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
  53         /** @var bool|DatabaseBase Database connection that caused a problem */
  54         private $mErrorConnection;
  55         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  56         private $mReadIndex;
  57         /** @var bool|DBMasterPos False if not set */
  58         private $mWaitForPos;
  59         /** @var bool Whether the generic reader fell back to a lagged slave */
  60         private $laggedSlaveMode = false;
  61         /** @var bool Whether the generic reader fell back to a lagged slave */
  62         private $slavesDownMode = false;
  63         /** @var string The last DB selection or connection error */
  64         private $mLastError = 'Unknown error';
  65         /** @var string|bool Reason the LB is read-only or false if not */
  66         private $readOnlyReason = false;
  67         /** @var integer Total connections opened */
  68         private $connsOpened = 0;
  69
  70         /** @var TransactionProfiler */
  71         protected $trxProfiler;
  72
  73         /** @var integer Warn when this many connection are held */
  74         const CONN_HELD_WARN_THRESHOLD = 10;
  75         /** @var integer Default 'max lag' when unspecified */
  76         const MAX_LAG = 10;
  77         /** @var integer Max time to wait for a slave to catch up (e.g. ChronologyProtector) */
  78         const POS_WAIT_TIMEOUT = 10;
  79
  80         /**
  81          * @var boolean
  82          */
  83         private $disabled = false;
  84
  85         /**
  86          * @param array $params Array with keys:
  87          *  - servers : Required. Array of server info structures.
  88          *  - loadMonitor : Name of a class used to fetch server lag and load.
  89          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  90          * @throws MWException
  91          */
  92         public function __construct( array $params ) {
  93                 if ( !isset( $params['servers'] ) ) {
  94                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  95                 }
  96                 $this->mServers = $params['servers'];
  97                 $this->mWaitTimeout = self::POS_WAIT_TIMEOUT;
  98
  99                 $this->mReadIndex = -1;
 100                 $this->mWriteIndex = -1;
 101                 $this->mConns = [
 102                         'local' => [],
 103                         'foreignUsed' => [],
 104                         'foreignFree' => [] ];
 105                 $this->mLoads = [];
 106                 $this->mWaitForPos = false;
 107                 $this->mErrorConnection = false;
 108                 $this->mAllowLagged = false;
 109
 110                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 111                         $this->readOnlyReason = $params['readOnlyReason'];
 112                 }
 113
 114                 if ( isset( $params['loadMonitor'] ) ) {
 115                         $this->mLoadMonitorClass = $params['loadMonitor'];
 116                 } else {
 117                         $master = reset( $params['servers'] );
 118                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 119                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 120                         } else {
 121                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 122                         }
 123                 }
 124
 125                 foreach ( $params['servers'] as $i => $server ) {
 126                         $this->mLoads[$i] = $server['load'];
 127                         if ( isset( $server['groupLoads'] ) ) {
 128                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 129                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 130                                                 $this->mGroupLoads[$group] = [];
 131                                         }
 132                                         $this->mGroupLoads[$group][$i] = $ratio;
 133                                 }
 134                         }
 135                 }
 136
 137                 $this->srvCache = ObjectCache::getLocalServerInstance();
 138
 139                 if ( isset( $params['trxProfiler'] ) ) {
 140                         $this->trxProfiler = $params['trxProfiler'];
 141                 } else {
 142                         $this->trxProfiler = new TransactionProfiler();
 143                 }
 144         }
 145
 146         /**
 147          * Get a LoadMonitor instance
 148          *
 149          * @return LoadMonitor
 150          */
 151         private function getLoadMonitor() {
 152                 if ( !isset( $this->mLoadMonitor ) ) {
 153                         $class = $this->mLoadMonitorClass;
 154                         $this->mLoadMonitor = new $class( $this );
 155                 }
 156
 157                 return $this->mLoadMonitor;
 158         }
 159
 160         /**
 161          * Get or set arbitrary data used by the parent object, usually an LBFactory
 162          * @param mixed $x
 163          * @return mixed
 164          */
 165         public function parentInfo( $x = null ) {
 166                 return wfSetVar( $this->mParentInfo, $x );
 167         }
 168
 169         /**
 170          * @param array $loads
 171          * @param bool|string $wiki Wiki to get non-lagged for
 172          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 173          * @return bool|int|string
 174          */
 175         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) {
 176                 $lags = $this->getLagTimes( $wiki );
 177
 178                 # Unset excessively lagged servers
 179                 foreach ( $lags as $i => $lag ) {
 180                         if ( $i != 0 ) {
 181                                 $maxServerLag = $maxLag;
 182                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 183                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 184                                 }
 185
 186                                 $host = $this->getServerName( $i );
 187                                 if ( $lag === false ) {
 188                                         wfDebugLog( 'replication', "Server $host (#$i) is not replicating?" );
 189                                         unset( $loads[$i] );
 190                                 } elseif ( $lag > $maxServerLag ) {
 191                                         wfDebugLog( 'replication', "Server $host (#$i) has >= $lag seconds of lag" );
 192                                         unset( $loads[$i] );
 193                                 }
 194                         }
 195                 }
 196
 197                 # Find out if all the slaves with non-zero load are lagged
 198                 $sum = 0;
 199                 foreach ( $loads as $load ) {
 200                         $sum += $load;
 201                 }
 202                 if ( $sum == 0 ) {
 203                         # No appropriate DB servers except maybe the master and some slaves with zero load
 204                         # Do NOT use the master
 205                         # Instead, this function will return false, triggering read-only mode,
 206                         # and a lagged slave will be used instead.
