includes/db/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23
  24 /**
  25  * Database load balancing object
  26  *
  27  * @todo document
  28  * @ingroup Database
  29  */
  30 class LoadBalancer {
  31         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard slave lag as a factor in slave selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on slave lag to resolve */
  42         private $mWaitTimeout;
  43         /** @var array LBFactory information */
  44         private $mParentInfo;
  45
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50         /** @var BagOStuff */
  51         private $srvCache;
  52         /** @var WANObjectCache */
  53         private $wanCache;
  54
  55         /** @var bool|DatabaseBase Database connection that caused a problem */
  56         private $mErrorConnection;
  57         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  58         private $mReadIndex;
  59         /** @var bool|DBMasterPos False if not set */
  60         private $mWaitForPos;
  61         /** @var bool Whether the generic reader fell back to a lagged slave */
  62         private $laggedSlaveMode = false;
  63         /** @var bool Whether the generic reader fell back to a lagged slave */
  64         private $slavesDownMode = false;
  65         /** @var string The last DB selection or connection error */
  66         private $mLastError = 'Unknown error';
  67         /** @var string|bool Reason the LB is read-only or false if not */
  68         private $readOnlyReason = false;
  69         /** @var integer Total connections opened */
  70         private $connsOpened = 0;
  71
  72         /** @var TransactionProfiler */
  73         protected $trxProfiler;
  74
  75         /** @var integer Warn when this many connection are held */
  76         const CONN_HELD_WARN_THRESHOLD = 10;
  77         /** @var integer Default 'max lag' when unspecified */
  78         const MAX_LAG = 10;
  79         /** @var integer Max time to wait for a slave to catch up (e.g. ChronologyProtector) */
  80         const POS_WAIT_TIMEOUT = 10;
  81         /** @var integer Seconds to cache master server read-only status */
  82         const TTL_CACHE_READONLY = 5;
  83
  84         /**
  85          * @var boolean
  86          */
  87         private $disabled = false;
  88
  89         /**
  90          * @param array $params Array with keys:
  91          *  - servers : Required. Array of server info structures.
  92          *  - loadMonitor : Name of a class used to fetch server lag and load.
  93          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  94          *  - srvCache : BagOStuff object [optional]
  95          *  - wanCache : WANObjectCache object [optional]
  96          * @throws MWException
  97          */
  98         public function __construct( array $params ) {
  99                 if ( !isset( $params['servers'] ) ) {
 100                         throw new MWException( __CLASS__ . ': missing servers parameter' );
 101                 }
 102                 $this->mServers = $params['servers'];
 103                 $this->mWaitTimeout = self::POS_WAIT_TIMEOUT;
 104
 105                 $this->mReadIndex = -1;
 106                 $this->mWriteIndex = -1;
 107                 $this->mConns = [
 108                         'local' => [],
 109                         'foreignUsed' => [],
 110                         'foreignFree' => [] ];
 111                 $this->mLoads = [];
 112                 $this->mWaitForPos = false;
 113                 $this->mErrorConnection = false;
 114                 $this->mAllowLagged = false;
 115
 116                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 117                         $this->readOnlyReason = $params['readOnlyReason'];
 118                 }
 119
 120                 if ( isset( $params['loadMonitor'] ) ) {
 121                         $this->mLoadMonitorClass = $params['loadMonitor'];
 122                 } else {
 123                         $master = reset( $params['servers'] );
 124                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 125                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 126                         } else {
 127                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 128                         }
 129                 }
 130
 131                 foreach ( $params['servers'] as $i => $server ) {
 132                         $this->mLoads[$i] = $server['load'];
 133                         if ( isset( $server['groupLoads'] ) ) {
 134                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 135                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 136                                                 $this->mGroupLoads[$group] = [];
 137                                         }
 138                                         $this->mGroupLoads[$group][$i] = $ratio;
 139                                 }
 140                         }
 141                 }
 142
 143                 if ( isset( $params['srvCache'] ) ) {
 144                         $this->srvCache = $params['srvCache'];
 145                 } else {
 146                         $this->srvCache = new EmptyBagOStuff();
 147                 }
 148                 if ( isset( $params['wanCache'] ) ) {
 149                         $this->wanCache = $params['wanCache'];
 150                 } else {
 151                         $this->wanCache = WANObjectCache::newEmpty();
 152                 }
 153                 if ( isset( $params['trxProfiler'] ) ) {
 154                         $this->trxProfiler = $params['trxProfiler'];
 155                 } else {
 156                         $this->trxProfiler = new TransactionProfiler();
 157                 }
 158         }
 159
 160         /**
 161          * Get a LoadMonitor instance
 162          *
 163          * @return LoadMonitor
 164          */
 165         private function getLoadMonitor() {
 166                 if ( !isset( $this->mLoadMonitor ) ) {
 167                         $class = $this->mLoadMonitorClass;
 168                         $this->mLoadMonitor = new $class( $this );
 169                 }
 170
 171                 return $this->mLoadMonitor;
 172         }
 173
 174         /**
 175          * Get or set arbitrary data used by the parent object, usually an LBFactory
 176          * @param mixed $x
 177          * @return mixed
 178          */
 179         public function parentInfo( $x = null ) {
 180                 return wfSetVar( $this->mParentInfo, $x );
 181         }
 182
 183         /**
 184          * @param array $loads
 185          * @param bool|string $wiki Wiki to get non-lagged for
 186          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 187          * @return bool|int|string
 188          */
 189         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) {
 190                 $lags = $this->getLagTimes( $wiki );
 191
 192                 # Unset excessively lagged servers
 193                 foreach ( $lags as $i => $lag ) {
 194                         if ( $i != 0 ) {
 195                                 $maxServerLag = $maxLag;
 196                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 197                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 198                                 }
 199
 200                                 $host = $this->getServerName( $i );
 201                                 if ( $lag === false ) {
 202                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 203                                         unset( $loads[$i] );
 204                                 } elseif ( $lag > $maxServerLag ) {
 205                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 206                                         unset( $loads[$i] );
 207                                 }
 208                         }
 209                 }
 210
 211                 # Find out if all the slaves with non-zero load are lagged
 212                 $sum = 0;
 213                 foreach ( $loads as $load ) {
 214                         $sum += $load;
 215                 }
 216                 if ( $sum == 0 ) {
 217                         # No appropriate DB servers except maybe the master and some slaves with zero load
 218                         # Do NOT use the master
 219                         # Instead, this function will return false, triggering read-only mode,
 220                         # and a lagged slave will be used instead.
