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          * @throws MWException
  95          */
  96         public function __construct( array $params ) {
  97                 if ( !isset( $params['servers'] ) ) {
  98                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  99                 }
 100                 $this->mServers = $params['servers'];
 101                 $this->mWaitTimeout = self::POS_WAIT_TIMEOUT;
 102
 103                 $this->mReadIndex = -1;
 104                 $this->mWriteIndex = -1;
 105                 $this->mConns = [
 106                         'local' => [],
 107                         'foreignUsed' => [],
 108                         'foreignFree' => [] ];
 109                 $this->mLoads = [];
 110                 $this->mWaitForPos = false;
 111                 $this->mErrorConnection = false;
 112                 $this->mAllowLagged = false;
 113
 114                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 115                         $this->readOnlyReason = $params['readOnlyReason'];
 116                 }
 117
 118                 if ( isset( $params['loadMonitor'] ) ) {
 119                         $this->mLoadMonitorClass = $params['loadMonitor'];
 120                 } else {
 121                         $master = reset( $params['servers'] );
 122                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 123                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 124                         } else {
 125                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 126                         }
 127                 }
 128
 129                 foreach ( $params['servers'] as $i => $server ) {
 130                         $this->mLoads[$i] = $server['load'];
 131                         if ( isset( $server['groupLoads'] ) ) {
 132                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 133                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 134                                                 $this->mGroupLoads[$group] = [];
 135                                         }
 136                                         $this->mGroupLoads[$group][$i] = $ratio;
 137                                 }
 138                         }
 139                 }
 140
 141                 $this->srvCache = ObjectCache::getLocalServerInstance();
 142                 $this->wanCache = ObjectCache::getMainWANInstance();
 143
 144                 if ( isset( $params['trxProfiler'] ) ) {
 145                         $this->trxProfiler = $params['trxProfiler'];
 146                 } else {
 147                         $this->trxProfiler = new TransactionProfiler();
 148                 }
 149         }
 150
 151         /**
 152          * Get a LoadMonitor instance
 153          *
 154          * @return LoadMonitor
 155          */
 156         private function getLoadMonitor() {
 157                 if ( !isset( $this->mLoadMonitor ) ) {
 158                         $class = $this->mLoadMonitorClass;
 159                         $this->mLoadMonitor = new $class( $this );
 160                 }
 161
 162                 return $this->mLoadMonitor;
 163         }
 164
 165         /**
 166          * Get or set arbitrary data used by the parent object, usually an LBFactory
 167          * @param mixed $x
 168          * @return mixed
 169          */
 170         public function parentInfo( $x = null ) {
 171                 return wfSetVar( $this->mParentInfo, $x );
 172         }
 173
 174         /**
 175          * @param array $loads
 176          * @param bool|string $wiki Wiki to get non-lagged for
 177          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 178          * @return bool|int|string
 179          */
 180         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) {
 181                 $lags = $this->getLagTimes( $wiki );
 182
 183                 # Unset excessively lagged servers
 184                 foreach ( $lags as $i => $lag ) {
 185                         if ( $i != 0 ) {
 186                                 $maxServerLag = $maxLag;
 187                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 188                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 189                                 }
 190
 191                                 $host = $this->getServerName( $i );
 192                                 if ( $lag === false ) {
 193                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 194                                         unset( $loads[$i] );
 195                                 } elseif ( $lag > $maxServerLag ) {
 196                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 197                                         unset( $loads[$i] );
 198                                 }
 199                         }
 200                 }
 201
 202                 # Find out if all the slaves with non-zero load are lagged
 203                 $sum = 0;
 204                 foreach ( $loads as $load ) {
 205                         $sum += $load;
 206                 }
 207                 if ( $sum == 0 ) {
 208                         # No appropriate DB servers except maybe the master and some slaves with zero load
 209                         # Do NOT use the master
 210                         # Instead, this function will return false, triggering read-only mode,
 211                         # and a lagged slave will be used instead.
 212                         return false;
 213                 }
 214
 215                 if ( count( $loads ) == 0 ) {
 216                         return false;
 217                 }
 218
 219                 # Return a random representative of the remainder
 220                 return ArrayUtils::pickRandom( $loads );
 221         }
 222
 223         /**
 224          * Get the index of the reader connection, which may be a slave
 225          * This takes into account load ratios and lag times. It should
 226          * always return a consistent index during a given invocation
 227          *
 228          * Side effect: opens connections to databases
 229          * @param string|bool $group Query group, or false for the generic reader
 230          * @param string|bool $wiki Wiki ID, or false for the current wiki
 231          * @throws MWException
 232          * @return bool|int|string
 233          */
 234         public function getReaderIndex( $group = false, $wiki = false ) {
 235                 global $wgDBtype;
 236
 237                 # @todo FIXME: For now, only go through all this for mysql databases
 238                 if ( $wgDBtype != 'mysql' ) {
 239                         return $this->getWriterIndex();
 240                 }
 241
 242                 if ( count( $this->mServers ) == 1 ) {
 243                         # Skip the load balancing if there's only one server
 244                         return 0;
 245                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 246                         # Shortcut if generic reader exists already
 247                         return $this->mReadIndex;
 248                 }
 249
 250                 # Find the relevant load array
 251                 if ( $group !== false ) {
 252                         if ( isset( $this->mGroupLoads[$group] ) ) {
 253                                 $nonErrorLoads = $this->mGroupLoads[$group];
 254                         } else {
 255                                 # No loads for this group, return false and the caller can use some other group
 256                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 257
 258                                 return false;
 259                         }
 260                 } else {
 261                         $nonErrorLoads = $this->mLoads;
 262                 }
 263
 264                 if ( !count( $nonErrorLoads ) ) {
 265                         throw new MWException( "Empty server array given to LoadBalancer" );
 266                 }
 267
 268                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 269                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 270
 271                 $laggedSlaveMode = false;
 272
 273                 # No server found yet
 274                 $i = false;
 275                 $conn = false;
 276                 # First try quickly looking through the available servers for a server that
 277                 # meets our criteria
 278                 $currentLoads = $nonErrorLoads;
 279                 while ( count( $currentLoads ) ) {
 280                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 281                                 $i = ArrayUtils::pickRandom( $currentLoads );
 282                         } else {
 283                                 $i = false;
 284                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 285                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 286                                         # This triggers doWait() after connect, so it's especially good to
 287                                         # avoid lagged servers so as to avoid just blocking in that method.
