @return DatabaseBase
 537          */
 538         public function getConnection( $i, $groups = [], $wiki = false ) {
 539                 if ( $i === null || $i === false ) {
 540                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 541                                 ' with invalid server index' );
 542                 }
 543
 544                 if ( $wiki === wfWikiID() ) {
 545                         $wiki = false;
 546                 }
 547
 548                 $groups = ( $groups === false || $groups === [] )
 549                         ? [ false ] // check one "group": the generic pool
 550                         : (array)$groups;
 551
 552                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 553                 $oldConnsOpened = $this->connsOpened; // connections open now
 554
 555                 if ( $i == DB_MASTER ) {
 556                         $i = $this->getWriterIndex();
 557                 } else {
 558                         # Try to find an available server in any the query groups (in order)
 559                         foreach ( $groups as $group ) {
 560                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 561                                 if ( $groupIndex !== false ) {
 562                                         $i = $groupIndex;
 563                                         break;
 564                                 }
 565                         }
 566                 }
 567
 568                 # Operation-based index
 569                 if ( $i == DB_REPLICA ) {
 570                         $this->mLastError = 'Unknown error'; // reset error string
 571                         # Try the general server pool if $groups are unavailable.
 572                         $i = in_array( false, $groups, true )
 573                                 ? false // don't bother with this if that is what was tried above
 574                                 : $this->getReaderIndex( false, $wiki );
 575                         # Couldn't find a working server in getReaderIndex()?
 576                         if ( $i === false ) {
 577                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 578
 579                                 return $this->reportConnectionError();
 580                         }
 581                 }
 582
 583                 # Now we have an explicit index into the servers array
 584                 $conn = $this->openConnection( $i, $wiki );
 585                 if ( !$conn ) {
 586                         return $this->reportConnectionError();
 587                 }
 588
 589                 # Profile any new connections that happen
 590                 if ( $this->connsOpened > $oldConnsOpened ) {
 591                         $host = $conn->getServer();
 592                         $dbname = $conn->getDBname();
 593                         $trxProf = Profiler::instance()->getTransactionProfiler();
 594                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 595                 }
 596
 597                 if ( $masterOnly ) {
 598                         # Make master-requested DB handles inherit any read-only mode setting
 599                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
 600                 }
 601
 602                 return $conn;
 603         }
 604
 605         /**
 606          * Mark a foreign connection as being available for reuse under a different
 607          * DB name or prefix. This mechanism is reference-counted, and must be called
 608          * the same number of times as getConnection() to work.
 609          *
 610          * @param DatabaseBase $conn
 611          * @throws MWException
 612          */
 613         public function reuseConnection( $conn ) {
 614                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 615                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 616                 if ( $serverIndex === null || $refCount === null ) {
 617                         /**
 618                          * This can happen in code like:
 619                          *   foreach ( $dbs as $db ) {
 620                          *     $conn = $lb->getConnection( DB_REPLICA, [], $db );
 621                          *     ...
 622                          *     $lb->reuseConnection( $conn );
 623                          *   }
 624                          * When a connection to the local DB is opened in this way, reuseConnection()
 625                          * should be ignored
 626                          */
 627                         return;
 628                 }
 629
 630                 $dbName = $conn->getDBname();
 631                 $prefix = $conn->tablePrefix();
 632                 if ( strval( $prefix ) !== '' ) {
 633                         $wiki = "$dbName-$prefix";
 634                 } else {
 635                         $wiki = $dbName;
 636                 }
 637                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 638                         throw new MWException( __METHOD__ . ": connection not found, has " .
 639                                 "the connection been freed already?" );
 640                 }
 641                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 642                 if ( $refCount <= 0 ) {
 643                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 644                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 645                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 646                 } else {
 647                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 648                 }
 649         }
 650
 651         /**
 652          * Get a database connection handle reference
 653          *
 654          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 655          *
 656          * @see LoadBalancer::getConnection() for parameter information
 657          *
 658          * @param int $db
 659          * @param array|string|bool $groups Query group(s), or false for the generic reader
 660          * @param string|bool $wiki Wiki ID, or false for the current wiki
 661          * @return DBConnRef
 662          */
 663         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 664                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 665         }
 666
 667         /**
 668          * Get a database connection handle reference without connecting yet
 669          *
 670          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 671          *
 672          * @see LoadBalancer::getConnection() for parameter information
 673          *
 674          * @param int $db
 675          * @param array|string|bool $groups Query group(s), or false for the generic reader
 676          * @param string|bool $wiki Wiki ID, or false for the current wiki
 677          * @return DBConnRef
 678          */
 679         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 680                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 681         }
 682
 683         /**
 684          * Open a connection to the server given by the specified index
 685          * Index must be an actual index into the array.