 221                         return false;
 222                 }
 223
 224                 if ( count( $loads ) == 0 ) {
 225                         return false;
 226                 }
 227
 228                 # Return a random representative of the remainder
 229                 return ArrayUtils::pickRandom( $loads );
 230         }
 231
 232         /**
 233          * Get the index of the reader connection, which may be a slave
 234          * This takes into account load ratios and lag times. It should
 235          * always return a consistent index during a given invocation
 236          *
 237          * Side effect: opens connections to databases
 238          * @param string|bool $group Query group, or false for the generic reader
 239          * @param string|bool $wiki Wiki ID, or false for the current wiki
 240          * @throws MWException
 241          * @return bool|int|string
 242          */
 243         public function getReaderIndex( $group = false, $wiki = false ) {
 244                 global $wgDBtype;
 245
 246                 # @todo FIXME: For now, only go through all this for mysql databases
 247                 if ( $wgDBtype != 'mysql' ) {
 248                         return $this->getWriterIndex();
 249                 }
 250
 251                 if ( count( $this->mServers ) == 1 ) {
 252                         # Skip the load balancing if there's only one server
 253                         return 0;
 254                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 255                         # Shortcut if generic reader exists already
 256                         return $this->mReadIndex;
 257                 }
 258
 259                 # Find the relevant load array
 260                 if ( $group !== false ) {
 261                         if ( isset( $this->mGroupLoads[$group] ) ) {
 262                                 $nonErrorLoads = $this->mGroupLoads[$group];
 263                         } else {
 264                                 # No loads for this group, return false and the caller can use some other group
 265                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 266
 267                                 return false;
 268                         }
 269                 } else {
 270                         $nonErrorLoads = $this->mLoads;
 271                 }
 272
 273                 if ( !count( $nonErrorLoads ) ) {
 274                         throw new MWException( "Empty server array given to LoadBalancer" );
 275                 }
 276
 277                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 278                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 279
 280                 $laggedSlaveMode = false;
 281
 282                 # No server found yet
 283                 $i = false;
 284                 $conn = false;
 285                 # First try quickly looking through the available servers for a server that
 286                 # meets our criteria
 287                 $currentLoads = $nonErrorLoads;
 288                 while ( count( $currentLoads ) ) {
 289                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 290                                 $i = ArrayUtils::pickRandom( $currentLoads );
 291                         } else {
 292                                 $i = false;
 293                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 294                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 295                                         # This triggers doWait() after connect, so it's especially good to
 296                                         # avoid lagged servers so as to avoid just blocking in that method.
 297                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 298                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 299                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 300                                 }
 301                                 if ( $i === false ) {
 302                                         # Any server with less lag than it's 'max lag' param is preferable
 303                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 304                                 }
 305                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 306                                         # All slaves lagged. Switch to read-only mode
 307                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 308                                         $i = ArrayUtils::pickRandom( $currentLoads );
 309                                         $laggedSlaveMode = true;
 310                                 }
 311                         }
 312
 313                         if ( $i === false ) {
 314                                 # pickRandom() returned false
 315                                 # This is permanent and means the configuration or the load monitor
 316                                 # wants us to return false.
 317                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 318
 319                                 return false;
 320                         }
 321
 322                         $serverName = $this->getServerName( $i );
 323                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 324
 325                         $conn = $this->openConnection( $i, $wiki );
 326                         if ( !$conn ) {
 327                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 328                                 unset( $nonErrorLoads[$i] );
 329                                 unset( $currentLoads[$i] );
 330                                 $i = false;
 331                                 continue;
 332                         }
 333
 334                         // Decrement reference counter, we are finished with this connection.
 335                         // It will be incremented for the caller later.
 336                         if ( $wiki !== false ) {
 337                                 $this->reuseConnection( $conn );
 338                         }
 339
 340                         # Return this server
 341                         break;
 342                 }
 343
 344                 # If all servers were down, quit now
 345                 if ( !count( $nonErrorLoads ) ) {
 346                         wfDebugLog( 'connect', "All servers down" );
 347                 }
 348
 349                 if ( $i !== false ) {
 350                         # Slave connection successful
 351                         # Wait for the session master pos for a short time
 352                         if ( $this->mWaitForPos && $i > 0 ) {
 353                                 if ( !$this->doWait( $i ) ) {
 354                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 355                                 }
 356                         }
 357                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 358                                 $this->mReadIndex = $i;
 359                                 # Record if the generic reader index is in "lagged slave" mode
 360                                 if ( $laggedSlaveMode ) {
 361                                         $this->laggedSlaveMode = true;
 362                                 }
 363                         }
 364                         $serverName = $this->getServerName( $i );
 365                         wfDebugLog( 'connect', __METHOD__ .