 288                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 289                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 290                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 291                                 }
 292                                 if ( $i === false ) {
 293                                         # Any server with less lag than it's 'max lag' param is preferable
 294                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 295                                 }
 296                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 297                                         # All slaves lagged. Switch to read-only mode
 298                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 299                                         $i = ArrayUtils::pickRandom( $currentLoads );
 300                                         $laggedSlaveMode = true;
 301                                 }
 302                         }
 303
 304                         if ( $i === false ) {
 305                                 # pickRandom() returned false
 306                                 # This is permanent and means the configuration or the load monitor
 307                                 # wants us to return false.
 308                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 309
 310                                 return false;
 311                         }
 312
 313                         $serverName = $this->getServerName( $i );
 314                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 315
 316                         $conn = $this->openConnection( $i, $wiki );
 317                         if ( !$conn ) {
 318                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 319                                 unset( $nonErrorLoads[$i] );
 320                                 unset( $currentLoads[$i] );
 321                                 $i = false;
 322                                 continue;
 323                         }
 324
 325                         // Decrement reference counter, we are finished with this connection.
 326                         // It will be incremented for the caller later.
 327                         if ( $wiki !== false ) {
 328                                 $this->reuseConnection( $conn );
 329                         }
 330
 331                         # Return this server
 332                         break;
 333                 }
 334
 335                 # If all servers were down, quit now
 336                 if ( !count( $nonErrorLoads ) ) {
 337                         wfDebugLog( 'connect', "All servers down" );
 338                 }
 339
 340                 if ( $i !== false ) {
 341                         # Slave connection successful
 342                         # Wait for the session master pos for a short time
 343                         if ( $this->mWaitForPos && $i > 0 ) {
 344                                 if ( !$this->doWait( $i ) ) {
 345                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 346                                 }
 347                         }
 348                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 349                                 $this->mReadIndex = $i;
 350                                 # Record if the generic reader index is in "lagged slave" mode
 351                                 if ( $laggedSlaveMode ) {
 352                                         $this->laggedSlaveMode = true;
 353                                 }
 354                         }
 355                         $serverName = $this->getServerName( $i );
 356                         wfDebugLog( 'connect', __METHOD__ .
 357                                 ": using server $serverName for group '$group'\n" );
 358                 }
 359
 360                 return $i;
 361         }
 362
 363         /**
 364          * Set the master wait position
 365          * If a DB_SLAVE connection has been opened already, waits
 366          * Otherwise sets a variable telling it to wait if such a connection is opened
 367          * @param DBMasterPos $pos
 368          */
 369         public function waitFor( $pos ) {
 370                 $this->mWaitForPos = $pos;
 371                 $i = $this->mReadIndex;
 372
 373                 if ( $i > 0 ) {
 374                         if ( !$this->doWait( $i ) ) {
 375                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 376                                 $this->laggedSlaveMode = true;
 377                         }
 378                 }
 379         }
 380
 381         /**
 382          * Set the master wait position and wait for a "generic" slave to catch up to it
 383          *
 384          * This can be used a faster proxy for waitForAll()
 385          *
 386          * @param DBMasterPos $pos
 387          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 388          * @return bool Success (able to connect and no timeouts reached)
 389          * @since 1.26
 390          */
 391         public function waitForOne( $pos, $timeout = null ) {
 392                 $this->mWaitForPos = $pos;
 393
 394                 $i = $this->mReadIndex;
 395                 if ( $i <= 0 ) {
 396                         // Pick a generic slave if there isn't one yet
 397                         $readLoads = $this->mLoads;
 398                         unset( $readLoads[$this->getWriterIndex()] ); // slaves only
 399                         $readLoads = array_filter( $readLoads ); // with non-zero load
 400                         $i = ArrayUtils::pickRandom( $readLoads );
 401                 }
 402
 403                 if ( $i > 0 ) {
 404                         $ok = $this->doWait( $i, true, $timeout );
 405                 } else {
 406                         $ok = true; // no applicable loads
 407                 }
 408
 409                 return $ok;
 410         }
 411
 412         /**
 413          * Set the master wait position and wait for ALL slaves to catch up to it
 414          * @param DBMasterPos $pos
 415          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 416          * @return bool Success (able to connect and no timeouts reached)
 417          */
 418         public function waitForAll( $pos, $timeout = null ) {
 419                 $this->mWaitForPos = $pos;
 420                 $serverCount = count( $this->mServers );
 421
 422                 $ok = true;
 423                 for ( $i = 1; $i < $serverCount; $i++ ) {
 424                         if ( $this->mLoads[$i] > 0 ) {
 425                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 426                         }
 427                 }
 428
 429                 return $ok;
 430         }
 431
 432         /**
 433          * Get any open connection to a given server index, local or foreign
 434          * Returns false if there is no connection open
 435          *
 436          * @param int $i
 437          * @return DatabaseBase|bool False on failure
 438          */
 439         public function getAnyOpenConnection( $i ) {
 440                 foreach ( $this->mConns as $conns ) {
 441                         if ( !empty( $conns[$i] ) ) {
 442                                 return reset( $conns[$i] );
 443                         }
 444                 }
 445
 446                 return false;
 447         }
 448
 449         /**
 450          * Wait for a given slave to catch up to the master pos stored in $this
 451          * @param int $index Server index
 452          * @param bool $open Check the server even if a new connection has to be made
 453          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 454          * @return bool
 455          */
 456         protected function doWait( $index, $open = false, $timeout = null ) {
 457                 $close = false; // close the connection afterwards
 458
 459                 // Check if we already know that the DB has reached this point
 460                 $server = $this->getServerName( $index );
 461                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 462                 /** @var DBMasterPos $knownReachedPos */
 463                 $knownReachedPos = $this->srvCache->get( $key );
 464                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 465                         wfDebugLog( 'replication', __METHOD__ .