 686          * If the server is already open, returns it.
 687          *
 688          * On error, returns false, and the connection which caused the
 689          * error will be available via $this->mErrorConnection.
 690          *
 691          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 692          *
 693          * @param int $i Server index
 694          * @param string|bool $wiki Wiki ID, or false for the current wiki
 695          * @return DatabaseBase|bool Returns false on errors
 696          */
 697         public function openConnection( $i, $wiki = false ) {
 698                 if ( $wiki !== false ) {
 699                         $conn = $this->openForeignConnection( $i, $wiki );
 700                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 701                         $conn = $this->mConns['local'][$i][0];
 702                 } else {
 703                         $server = $this->mServers[$i];
 704                         $server['serverIndex'] = $i;
 705                         $conn = $this->reallyOpenConnection( $server, false );
 706                         $serverName = $this->getServerName( $i );
 707                         if ( $conn->isOpen() ) {
 708                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 709                                 $this->mConns['local'][$i][0] = $conn;
 710                         } else {
 711                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 712                                 $this->mErrorConnection = $conn;
 713                                 $conn = false;
 714                         }
 715                 }
 716
 717                 if ( $conn && !$conn->isOpen() ) {
 718                         // Connection was made but later unrecoverably lost for some reason.
 719                         // Do not return a handle that will just throw exceptions on use,
 720                         // but let the calling code (e.g. getReaderIndex) try another server.
 721                         // See DatabaseMyslBase::ping() for how this can happen.
 722                         $this->mErrorConnection = $conn;
 723                         $conn = false;
 724                 }
 725
 726                 return $conn;
 727         }
 728
 729         /**
 730          * Open a connection to a foreign DB, or return one if it is already open.
 731          *
 732          * Increments a reference count on the returned connection which locks the
 733          * connection to the requested wiki. This reference count can be
 734          * decremented by calling reuseConnection().
 735          *
 736          * If a connection is open to the appropriate server already, but with the wrong
 737          * database, it will be switched to the right database and returned, as long as
 738          * it has been freed first with reuseConnection().
 739          *
 740          * On error, returns false, and the connection which caused the
 741          * error will be available via $this->mErrorConnection.
 742          *
 743          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 744          *
 745          * @param int $i Server index
 746          * @param string $wiki Wiki ID to open
 747          * @return DatabaseBase
 748          */
 749         private function openForeignConnection( $i, $wiki ) {
 750                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 751                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 752                         // Reuse an already-used connection
 753                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 754                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 755                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 756                         // Reuse a free connection for the same wiki
 757                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 758                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 759                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 760                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 761                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 762                         // Reuse a connection from another wiki
 763                         $conn = reset( $this->mConns['foreignFree'][$i] );
 764                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 765
 766                         // The empty string as a DB name means "don't care".
 767                         // DatabaseMysqlBase::open() already handle this on connection.
 768                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 769                                 $this->mLastError = "Error selecting database $dbName on server " .
 770                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 771                                 $this->mErrorConnection = $conn;
 772                                 $conn = false;
 773                         } else {
 774                                 $conn->tablePrefix( $prefix );
 775                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 776                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 777                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 778                         }
 779                 } else {
 780                         // Open a new connection
 781                         $server = $this->mServers[$i];
 782                         $server['serverIndex'] = $i;
 783                         $server['foreignPoolRefCount'] = 0;
 784                         $server['foreign'] = true;
 785                         $conn = $this->reallyOpenConnection( $server, $dbName );
 786                         if ( !$conn->isOpen() ) {
 787                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 788                                 $this->mErrorConnection = $conn;
 789                                 $conn = false;
 790                         } else {
 791                                 $conn->tablePrefix( $prefix );
 792                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 793                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 794                         }
 795                 }
 796
 797                 // Increment reference count
 798                 if ( $conn ) {
 799                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 800                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 801                 }
 802
 803                 return $conn;
 804         }
 805
 806         /**
 807          * Test if the specified index represents an open connection
 808          *
 809          * @param int $index Server index
 810          * @access private
 811          * @return bool
 812          */
 813         private function isOpen( $index ) {
 814                 if ( !is_integer( $index ) ) {
 815                         return false;
 816                 }
 817
 818                 return (bool)$this->getAnyOpenConnection( $index );
 819         }
 820
 821         /**
 822          * Really opens a connection. Uncached.
 823          * Returns a Database object whether or not the connection was successful.