 207                         return false;
 208                 }
 209
 210                 if ( count( $loads ) == 0 ) {
 211                         return false;
 212                 }
 213
 214                 # Return a random representative of the remainder
 215                 return ArrayUtils::pickRandom( $loads );
 216         }
 217
 218         /**
 219          * Get the index of the reader connection, which may be a slave
 220          * This takes into account load ratios and lag times. It should
 221          * always return a consistent index during a given invocation
 222          *
 223          * Side effect: opens connections to databases
 224          * @param string|bool $group Query group, or false for the generic reader
 225          * @param string|bool $wiki Wiki ID, or false for the current wiki
 226          * @throws MWException
 227          * @return bool|int|string
 228          */
 229         public function getReaderIndex( $group = false, $wiki = false ) {
 230                 global $wgDBtype;
 231
 232                 # @todo FIXME: For now, only go through all this for mysql databases
 233                 if ( $wgDBtype != 'mysql' ) {
 234                         return $this->getWriterIndex();
 235                 }
 236
 237                 if ( count( $this->mServers ) == 1 ) {
 238                         # Skip the load balancing if there's only one server
 239                         return 0;
 240                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 241                         # Shortcut if generic reader exists already
 242                         return $this->mReadIndex;
 243                 }
 244
 245                 # Find the relevant load array
 246                 if ( $group !== false ) {
 247                         if ( isset( $this->mGroupLoads[$group] ) ) {
 248                                 $nonErrorLoads = $this->mGroupLoads[$group];
 249                         } else {
 250                                 # No loads for this group, return false and the caller can use some other group
 251                                 wfDebugLog( 'connect', __METHOD__ . ": no loads for group $group\n" );
 252
 253                                 return false;
 254                         }
 255                 } else {
 256                         $nonErrorLoads = $this->mLoads;
 257                 }
 258
 259                 if ( !count( $nonErrorLoads ) ) {
 260                         throw new MWException( "Empty server array given to LoadBalancer" );
 261                 }
 262
 263                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 264                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 265
 266                 $laggedSlaveMode = false;
 267
 268                 # No server found yet
 269                 $i = false;
 270                 $conn = false;
 271                 # First try quickly looking through the available servers for a server that
 272                 # meets our criteria
 273                 $currentLoads = $nonErrorLoads;
 274                 while ( count( $currentLoads ) ) {
 275                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 276                                 $i = ArrayUtils::pickRandom( $currentLoads );
 277                         } else {
 278                                 $i = false;
 279                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 280                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 281                                         # This triggers doWait() after connect, so it's especially good to
 282                                         # avoid lagged servers so as to avoid just blocking in that method.
 283                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 284                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 285                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 286                                 }
 287                                 if ( $i === false ) {
 288                                         # Any server with less lag than it's 'max lag' param is preferable
 289                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 290                                 }
 291                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 292                                         # All slaves lagged. Switch to read-only mode
 293                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 294                                         $i = ArrayUtils::pickRandom( $currentLoads );
 295                                         $laggedSlaveMode = true;
 296                                 }
 297                         }
 298
 299                         if ( $i === false ) {
 300                                 # pickRandom() returned false
 301                                 # This is permanent and means the configuration or the load monitor
 302                                 # wants us to return false.
 303                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 304
 305                                 return false;
 306                         }
 307
 308                         $serverName = $this->getServerName( $i );
 309                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 310
 311                         $conn = $this->openConnection( $i, $wiki );
 312                         if ( !$conn ) {
 313                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 314                                 unset( $nonErrorLoads[$i] );
 315                                 unset( $currentLoads[$i] );
 316                                 $i = false;
 317                                 continue;
 318                         }
 319
 320                         // Decrement reference counter, we are finished with this connection.
 321                         // It will be incremented for the caller later.
 322                         if ( $wiki !== false ) {
 323                                 $this->reuseConnection( $conn );
 324                         }
 325
 326                         # Return this server
 327                         break;
 328                 }
 329
 330                 # If all servers were down, quit now
 331                 if ( !count( $nonErrorLoads ) ) {
 332                         wfDebugLog( 'connect', "All servers down" );
 333                 }
 334
 335                 if ( $i !== false ) {
 336                         # Slave connection successful
 337                         # Wait for the session master pos for a short time
 338                         if ( $this->mWaitForPos && $i > 0 ) {
 339                                 if ( !$this->doWait( $i ) ) {
 340                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 341                                 }
 342                         }
 343                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 344                                 $this->mReadIndex = $i;
 345                                 # Record if the generic reader index is in "lagged slave" mode
 346                                 if ( $laggedSlaveMode ) {
 347                                         $this->laggedSlaveMode = true;
 348                                 }
 349                         }
 350                         $serverName = $this->getServerName( $i );
 351                         wfDebugLog( 'connect', __METHOD__ .