 466                                 ": slave $server known to be caught up (pos >= $knownReachedPos).\n" );
 467                         return true;
 468                 }
 469
 470                 // Find a connection to wait on, creating one if needed and allowed
 471                 $conn = $this->getAnyOpenConnection( $index );
 472                 if ( !$conn ) {
 473                         if ( !$open ) {
 474                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 475
 476                                 return false;
 477                         } else {
 478                                 $conn = $this->openConnection( $index, '' );
 479                                 if ( !$conn ) {
 480                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 481
 482                                         return false;
 483                                 }
 484                                 // Avoid connection spam in waitForAll() when connections
 485                                 // are made just for the sake of doing this lag check.
 486                                 $close = true;
 487                         }
 488                 }
 489
 490                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for slave $server to catch up...\n" );
 491                 $timeout = $timeout ?: $this->mWaitTimeout;
 492                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 493
 494                 if ( $result == -1 || is_null( $result ) ) {
 495                         // Timed out waiting for slave, use master instead
 496                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 497                         wfDebugLog( 'replication', "$msg\n" );
 498                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 499                         $ok = false;
 500                 } else {
 501                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 502                         $ok = true;
 503                         // Remember that the DB reached this point
 504                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 505                 }
 506
 507                 if ( $close ) {
 508                         $this->closeConnection( $conn );
 509                 }
 510
 511                 return $ok;
 512         }
 513
 514         /**
 515          * Get a connection by index
 516          * This is the main entry point for this class.
 517          *
 518          * @param int $i Server index
 519          * @param array|string|bool $groups Query group(s), or false for the generic reader
 520          * @param string|bool $wiki Wiki ID, or false for the current wiki
 521          *
 522          * @throws MWException
 523          * @return DatabaseBase
 524          */
 525         public function getConnection( $i, $groups = [], $wiki = false ) {
 526                 if ( $i === null || $i === false ) {
 527                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 528                                 ' with invalid server index' );
 529                 }
 530
 531                 if ( $wiki === wfWikiID() ) {
 532                         $wiki = false;
 533                 }
 534
 535                 $groups = ( $groups === false || $groups === [] )
 536                         ? [ false ] // check one "group": the generic pool
 537                         : (array)$groups;
 538
 539                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 540                 $oldConnsOpened = $this->connsOpened; // connections open now
 541
 542                 if ( $i == DB_MASTER ) {
 543                         $i = $this->getWriterIndex();
 544                 } else {
 545                         # Try to find an available server in any the query groups (in order)
 546                         foreach ( $groups as $group ) {
 547                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 548                                 if ( $groupIndex !== false ) {
 549                                         $i = $groupIndex;
 550                                         break;
 551                                 }
 552                         }
 553                 }
 554
 555                 # Operation-based index
 556                 if ( $i == DB_SLAVE ) {
 557                         $this->mLastError = 'Unknown error'; // reset error string
 558                         # Try the general server pool if $groups are unavailable.
 559                         $i = in_array( false, $groups, true )
 560                                 ? false // don't bother with this if that is what was tried above
 561                                 : $this->getReaderIndex( false, $wiki );
 562                         # Couldn't find a working server in getReaderIndex()?
 563                         if ( $i === false ) {
 564                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 565
 566                                 return $this->reportConnectionError();
 567                         }
 568                 }
 569
 570                 # Now we have an explicit index into the servers array
 571                 $conn = $this->openConnection( $i, $wiki );
 572                 if ( !$conn ) {
 573                         return $this->reportConnectionError();
 574                 }
 575
 576                 # Profile any new connections that happen
 577                 if ( $this->connsOpened > $oldConnsOpened ) {
 578                         $host = $conn->getServer();
 579                         $dbname = $conn->getDBname();
 580                         $trxProf = Profiler::instance()->getTransactionProfiler();
 581                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 582                 }
 583
 584                 if ( $masterOnly ) {
 585                         # Make master-requested DB handles inherit any read-only mode setting
 586                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
 587                 }
 588
 589                 return $conn;
 590         }
 591
 592         /**
 593          * Mark a foreign connection as being available for reuse under a different
 594          * DB name or prefix. This mechanism is reference-counted, and must be called
 595          * the same number of times as getConnection() to work.
 596          *
 597          * @param DatabaseBase $conn
 598          * @throws MWException
 599          */
 600         public function reuseConnection( $conn ) {
 601                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 602                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 603                 if ( $serverIndex === null || $refCount === null ) {
 604                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 605                         /**
 606                          * This can happen in code like:
 607                          *   foreach ( $dbs as $db ) {
 608                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 609                          *     ...