 366                                 ": using server $serverName for group '$group'\n" );
 367                 }
 368
 369                 return $i;
 370         }
 371
 372         /**
 373          * Set the master wait position
 374          * If a DB_SLAVE connection has been opened already, waits
 375          * Otherwise sets a variable telling it to wait if such a connection is opened
 376          * @param DBMasterPos $pos
 377          */
 378         public function waitFor( $pos ) {
 379                 $this->mWaitForPos = $pos;
 380                 $i = $this->mReadIndex;
 381
 382                 if ( $i > 0 ) {
 383                         if ( !$this->doWait( $i ) ) {
 384                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 385                                 $this->laggedSlaveMode = true;
 386                         }
 387                 }
 388         }
 389
 390         /**
 391          * Set the master wait position and wait for a "generic" slave to catch up to it
 392          *
 393          * This can be used a faster proxy for waitForAll()
 394          *
 395          * @param DBMasterPos $pos
 396          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 397          * @return bool Success (able to connect and no timeouts reached)
 398          * @since 1.26
 399          */
 400         public function waitForOne( $pos, $timeout = null ) {
 401                 $this->mWaitForPos = $pos;
 402
 403                 $i = $this->mReadIndex;
 404                 if ( $i <= 0 ) {
 405                         // Pick a generic slave if there isn't one yet
 406                         $readLoads = $this->mLoads;
 407                         unset( $readLoads[$this->getWriterIndex()] ); // slaves only
 408                         $readLoads = array_filter( $readLoads ); // with non-zero load
 409                         $i = ArrayUtils::pickRandom( $readLoads );
 410                 }
 411
 412                 if ( $i > 0 ) {
 413                         $ok = $this->doWait( $i, true, $timeout );
 414                 } else {
 415                         $ok = true; // no applicable loads
 416                 }
 417
 418                 return $ok;
 419         }
 420
 421         /**
 422          * Set the master wait position and wait for ALL slaves to catch up to it
 423          * @param DBMasterPos $pos
 424          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 425          * @return bool Success (able to connect and no timeouts reached)
 426          */
 427         public function waitForAll( $pos, $timeout = null ) {
 428                 $this->mWaitForPos = $pos;
 429                 $serverCount = count( $this->mServers );
 430
 431                 $ok = true;
 432                 for ( $i = 1; $i < $serverCount; $i++ ) {
 433                         if ( $this->mLoads[$i] > 0 ) {
 434                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 435                         }
 436                 }
 437
 438                 return $ok;
 439         }
 440
 441         /**
 442          * Get any open connection to a given server index, local or foreign
 443          * Returns false if there is no connection open
 444          *
 445          * @param int $i
 446          * @return DatabaseBase|bool False on failure
 447          */
 448         public function getAnyOpenConnection( $i ) {
 449                 foreach ( $this->mConns as $conns ) {
 450                         if ( !empty( $conns[$i] ) ) {
 451                                 return reset( $conns[$i] );
 452                         }
 453                 }
 454
 455                 return false;
 456         }
 457
 458         /**
 459          * Wait for a given slave to catch up to the master pos stored in $this
 460          * @param int $index Server index
 461          * @param bool $open Check the server even if a new connection has to be made
 462          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 463          * @return bool
 464          */
 465         protected function doWait( $index, $open = false, $timeout = null ) {
 466                 $close = false; // close the connection afterwards
 467
 468                 // Check if we already know that the DB has reached this point
 469                 $server = $this->getServerName( $index );
 470                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 471                 /** @var DBMasterPos $knownReachedPos */
 472                 $knownReachedPos = $this->srvCache->get( $key );
 473                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 474                         wfDebugLog( 'replication', __METHOD__ .
 475                                 ": slave $server known to be caught up (pos >= $knownReachedPos).\n" );
 476                         return true;
 477                 }
 478
 479                 // Find a connection to wait on, creating one if needed and allowed
 480                 $conn = $this->getAnyOpenConnection( $index );
 481                 if ( !$conn ) {
 482                         if ( !$open ) {
 483                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 484
 485                                 return false;
 486                         } else {
 487                                 $conn = $this->openConnection( $index, '' );
 488                                 if ( !$conn ) {
 489                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 490
 491                                         return false;
 492                                 }
 493                                 // Avoid connection spam in waitForAll() when connections
 494                                 // are made just for the sake of doing this lag check.
 495                                 $close = true;
 496                         }
 497                 }
 498
 499                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for slave $server to catch up...\n" );
 500                 $timeout = $timeout ?: $this->mWaitTimeout;
 501                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 502
 503                 if ( $result == -1 || is_null( $result ) ) {
 504                         // Timed out waiting for slave, use master instead
 505                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 506                         wfDebugLog( 'replication', "$msg\n" );
 507                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 508                         $ok = false;
 509                 } else {
 510                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 511                         $ok = true;
 512                         // Remember that the DB reached this point
 513                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 514                 }
 515
 516                 if ( $close ) {
 517                         $this->closeConnection( $conn );
 518                 }
 519
 520                 return $ok;
 521         }
 522
 523         /**
 524          * Get a connection by index
 525          * This is the main entry point for this class.
 526          *
 527          * @param int $i Server index
 528          * @param array|string|bool $groups Query group(s), or false for the generic reader
 529          * @param string|bool $wiki Wiki ID, or false for the current wiki
 530          *
 531          * @throws MWException
 532          * @return DatabaseBase
 533          */
 534         public function getConnection( $i, $groups = [], $wiki = false ) {
 535                 if ( $i === null || $i === false ) {
 536                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 537                                 ' with invalid server index' );
 538                 }
 539
 540                 if ( $wiki === wfWikiID() ) {
 541                         $wiki = false;
 542                 }
 543
 544                 $groups = ( $groups === false || $groups === [] )
 545                         ? [ false ] // check one "group": the generic pool
 546                         : (array)$groups;
 547
 548                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 549                 $oldConnsOpened = $this->connsOpened; // connections open now
 550
 551                 if ( $i == DB_MASTER ) {
 552                         $i = $this->getWriterIndex();
 553                 } else {
 554                         # Try to find an available server in any the query groups (in order)
 555                         foreach ( $groups as $group ) {
 556                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 557                                 if ( $groupIndex !== false ) {
 558                                         $i = $groupIndex;
 559                                         break;
 560                                 }
 561                         }
 562                 }
 563
 564                 # Operation-based index
 565                 if ( $i == DB_SLAVE ) {
 566                         $this->mLastError = 'Unknown error'; // reset error string
 567                         # Try the general server pool if $groups are unavailable.