 352                                 ": using server $serverName for group '$group'\n" );
 353                 }
 354
 355                 return $i;
 356         }
 357
 358         /**
 359          * Set the master wait position
 360          * If a DB_SLAVE connection has been opened already, waits
 361          * Otherwise sets a variable telling it to wait if such a connection is opened
 362          * @param DBMasterPos $pos
 363          */
 364         public function waitFor( $pos ) {
 365                 $this->mWaitForPos = $pos;
 366                 $i = $this->mReadIndex;
 367
 368                 if ( $i > 0 ) {
 369                         if ( !$this->doWait( $i ) ) {
 370                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 371                                 $this->laggedSlaveMode = true;
 372                         }
 373                 }
 374         }
 375
 376         /**
 377          * Set the master wait position and wait for a "generic" slave to catch up to it
 378          *
 379          * This can be used a faster proxy for waitForAll()
 380          *
 381          * @param DBMasterPos $pos
 382          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 383          * @return bool Success (able to connect and no timeouts reached)
 384          * @since 1.26
 385          */
 386         public function waitForOne( $pos, $timeout = null ) {
 387                 $this->mWaitForPos = $pos;
 388
 389                 $i = $this->mReadIndex;
 390                 if ( $i <= 0 ) {
 391                         // Pick a generic slave if there isn't one yet
 392                         $readLoads = $this->mLoads;
 393                         unset( $readLoads[$this->getWriterIndex()] ); // slaves only
 394                         $readLoads = array_filter( $readLoads ); // with non-zero load
 395                         $i = ArrayUtils::pickRandom( $readLoads );
 396                 }
 397
 398                 if ( $i > 0 ) {
 399                         $ok = $this->doWait( $i, true, $timeout );
 400                 } else {
 401                         $ok = true; // no applicable loads
 402                 }
 403
 404                 return $ok;
 405         }
 406
 407         /**
 408          * Set the master wait position and wait for ALL slaves to catch up to it
 409          * @param DBMasterPos $pos
 410          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 411          * @return bool Success (able to connect and no timeouts reached)
 412          */
 413         public function waitForAll( $pos, $timeout = null ) {
 414                 $this->mWaitForPos = $pos;
 415                 $serverCount = count( $this->mServers );
 416
 417                 $ok = true;
 418                 for ( $i = 1; $i < $serverCount; $i++ ) {
 419                         if ( $this->mLoads[$i] > 0 ) {
 420                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 421                         }
 422                 }
 423
 424                 return $ok;
 425         }
 426
 427         /**
 428          * Get any open connection to a given server index, local or foreign
 429          * Returns false if there is no connection open
 430          *
 431          * @param int $i
 432          * @return DatabaseBase|bool False on failure
 433          */
 434         public function getAnyOpenConnection( $i ) {
 435                 foreach ( $this->mConns as $conns ) {
 436                         if ( !empty( $conns[$i] ) ) {
 437                                 return reset( $conns[$i] );
 438                         }
 439                 }
 440
 441                 return false;
 442         }
 443
 444         /**
 445          * Wait for a given slave to catch up to the master pos stored in $this
 446          * @param int $index Server index
 447          * @param bool $open Check the server even if a new connection has to be made
 448          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 449          * @return bool
 450          */
 451         protected function doWait( $index, $open = false, $timeout = null ) {
 452                 $close = false; // close the connection afterwards
 453
 454                 // Check if we already know that the DB has reached this point
 455                 $server = $this->getServerName( $index );
 456                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 457                 /** @var DBMasterPos $knownReachedPos */
 458                 $knownReachedPos = $this->srvCache->get( $key );
 459                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 460                         wfDebugLog( 'replication', __METHOD__ .
 461                                 ": slave $server known to be caught up (pos >= $knownReachedPos).\n" );
 462                         return true;
 463                 }
 464
 465                 // Find a connection to wait on, creating one if needed and allowed
 466                 $conn = $this->getAnyOpenConnection( $index );
 467                 if ( !$conn ) {
 468                         if ( !$open ) {
 469                                 wfDebugLog( 'replication', __METHOD__ . ": no connection open for $server\n" );
 470
 471                                 return false;
 472                         } else {
 473                                 $conn = $this->openConnection( $index, '' );
 474                                 if ( !$conn ) {
 475                                         wfDebugLog( 'replication', __METHOD__ . ": failed to connect to $server\n" );
 476
 477                                         return false;
 478                                 }
 479                                 // Avoid connection spam in waitForAll() when connections
 480                                 // are made just for the sake of doing this lag check.
 481                                 $close = true;
 482                         }
 483                 }
 484
 485                 wfDebugLog( 'replication', __METHOD__ . ": Waiting for slave $server to catch up...\n" );
 486                 $timeout = $timeout ?: $this->mWaitTimeout;
 487                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 488
 489                 if ( $result == -1 || is_null( $result ) ) {
 490                         // Timed out waiting for slave, use master instead
 491                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 492                         wfDebugLog( 'replication', "$msg\n" );
 493                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 494                         $ok = false;
 495                 } else {
 496                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
 497                         $ok = true;
 498                         // Remember that the DB reached this point
 499                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 500                 }
 501
 502                 if ( $close ) {
 503                         $this->closeConnection( $conn );
 504                 }
 505
 506                 return $ok;
 507         }
 508
 509         /**
 510          * Get a connection by index
 511          * This is the main entry point for this class.
 512          *
 513          * @param int $i Server index
 514          * @param array|string|bool $groups Query group(s), or false for the generic reader
 515          * @param string|bool $wiki Wiki ID, or false for the current wiki
 516          *
 517          * @throws MWException
 518          * @return DatabaseBase
 519          */
 520         public function getConnection( $i, $groups = [], $wiki = false ) {
 521                 if ( $i === null || $i === false ) {
 522                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 523                                 ' with invalid server index' );
 524                 }
 525
 526                 if ( $wiki === wfWikiID() ) {
 527                         $wiki = false;
 528                 }
 529
 530                 $groups = ( $groups === false || $groups === [] )
 531                         ? [ false ] // check one "group": the generic pool
 532                         : (array)$groups;
 533
 534                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 535                 $oldConnsOpened = $this->connsOpened; // connections open now
 536
 537                 if ( $i == DB_MASTER ) {
 538                         $i = $this->getWriterIndex();
 539                 } else {
 540                         # Try to find an available server in any the query groups (in order)
 541                         foreach ( $groups as $group ) {
 542                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 543                                 if ( $groupIndex !== false ) {
 544                                         $i = $groupIndex;
 545                                         break;
 546                                 }
 547                         }
 548                 }
 549
 550                 # Operation-based index
 551                 if ( $i == DB_SLAVE ) {
 552                         $this->mLastError = 'Unknown error'; // reset error string
 553                         # Try the general server pool if $groups are unavailable.