 610                          *     $lb->reuseConnection( $conn );
 611                          *   }
 612                          * When a connection to the local DB is opened in this way, reuseConnection()
 613                          * should be ignored
 614                          */
 615                         return;
 616                 }
 617
 618                 $dbName = $conn->getDBname();
 619                 $prefix = $conn->tablePrefix();
 620                 if ( strval( $prefix ) !== '' ) {
 621                         $wiki = "$dbName-$prefix";
 622                 } else {
 623                         $wiki = $dbName;
 624                 }
 625                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 626                         throw new MWException( __METHOD__ . ": connection not found, has " .
 627                                 "the connection been freed already?" );
 628                 }
 629                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 630                 if ( $refCount <= 0 ) {
 631                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 632                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 633                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 634                 } else {
 635                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 636                 }
 637         }
 638
 639         /**
 640          * Get a database connection handle reference
 641          *
 642          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 643          *
 644          * @see LoadBalancer::getConnection() for parameter information
 645          *
 646          * @param int $db
 647          * @param array|string|bool $groups Query group(s), or false for the generic reader
 648          * @param string|bool $wiki Wiki ID, or false for the current wiki
 649          * @return DBConnRef
 650          */
 651         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 652                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 653         }
 654
 655         /**
 656          * Get a database connection handle reference without connecting yet
 657          *
 658          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 659          *
 660          * @see LoadBalancer::getConnection() for parameter information
 661          *
 662          * @param int $db
 663          * @param array|string|bool $groups Query group(s), or false for the generic reader
 664          * @param string|bool $wiki Wiki ID, or false for the current wiki
 665          * @return DBConnRef
 666          */
 667         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 668                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 669         }
 670
 671         /**
 672          * Open a connection to the server given by the specified index
 673          * Index must be an actual index into the array.
 674          * If the server is already open, returns it.
 675          *
 676          * On error, returns false, and the connection which caused the
 677          * error will be available via $this->mErrorConnection.
 678          *
 679          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 680          *
 681          * @param int $i Server index
 682          * @param string|bool $wiki Wiki ID, or false for the current wiki
 683          * @return DatabaseBase|bool Returns false on errors
 684          */
 685         public function openConnection( $i, $wiki = false ) {
 686                 if ( $wiki !== false ) {
 687                         $conn = $this->openForeignConnection( $i, $wiki );
 688                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 689                         $conn = $this->mConns['local'][$i][0];
 690                 } else {
 691                         $server = $this->mServers[$i];
 692                         $server['serverIndex'] = $i;
 693                         $conn = $this->reallyOpenConnection( $server, false );
 694                         $serverName = $this->getServerName( $i );
 695                         if ( $conn->isOpen() ) {
 696                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 697                                 $this->mConns['local'][$i][0] = $conn;
 698                         } else {
 699                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 700                                 $this->mErrorConnection = $conn;
 701                                 $conn = false;
 702                         }
 703                 }
 704
 705                 if ( $conn && !$conn->isOpen() ) {
 706                         // Connection was made but later unrecoverably lost for some reason.
 707                         // Do not return a handle that will just throw exceptions on use,
 708                         // but let the calling code (e.g. getReaderIndex) try another server.
 709                         // See DatabaseMyslBase::ping() for how this can happen.
 710                         $this->mErrorConnection = $conn;
 711                         $conn = false;
 712                 }
 713
 714                 return $conn;
 715         }
 716
 717         /**
 718          * Open a connection to a foreign DB, or return one if it is already open.
 719          *
 720          * Increments a reference count on the returned connection which locks the
 721          * connection to the requested wiki. This reference count can be
 722          * decremented by calling reuseConnection().
 723          *
 724          * If a connection is open to the appropriate server already, but with the wrong
 725          * database, it will be switched to the right database and returned, as long as
 726          * it has been freed first with reuseConnection().
 727          *
 728          * On error, returns false, and the connection which caused the
 729          * error will be available via $this->mErrorConnection.
 730          *
 731          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 732          *
 733          * @param int $i Server index
 734          * @param string $wiki Wiki ID to open
 735          * @return DatabaseBase
 736          */
 737         private function openForeignConnection( $i, $wiki ) {
 738                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 739                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 740                         // Reuse an already-used connection
 741                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 742                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 743                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 744                         // Reuse a free connection for the same wiki
 745                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 746                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 747                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 748                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 749                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 750                         // Reuse a connection from another wiki
 751                         $conn = reset( $this->mConns['foreignFree'][$i] );
 752                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 753
 754                         // The empty string as a DB name means "don't care".
 755                         // DatabaseMysqlBase::open() already handle this on connection.
 756                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 757                                 $this->mLastError = "Error selecting database $dbName on server " .
 758                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 759                                 $this->mErrorConnection = $conn;
 760                                 $conn = false;
 761                         } else {
 762                                 $conn->tablePrefix( $prefix );
 763                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 764                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 765                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 766                         }
 767                 } else {
 768                         // Open a new connection
 769                         $server = $this->mServers[$i];
 770                         $server['serverIndex'] = $i;
 771                         $server['foreignPoolRefCount'] = 0;
 772                         $server['foreign'] = true;
 773                         $conn = $this->reallyOpenConnection( $server, $dbName );
 774                         if ( !$conn->isOpen() ) {
 775                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 776                                 $this->mErrorConnection = $conn;
 777                                 $conn = false;
 778                         } else {
 779                                 $conn->tablePrefix( $prefix );
 780                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 781                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 782                         }
 783                 }
 784
 785                 // Increment reference count
 786                 if ( $conn ) {
 787                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 788                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 789                 }
 790
 791                 return $conn;
 792         }
 793
 794         /**
 795          * Test if the specified index represents an open connection
 796          *
 797          * @param int $index Server index
 798          * @access private
 799          * @return bool
 800          */
 801         private function isOpen( $index ) {
 802                 if ( !is_integer( $index ) ) {
 803                         return false;
 804                 }
 805
 806                 return (bool)$this->getAnyOpenConnection( $index );
 807         }
 808
 809         /**
 810          * Really opens a connection. Uncached.