 568                         $i = in_array( false, $groups, true )
 569                                 ? false // don't bother with this if that is what was tried above
 570                                 : $this->getReaderIndex( false, $wiki );
 571                         # Couldn't find a working server in getReaderIndex()?
 572                         if ( $i === false ) {
 573                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 574
 575                                 return $this->reportConnectionError();
 576                         }
 577                 }
 578
 579                 # Now we have an explicit index into the servers array
 580                 $conn = $this->openConnection( $i, $wiki );
 581                 if ( !$conn ) {
 582                         return $this->reportConnectionError();
 583                 }
 584
 585                 # Profile any new connections that happen
 586                 if ( $this->connsOpened > $oldConnsOpened ) {
 587                         $host = $conn->getServer();
 588                         $dbname = $conn->getDBname();
 589                         $trxProf = Profiler::instance()->getTransactionProfiler();
 590                         $trxProf->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                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 614                         /**
 615                          * This can happen in code like:
 616                          *   foreach ( $dbs as $db ) {
 617                          *     $conn = $lb->getConnection( DB_SLAVE, [], $db );
 618                          *     ...
 619                          *     $lb->reuseConnection( $conn );
 620                          *   }
 621                          * When a connection to the local DB is opened in this way, reuseConnection()
 622                          * should be ignored
 623                          */
 624                         return;
 625                 }
 626
 627                 $dbName = $conn->getDBname();
 628                 $prefix = $conn->tablePrefix();
 629                 if ( strval( $prefix ) !== '' ) {
 630                         $wiki = "$dbName-$prefix";
 631                 } else {
 632                         $wiki = $dbName;
 633                 }
 634                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 635                         throw new MWException( __METHOD__ . ": connection not found, has " .
 636                                 "the connection been freed already?" );
 637                 }
 638                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 639                 if ( $refCount <= 0 ) {
 640                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 641                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 642                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 643                 } else {
 644                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 645                 }
 646         }
 647
 648         /**
 649          * Get a database connection handle reference
 650          *
 651          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 652          *
 653          * @see LoadBalancer::getConnection() for parameter information
 654          *
 655          * @param int $db
 656          * @param array|string|bool $groups Query group(s), or false for the generic reader
 657          * @param string|bool $wiki Wiki ID, or false for the current wiki
 658          * @return DBConnRef
 659          */
 660         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 661                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 662         }
 663
 664         /**
 665          * Get a database connection handle reference without connecting yet
 666          *
 667          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 668          *
 669          * @see LoadBalancer::getConnection() for parameter information
 670          *
 671          * @param int $db
 672          * @param array|string|bool $groups Query group(s), or false for the generic reader
 673          * @param string|bool $wiki Wiki ID, or false for the current wiki
 674          * @return DBConnRef
 675          */
 676         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 677                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 678         }
 679
 680         /**
 681          * Open a connection to the server given by the specified index
 682          * Index must be an actual index into the array.
 683          * If the server is already open, returns it.
 684          *
 685          * On error, returns false, and the connection which caused the
 686          * error will be available via $this->mErrorConnection.
 687          *
 688          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 689          *
 690          * @param int $i Server index
 691          * @param string|bool $wiki Wiki ID, or false for the current wiki
 692          * @return DatabaseBase|bool Returns false on errors
 693          */
 694         public function openConnection( $i, $wiki = false ) {
 695                 if ( $wiki !== false ) {
 696                         $conn = $this->openForeignConnection( $i, $wiki );
 697                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 698                         $conn = $this->mConns['local'][$i][0];
 699                 } else {
 700                         $server = $this->mServers[$i];
 701                         $server['serverIndex'] = $i;
 702                         $conn = $this->reallyOpenConnection( $server, false );
 703                         $serverName = $this->getServerName( $i );
 704                         if ( $conn->isOpen() ) {
 705                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 706                                 $this->mConns['local'][$i][0] = $conn;
 707                         } else {
 708                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 709                                 $this->mErrorConnection = $conn;
 710                                 $conn = false;
 711                         }
 712                 }
 713
 714                 if ( $conn && !$conn->isOpen() ) {
 715                         // Connection was made but later unrecoverably lost for some reason.
 716                         // Do not return a handle that will just throw exceptions on use,
 717                         // but let the calling code (e.g. getReaderIndex) try another server.
 718                         // See DatabaseMyslBase::ping() for how this can happen.
 719                         $this->mErrorConnection = $conn;
 720                         $conn = false;
 721                 }
 722
 723                 return $conn;
 724         }
 725
 726         /**
 727          * Open a connection to a foreign DB, or return one if it is already open.
 728          *
 729          * Increments a reference count on the returned connection which locks the
 730          * connection to the requested wiki. This reference count can be
 731          * decremented by calling reuseConnection().
 732          *
 733          * If a connection is open to the appropriate server already, but with the wrong
 734          * database, it will be switched to the right database and returned, as long as
 735          * it has been freed first with reuseConnection().
 736          *
 737          * On error, returns false, and the connection which caused the
 738          * error will be available via $this->mErrorConnection.
 739          *
 740          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 741          *
 742          * @param int $i Server index
 743          * @param string $wiki Wiki ID to open
 744          * @return DatabaseBase
 745          */
 746         private function openForeignConnection( $i, $wiki ) {
 747                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 748                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 749                         // Reuse an already-used connection
 750                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 751                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 752                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 753                         // Reuse a free connection for the same wiki
 754                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 755                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 756                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 757                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 758                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 759                         // Reuse a connection from another wiki
 760                         $conn = reset( $this->mConns['foreignFree'][$i] );
 761                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 762
 763                         // The empty string as a DB name means "don't care".