 824          * @access private
 825          *
 826          * @param array $server
 827          * @param bool $dbNameOverride
 828          * @throws MWException
 829          * @return DatabaseBase
 830          */
 831         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 832                 if ( $this->disabled ) {
 833                         throw new DBAccessError();
 834                 }
 835
 836                 if ( !is_array( $server ) ) {
 837                         throw new MWException( 'You must update your load-balancing configuration. ' .
 838                                 'See DefaultSettings.php entry for $wgDBservers.' );
 839                 }
 840
 841                 if ( $dbNameOverride !== false ) {
 842                         $server['dbname'] = $dbNameOverride;
 843                 }
 844
 845                 // Let the handle know what the cluster master is (e.g. "db1052")
 846                 $masterName = $this->getServerName( $this->getWriterIndex() );
 847                 $server['clusterMasterHost'] = $masterName;
 848
 849                 // Log when many connection are made on requests
 850                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 851                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 852                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 853                                 wfBacktrace( true ) );
 854                 }
 855
 856                 # Create object
 857                 try {
 858                         $db = DatabaseBase::factory( $server['type'], $server );
 859                 } catch ( DBConnectionError $e ) {
 860                         // FIXME: This is probably the ugliest thing I have ever done to
 861                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 862                         $db = $e->db;
 863                 }
 864
 865                 $db->setLBInfo( $server );
 866                 $db->setLazyMasterHandle(
 867                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 868                 );
 869                 $db->setTransactionProfiler( $this->trxProfiler );
 870
 871                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 872                         if ( $this->trxRoundId !== false ) {
 873                                 $this->applyTransactionRoundFlags( $db );
 874                         }
 875                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 876                                 $db->setTransactionListener( $name, $callback );
 877                         }
 878                 }
 879
 880                 return $db;
 881         }
 882
 883         /**
 884          * @throws DBConnectionError
 885          * @return bool
 886          */
 887         private function reportConnectionError() {
 888                 $conn = $this->mErrorConnection; // The connection which caused the error
 889                 $context = [
 890                         'method' => __METHOD__,
 891                         'last_error' => $this->mLastError,
 892                 ];
 893
 894                 if ( !is_object( $conn ) ) {
 895                         // No last connection, probably due to all servers being too busy
 896                         wfLogDBError(
 897                                 "LB failure with no last connection. Connection error: {last_error}",
 898                                 $context
 899                         );
 900
 901                         // If all servers were busy, mLastError will contain something sensible
 902                         throw new DBConnectionError( null, $this->mLastError );
 903                 } else {
 904                         $context['db_server'] = $conn->getProperty( 'mServer' );
 905                         wfLogDBError(
 906                                 "Connection error: {last_error} ({db_server})",
 907                                 $context
 908                         );
 909
 910                         // throws DBConnectionError
 911                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 912                 }
 913
 914                 return false; /* not reached */
 915         }
 916
 917         /**
 918          * @return int
 919          * @since 1.26
 920          */
 921         public function getWriterIndex() {
 922                 return 0;
 923         }
 924
 925         /**
 926          * Returns true if the specified index is a valid server index
 927          *
 928          * @param string $i
 929          * @return bool
 930          */
 931         public function haveIndex( $i ) {
 932                 return array_key_exists( $i, $this->mServers );
 933         }
 934
 935         /**
 936          * Returns true if the specified index is valid and has non-zero load
 937          *
 938          * @param string $i
 939          * @return bool
 940          */
 941         public function isNonZeroLoad( $i ) {
 942                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 943         }
 944
 945         /**
 946          * Get the number of defined servers (not the number of open connections)
 947          *
 948          * @return int
 949          */
 950         public function getServerCount() {
 951                 return count( $this->mServers );
 952         }
 953
 954         /**
 955          * Get the host name or IP address of the server with the specified index
 956          * Prefer a readable name if available.
 957          * @param string $i
 958          * @return string
 959          */
 960         public function getServerName( $i ) {
 961                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 962                         $name = $this->mServers[$i]['hostName'];
 963                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 964                         $name = $this->mServers[$i]['host'];
 965                 } else {
 966                         $name = '';
 967                 }
 968
 969                 return ( $name != '' ) ? $name : 'localhost';
 970         }
 971
 972         /**
 973          * Return the server info structure for a given index, or false if the index is invalid.