 811          * Returns a Database object whether or not the connection was successful.
 812          * @access private
 813          *
 814          * @param array $server
 815          * @param bool $dbNameOverride
 816          * @throws MWException
 817          * @return DatabaseBase
 818          */
 819         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 820                 if ( $this->disabled ) {
 821                         throw new DBAccessError();
 822                 }
 823
 824                 if ( !is_array( $server ) ) {
 825                         throw new MWException( 'You must update your load-balancing configuration. ' .
 826                                 'See DefaultSettings.php entry for $wgDBservers.' );
 827                 }
 828
 829                 if ( $dbNameOverride !== false ) {
 830                         $server['dbname'] = $dbNameOverride;
 831                 }
 832
 833                 // Let the handle know what the cluster master is (e.g. "db1052")
 834                 $masterName = $this->getServerName( 0 );
 835                 $server['clusterMasterHost'] = $masterName;
 836
 837                 // Log when many connection are made on requests
 838                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 839                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 840                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 841                                 wfBacktrace( true ) );
 842                 }
 843
 844                 # Create object
 845                 try {
 846                         $db = DatabaseBase::factory( $server['type'], $server );
 847                 } catch ( DBConnectionError $e ) {
 848                         // FIXME: This is probably the ugliest thing I have ever done to
 849                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 850                         $db = $e->db;
 851                 }
 852
 853                 $db->setLBInfo( $server );
 854                 $db->setLazyMasterHandle(
 855                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 856                 );
 857                 $db->setTransactionProfiler( $this->trxProfiler );
 858
 859                 return $db;
 860         }
 861
 862         /**
 863          * @throws DBConnectionError
 864          * @return bool
 865          */
 866         private function reportConnectionError() {
 867                 $conn = $this->mErrorConnection; // The connection which caused the error
 868                 $context = [
 869                         'method' => __METHOD__,
 870                         'last_error' => $this->mLastError,
 871                 ];
 872
 873                 if ( !is_object( $conn ) ) {
 874                         // No last connection, probably due to all servers being too busy
 875                         wfLogDBError(
 876                                 "LB failure with no last connection. Connection error: {last_error}",
 877                                 $context
 878                         );
 879
 880                         // If all servers were busy, mLastError will contain something sensible
 881                         throw new DBConnectionError( null, $this->mLastError );
 882                 } else {
 883                         $context['db_server'] = $conn->getProperty( 'mServer' );
 884                         wfLogDBError(
 885                                 "Connection error: {last_error} ({db_server})",
 886                                 $context
 887                         );
 888
 889                         // throws DBConnectionError
 890                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 891                 }
 892
 893                 return false; /* not reached */
 894         }
 895
 896         /**
 897          * @return int
 898          * @since 1.26
 899          */
 900         public function getWriterIndex() {
 901                 return 0;
 902         }
 903
 904         /**
 905          * Returns true if the specified index is a valid server index
 906          *
 907          * @param string $i
 908          * @return bool
 909          */
 910         public function haveIndex( $i ) {
 911                 return array_key_exists( $i, $this->mServers );
 912         }
 913
 914         /**
 915          * Returns true if the specified index is valid and has non-zero load
 916          *
 917          * @param string $i
 918          * @return bool
 919          */
 920         public function isNonZeroLoad( $i ) {
 921                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 922         }
 923
 924         /**
 925          * Get the number of defined servers (not the number of open connections)
 926          *
 927          * @return int
 928          */
 929         public function getServerCount() {
 930                 return count( $this->mServers );
 931         }
 932
 933         /**
 934          * Get the host name or IP address of the server with the specified index
 935          * Prefer a readable name if available.
 936          * @param string $i
 937          * @return string
 938          */
 939         public function getServerName( $i ) {
 940                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 941                         $name = $this->mServers[$i]['hostName'];
 942                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 943                         $name = $this->mServers[$i]['host'];
 944                 } else {
 945                         $name = '';
 946                 }
 947
 948                 return ( $name != '' ) ? $name : 'localhost';
 949         }
 950
 951         /**
 952          * Return the server info structure for a given index, or false if the index is invalid.
 953          * @param int $i
 954          * @return array|bool
 955          */
 956         public function getServerInfo( $i ) {
 957                 if ( isset( $this->mServers[$i] ) ) {
 958                         return $this->mServers[$i];
 959                 } else {
 960                         return false;
 961                 }
 962         }
 963
 964         /**
 965          * Sets the server info structure for the given index. Entry at index $i
 966          * is created if it doesn't exist
 967          * @param int $i
 968          * @param array $serverInfo
 969          */
 970         public function setServerInfo( $i, array $serverInfo ) {
 971                 $this->mServers[$i] = $serverInfo;
 972         }
 973
 974         /**
 975          * Get the current master position for chronology control purposes
 976          * @return mixed
 977          */
 978         public function getMasterPos() {
 979                 # If this entire request was served from a slave without opening a connection to the
 980                 # master (however unlikely that may be), then we can fetch the position from the slave.