 554                         $i = in_array( false, $groups, true )
 555                                 ? false // don't bother with this if that is what was tried above
 556                                 : $this->getReaderIndex( false, $wiki );
 557                         # Couldn't find a working server in getReaderIndex()?
 558                         if ( $i === false ) {
 559                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 560
 561                                 return $this->reportConnectionError();
 562                         }
 563                 }
 564
 565                 # Now we have an explicit index into the servers array
 566                 $conn = $this->openConnection( $i, $wiki );
 567                 if ( !$conn ) {
 568                         return $this->reportConnectionError();
 569                 }
 570
 571                 # Profile any new connections that happen
 572                 if ( $this->connsOpened > $oldConnsOpened ) {
 573                         $host = $conn->getServer();
 574                         $dbname = $conn->getDBname();
 575                         $trxProf = Profiler::instance()->getTransactionProfiler();
 576                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 577                 }
 578
 579                 if ( $masterOnly ) {
 580                         # Make master-requested DB handles inherit any read-only mode setting
 581                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki ) );
 582                 }
 583
 584                 return $conn;
 585         }
 586
 587         /**
 588          * Mark a foreign connection as being available for reuse under a different
 589          * DB name or prefix. This mechanism is reference-counted, and must be called
 590          * the same number of times as getConnection() to work.
 591          *
 592          * @param DatabaseBase $conn
 593          * @throws MWException
 594          */
 595         public function reuseConnection( $conn ) {
 596                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 597                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 598                 if ( $serverIndex === null || $refCount === null ) {
 599                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 600                         /**
 601                          * This can happen in code like:
 602                          *   foreach ( $dbs as $db ) {
 603                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 604                          *     ...
 605                          *     $lb->reuseConnection( $conn );
 606                          *   }
 607                          * When a connection to the local DB is opened in this way, reuseConnection()
 608                          * should be ignored
 609                          */
 610                         return;
 611                 }
 612
 613                 $dbName = $conn->getDBname();
 614                 $prefix = $conn->tablePrefix();
 615                 if ( strval( $prefix ) !== '' ) {
 616                         $wiki = "$dbName-$prefix";
 617                 } else {
 618                         $wiki = $dbName;
 619                 }
 620                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 621                         throw new MWException( __METHOD__ . ": connection not found, has " .
 622                                 "the connection been freed already?" );
 623                 }
 624                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 625                 if ( $refCount <= 0 ) {
 626                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 627                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 628                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 629                 } else {
 630                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 631                 }
 632         }
 633
 634         /**
 635          * Get a database connection handle reference
 636          *
 637          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 638          *
 639          * @see LoadBalancer::getConnection() for parameter information
 640          *
 641          * @param int $db
 642          * @param array|string|bool $groups Query group(s), or false for the generic reader
 643          * @param string|bool $wiki Wiki ID, or false for the current wiki
 644          * @return DBConnRef
 645          */
 646         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 647                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 648         }
 649
 650         /**
 651          * Get a database connection handle reference without connecting yet
 652          *
 653          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 654          *
 655          * @see LoadBalancer::getConnection() for parameter information
 656          *
 657          * @param int $db
 658          * @param array|string|bool $groups Query group(s), or false for the generic reader
 659          * @param string|bool $wiki Wiki ID, or false for the current wiki
 660          * @return DBConnRef
 661          */
 662         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 663                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 664         }
 665
 666         /**
 667          * Open a connection to the server given by the specified index
 668          * Index must be an actual index into the array.
 669          * If the server is already open, returns it.
 670          *
 671          * On error, returns false, and the connection which caused the
 672          * error will be available via $this->mErrorConnection.
 673          *
 674          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 675          *
 676          * @param int $i Server index
 677          * @param string|bool $wiki Wiki ID, or false for the current wiki
 678          * @return DatabaseBase|bool Returns false on errors
 679          */
 680         public function openConnection( $i, $wiki = false ) {
 681                 if ( $wiki !== false ) {
 682                         $conn = $this->openForeignConnection( $i, $wiki );
 683                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 684                         $conn = $this->mConns['local'][$i][0];
 685                 } else {
 686                         $server = $this->mServers[$i];
 687                         $server['serverIndex'] = $i;
 688                         $conn = $this->reallyOpenConnection( $server, false );
 689                         $serverName = $this->getServerName( $i );
 690                         if ( $conn->isOpen() ) {
 691                                 wfDebugLog( 'connect', "Connected to database $i at $serverName\n" );
 692                                 $this->mConns['local'][$i][0] = $conn;
 693                         } else {
 694                                 wfDebugLog( 'connect', "Failed to connect to database $i at $serverName\n" );
 695                                 $this->mErrorConnection = $conn;
 696                                 $conn = false;
 697                         }
 698                 }
 699
 700                 if ( $conn && !$conn->isOpen() ) {
 701                         // Connection was made but later unrecoverably lost for some reason.
 702                         // Do not return a handle that will just throw exceptions on use,
 703                         // but let the calling code (e.g. getReaderIndex) try another server.
 704                         // See DatabaseMyslBase::ping() for how this can happen.
 705                         $this->mErrorConnection = $conn;
 706                         $conn = false;
 707                 }
 708
 709                 return $conn;
 710         }
 711
 712         /**
 713          * Open a connection to a foreign DB, or return one if it is already open.