 764                         // DatabaseMysqlBase::open() already handle this on connection.
 765                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 766                                 $this->mLastError = "Error selecting database $dbName on server " .
 767                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 768                                 $this->mErrorConnection = $conn;
 769                                 $conn = false;
 770                         } else {
 771                                 $conn->tablePrefix( $prefix );
 772                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 773                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 774                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 775                         }
 776                 } else {
 777                         // Open a new connection
 778                         $server = $this->mServers[$i];
 779                         $server['serverIndex'] = $i;
 780                         $server['foreignPoolRefCount'] = 0;
 781                         $server['foreign'] = true;
 782                         $conn = $this->reallyOpenConnection( $server, $dbName );
 783                         if ( !$conn->isOpen() ) {
 784                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 785                                 $this->mErrorConnection = $conn;
 786                                 $conn = false;
 787                         } else {
 788                                 $conn->tablePrefix( $prefix );
 789                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 790                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 791                         }
 792                 }
 793
 794                 // Increment reference count
 795                 if ( $conn ) {
 796                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 797                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 798                 }
 799
 800                 return $conn;
 801         }
 802
 803         /**
 804          * Test if the specified index represents an open connection
 805          *
 806          * @param int $index Server index
 807          * @access private
 808          * @return bool
 809          */
 810         private function isOpen( $index ) {
 811                 if ( !is_integer( $index ) ) {
 812                         return false;
 813                 }
 814
 815                 return (bool)$this->getAnyOpenConnection( $index );
 816         }
 817
 818         /**
 819          * Really opens a connection. Uncached.
 820          * Returns a Database object whether or not the connection was successful.
 821          * @access private
 822          *
 823          * @param array $server
 824          * @param bool $dbNameOverride
 825          * @throws MWException
 826          * @return DatabaseBase
 827          */
 828         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 829                 if ( $this->disabled ) {
 830                         throw new DBAccessError();
 831                 }
 832
 833                 if ( !is_array( $server ) ) {
 834                         throw new MWException( 'You must update your load-balancing configuration. ' .
 835                                 'See DefaultSettings.php entry for $wgDBservers.' );
 836                 }
 837
 838                 if ( $dbNameOverride !== false ) {
 839                         $server['dbname'] = $dbNameOverride;
 840                 }
 841
 842                 // Let the handle know what the cluster master is (e.g. "db1052")
 843                 $masterName = $this->getServerName( 0 );
 844                 $server['clusterMasterHost'] = $masterName;
 845
 846                 // Log when many connection are made on requests
 847                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 848                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 849                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 850                                 wfBacktrace( true ) );
 851                 }
 852
 853                 # Create object
 854                 try {
 855                         $db = DatabaseBase::factory( $server['type'], $server );
 856                 } catch ( DBConnectionError $e ) {
 857                         // FIXME: This is probably the ugliest thing I have ever done to
 858                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 859                         $db = $e->db;
 860                 }
 861
 862                 $db->setLBInfo( $server );
 863                 $db->setLazyMasterHandle(
 864                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 865                 );
 866                 $db->setTransactionProfiler( $this->trxProfiler );
 867
 868                 return $db;
 869         }
 870
 871         /**
 872          * @throws DBConnectionError
 873          * @return bool
 874          */
 875         private function reportConnectionError() {
 876                 $conn = $this->mErrorConnection; // The connection which caused the error
 877                 $context = [
 878                         'method' => __METHOD__,
 879                         'last_error' => $this->mLastError,
 880                 ];
 881
 882                 if ( !is_object( $conn ) ) {
 883                         // No last connection, probably due to all servers being too busy
 884                         wfLogDBError(
 885                                 "LB failure with no last connection. Connection error: {last_error}",
 886                                 $context
 887                         );
 888
 889                         // If all servers were busy, mLastError will contain something sensible
 890                         throw new DBConnectionError( null, $this->mLastError );
 891                 } else {
 892                         $context['db_server'] = $conn->getProperty( 'mServer' );
 893                         wfLogDBError(
 894                                 "Connection error: {last_error} ({db_server})",
 895                                 $context
 896                         );
 897
 898                         // throws DBConnectionError
 899                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 900                 }
 901
 902                 return false; /* not reached */
 903         }
 904
 905         /**
 906          * @return int
 907          * @since 1.26
 908          */
 909         public function getWriterIndex() {
 910                 return 0;
 911         }
 912
 913         /**
 914          * Returns true if the specified index is a valid server index
 915          *
 916          * @param string $i
 917          * @return bool
 918          */
 919         public function haveIndex( $i ) {
 920                 return array_key_exists( $i, $this->mServers );
 921         }
 922
 923         /**
 924          * Returns true if the specified index is valid and has non-zero load
 925          *
 926          * @param string $i
 927          * @return bool
 928          */
 929         public function isNonZeroLoad( $i ) {
 930                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 931         }
 932
 933         /**
 934          * Get the number of defined servers (not the number of open connections)
 935          *
 936          * @return int
 937          */
 938         public function getServerCount() {
 939                 return count( $this->mServers );
 940         }
 941
 942         /**
 943          * Get the host name or IP address of the server with the specified index
 944          * Prefer a readable name if available.
 945          * @param string $i
 946          * @return string
 947          */
 948         public function getServerName( $i ) {
 949                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 950                         $name = $this->mServers[$i]['hostName'];
 951                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 952                         $name = $this->mServers[$i]['host'];
 953                 } else {
 954                         $name = '';
 955                 }
 956
 957                 return ( $name != '' ) ? $name : 'localhost';
 958         }
 959
 960         /**
 961          * Return the server info structure for a given index, or false if the index is invalid.