 981                 $masterConn = $this->getAnyOpenConnection( 0 );
 982                 if ( !$masterConn ) {
 983                         $serverCount = count( $this->mServers );
 984                         for ( $i = 1; $i < $serverCount; $i++ ) {
 985                                 $conn = $this->getAnyOpenConnection( $i );
 986                                 if ( $conn ) {
 987                                         return $conn->getSlavePos();
 988                                 }
 989                         }
 990                 } else {
 991                         return $masterConn->getMasterPos();
 992                 }
 993
 994                 return false;
 995         }
 996
 997         /**
 998          * Disable this load balancer. All connections are closed, and any attempt to
 999          * open a new connection will result in a DBAccessError.
1000          *
1001          * @since 1.27
1002          */
1003         public function disable() {
1004                 $this->closeAll();
1005                 $this->disabled = true;
1006         }
1007
1008         /**
1009          * Close all open connections
1010          */
1011         public function closeAll() {
1012                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1013                         $conn->close();
1014                 } );
1015
1016                 $this->mConns = [
1017                         'local' => [],
1018                         'foreignFree' => [],
1019                         'foreignUsed' => [],
1020                 ];
1021                 $this->connsOpened = 0;
1022         }
1023
1024         /**
1025          * Close a connection
1026          * Using this function makes sure the LoadBalancer knows the connection is closed.
1027          * If you use $conn->close() directly, the load balancer won't update its state.
1028          * @param DatabaseBase $conn
1029          */
1030         public function closeConnection( $conn ) {
1031                 $done = false;
1032                 foreach ( $this->mConns as $i1 => $conns2 ) {
1033                         foreach ( $conns2 as $i2 => $conns3 ) {
1034                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1035                                         if ( $conn === $candidateConn ) {
1036                                                 $conn->close();
1037                                                 unset( $this->mConns[$i1][$i2][$i3] );
1038                                                 --$this->connsOpened;
1039                                                 $done = true;
1040                                                 break;
1041                                         }
1042                                 }
1043                         }
1044                 }
1045                 if ( !$done ) {
1046                         $conn->close();
1047                 }
1048         }
1049
1050         /**
1051          * Commit transactions on all open connections
1052          * @param string $fname Caller name
1053          */
1054         public function commitAll( $fname = __METHOD__ ) {
1055                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( $fname ) {
1056                         $conn->commit( $fname, 'flush' );
1057                 } );
1058         }
1059
1060         /**
1061          * Perform all pre-commit callbacks that remain part of the atomic transactions
1062          * and disable any post-commit callbacks until runMasterPostCommitCallbacks()
1063          * @since 1.28
1064          */
1065         public function runMasterPreCommitCallbacks() {
1066                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1067                         // Any error will cause all DB transactions to be rolled back together.
1068                         $conn->runOnTransactionPreCommitCallbacks();
1069                         // Defer post-commit callbacks until COMMIT finishes for all DBs.
1070                         $conn->setPostCommitCallbackSupression( true );
1071                 } );
1072         }
1073
1074         /**
1075          * Perform all pre-commit checks for things like replication safety
1076          * @param array $options Includes:
1077          *   - maxWriteDuration : max write query duration time in seconds
1078          * @throws DBTransactionError
1079          * @since 1.28
1080          */
1081         public function approveMasterChanges( array $options ) {
1082                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1083                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1084                         // Assert that the time to replicate the transaction will be sane.
1085                         // If this fails, then all DB transactions will be rollback back together.
1086                         $time = $conn->pendingWriteQueryDuration();
1087                         if ( $limit > 0 && $time > $limit ) {
1088                                 throw new DBTransactionError(
1089                                         $conn,
1090                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1091                                 );
1092                         }
1093                 } );
1094         }
1095
1096         /**
1097          * Issue COMMIT on all master connections where writes where done
1098          * @param string $fname Caller name
1099          */
1100         public function commitMasterChanges( $fname = __METHOD__ ) {
1101                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $fname ) {
1102                         if ( $conn->writesOrCallbacksPending() ) {
1103                                 $conn->commit( $fname, 'flush' );
1104                         }
1105                 } );
1106         }
1107
1108         /**
1109          * Issue all pending post-commit callbacks
1110          * @since 1.28
1111          */
1112         public function runMasterPostCommitCallbacks() {
1113                 $this->forEachOpenMasterConnection( function ( DatabaseBase $db ) {
1114                         $db->setPostCommitCallbackSupression( false );
1115                         $db->runOnTransactionIdleCallbacks( IDatabase::TRIGGER_COMMIT );
1116                 } );
1117         }
1118
1119         /**
1120          * Issue ROLLBACK only on master, only if queries were done on connection
1121          * @param string $fname Caller name
1122          * @throws DBExpectedError
1123          * @since 1.23
1124          */
1125         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1126                 $failedServers = [];
1127
1128                 $masterIndex = $this->getWriterIndex();
1129                 foreach ( $this->mConns as $conns2 ) {
1130                         if ( empty( $conns2[$masterIndex] ) ) {
1131                                 continue;
1132                         }
1133                         /** @var DatabaseBase $conn */
1134                         foreach ( $conns2[$masterIndex] as $conn ) {
1135                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1136                                         try {
1137                                                 $conn->rollback( $fname, 'flush' );
1138                                         } catch ( DBError $e ) {
1139                                                 MWExceptionHandler::logException( $e );
1140                                                 $failedServers[] = $conn->getServer();
1141                                         }
1142                                 }
1143                         }
1144                 }
1145
1146                 if ( $failedServers ) {
1147                         throw new DBExpectedError( null, "Rollback failed on server(s) " .