 974          * @param int $i
 975          * @return array|bool
 976          */
 977         public function getServerInfo( $i ) {
 978                 if ( isset( $this->mServers[$i] ) ) {
 979                         return $this->mServers[$i];
 980                 } else {
 981                         return false;
 982                 }
 983         }
 984
 985         /**
 986          * Sets the server info structure for the given index. Entry at index $i
 987          * is created if it doesn't exist
 988          * @param int $i
 989          * @param array $serverInfo
 990          */
 991         public function setServerInfo( $i, array $serverInfo ) {
 992                 $this->mServers[$i] = $serverInfo;
 993         }
 994
 995         /**
 996          * Get the current master position for chronology control purposes
 997          * @return DBMasterPos|bool Returns false if not applicable
 998          */
 999         public function getMasterPos() {
1000                 # If this entire request was served from a replica DB without opening a connection to the
1001                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1002                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1003                 if ( !$masterConn ) {
1004                         $serverCount = count( $this->mServers );
1005                         for ( $i = 1; $i < $serverCount; $i++ ) {
1006                                 $conn = $this->getAnyOpenConnection( $i );
1007                                 if ( $conn ) {
1008                                         return $conn->getSlavePos();
1009                                 }
1010                         }
1011                 } else {
1012                         return $masterConn->getMasterPos();
1013                 }
1014
1015                 return false;
1016         }
1017
1018         /**
1019          * Disable this load balancer. All connections are closed, and any attempt to
1020          * open a new connection will result in a DBAccessError.
1021          *
1022          * @since 1.27
1023          */
1024         public function disable() {
1025                 $this->closeAll();
1026                 $this->disabled = true;
1027         }
1028
1029         /**
1030          * Close all open connections
1031          */
1032         public function closeAll() {
1033                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1034                         $conn->close();
1035                 } );
1036
1037                 $this->mConns = [
1038                         'local' => [],
1039                         'foreignFree' => [],
1040                         'foreignUsed' => [],
1041                 ];
1042                 $this->connsOpened = 0;
1043         }
1044
1045         /**
1046          * Close a connection
1047          *
1048          * Using this function makes sure the LoadBalancer knows the connection is closed.
1049          * If you use $conn->close() directly, the load balancer won't update its state.
1050          *
1051          * @param DatabaseBase $conn
1052          */
1053         public function closeConnection( DatabaseBase $conn ) {
1054                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1055                 foreach ( $this->mConns as $type => $connsByServer ) {
1056                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1057                                 continue;
1058                         }
1059
1060                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1061                                 if ( $conn === $trackedConn ) {
1062                                         unset( $this->mConns[$type][$serverIndex][$i] );
1063                                         --$this->connsOpened;
1064                                         break 2;
1065                                 }
1066                         }
1067                 }
1068
1069                 $conn->close();
1070         }
1071
1072         /**
1073          * Commit transactions on all open connections
1074          * @param string $fname Caller name
1075          * @throws DBExpectedError
1076          */
1077         public function commitAll( $fname = __METHOD__ ) {
1078                 $failures = [];
1079
1080                 $restore = ( $this->trxRoundId !== false );
1081                 $this->trxRoundId = false;
1082                 $this->forEachOpenConnection(
1083                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1084                                 try {
1085                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1086                                 } catch ( DBError $e ) {
1087                                         MWExceptionHandler::logException( $e );
1088                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1089                                 }
1090                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1091                                         $this->undoTransactionRoundFlags( $conn );
1092                                 }
1093                         }
1094                 );
1095
1096                 if ( $failures ) {
1097                         throw new DBExpectedError(
1098                                 null,
1099                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1100                         );
1101                 }
1102         }
1103
1104         /**
1105          * Perform all pre-commit callbacks that remain part of the atomic transactions
1106          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
1107          * @since 1.28
1108          */
1109         public function finalizeMasterChanges() {
1110                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1111                         // Any error should cause all DB transactions to be rolled back together
1112                         $conn->setTrxEndCallbackSuppression( false );
1113                         $conn->runOnTransactionPreCommitCallbacks();
1114                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1115                         $conn->setTrxEndCallbackSuppression( true );
1116                 } );
1117         }
1118
1119         /**
1120          * Perform all pre-commit checks for things like replication safety
1121          * @param array $options Includes:
1122          *   - maxWriteDuration : max write query duration time in seconds
1123          * @throws DBTransactionError
1124          * @since 1.28
1125          */
1126         public function approveMasterChanges( array $options ) {
1127                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1128                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1129                         // If atomic sections or explicit transactions are still open, some caller must have
1130                         // caught an exception but failed to properly rollback any changes. Detect that and
1131                         // throw and error (causing rollback).
1132                         if ( $conn->explicitTrxActive() ) {
1133                                 throw new DBTransactionError(
1134                                         $conn,
1135                                         "Explicit transaction still active. A caller may have caught an error."
