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
  44         /** @var array LBFactory information */
  45         private $mParentInfo;
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50
  51         /** @var bool|DatabaseBase Database connection that caused a problem */
  52         private $mErrorConnection;
  53         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  54         private $mReadIndex;
  55         /** @var bool|DBMasterPos False if not set */
  56         private $mWaitForPos;
  57         /** @var bool Whether the generic reader fell back to a lagged slave */
  58         private $mLaggedSlaveMode;
  59         /** @var string The last DB selection or connection error */
  60         private $mLastError = 'Unknown error';
  61         /** @var integer Total connections opened */
  62         private $connsOpened = 0;
  63
  64         /** @var integer Warn when this many connection are held */
  65         const CONN_HELD_WARN_THRESHOLD = 10;
  66
  67         /**
  68          * @param array $params Array with keys:
  69          *   servers           Required. Array of server info structures.
  70          *   loadMonitor       Name of a class used to fetch server lag and load.
  71          * @throws MWException
  72          */
  73         public function __construct( array $params ) {
  74                 if ( !isset( $params['servers'] ) ) {
  75                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  76                 }
  77                 $this->mServers = $params['servers'];
  78                 $this->mWaitTimeout = 10;
  79
  80                 $this->mReadIndex = -1;
  81                 $this->mWriteIndex = -1;
  82                 $this->mConns = array(
  83                         'local' => array(),
  84                         'foreignUsed' => array(),
  85                         'foreignFree' => array() );
  86                 $this->mLoads = array();
  87                 $this->mWaitForPos = false;
  88                 $this->mLaggedSlaveMode = false;
  89                 $this->mErrorConnection = false;
  90                 $this->mAllowLagged = false;
  91
  92                 if ( isset( $params['loadMonitor'] ) ) {
  93                         $this->mLoadMonitorClass = $params['loadMonitor'];
  94                 } else {
  95                         $master = reset( $params['servers'] );
  96                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  97                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  98                         } else {
  99                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 100                         }
 101                 }
 102
 103                 foreach ( $params['servers'] as $i => $server ) {
 104                         $this->mLoads[$i] = $server['load'];
 105                         if ( isset( $server['groupLoads'] ) ) {
 106                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 107                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 108                                                 $this->mGroupLoads[$group] = array();
 109                                         }
 110                                         $this->mGroupLoads[$group][$i] = $ratio;
 111                                 }
 112                         }
 113                 }
 114         }
 115
 116         /**
 117          * Get a LoadMonitor instance
 118          *
 119          * @return LoadMonitor
 120          */
 121         private function getLoadMonitor() {
 122                 if ( !isset( $this->mLoadMonitor ) ) {
 123                         $class = $this->mLoadMonitorClass;
 124                         $this->mLoadMonitor = new $class( $this );
 125                 }
 126
 127                 return $this->mLoadMonitor;
 128         }
 129
 130         /**
 131          * Get or set arbitrary data used by the parent object, usually an LBFactory
 132          * @param mixed $x
 133          * @return mixed
 134          */
 135         public function parentInfo( $x = null ) {
 136                 return wfSetVar( $this->mParentInfo, $x );
 137         }
 138
 139         /**
 140          * Given an array of non-normalised probabilities, this function will select
 141          * an element and return the appropriate key
 142          *
 143          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 144          *
 145          * @param array $weights
 146          * @return bool|int|string
 147          */
 148         public function pickRandom( array $weights ) {
 149                 return ArrayUtils::pickRandom( $weights );
 150         }
 151
 152         /**
 153          * @param array $loads
 154          * @param bool|string $wiki Wiki to get non-lagged for
 155          * @param float $maxLag Restrict the maximum allowed lag to this many seconds
 156          * @return bool|int|string
 157          */
 158         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 159                 $lags = $this->getLagTimes( $wiki );
 160
 161                 # Unset excessively lagged servers
 162                 foreach ( $lags as $i => $lag ) {
 163                         if ( $i != 0 ) {
 164                                 $maxServerLag = $maxLag;
 165                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 166                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 167                                 }
 168                                 if ( $lag === false ) {
 169                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 170                                         unset( $loads[$i] );
 171                                 } elseif ( $lag > $maxServerLag ) {
 172                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 173                                         unset( $loads[$i] );
 174                                 }
 175                         }
 176                 }
 177
 178                 # Find out if all the slaves with non-zero load are lagged
 179                 $sum = 0;
 180                 foreach ( $loads as $load ) {
 181                         $sum += $load;
 182                 }
 183                 if ( $sum == 0 ) {
 184                         # No appropriate DB servers except maybe the master and some slaves with zero load
 185                         # Do NOT use the master
 186                         # Instead, this function will return false, triggering read-only mode,
 187                         # and a lagged slave will be used instead.