1148                                 implode( ', ', array_unique( $failedServers ) ) );
1149                 }
1150         }
1151
1152         /**
1153          * @return bool Whether a master connection is already open
1154          * @since 1.24
1155          */
1156         public function hasMasterConnection() {
1157                 return $this->isOpen( $this->getWriterIndex() );
1158         }
1159
1160         /**
1161          * Determine if there are pending changes in a transaction by this thread
1162          * @since 1.23
1163          * @return bool
1164          */
1165         public function hasMasterChanges() {
1166                 $masterIndex = $this->getWriterIndex();
1167                 foreach ( $this->mConns as $conns2 ) {
1168                         if ( empty( $conns2[$masterIndex] ) ) {
1169                                 continue;
1170                         }
1171                         /** @var DatabaseBase $conn */
1172                         foreach ( $conns2[$masterIndex] as $conn ) {
1173                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1174                                         return true;
1175                                 }
1176                         }
1177                 }
1178                 return false;
1179         }
1180
1181         /**
1182          * Get the timestamp of the latest write query done by this thread
1183          * @since 1.25
1184          * @return float|bool UNIX timestamp or false
1185          */
1186         public function lastMasterChangeTimestamp() {
1187                 $lastTime = false;
1188                 $masterIndex = $this->getWriterIndex();
1189                 foreach ( $this->mConns as $conns2 ) {
1190                         if ( empty( $conns2[$masterIndex] ) ) {
1191                                 continue;
1192                         }
1193                         /** @var DatabaseBase $conn */
1194                         foreach ( $conns2[$masterIndex] as $conn ) {
1195                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1196                         }
1197                 }
1198                 return $lastTime;
1199         }
1200
1201         /**
1202          * Check if this load balancer object had any recent or still
1203          * pending writes issued against it by this PHP thread
1204          *
1205          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1206          * @return bool
1207          * @since 1.25
1208          */
1209         public function hasOrMadeRecentMasterChanges( $age = null ) {
1210                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1211
1212                 return ( $this->hasMasterChanges()
1213                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1214         }
1215
1216         /**
1217          * Get the list of callers that have pending master changes
1218          *
1219          * @return array
1220          * @since 1.27
1221          */
1222         public function pendingMasterChangeCallers() {
1223                 $fnames = [];
1224
1225                 $masterIndex = $this->getWriterIndex();
1226                 foreach ( $this->mConns as $conns2 ) {
1227                         if ( empty( $conns2[$masterIndex] ) ) {
1228                                 continue;
1229                         }
1230                         /** @var DatabaseBase $conn */
1231                         foreach ( $conns2[$masterIndex] as $conn ) {
1232                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1233                         }
1234                 }
1235
1236                 return $fnames;
1237         }
1238
1239         /**
1240          * @param mixed $value
1241          * @return mixed
1242          */
1243         public function waitTimeout( $value = null ) {
1244                 return wfSetVar( $this->mWaitTimeout, $value );
1245         }
1246
1247         /**
1248          * @note This method will trigger a DB connection if not yet done
1249          *
1250          * @param string|bool $wiki Wiki ID, or false for the current wiki
1251          * @return bool Whether the generic connection for reads is highly "lagged"
1252          */
1253         public function getLaggedSlaveMode( $wiki = false ) {
1254                 // No-op if there is only one DB (also avoids recursion)
1255                 if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
1256                         try {
1257                                 // See if laggedSlaveMode gets set
1258                                 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1259                                 $this->reuseConnection( $conn );
1260                         } catch ( DBConnectionError $e ) {
1261                                 // Avoid expensive re-connect attempts and failures
1262                                 $this->slavesDownMode = true;
1263                                 $this->laggedSlaveMode = true;
1264                         }
1265                 }
1266
1267                 return $this->laggedSlaveMode;
1268         }
1269
1270         /**
1271          * @note This method will never cause a new DB connection
1272          * @return bool Whether any generic connection used for reads was highly "lagged"
1273          * @since 1.27
1274          */
1275         public function laggedSlaveUsed() {
1276                 return $this->laggedSlaveMode;
1277         }
1278
1279         /**
1280          * @note This method may trigger a DB connection if not yet done
1281          * @param string|bool $wiki Wiki ID, or false for the current wiki
1282          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1283          * @return string|bool Reason the master is read-only or false if it is not
1284          * @since 1.27
1285          */
1286         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1287                 if ( $this->readOnlyReason !== false ) {
1288                         return $this->readOnlyReason;
1289                 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1290                         if ( $this->slavesDownMode ) {
1291                                 return 'The database has been automatically locked ' .
1292                                         'until the slave database servers become available';
1293                         } else {
1294                                 return 'The database has been automatically locked ' .