 714          *
 715          * Increments a reference count on the returned connection which locks the
 716          * connection to the requested wiki. This reference count can be
 717          * decremented by calling reuseConnection().
 718          *
 719          * If a connection is open to the appropriate server already, but with the wrong
 720          * database, it will be switched to the right database and returned, as long as
 721          * it has been freed first with reuseConnection().
 722          *
 723          * On error, returns false, and the connection which caused the
 724          * error will be available via $this->mErrorConnection.
 725          *
 726          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 727          *
 728          * @param int $i Server index
 729          * @param string $wiki Wiki ID to open
 730          * @return DatabaseBase
 731          */
 732         private function openForeignConnection( $i, $wiki ) {
 733                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 734                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 735                         // Reuse an already-used connection
 736                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 737                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 738                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 739                         // Reuse a free connection for the same wiki
 740                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 741                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 742                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 743                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 744                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 745                         // Reuse a connection from another wiki
 746                         $conn = reset( $this->mConns['foreignFree'][$i] );
 747                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 748
 749                         // The empty string as a DB name means "don't care".
 750                         // DatabaseMysqlBase::open() already handle this on connection.
 751                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 752                                 $this->mLastError = "Error selecting database $dbName on server " .
 753                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 754                                 $this->mErrorConnection = $conn;
 755                                 $conn = false;
 756                         } else {
 757                                 $conn->tablePrefix( $prefix );
 758                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 759                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 760                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 761                         }
 762                 } else {
 763                         // Open a new connection
 764                         $server = $this->mServers[$i];
 765                         $server['serverIndex'] = $i;
 766                         $server['foreignPoolRefCount'] = 0;
 767                         $server['foreign'] = true;
 768                         $conn = $this->reallyOpenConnection( $server, $dbName );
 769                         if ( !$conn->isOpen() ) {
 770                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 771                                 $this->mErrorConnection = $conn;
 772                                 $conn = false;
 773                         } else {
 774                                 $conn->tablePrefix( $prefix );
 775                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 776                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 777                         }
 778                 }
 779
 780                 // Increment reference count
 781                 if ( $conn ) {
 782                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 783                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 784                 }
 785
 786                 return $conn;
 787         }
 788
 789         /**
 790          * Test if the specified index represents an open connection
 791          *
 792          * @param int $index Server index
 793          * @access private
 794          * @return bool
 795          */
 796         private function isOpen( $index ) {
 797                 if ( !is_integer( $index ) ) {
 798                         return false;
 799                 }
 800
 801                 return (bool)$this->getAnyOpenConnection( $index );
 802         }
 803
 804         /**
 805          * Really opens a connection. Uncached.
 806          * Returns a Database object whether or not the connection was successful.
 807          * @access private
 808          *
 809          * @param array $server
 810          * @param bool $dbNameOverride
 811          * @throws MWException
 812          * @return DatabaseBase
 813          */
 814         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 815                 if ( $this->disabled ) {
 816                         throw new DBAccessError();
 817                 }
 818
 819                 if ( !is_array( $server ) ) {
 820                         throw new MWException( 'You must update your load-balancing configuration. ' .
 821                                 'See DefaultSettings.php entry for $wgDBservers.' );
 822                 }
 823
 824                 if ( $dbNameOverride !== false ) {
 825                         $server['dbname'] = $dbNameOverride;
 826                 }
 827
 828                 // Let the handle know what the cluster master is (e.g. "db1052")
 829                 $masterName = $this->getServerName( 0 );
 830                 $server['clusterMasterHost'] = $masterName;
 831
 832                 // Log when many connection are made on requests
 833                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 834                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 835                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 836                                 wfBacktrace( true ) );
 837                 }
 838
 839                 # Create object
 840                 try {
 841                         $db = DatabaseBase::factory( $server['type'], $server );
 842                 } catch ( DBConnectionError $e ) {
 843                         // FIXME: This is probably the ugliest thing I have ever done to
 844                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 845                         $db = $e->db;
 846                 }
 847
 848                 $db->setLBInfo( $server );
 849                 $db->setLazyMasterHandle(
 850                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 851                 );
 852                 $db->setTransactionProfiler( $this->trxProfiler );
 853
 854                 return $db;
 855         }
 856
 857         /**
 858          * @throws DBConnectionError
 859          * @return bool
 860          */
 861         private function reportConnectionError() {
 862                 $conn = $this->mErrorConnection; // The connection which caused the error
 863                 $context = [
 864                         'method' => __METHOD__,
 865                         'last_error' => $this->mLastError,
 866                 ];
 867
 868                 if ( !is_object( $conn ) ) {
 869                         // No last connection, probably due to all servers being too busy
 870                         wfLogDBError(
 871                                 "LB failure with no last connection. Connection error: {last_error}",
 872                                 $context
 873                         );
 874
 875                         // If all servers were busy, mLastError will contain something sensible
 876                         throw new DBConnectionError( null, $this->mLastError );
 877                 } else {
 878                         $context['db_server'] = $conn->getProperty( 'mServer' );
 879                         wfLogDBError(
 880                                 "Connection error: {last_error} ({db_server})",
 881                                 $context
 882                         );
 883
 884                         // throws DBConnectionError
 885                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 886                 }
 887
 888                 return false; /* not reached */
 889         }
 890
 891         /**
 892          * @return int
 893          * @since 1.26
 894          */
 895         public function getWriterIndex() {
 896                 return 0;
 897         }
 898
 899         /**
 900          * Returns true if the specified index is a valid server index
 901          *
 902          * @param string $i
 903          * @return bool
 904          */
 905         public function haveIndex( $i ) {
 906                 return array_key_exists( $i, $this->mServers );
 907         }
 908
 909         /**
 910          * Returns true if the specified index is valid and has non-zero load
 911          *
 912          * @param string $i
 913          * @return bool
 914          */
 915         public function isNonZeroLoad( $i ) {
 916                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 917         }
 918
 919         /**
 920          * Get the number of defined servers (not the number of open connections)
 921          *
 922          * @return int
 923          */
 924         public function getServerCount() {
 925                 return count( $this->mServers );
 926         }
 927
 928         /**
 929          * Get the host name or IP address of the server with the specified index
 930          * Prefer a readable name if available.