1136                                 );
1137                         }
1138                         // Assert that the time to replicate the transaction will be sane.
1139                         // If this fails, then all DB transactions will be rollback back together.
1140                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1141                         if ( $limit > 0 && $time > $limit ) {
1142                                 throw new DBTransactionError(
1143                                         $conn,
1144                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1145                                 );
1146                         }
1147                         // If a connection sits idle while slow queries execute on another, that connection
1148                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1149                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1150                                 throw new DBTransactionError(
1151                                         $conn,
1152                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1153                                 );
1154                         }
1155                 } );
1156         }
1157
1158         /**
1159          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
1160          *
1161          * The DBO_TRX setting will be reverted to the default in each of these methods:
1162          *   - commitMasterChanges()
1163          *   - rollbackMasterChanges()
1164          *   - commitAll()
1165          * This allows for custom transaction rounds from any outer transaction scope.
1166          *
1167          * @param string $fname
1168          * @throws DBExpectedError
1169          * @since 1.28
1170          */
1171         public function beginMasterChanges( $fname = __METHOD__ ) {
1172                 if ( $this->trxRoundId !== false ) {
1173                         throw new DBTransactionError(
1174                                 null,
1175                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1176                         );
1177                 }
1178                 $this->trxRoundId = $fname;
1179
1180                 $failures = [];
1181                 $this->forEachOpenMasterConnection(
1182                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1183                                 $conn->setTrxEndCallbackSuppression( true );
1184                                 try {
1185                                         $conn->flushSnapshot( $fname );
1186                                 } catch ( DBError $e ) {
1187                                         MWExceptionHandler::logException( $e );
1188                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1189                                 }
1190                                 $conn->setTrxEndCallbackSuppression( false );
1191                                 $this->applyTransactionRoundFlags( $conn );
1192                         }
1193                 );
1194
1195                 if ( $failures ) {
1196                         throw new DBExpectedError(
1197                                 null,
1198                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1199                         );
1200                 }
1201         }
1202
1203         /**
1204          * Issue COMMIT on all master connections where writes where done
1205          * @param string $fname Caller name
1206          * @throws DBExpectedError
1207          */
1208         public function commitMasterChanges( $fname = __METHOD__ ) {
1209                 $failures = [];
1210
1211                 $restore = ( $this->trxRoundId !== false );
1212                 $this->trxRoundId = false;
1213                 $this->forEachOpenMasterConnection(
1214                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1215                                 try {
1216                                         if ( $conn->writesOrCallbacksPending() ) {
1217                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1218                                         } elseif ( $restore ) {
1219                                                 $conn->flushSnapshot( $fname );
1220                                         }
1221                                 } catch ( DBError $e ) {
1222                                         MWExceptionHandler::logException( $e );
1223                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1224                                 }
1225                                 if ( $restore ) {
1226                                         $this->undoTransactionRoundFlags( $conn );
1227                                 }
1228                         }
1229                 );
1230
1231                 if ( $failures ) {
1232                         throw new DBExpectedError(
1233                                 null,
1234                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1235                         );
1236                 }
1237         }
1238
1239         /**
1240          * Issue all pending post-COMMIT/ROLLBACK callbacks
1241          * @param integer $type IDatabase::TRIGGER_* constant
1242          * @return Exception|null The first exception or null if there were none
1243          * @since 1.28
1244          */
1245         public function runMasterPostTrxCallbacks( $type ) {
1246                 $e = null; // first exception
1247                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1248                         $conn->setTrxEndCallbackSuppression( false );
1249                         if ( $conn->writesOrCallbacksPending() ) {
1250                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1251                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1252                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1253                                 wfWarn( __METHOD__ . ": did not expect writes/callbacks pending." );
1254                                 return;
1255                         } elseif ( $conn->trxLevel() ) {
1256                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1257                                 // thus leaving an implicit read-only transaction open at this point. It
1258                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1259                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1260                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1261                                 return;
1262                         }
1263                         try {
1264                                 $conn->runOnTransactionIdleCallbacks( $type );
1265                         } catch ( Exception $ex ) {
1266                                 $e = $e ?: $ex;
1267                         }
1268                         try {
1269                                 $conn->runTransactionListenerCallbacks( $type );
1270                         } catch ( Exception $ex ) {
1271                                 $e = $e ?: $ex;
1272                         }
1273                 } );
1274
1275                 return $e;
1276         }
1277
1278         /**
1279          * Issue ROLLBACK only on master, only if queries were done on connection
1280          * @param string $fname Caller name
1281          * @throws DBExpectedError
1282          * @since 1.23
1283          */
1284         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1285                 $restore = ( $this->trxRoundId !== false );
1286                 $this->trxRoundId = false;
1287                 $this->forEachOpenMasterConnection(
1288                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1289                                 if ( $conn->writesOrCallbacksPending() ) {