 188                         return false;
 189                 }
 190
 191                 if ( count( $loads ) == 0 ) {
 192                         return false;
 193                 }
 194
 195                 # wfDebugLog( 'connect', var_export( $loads, true ) );
 196
 197                 # Return a random representative of the remainder
 198                 return ArrayUtils::pickRandom( $loads );
 199         }
 200
 201         /**
 202          * Get the index of the reader connection, which may be a slave
 203          * This takes into account load ratios and lag times. It should
 204          * always return a consistent index during a given invocation
 205          *
 206          * Side effect: opens connections to databases
 207          * @param string|bool $group Query group, or false for the generic reader
 208          * @param string|bool $wiki Wiki ID, or false for the current wiki
 209          * @throws MWException
 210          * @return bool|int|string
 211          */
 212         public function getReaderIndex( $group = false, $wiki = false ) {
 213                 global $wgDBtype;
 214
 215                 # @todo FIXME: For now, only go through all this for mysql databases
 216                 if ( $wgDBtype != 'mysql' ) {
 217                         return $this->getWriterIndex();
 218                 }
 219
 220                 if ( count( $this->mServers ) == 1 ) {
 221                         # Skip the load balancing if there's only one server
 222                         return 0;
 223                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 224                         # Shortcut if generic reader exists already
 225                         return $this->mReadIndex;
 226                 }
 227
 228                 # Find the relevant load array
 229                 if ( $group !== false ) {
 230                         if ( isset( $this->mGroupLoads[$group] ) ) {
 231                                 $nonErrorLoads = $this->mGroupLoads[$group];
 232                         } else {
 233                                 # No loads for this group, return false and the caller can use some other group
 234                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 235
 236                                 return false;
 237                         }
 238                 } else {
 239                         $nonErrorLoads = $this->mLoads;
 240                 }
 241
 242                 if ( !count( $nonErrorLoads ) ) {
 243                         throw new MWException( "Empty server array given to LoadBalancer" );
 244                 }
 245
 246                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 247                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 248
 249                 $laggedSlaveMode = false;
 250
 251                 # No server found yet
 252                 $i = false;
 253                 $conn = false;
 254                 # First try quickly looking through the available servers for a server that
 255                 # meets our criteria
 256                 $currentLoads = $nonErrorLoads;
 257                 while ( count( $currentLoads ) ) {
 258                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 259                                 $i = ArrayUtils::pickRandom( $currentLoads );
 260                         } else {
 261                                 $i = false;
 262                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 263                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 264                                         # This triggers doWait() after connect, so it's especially good to
 265                                         # avoid lagged servers so as to avoid just blocking in that method.
 266                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 267                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 268                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 269                                 }
 270                                 if ( $i === false ) {
 271                                         # Any server with less lag than it's 'max lag' param is preferable
 272                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 273                                 }
 274                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 275                                         # All slaves lagged. Switch to read-only mode
 276                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 277                                         $i = ArrayUtils::pickRandom( $currentLoads );
 278                                         $laggedSlaveMode = true;
 279                                 }
 280                         }
 281
 282                         if ( $i === false ) {
 283                                 # pickRandom() returned false
 284                                 # This is permanent and means the configuration or the load monitor
 285                                 # wants us to return false.
 286                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 287
 288                                 return false;
 289                         }
 290
 291                         $serverName = $this->getServerName( $i );
 292                         wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: $serverName..." );
 293
 294                         $conn = $this->openConnection( $i, $wiki );
 295                         if ( !$conn ) {
 296                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 297                                 unset( $nonErrorLoads[$i] );
 298                                 unset( $currentLoads[$i] );
 299                                 $i = false;
 300                                 continue;
 301                         }
 302
 303                         // Decrement reference counter, we are finished with this connection.