 931          * @param string $i
 932          * @return string
 933          */
 934         public function getServerName( $i ) {
 935                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 936                         $name = $this->mServers[$i]['hostName'];
 937                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 938                         $name = $this->mServers[$i]['host'];
 939                 } else {
 940                         $name = '';
 941                 }
 942
 943                 return ( $name != '' ) ? $name : 'localhost';
 944         }
 945
 946         /**
 947          * Return the server info structure for a given index, or false if the index is invalid.
 948          * @param int $i
 949          * @return array|bool
 950          */
 951         public function getServerInfo( $i ) {
 952                 if ( isset( $this->mServers[$i] ) ) {
 953                         return $this->mServers[$i];
 954                 } else {
 955                         return false;
 956                 }
 957         }
 958
 959         /**
 960          * Sets the server info structure for the given index. Entry at index $i
 961          * is created if it doesn't exist
 962          * @param int $i
 963          * @param array $serverInfo
 964          */
 965         public function setServerInfo( $i, array $serverInfo ) {
 966                 $this->mServers[$i] = $serverInfo;
 967         }
 968
 969         /**
 970          * Get the current master position for chronology control purposes
 971          * @return mixed
 972          */
 973         public function getMasterPos() {
 974                 # If this entire request was served from a slave without opening a connection to the
 975                 # master (however unlikely that may be), then we can fetch the position from the slave.
 976                 $masterConn = $this->getAnyOpenConnection( 0 );
 977                 if ( !$masterConn ) {
 978                         $serverCount = count( $this->mServers );
 979                         for ( $i = 1; $i < $serverCount; $i++ ) {
 980                                 $conn = $this->getAnyOpenConnection( $i );
 981                                 if ( $conn ) {
 982                                         return $conn->getSlavePos();
 983                                 }
 984                         }
 985                 } else {
 986                         return $masterConn->getMasterPos();
 987                 }
 988
 989                 return false;
 990         }
 991
 992         /**
 993          * Disable this load balancer. All connections are closed, and any attempt to
 994          * open a new connection will result in a DBAccessError.
 995          *
 996          * @since 1.27
 997          */
 998         public function disable() {
 999                 $this->closeAll();
1000                 $this->disabled = true;
1001         }
1002
1003         /**
1004          * Close all open connections
1005          */
1006         public function closeAll() {
1007                 foreach ( $this->mConns as $conns2 ) {
1008                         foreach ( $conns2 as $conns3 ) {
1009                                 /** @var DatabaseBase $conn */
1010                                 foreach ( $conns3 as $conn ) {
1011                                         $conn->close();
1012                                 }
1013                         }
1014                 }
1015                 $this->mConns = [
1016                         'local' => [],
1017                         'foreignFree' => [],
1018                         'foreignUsed' => [],
1019                 ];
1020                 $this->connsOpened = 0;
1021         }
1022
1023         /**
1024          * Close a connection
1025          * Using this function makes sure the LoadBalancer knows the connection is closed.
1026          * If you use $conn->close() directly, the load balancer won't update its state.
1027          * @param DatabaseBase $conn
1028          */
1029         public function closeConnection( $conn ) {
1030                 $done = false;
1031                 foreach ( $this->mConns as $i1 => $conns2 ) {
1032                         foreach ( $conns2 as $i2 => $conns3 ) {
1033                                 foreach ( $conns3 as $i3 => $candidateConn ) {
1034                                         if ( $conn === $candidateConn ) {
1035                                                 $conn->close();
1036                                                 unset( $this->mConns[$i1][$i2][$i3] );
1037                                                 --$this->connsOpened;
1038                                                 $done = true;
1039                                                 break;
1040                                         }
1041                                 }
1042                         }
1043                 }
1044                 if ( !$done ) {
1045                         $conn->close();
1046                 }
1047         }
1048
1049         /**
1050          * Commit transactions on all open connections
1051          * @param string $fname Caller name
1052          */
1053         public function commitAll( $fname = __METHOD__ ) {
1054                 foreach ( $this->mConns as $conns2 ) {
1055                         foreach ( $conns2 as $conns3 ) {
1056                                 /** @var DatabaseBase[] $conns3 */
1057                                 foreach ( $conns3 as $conn ) {
1058                                         if ( $conn->trxLevel() ) {
1059                                                 $conn->commit( $fname, 'flush' );
1060                                         }
1061                                 }
1062                         }
1063                 }
1064         }
1065
1066         /**
1067          * Issue COMMIT only on master, only if queries were done on connection
1068          * @param string $fname Caller name
1069          */
1070         public function commitMasterChanges( $fname = __METHOD__ ) {
1071                 $masterIndex = $this->getWriterIndex();
1072                 foreach ( $this->mConns as $conns2 ) {
1073                         if ( empty( $conns2[$masterIndex] ) ) {
1074                                 continue;
1075                         }
1076                         /** @var DatabaseBase $conn */
1077                         foreach ( $conns2[$masterIndex] as $conn ) {
1078                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1079                                         $conn->commit( $fname, 'flush' );
1080                                 }
1081                         }
1082                 }
1083         }
1084
1085         /**
1086          * Issue ROLLBACK only on master, only if queries were done on connection
1087          * @param string $fname Caller name
1088          * @throws DBExpectedError
1089          * @since 1.23
1090          */
1091         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1092                 $failedServers = [];
1093
1094                 $masterIndex = $this->getWriterIndex();
1095                 foreach ( $this->mConns as $conns2 ) {
1096                         if ( empty( $conns2[$masterIndex] ) ) {
1097                                 continue;
1098                         }
1099                         /** @var DatabaseBase $conn */
1100                         foreach ( $conns2[$masterIndex] as $conn ) {
1101                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1102                                         try {
1103                                                 $conn->rollback( $fname, 'flush' );
1104                                         } catch ( DBError $e ) {
1105                                                 MWExceptionHandler::logException( $e );
1106                                                 $failedServers[] = $conn->getServer();
1107                                         }
1108                                 }
1109                         }
1110                 }
1111
1112                 if ( $failedServers ) {
1113                         throw new DBExpectedError( null, "Rollback failed on server(s) " .