 962          * @param int $i
 963          * @return array|bool
 964          */
 965         public function getServerInfo( $i ) {
 966                 if ( isset( $this->mServers[$i] ) ) {
 967                         return $this->mServers[$i];
 968                 } else {
 969                         return false;
 970                 }
 971         }
 972
 973         /**
 974          * Sets the server info structure for the given index. Entry at index $i
 975          * is created if it doesn't exist
 976          * @param int $i
 977          * @param array $serverInfo
 978          */
 979         public function setServerInfo( $i, array $serverInfo ) {
 980                 $this->mServers[$i] = $serverInfo;
 981         }
 982
 983         /**
 984          * Get the current master position for chronology control purposes
 985          * @return mixed
 986          */
 987         public function getMasterPos() {
 988                 # If this entire request was served from a slave without opening a connection to the
 989                 # master (however unlikely that may be), then we can fetch the position from the slave.
 990                 $masterConn = $this->getAnyOpenConnection( 0 );
 991                 if ( !$masterConn ) {
 992                         $serverCount = count( $this->mServers );
 993                         for ( $i = 1; $i < $serverCount; $i++ ) {
 994                                 $conn = $this->getAnyOpenConnection( $i );
 995                                 if ( $conn ) {
 996                                         return $conn->getSlavePos();
 997                                 }
 998                         }
 999                 } else {
1000                         return $masterConn->getMasterPos();
1001                 }
1002
1003                 return false;
1004         }
1005
1006         /**
1007          * Disable this load balancer. All connections are closed, and any attempt to
1008          * open a new connection will result in a DBAccessError.
1009          *
1010          * @since 1.27
1011          */
1012         public function disable() {
1013                 $this->closeAll();
1014                 $this->disabled = true;
1015         }
1016
1017         /**
1018          * Close all open connections
1019          */
1020         public function closeAll() {
1021                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1022                         $conn->close();
1023                 } );
1024
1025                 $this->mConns = [
1026                         'local' => [],
1027                         'foreignFree' => [],
1028                         'foreignUsed' => [],
1029                 ];
1030                 $this->connsOpened = 0;
1031         }
1032
1033         /**
1034          * Close a connection
1035          * Using this function makes sure the LoadBalancer knows the connection is closed.
1036          * If you use $conn->close() directly, the load balancer won't update its state.
1037          * @param DatabaseBase $conn
1038          */
1039         public function closeConnection( $conn ) {
1040                 $done = false;
1041                 foreach ( $this->mConns as $i1 => $conns2 ) {
1042                         foreach ( $conns2 as $i2 => $conns3 ) {
1043                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1044                                         if ( $conn === $candidateConn ) {
1045                                                 $conn->close();
1046                                                 unset( $this->mConns[$i1][$i2][$i3] );
1047                                                 --$this->connsOpened;
1048                                                 $done = true;
1049                                                 break;
1050                                         }
1051                                 }
1052                         }
1053                 }
1054                 if ( !$done ) {
1055                         $conn->close();
1056                 }
1057         }
1058
1059         /**
1060          * Commit transactions on all open connections
1061          * @param string $fname Caller name
1062          */
1063         public function commitAll( $fname = __METHOD__ ) {
1064                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( $fname ) {
1065                         $conn->commit( $fname, IDatabase::FLUSHING_ALL_PEERS );
1066                 } );
1067         }
1068
1069         /**
1070          * Perform all pre-commit callbacks that remain part of the atomic transactions
1071          * and disable any post-commit callbacks until runMasterPostCommitCallbacks()
1072          * @since 1.28
1073          */
1074         public function runMasterPreCommitCallbacks() {
1075                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1076                         // Any error will cause all DB transactions to be rolled back together.
1077                         $conn->runOnTransactionPreCommitCallbacks();
1078                         // Defer post-commit callbacks until COMMIT finishes for all DBs.
1079                         $conn->setPostCommitCallbackSupression( true );
1080                 } );
1081         }
1082
1083         /**
1084          * Perform all pre-commit checks for things like replication safety
1085          * @param array $options Includes:
1086          *   - maxWriteDuration : max write query duration time in seconds
1087          * @throws DBTransactionError
1088          * @since 1.28
1089          */
1090         public function approveMasterChanges( array $options ) {
1091                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1092                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1093                         // Assert that the time to replicate the transaction will be sane.
1094                         // If this fails, then all DB transactions will be rollback back together.
1095                         $time = $conn->pendingWriteQueryDuration();
1096                         if ( $limit > 0 && $time > $limit ) {
1097                                 throw new DBTransactionError(
1098                                         $conn,
1099                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1100                                 );
1101                         }
1102                 } );
1103         }
1104
1105         /**
1106          * Issue COMMIT on all master connections where writes where done
1107          * @param string $fname Caller name
1108          */
1109         public function commitMasterChanges( $fname = __METHOD__ ) {
1110                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $fname ) {
1111                         if ( $conn->writesOrCallbacksPending() ) {
1112                                 $conn->commit( $fname, IDatabase::FLUSHING_ALL_PEERS );
1113                         }
1114                 } );
1115         }
1116
1117         /**
1118          * Issue all pending post-commit callbacks
1119          * @since 1.28
1120          */
1121         public function runMasterPostCommitCallbacks() {
1122                 $this->forEachOpenMasterConnection( function ( DatabaseBase $db ) {
1123                         $db->setPostCommitCallbackSupression( false );
1124                         $db->runOnTransactionIdleCallbacks( IDatabase::TRIGGER_COMMIT );
1125                 } );
1126         }
1127
1128         /**
1129          * Issue ROLLBACK only on master, only if queries were done on connection
1130          * @param string $fname Caller name
1131          * @throws DBExpectedError
1132          * @since 1.23
1133          */
1134         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1135                 $failedServers = [];
1136
1137                 $masterIndex = $this->getWriterIndex();
1138                 foreach ( $this->mConns as $conns2 ) {
1139                         if ( empty( $conns2[$masterIndex] ) ) {
1140                                 continue;
1141                         }
1142                         /** @var DatabaseBase $conn */
1143                         foreach ( $conns2[$masterIndex] as $conn ) {
1144                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1145                                         try {
1146                                                 $conn->rollback( $fname, IDatabase::FLUSHING_ALL_PEERS );
1147                                         } catch ( DBError $e ) {
1148                                                 MWExceptionHandler::logException( $e );
1149                                                 $failedServers[] = $conn->getServer();
1150                                         }
1151                                 }
1152                         }
1153                 }
1154
1155                 if ( $failedServers ) {
1156                         throw new DBExpectedError( null, "Rollback failed on server(s) " .