 304                         // It will be incremented for the caller later.
 305                         if ( $wiki !== false ) {
 306                                 $this->reuseConnection( $conn );
 307                         }
 308
 309                         # Return this server
 310                         break;
 311                 }
 312
 313                 # If all servers were down, quit now
 314                 if ( !count( $nonErrorLoads ) ) {
 315                         wfDebugLog( 'connect', "All servers down" );
 316                 }
 317
 318                 if ( $i !== false ) {
 319                         # Slave connection successful
 320                         # Wait for the session master pos for a short time
 321                         if ( $this->mWaitForPos && $i > 0 ) {
 322                                 if ( !$this->doWait( $i ) ) {
 323                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 324                                 }
 325                         }
 326                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 327                                 $this->mReadIndex = $i;
 328                                 # Record if the generic reader index is in "lagged slave" mode
 329                                 if ( $laggedSlaveMode ) {
 330                                         $this->mLaggedSlaveMode = true;
 331                                 }
 332                         }
 333                         $serverName = $this->getServerName( $i );
 334                         wfDebug( __METHOD__ . ": using server $serverName for group '$group'\n" );
 335                 }
 336
 337                 return $i;
 338         }
 339
 340         /**
 341          * Set the master wait position
 342          * If a DB_SLAVE connection has been opened already, waits
 343          * Otherwise sets a variable telling it to wait if such a connection is opened
 344          * @param DBMasterPos $pos
 345          */
 346         public function waitFor( $pos ) {
 347                 $this->mWaitForPos = $pos;
 348                 $i = $this->mReadIndex;
 349
 350                 if ( $i > 0 ) {
 351                         if ( !$this->doWait( $i ) ) {
 352                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 353                                 $this->mLaggedSlaveMode = true;
 354                         }
 355                 }
 356         }
 357
 358         /**
 359          * Set the master wait position and wait for a "generic" slave to catch up to it
 360          *
 361          * This can be used a faster proxy for waitForAll()
 362          *
 363          * @param DBMasterPos $pos
 364          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 365          * @return bool Success (able to connect and no timeouts reached)
 366          * @since 1.26
 367          */
 368         public function waitForOne( $pos, $timeout = null ) {
 369                 $this->mWaitForPos = $pos;
 370
 371                 $i = $this->mReadIndex;
 372                 if ( $i <= 0 ) {
 373                         // Pick a generic slave if there isn't one yet
 374                         $readLoads = $this->mLoads;
 375                         unset( $readLoads[$this->getWriterIndex()] ); // slaves only
 376                         $readLoads = array_filter( $readLoads ); // with non-zero load
 377                         $i = ArrayUtils::pickRandom( $readLoads );
 378                 }
 379
 380                 if ( $i > 0 ) {
 381                         $ok = $this->doWait( $i, true, $timeout );
 382                 } else {
 383                         $ok = true; // no applicable loads
 384                 }
 385
 386                 return $ok;
 387         }
 388
 389         /**
 390          * Set the master wait position and wait for ALL slaves to catch up to it
 391          * @param DBMasterPos $pos
 392          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 393          * @return bool Success (able to connect and no timeouts reached)
 394          */
 395         public function waitForAll( $pos, $timeout = null ) {
 396                 $this->mWaitForPos = $pos;
 397                 $serverCount = count( $this->mServers );
 398
 399                 $ok = true;
 400                 for ( $i = 1; $i < $serverCount; $i++ ) {
 401                         if ( $this->mLoads[$i] > 0 ) {
 402                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 403                         }
 404                 }
 405
 406                 return $ok;
 407         }
 408
 409         /**
 410          * Get any open connection to a given server index, local or foreign
 411          * Returns false if there is no connection open
 412          *
 413          * @param int $i
 414          * @return DatabaseBase|bool False on failure
 415          */
 416         public function getAnyOpenConnection( $i ) {
 417                 foreach ( $this->mConns as $conns ) {
 418                         if ( !empty( $conns[$i] ) ) {
 419                                 return reset( $conns[$i] );
 420                         }
 421                 }
 422
 423                 return false;
 424         }
 425
 426         /**
 427          * Wait for a given slave to catch up to the master pos stored in $this
 428          * @param int $index Server index
 429          * @param bool $open Check the server even if a new connection has to be made
 430          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 431          * @return bool
 432          */
 433         protected function doWait( $index, $open = false, $timeout = null ) {
 434                 $close = false; // close the connection afterwards
 435
 436                 # Find a connection to wait on, creating one if needed and allowed
 437                 $conn = $this->getAnyOpenConnection( $index );
 438                 if ( !$conn ) {
 439                         if ( !$open ) {
 440                                 wfDebug( __METHOD__ . ": no connection open\n" );
 441
 442                                 return false;
 443                         } else {
 444                                 $conn = $this->openConnection( $index, '' );
 445                                 if ( !$conn ) {
 446                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 447
 448                                         return false;
 449                                 }
 450                                 // Avoid connection spam in waitForAll() when connections
 451                                 // are made just for the sake of doing this lag check.