1114                                 implode( ', ', array_unique( $failedServers ) ) );
1115                 }
1116         }
1117
1118         /**
1119          * @return bool Whether a master connection is already open
1120          * @since 1.24
1121          */
1122         public function hasMasterConnection() {
1123                 return $this->isOpen( $this->getWriterIndex() );
1124         }
1125
1126         /**
1127          * Determine if there are pending changes in a transaction by this thread
1128          * @since 1.23
1129          * @return bool
1130          */
1131         public function hasMasterChanges() {
1132                 $masterIndex = $this->getWriterIndex();
1133                 foreach ( $this->mConns as $conns2 ) {
1134                         if ( empty( $conns2[$masterIndex] ) ) {
1135                                 continue;
1136                         }
1137                         /** @var DatabaseBase $conn */
1138                         foreach ( $conns2[$masterIndex] as $conn ) {
1139                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1140                                         return true;
1141                                 }
1142                         }
1143                 }
1144                 return false;
1145         }
1146
1147         /**
1148          * Get the timestamp of the latest write query done by this thread
1149          * @since 1.25
1150          * @return float|bool UNIX timestamp or false
1151          */
1152         public function lastMasterChangeTimestamp() {
1153                 $lastTime = false;
1154                 $masterIndex = $this->getWriterIndex();
1155                 foreach ( $this->mConns as $conns2 ) {
1156                         if ( empty( $conns2[$masterIndex] ) ) {
1157                                 continue;
1158                         }
1159                         /** @var DatabaseBase $conn */
1160                         foreach ( $conns2[$masterIndex] as $conn ) {
1161                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1162                         }
1163                 }
1164                 return $lastTime;
1165         }
1166
1167         /**
1168          * Check if this load balancer object had any recent or still
1169          * pending writes issued against it by this PHP thread
1170          *
1171          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1172          * @return bool
1173          * @since 1.25
1174          */
1175         public function hasOrMadeRecentMasterChanges( $age = null ) {
1176                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1177
1178                 return ( $this->hasMasterChanges()
1179                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1180         }
1181
1182         /**
1183          * Get the list of callers that have pending master changes
1184          *
1185          * @return array
1186          * @since 1.27
1187          */
1188         public function pendingMasterChangeCallers() {
1189                 $fnames = [];
1190
1191                 $masterIndex = $this->getWriterIndex();
1192                 foreach ( $this->mConns as $conns2 ) {
1193                         if ( empty( $conns2[$masterIndex] ) ) {
1194                                 continue;
1195                         }
1196                         /** @var DatabaseBase $conn */
1197                         foreach ( $conns2[$masterIndex] as $conn ) {
1198                                 $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1199                         }
1200                 }
1201
1202                 return $fnames;
1203         }
1204
1205         /**
1206          * @param mixed $value
1207          * @return mixed
1208          */
1209         public function waitTimeout( $value = null ) {
1210                 return wfSetVar( $this->mWaitTimeout, $value );
1211         }
1212
1213         /**
1214          * @note This method will trigger a DB connection if not yet done
1215          *
1216          * @param string|bool $wiki Wiki ID, or false for the current wiki
1217          * @return bool Whether the generic connection for reads is highly "lagged"
1218          */
1219         public function getLaggedSlaveMode( $wiki = false ) {
1220                 // No-op if there is only one DB (also avoids recursion)
1221                 if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
1222                         try {
1223                                 // See if laggedSlaveMode gets set
1224                                 $conn = $this->getConnection( DB_SLAVE, false, $wiki );
1225                                 $this->reuseConnection( $conn );
1226                         } catch ( DBConnectionError $e ) {
1227                                 // Avoid expensive re-connect attempts and failures
1228                                 $this->slavesDownMode = true;
1229                                 $this->laggedSlaveMode = true;
1230                         }
1231                 }
1232
1233                 return $this->laggedSlaveMode;
1234         }
1235
1236         /**
1237          * @note This method will never cause a new DB connection
1238          * @return bool Whether any generic connection used for reads was highly "lagged"
1239          * @since 1.27
1240          */
1241         public function laggedSlaveUsed() {
1242                 return $this->laggedSlaveMode;
1243         }
1244
1245         /**
1246          * @note This method may trigger a DB connection if not yet done
1247          * @param string|bool $wiki Wiki ID, or false for the current wiki
1248          * @return string|bool Reason the master is read-only or false if it is not
1249          * @since 1.27
1250          */
1251         public function getReadOnlyReason( $wiki = false ) {
1252                 if ( $this->readOnlyReason !== false ) {
1253                         return $this->readOnlyReason;
1254                 } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
1255                         if ( $this->slavesDownMode ) {
1256                                 return 'The database has been automatically locked ' .