1290                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1291                                 }
1292                                 if ( $restore ) {
1293                                         $this->undoTransactionRoundFlags( $conn );
1294                                 }
1295                         }
1296                 );
1297         }
1298
1299         /**
1300          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1301          * @return Exception|null The first exception or null if there were none
1302          * @since 1.28
1303          */
1304         public function suppressTransactionEndCallbacks() {
1305                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1306                         $conn->setTrxEndCallbackSuppression( true );
1307                 } );
1308         }
1309
1310         /**
1311          * @param DatabaseBase $conn
1312          */
1313         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1314                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1315                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1316                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1317                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1318                         // If config has explicitly requested DBO_TRX be either on or off by not
1319                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1320                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1321                 }
1322         }
1323
1324         /**
1325          * @param DatabaseBase $conn
1326          */
1327         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1328                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1329                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1330                 }
1331         }
1332
1333         /**
1334          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
1335          *
1336          * @param string $fname Caller name
1337          * @since 1.28
1338          */
1339         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1340                 $this->forEachOpenReplicaConnection( function ( DatabaseBase $conn ) {
1341                         $conn->flushSnapshot( __METHOD__ );
1342                 } );
1343         }
1344
1345         /**
1346          * @return bool Whether a master connection is already open
1347          * @since 1.24
1348          */
1349         public function hasMasterConnection() {
1350                 return $this->isOpen( $this->getWriterIndex() );
1351         }
1352
1353         /**
1354          * Determine if there are pending changes in a transaction by this thread
1355          * @since 1.23
1356          * @return bool
1357          */
1358         public function hasMasterChanges() {
1359                 $pending = 0;
1360                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$pending ) {
1361                         $pending |= $conn->writesOrCallbacksPending();
1362                 } );
1363
1364                 return (bool)$pending;
1365         }
1366
1367         /**
1368          * Get the timestamp of the latest write query done by this thread
1369          * @since 1.25
1370          * @return float|bool UNIX timestamp or false
1371          */
1372         public function lastMasterChangeTimestamp() {
1373                 $lastTime = false;
1374                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$lastTime ) {
1375                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1376                 } );
1377
1378                 return $lastTime;
1379         }
1380
1381         /**
1382          * Check if this load balancer object had any recent or still
1383          * pending writes issued against it by this PHP thread
1384          *
1385          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1386          * @return bool
1387          * @since 1.25
1388          */
1389         public function hasOrMadeRecentMasterChanges( $age = null ) {
1390                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1391
1392                 return ( $this->hasMasterChanges()
1393                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1394         }
1395
1396         /**
1397          * Get the list of callers that have pending master changes
1398          *
1399          * @return string[] List of method names
1400          * @since 1.27
1401          */
1402         public function pendingMasterChangeCallers() {
1403                 $fnames = [];
1404                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$fnames ) {
1405                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1406                 } );
1407
1408                 return $fnames;
1409         }
1410
1411         /**
1412          * @note This method will trigger a DB connection if not yet done
1413          * @param string|bool $wiki Wiki ID, or false for the current wiki
1414          * @return bool Whether the generic connection for reads is highly "lagged"
1415          */
1416         public function getLaggedReplicaMode( $wiki = false ) {
1417                 // No-op if there is only one DB (also avoids recursion)
1418                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1419                         try {
1420                                 // See if laggedReplicaMode gets set
1421                                 $conn = $this->getConnection( DB_REPLICA, false, $wiki );
1422                                 $this->reuseConnection( $conn );
1423                         } catch ( DBConnectionError $e ) {
1424                                 // Avoid expensive re-connect attempts and failures
1425                                 $this->allReplicasDownMode = true;
1426                                 $this->laggedReplicaMode = true;
1427                         }
1428                 }
1429
1430                 return $this->laggedReplicaMode;
1431         }
1432
1433         /**
1434          * @param bool $wiki
1435          * @return bool
1436          * @deprecated 1.28; use getLaggedReplicaMode()
1437          */
1438         public function getLaggedSlaveMode( $wiki = false ) {
1439                 return $this->getLaggedReplicaMode( $wiki );
1440         }
1441
1442         /**
1443          * @note This method will never cause a new DB connection
1444          * @return bool Whether any generic connection used for reads was highly "lagged"
1445          * @since 1.28
1446          */
1447         public function laggedReplicaUsed() {
1448                 return $this->laggedReplicaMode;
1449         }
1450
1451         /**
1452          * @return bool
1453          * @since 1.27
1454          * @deprecated Since 1.28; use laggedReplicaUsed()
1455          */
1456         public function laggedSlaveUsed() {
1457                 return $this->laggedReplicaUsed();
1458         }
1459
1460         /**
1461          * @note This method may trigger a DB connection if not yet done
1462          * @param string|bool $wiki Wiki ID, or false for the current wiki
1463          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1464          * @return string|bool Reason the master is read-only or false if it is not
1465          * @since 1.27
1466          */
1467         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1468                 if ( $this->readOnlyReason !== false ) {
1469                         return $this->readOnlyReason;
1470                 } elseif ( $this->getLaggedReplicaMode( $wiki ) ) {
1471                         if ( $this->allReplicasDownMode ) {
1472                                 return 'The database has been automatically locked ' .