1295                                         'while the slave database servers catch up to the master.';
1296                         }
1297                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1298                         return 'The database master is running in read-only mode.';
1299                 }
1300
1301                 return false;
1302         }
1303
1304         /**
1305          * @param string $wiki Wiki ID, or false for the current wiki
1306          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1307          * @return bool
1308          */
1309         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1310                 $cache = $this->wanCache;
1311                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1312
1313                 return (bool)$cache->getWithSetCallback(
1314                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1315                         self::TTL_CACHE_READONLY,
1316                         function () use ( $wiki, $conn ) {
1317                                 $this->trxProfiler->setSilenced( true );
1318                                 try {
1319                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1320                                         $readOnly = (int)$dbw->serverIsReadOnly();
1321                                 } catch ( DBError $e ) {
1322                                         $readOnly = 0;
1323                                 }
1324                                 $this->trxProfiler->setSilenced( false );
1325                                 return $readOnly;
1326                         },
1327                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1328                 );
1329         }
1330
1331         /**
1332          * Disables/enables lag checks
1333          * @param null|bool $mode
1334          * @return bool
1335          */
1336         public function allowLagged( $mode = null ) {
1337                 if ( $mode === null ) {
1338                         return $this->mAllowLagged;
1339                 }
1340                 $this->mAllowLagged = $mode;
1341
1342                 return $this->mAllowLagged;
1343         }
1344
1345         /**
1346          * @return bool
1347          */
1348         public function pingAll() {
1349                 $success = true;
1350                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1351                         if ( !$conn->ping() ) {
1352                                 $success = false;
1353                         }
1354                 } );
1355
1356                 return $success;
1357         }
1358
1359         /**
1360          * Call a function with each open connection object
1361          * @param callable $callback
1362          * @param array $params
1363          */
1364         public function forEachOpenConnection( $callback, array $params = [] ) {
1365                 foreach ( $this->mConns as $connsByServer ) {
1366                         foreach ( $connsByServer as $serverConns ) {
1367                                 foreach ( $serverConns as $conn ) {
1368                                         $mergedParams = array_merge( [ $conn ], $params );
1369                                         call_user_func_array( $callback, $mergedParams );
1370                                 }
1371                         }
1372                 }
1373         }
1374
1375         /**
1376          * Call a function with each open connection object to a master
1377          * @param callable $callback
1378          * @param array $params
1379          * @since 1.28
1380          */
1381         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1382                 $masterIndex = $this->getWriterIndex();
1383                 foreach ( $this->mConns as $connsByServer ) {
1384                         if ( isset( $connsByServer[$masterIndex] ) ) {
1385                                 /** @var DatabaseBase $conn */
1386                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1387                                         $mergedParams = array_merge( [ $conn ], $params );
1388                                         call_user_func_array( $callback, $mergedParams );
1389                                 }
1390                         }
1391                 }
1392         }
1393
1394         /**
1395          * Get the hostname and lag time of the most-lagged slave
1396          *
1397          * This is useful for maintenance scripts that need to throttle their updates.
1398          * May attempt to open connections to slaves on the default DB. If there is
1399          * no lag, the maximum lag will be reported as -1.
1400          *
1401          * @param bool|string $wiki Wiki ID, or false for the default database
1402          * @return array ( host, max lag, index of max lagged host )
1403          */
1404         public function getMaxLag( $wiki = false ) {
1405                 $maxLag = -1;
1406                 $host = '';
1407                 $maxIndex = 0;
1408
1409                 if ( $this->getServerCount() <= 1 ) {
1410                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1411                 }
1412
1413                 $lagTimes = $this->getLagTimes( $wiki );
1414                 foreach ( $lagTimes as $i => $lag ) {
1415                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1416                                 $maxLag = $lag;
1417                                 $host = $this->mServers[$i]['host'];
1418                                 $maxIndex = $i;
1419                         }
1420                 }
1421
1422                 return [ $host, $maxLag, $maxIndex ];
1423         }
1424
1425         /**
1426          * Get an estimate of replication lag (in seconds) for each server
1427          *
1428          * Results are cached for a short time in memcached/process cache
1429          *
1430          * Values may be "false" if replication is too broken to estimate
1431          *
1432          * @param string|bool $wiki
1433          * @return int[] Map of (server index => float|int|bool)
1434          */
1435         public function getLagTimes( $wiki = false ) {
1436                 if ( $this->getServerCount() <= 1 ) {
1437                         return [ 0 => 0 ]; // no replication = no lag
1438                 }
1439
1440                 # Send the request to the load monitor
1441                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1442         }
1443
1444         /**
1445          * Get the lag in seconds for a given connection, or zero if this load
1446          * balancer does not have replication enabled.
1447          *
1448          * This should be used in preference to Database::getLag() in cases where
1449          * replication may not be in use, since there is no way to determine if
1450          * replication is in use at the connection level without running
1451          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1452          * function instead of Database::getLag() avoids a fatal error in this
1453          * case on many installations.
1454          *
1455          * @param IDatabase $conn
1456          * @return int|bool Returns false on error
1457          */
1458         public function safeGetLag( IDatabase $conn ) {
1459                 if ( $this->getServerCount() == 1 ) {
1460                         return 0;
1461                 } else {
1462                         return $conn->getLag();
1463                 }
1464         }
1465
1466         /**
1467          * Wait for a slave DB to reach a specified master position
1468          *
1469          * This will connect to the master to get an accurate position if $pos is not given
1470          *
1471          * @param IDatabase $conn Slave DB
1472          * @param DBMasterPos|bool $pos Master position; default: current position
1473          * @param integer $timeout Timeout in seconds
1474          * @return bool Success
1475          * @since 1.27
1476          */
1477         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1478                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
1479                         return true; // server is not a slave DB
1480                 }
1481
1482                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1483                 if ( !( $pos instanceof DBMasterPos ) ) {
1484                         return false; // something is misconfigured
1485                 }
1486
1487                 $result = $conn->masterPosWait( $pos, $timeout );
1488                 if ( $result == -1 || is_null( $result ) ) {
1489                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1490                         wfDebugLog( 'replication', "$msg\n" );
1491                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1492                         $ok = false;
1493                 } else {
1494                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1495                         $ok = true;
1496                 }
1497
1498                 return $ok;
1499         }
1500
1501         /**
1502          * Clear the cache for slag lag delay times
1503          *
1504          * This is only used for testing
1505          */
1506         public function clearLagTimeCache() {
1507                 $this->getLoadMonitor()->clearCaches();
1508         }
1509 }