1257                                         'until the slave database servers become available';
1258                         } else {
1259                                 return 'The database has been automatically locked ' .
1260                                         'while the slave database servers catch up to the master.';
1261                         }
1262                 }
1263
1264                 return false;
1265         }
1266
1267         /**
1268          * Disables/enables lag checks
1269          * @param null|bool $mode
1270          * @return bool
1271          */
1272         public function allowLagged( $mode = null ) {
1273                 if ( $mode === null ) {
1274                         return $this->mAllowLagged;
1275                 }
1276                 $this->mAllowLagged = $mode;
1277
1278                 return $this->mAllowLagged;
1279         }
1280
1281         /**
1282          * @return bool
1283          */
1284         public function pingAll() {
1285                 $success = true;
1286                 foreach ( $this->mConns as $conns2 ) {
1287                         foreach ( $conns2 as $conns3 ) {
1288                                 /** @var DatabaseBase[] $conns3 */
1289                                 foreach ( $conns3 as $conn ) {
1290                                         if ( !$conn->ping() ) {
1291                                                 $success = false;
1292                                         }
1293                                 }
1294                         }
1295                 }
1296
1297                 return $success;
1298         }
1299
1300         /**
1301          * Call a function with each open connection object
1302          * @param callable $callback
1303          * @param array $params
1304          */
1305         public function forEachOpenConnection( $callback, array $params = [] ) {
1306                 foreach ( $this->mConns as $conns2 ) {
1307                         foreach ( $conns2 as $conns3 ) {
1308                                 foreach ( $conns3 as $conn ) {
1309                                         $mergedParams = array_merge( [ $conn ], $params );
1310                                         call_user_func_array( $callback, $mergedParams );
1311                                 }
1312                         }
1313                 }
1314         }
1315
1316         /**
1317          * Get the hostname and lag time of the most-lagged slave
1318          *
1319          * This is useful for maintenance scripts that need to throttle their updates.
1320          * May attempt to open connections to slaves on the default DB. If there is
1321          * no lag, the maximum lag will be reported as -1.
1322          *
1323          * @param bool|string $wiki Wiki ID, or false for the default database
1324          * @return array ( host, max lag, index of max lagged host )
1325          */
1326         public function getMaxLag( $wiki = false ) {
1327                 $maxLag = -1;
1328                 $host = '';
1329                 $maxIndex = 0;
1330
1331                 if ( $this->getServerCount() <= 1 ) {
1332                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1333                 }
1334
1335                 $lagTimes = $this->getLagTimes( $wiki );
1336                 foreach ( $lagTimes as $i => $lag ) {
1337                         if ( $lag > $maxLag ) {
1338                                 $maxLag = $lag;
1339                                 $host = $this->mServers[$i]['host'];
1340                                 $maxIndex = $i;
1341                         }
1342                 }
1343
1344                 return [ $host, $maxLag, $maxIndex ];
1345         }
1346
1347         /**
1348          * Get an estimate of replication lag (in seconds) for each server
1349          *
1350          * Results are cached for a short time in memcached/process cache
1351          *
1352          * Values may be "false" if replication is too broken to estimate
1353          *
1354          * @param string|bool $wiki
1355          * @return int[] Map of (server index => float|int|bool)
1356          */
1357         public function getLagTimes( $wiki = false ) {
1358                 if ( $this->getServerCount() <= 1 ) {
1359                         return [ 0 => 0 ]; // no replication = no lag
1360                 }
1361
1362                 # Send the request to the load monitor
1363                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1364         }
1365
1366         /**
1367          * Get the lag in seconds for a given connection, or zero if this load
1368          * balancer does not have replication enabled.
1369          *
1370          * This should be used in preference to Database::getLag() in cases where
1371          * replication may not be in use, since there is no way to determine if
1372          * replication is in use at the connection level without running
1373          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1374          * function instead of Database::getLag() avoids a fatal error in this
1375          * case on many installations.
1376          *
1377          * @param IDatabase $conn
1378          * @return int|bool Returns false on error
1379          */
1380         public function safeGetLag( IDatabase $conn ) {
1381                 if ( $this->getServerCount() == 1 ) {
1382                         return 0;
1383                 } else {
1384                         return $conn->getLag();
1385                 }
1386         }
1387
1388         /**
1389          * Wait for a slave DB to reach a specified master position
1390          *
1391          * This will connect to the master to get an accurate position if $pos is not given
1392          *
1393          * @param IDatabase $conn Slave DB
1394          * @param DBMasterPos|bool $pos Master position; default: current position
1395          * @param integer $timeout Timeout in seconds
1396          * @return bool Success
1397          * @since 1.27
1398          */
1399         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1400                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'slave' ) ) {
1401                         return true; // server is not a slave DB
1402                 }
1403
1404                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1405                 if ( !$pos ) {
1406                         return false; // something is misconfigured
1407                 }
1408
1409                 $result = $conn->masterPosWait( $pos, $timeout );
1410                 if ( $result == -1 || is_null( $result ) ) {
1411                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1412                         wfDebugLog( 'replication', "$msg\n" );
1413                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
1414                         $ok = false;
1415                 } else {
1416                         wfDebugLog( 'replication', __METHOD__ . ": Done\n" );
1417                         $ok = true;
1418                 }
1419
1420                 return $ok;
1421         }
1422
1423         /**
1424          * Clear the cache for slag lag delay times
1425          *
1426          * This is only used for testing
1427          */
1428         public function clearLagTimeCache() {
1429                 $this->getLoadMonitor()->clearCaches();
1430         }
1431 }