1473                                         'until the replica database servers become available';
1474                         } else {
1475                                 return 'The database has been automatically locked ' .
1476                                         'while the replica database servers catch up to the master.';
1477                         }
1478                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1479                         return 'The database master is running in read-only mode.';
1480                 }
1481
1482                 return false;
1483         }
1484
1485         /**
1486          * @param string $wiki Wiki ID, or false for the current wiki
1487          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1488          * @return bool
1489          */
1490         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1491                 $cache = $this->wanCache;
1492                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1493
1494                 return (bool)$cache->getWithSetCallback(
1495                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1496                         self::TTL_CACHE_READONLY,
1497                         function () use ( $wiki, $conn ) {
1498                                 $this->trxProfiler->setSilenced( true );
1499                                 try {
1500                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1501                                         $readOnly = (int)$dbw->serverIsReadOnly();
1502                                 } catch ( DBError $e ) {
1503                                         $readOnly = 0;
1504                                 }
1505                                 $this->trxProfiler->setSilenced( false );
1506                                 return $readOnly;
1507                         },
1508                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1509                 );
1510         }
1511
1512         /**
1513          * Disables/enables lag checks
1514          * @param null|bool $mode
1515          * @return bool
1516          */
1517         public function allowLagged( $mode = null ) {
1518                 if ( $mode === null ) {
1519                         return $this->mAllowLagged;
1520                 }
1521                 $this->mAllowLagged = $mode;
1522
1523                 return $this->mAllowLagged;
1524         }
1525
1526         /**
1527          * @return bool
1528          */
1529         public function pingAll() {
1530                 $success = true;
1531                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1532                         if ( !$conn->ping() ) {
1533                                 $success = false;
1534                         }
1535                 } );
1536
1537                 return $success;
1538         }
1539
1540         /**
1541          * Call a function with each open connection object
1542          * @param callable $callback
1543          * @param array $params
1544          */
1545         public function forEachOpenConnection( $callback, array $params = [] ) {
1546                 foreach ( $this->mConns as $connsByServer ) {
1547                         foreach ( $connsByServer as $serverConns ) {
1548                                 foreach ( $serverConns as $conn ) {
1549                                         $mergedParams = array_merge( [ $conn ], $params );
1550                                         call_user_func_array( $callback, $mergedParams );
1551                                 }
1552                         }
1553                 }
1554         }
1555
1556         /**
1557          * Call a function with each open connection object to a master
1558          * @param callable $callback
1559          * @param array $params
1560          * @since 1.28
1561          */
1562         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1563                 $masterIndex = $this->getWriterIndex();
1564                 foreach ( $this->mConns as $connsByServer ) {
1565                         if ( isset( $connsByServer[$masterIndex] ) ) {
1566                                 /** @var DatabaseBase $conn */
1567                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1568                                         $mergedParams = array_merge( [ $conn ], $params );
1569                                         call_user_func_array( $callback, $mergedParams );
1570                                 }
1571                         }
1572                 }
1573         }
1574
1575         /**
1576          * Call a function with each open replica DB connection object
1577          * @param callable $callback
1578          * @param array $params
1579          * @since 1.28
1580          */
1581         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1582                 foreach ( $this->mConns as $connsByServer ) {
1583                         foreach ( $connsByServer as $i => $serverConns ) {
1584                                 if ( $i === $this->getWriterIndex() ) {
1585                                         continue; // skip master
1586                                 }
1587                                 foreach ( $serverConns as $conn ) {
1588                                         $mergedParams = array_merge( [ $conn ], $params );
1589                                         call_user_func_array( $callback, $mergedParams );
1590                                 }
1591                         }
1592                 }
1593         }
1594
1595         /**
1596          * Get the hostname and lag time of the most-lagged replica DB
1597          *
1598          * This is useful for maintenance scripts that need to throttle their updates.