1157                                 implode( ', ', array_unique( $failedServers ) ) );
1158                 }
1159         }
1160
1161         /**
1162          * @return bool Whether a master connection is already open
1163          * @since 1.24
1164          */
1165         public function hasMasterConnection() {
1166                 return $this->isOpen( $this->getWriterIndex() );
1167         }
1168
1169         /**
1170          * Determine if there are pending changes in a transaction by this thread
1171          * @since 1.23
1172          * @return bool
1173          */
1174         public function hasMasterChanges() {
1175                 $masterIndex = $this->getWriterIndex();
1176                 foreach ( $this->mConns as $conns2 ) {
1177                         if ( empty( $conns2[$masterIndex] ) ) {
1178                                 continue;
1179                         }
1180                         /** @var DatabaseBase $conn */
1181                         foreach ( $conns2[$masterIndex] as $conn ) {
1182                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1183                                         return true;
1184                                 }
1185                         }
1186                 }
1187                 return false;
1188         }
1189
1190         /**
1191          * Get the timestamp of the latest write query done by this thread
1192          * @since 1.25
1193          * @return float|bool UNIX timestamp or false
1194          */
1195         public function lastMasterChangeTimestamp() {
1196                 $lastTime = false;
1197                 $masterIndex = $this->getWriterIndex();
1198                 foreach ( $this->mConns as $conns2 ) {
1199                         if ( empty( $conns2[$masterIndex] ) ) {
1200                                 continue;
1201                         }
1202                         /** @var DatabaseBase $conn */
1203                         foreach ( $conns2[$masterIndex] as $conn ) {
1204                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1205                         }
1206                 }
1207                 return $lastTime;
1208         }
1209
1210         /**
1211          * Check if this load balancer object had any recent or still
1212          * pending writes issued against it by this PHP thread
1213          *
1214          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1215          * @return bool
1216          * @since 1.25
1217          */
1218         public function hasOrMadeRecentMasterChanges( $age = null ) {
1219                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1220
1221                 return ( $this->hasMasterChanges()
1222                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1223         }
1224
1225         /**
1226          * Get the list of callers that have pending master changes
1227          *
1228          * @return array
1229          * @since 1.27
1230          */
1231         public function pendingMasterChangeCallers() {
1232                 $fnames = [];
1233
1234                 $masterIndex = $this->getWriterIndex();
1235                 foreach ( $this->mConns as $conns2 ) {
1236                         if ( empty( $conns2[$masterIndex] ) ) {
1237                                 continue;
1238                         }
1239                         /** @var DatabaseBase $conn */
1240                         foreach ( $conns2[$masterIndex] as $conn ) {
1241                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1242                         }
1243                 }
1244
1245                 return $fnames;
1246         }
1247
1248         /**
1249          * @param mixed $value
1250          * @return mixed
1251          */
1252         public function waitTimeout( $value = null ) {
1253                 return wfSetVar( $this->mWaitTimeout, $value );
1254         }
1255
1256         /**
1257          * @note This method will trigger a DB connection if not yet done
1258          *
1259          * @param string|bool $wiki Wiki ID, or false for the current wiki
1260          * @return bool Whether the generic connection for reads is highly "lagged"
1261          */
1262         public function getLaggedSlaveMode( $wiki = false ) {
1263                 // No-op if there is only one DB (also avoids recursion)
1264                 if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
1265                         try {
1266                                 // See if laggedSlaveMode gets set
1267                                 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1268                                 $this->reuseConnection( $conn );
1269                         } catch ( DBConnectionError $e ) {
1270                                 // Avoid expensive re-connect attempts and failures
1271                                 $this->slavesDownMode = true;
1272                                 $this->laggedSlaveMode = true;
1273                         }
1274                 }
1275
1276                 return $this->laggedSlaveMode;
1277         }
1278
1279         /**
1280          * @note This method will never cause a new DB connection
1281          * @return bool Whether any generic connection used for reads was highly "lagged"
1282          * @since 1.27
1283          */
1284         public function laggedSlaveUsed() {
1285                 return $this->laggedSlaveMode;
1286         }
1287
1288         /**
1289          * @note This method may trigger a DB connection if not yet done
1290          * @param string|bool $wiki Wiki ID, or false for the current wiki
1291          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1292          * @return string|bool Reason the master is read-only or false if it is not
1293          * @since 1.27
1294          */
1295         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1296                 if ( $this->readOnlyReason !== false ) {
1297                         return $this->readOnlyReason;
1298                 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1299                         if ( $this->slavesDownMode ) {
1300                                 return 'The database has been automatically locked ' .
1301                                         'until the slave database servers become available';
1302                         } else {
1303                                 return 'The database has been automatically locked ' .
1304                                         'while the slave database servers catch up to the master.';
1305                         }
1306                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1307                         return 'The database master is running in read-only mode.';
1308                 }
1309
1310                 return false;
1311         }
1312
1313         /**
1314          * @param string $wiki Wiki ID, or false for the current wiki
1315          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1316          * @return bool
1317          */
1318         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1319                 $cache = $this->wanCache;
1320                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1321
1322                 return (bool)$cache->getWithSetCallback(
1323                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1324                         self::TTL_CACHE_READONLY,
1325                         function () use ( $wiki, $conn ) {
1326                                 $this->trxProfiler->setSilenced( true );
1327                                 try {
1328                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1329                                         $readOnly = (int)$dbw->serverIsReadOnly();
1330                                 } catch ( DBError $e ) {
1331                                         $readOnly = 0;
1332                                 }
1333                                 $this->trxProfiler->setSilenced( false );
1334                                 return $readOnly;
1335                         },
1336                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1337                 );
1338         }
1339
1340         /**
1341          * Disables/enables lag checks
1342          * @param null|bool $mode
1343          * @return bool
1344          */
1345         public function allowLagged( $mode = null ) {
1346                 if ( $mode === null ) {
1347                         return $this->mAllowLagged;
1348                 }
1349                 $this->mAllowLagged = $mode;
1350
1351                 return $this->mAllowLagged;
1352         }
1353
1354         /**
1355          * @return bool
1356          */
1357         public function pingAll() {
1358                 $success = true;
1359                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1360                         if ( !$conn->ping() ) {
1361                                 $success = false;
1362                         }
1363                 } );
1364
1365                 return $success;
1366         }
1367
1368         /**
1369          * Call a function with each open connection object
1370          * @param callable $callback
1371          * @param array $params
1372          */
1373         public function forEachOpenConnection( $callback, array $params = [] ) {
1374                 foreach ( $this->mConns as $connsByServer ) {
1375                         foreach ( $connsByServer as $serverConns ) {
1376                                 foreach ( $serverConns as $conn ) {
1377                                         $mergedParams = array_merge( [ $conn ], $params );
1378                                         call_user_func_array( $callback, $mergedParams );
1379                                 }
1380                         }
1381                 }
1382         }
1383
1384         /**
1385          * Call a function with each open connection object to a master
1386          * @param callable $callback
1387          * @param array $params
1388          * @since 1.28
1389          */
1390         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1391                 $masterIndex = $this->getWriterIndex();
1392                 foreach ( $this->mConns as $connsByServer ) {
1393                         if ( isset( $connsByServer[$masterIndex] ) ) {
1394                                 /** @var DatabaseBase $conn */
1395                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1396                                         $mergedParams = array_merge( [ $conn ], $params );
1397                                         call_user_func_array( $callback, $mergedParams );
1398                                 }
1399                         }
1400                 }
1401         }
1402
1403         /**
1404          * Get the hostname and lag time of the most-lagged slave
1405          *
1406          * This is useful for maintenance scripts that need to throttle their updates.
1407          * May attempt to open connections to slaves on the default DB. If there is
1408          * no lag, the maximum lag will be reported as -1.
1409          *
1410          * @param bool|string $wiki Wiki ID, or false for the default database
1411          * @return array ( host, max lag, index of max lagged host )
1412          */
1413         public function getMaxLag( $wiki = false ) {
1414                 $maxLag = -1;
1415                 $host = '';
1416                 $maxIndex = 0;
1417
1418                 if ( $this->getServerCount() <= 1 ) {
1419                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1420                 }
1421
1422                 $lagTimes = $this->getLagTimes( $wiki );
1423                 foreach ( $lagTimes as $i => $lag ) {
1424                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1425                                 $maxLag = $lag;
1426                                 $host = $this->mServers[$i]['host'];
1427                                 $maxIndex = $i;
1428                         }
1429                 }
1430
1431                 return [ $host, $maxLag, $maxIndex ];
1432         }
1433
1434         /**
1435          * Get an estimate of replication lag (in seconds) for each server
1436          *
1437          * Results are cached for a short time in memcached/process cache
1438          *
1439          * Values may be "false" if replication is too broken to estimate
1440          *
1441          * @param string|bool $wiki
1442          * @return int[] Map of (server index => float|int|bool)
1443          */
1444         public function getLagTimes( $wiki = false ) {
1445                 if ( $this->getServerCount() <= 1 ) {
1446                         return [ 0 => 0 ]; // no replication = no lag
1447                 }
1448
1449                 # Send the request to the load monitor
1450                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1451         }
1452
1453         /**
1454          * Get the lag in seconds for a given connection, or zero if this load
1455          * balancer does not have replication enabled.
1456          *
1457          * This should be used in preference to Database::getLag() in cases where
1458          * replication may not be in use, since there is no way to determine if
1459          * replication is in use at the connection level without running
1460          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1461          * function instead of Database::getLag() avoids a fatal error in this
1462          * case on many installations.
1463          *
1464          * @param IDatabase $conn
1465          * @return int|bool Returns false on error
1466          */
1467         public function safeGetLag( IDatabase $conn ) {
1468                 if ( $this->getServerCount() == 1 ) {
1469                         return 0;
1470                 } else {
1471                         return $conn->getLag();
1472                 }
1473         }
1474
1475         /**
1476          * Wait for a slave DB to reach a specified master position
1477          *
1478          * This will connect to the master to get an accurate position if $pos is not given
1479          *
1480          * @param IDatabase $conn Slave DB
1481          * @param DBMasterPos|bool $pos Master position; default: current position
1482          * @param integer $timeout Timeout in seconds
1483          * @return bool Success
1484          * @since 1.27
1485          */
1486         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1487                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
1488                         return true; // server is not a slave DB
1489                 }
1490
1491                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1492                 if ( !( $pos instanceof DBMasterPos ) ) {
1493                         return false; // something is misconfigured
1494                 }
1495
1496                 $result = $conn->masterPosWait( $pos, $timeout );
1497                 if ( $result == -1 || is_null( $result ) ) {
1498                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1499                         wfDebugLog( 'replication', "$msg\n" );
1500                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1501                         $ok = false;
1502                 } else {
1503                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1504                         $ok = true;
1505                 }
1506
1507                 return $ok;
1508         }
1509
1510         /**
1511          * Clear the cache for slag lag delay times
1512          *
1513          * This is only used for testing
1514          */
1515         public function clearLagTimeCache() {
1516                 $this->getLoadMonitor()->clearCaches();
1517         }
1518 }