1599          * May attempt to open connections to replica DBs on the default DB. If there is
1600          * no lag, the maximum lag will be reported as -1.
1601          *
1602          * @param bool|string $wiki Wiki ID, or false for the default database
1603          * @return array ( host, max lag, index of max lagged host )
1604          */
1605         public function getMaxLag( $wiki = false ) {
1606                 $maxLag = -1;
1607                 $host = '';
1608                 $maxIndex = 0;
1609
1610                 if ( $this->getServerCount() <= 1 ) {
1611                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1612                 }
1613
1614                 $lagTimes = $this->getLagTimes( $wiki );
1615                 foreach ( $lagTimes as $i => $lag ) {
1616                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1617                                 $maxLag = $lag;
1618                                 $host = $this->mServers[$i]['host'];
1619                                 $maxIndex = $i;
1620                         }
1621                 }
1622
1623                 return [ $host, $maxLag, $maxIndex ];
1624         }
1625
1626         /**
1627          * Get an estimate of replication lag (in seconds) for each server
1628          *
1629          * Results are cached for a short time in memcached/process cache
1630          *
1631          * Values may be "false" if replication is too broken to estimate
1632          *
1633          * @param string|bool $wiki
1634          * @return int[] Map of (server index => float|int|bool)
1635          */
1636         public function getLagTimes( $wiki = false ) {
1637                 if ( $this->getServerCount() <= 1 ) {
1638                         return [ 0 => 0 ]; // no replication = no lag
1639                 }
1640
1641                 # Send the request to the load monitor
1642                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1643         }
1644
1645         /**
1646          * Get the lag in seconds for a given connection, or zero if this load
1647          * balancer does not have replication enabled.
1648          *
1649          * This should be used in preference to Database::getLag() in cases where
1650          * replication may not be in use, since there is no way to determine if
1651          * replication is in use at the connection level without running
1652          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1653          * function instead of Database::getLag() avoids a fatal error in this
1654          * case on many installations.
1655          *
1656          * @param IDatabase $conn
1657          * @return int|bool Returns false on error
1658          */
1659         public function safeGetLag( IDatabase $conn ) {
1660                 if ( $this->getServerCount() == 1 ) {
1661                         return 0;
1662                 } else {
1663                         return $conn->getLag();
1664                 }
1665         }
1666
1667         /**
1668          * Wait for a replica DB to reach a specified master position
1669          *
1670          * This will connect to the master to get an accurate position if $pos is not given
1671          *
1672          * @param IDatabase $conn Replica DB
1673          * @param DBMasterPos|bool $pos Master position; default: current position
1674          * @param integer $timeout Timeout in seconds
1675          * @return bool Success
1676          * @since 1.27
1677          */
1678         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1679                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'replica' ) ) {
1680                         return true; // server is not a replica DB
1681                 }
1682
1683                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1684                 if ( !( $pos instanceof DBMasterPos ) ) {
1685                         return false; // something is misconfigured
1686                 }
1687
1688                 $result = $conn->masterPosWait( $pos, $timeout );
1689                 if ( $result == -1 || is_null( $result ) ) {
1690                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1691                         wfDebugLog( 'replication', "$msg\n" );
1692                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1693                         $ok = false;
1694                 } else {
1695                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1696                         $ok = true;
1697                 }
1698
1699                 return $ok;
1700         }
1701
1702         /**
1703          * Clear the cache for slag lag delay times
1704          *
1705          * This is only used for testing
1706          */
1707         public function clearLagTimeCache() {
1708                 $this->getLoadMonitor()->clearCaches();
1709         }
1710
1711         /**
1712          * Set a callback via DatabaseBase::setTransactionListener() on
1713          * all current and future master connections of this load balancer
1714          *
1715          * @param string $name Callback name
1716          * @param callable|null $callback
1717          * @since 1.28
1718          */
1719         public function setTransactionListener( $name, callable $callback = null ) {
1720                 if ( $callback ) {
1721                         $this->trxRecurringCallbacks[$name] = $callback;
1722                 } else {
1723                         unset( $this->trxRecurringCallbacks[$name] );
1724                 }
1725                 $this->forEachOpenMasterConnection(
1726                         function ( DatabaseBase $conn ) use ( $name, $callback ) {
1727                                 $conn->setTransactionListener( $name, $callback );
1728                         }
1729                 );
1730         }
1731 }