 452                                 $close = true;
 453                         }
 454                 }
 455
 456                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 457                 $timeout = $timeout ?: $this->mWaitTimeout;
 458                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 459
 460                 if ( $result == -1 || is_null( $result ) ) {
 461                         # Timed out waiting for slave, use master instead
 462                         $server = $server = $this->getServerName( $index );
 463                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 464                         wfDebug( "$msg\n" );
 465                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 466                         $ok = false;
 467                 } else {
 468                         wfDebug( __METHOD__ . ": Done\n" );
 469                         $ok = true;
 470                 }
 471
 472                 if ( $close ) {
 473                         $this->closeConnection( $conn );
 474                 }
 475
 476                 return $ok;
 477         }
 478
 479         /**
 480          * Get a connection by index
 481          * This is the main entry point for this class.
 482          *
 483          * @param int $i Server index
 484          * @param array|string|bool $groups Query group(s), or false for the generic reader
 485          * @param string|bool $wiki Wiki ID, or false for the current wiki
 486          *
 487          * @throws MWException
 488          * @return DatabaseBase
 489          */
 490         public function getConnection( $i, $groups = array(), $wiki = false ) {
 491                 if ( $i === null || $i === false ) {
 492                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 493                                 ' with invalid server index' );
 494                 }
 495
 496                 if ( $wiki === wfWikiID() ) {
 497                         $wiki = false;
 498                 }
 499
 500                 $groups = ( $groups === false || $groups === array() )
 501                         ? array( false ) // check one "group": the generic pool
 502                         : (array)$groups;
 503
 504                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 505                 $oldConnsOpened = $this->connsOpened; // connections open now
 506
 507                 if ( $i == DB_MASTER ) {
 508                         $i = $this->getWriterIndex();
 509                 } else {
 510                         # Try to find an available server in any the query groups (in order)
 511                         foreach ( $groups as $group ) {
 512                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 513                                 if ( $groupIndex !== false ) {
 514                                         $i = $groupIndex;
 515                                         break;
 516                                 }
 517                         }
 518                 }
 519
 520                 # Operation-based index
 521                 if ( $i == DB_SLAVE ) {
 522                         $this->mLastError = 'Unknown error'; // reset error string
 523                         # Try the general server pool if $groups are unavailable.
 524                         $i = in_array( false, $groups, true )
 525                                 ? false // don't bother with this if that is what was tried above
 526                                 : $this->getReaderIndex( false, $wiki );
 527                         # Couldn't find a working server in getReaderIndex()?
 528                         if ( $i === false ) {
 529                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 530
 531                                 return $this->reportConnectionError();
 532                         }
 533                 }
 534
 535                 # Now we have an explicit index into the servers array
 536                 $conn = $this->openConnection( $i, $wiki );
 537                 if ( !$conn ) {
 538                         return $this->reportConnectionError();
 539                 }
 540
 541                 # Profile any new connections that happen
 542                 if ( $this->connsOpened > $oldConnsOpened ) {
 543                         $host = $conn->getServer();
 544                         $dbname = $conn->getDBname();
 545                         $trxProf = Profiler::instance()->getTransactionProfiler();
 546                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 547                 }
 548
 549                 return $conn;
 550         }
 551
 552         /**
 553          * Mark a foreign connection as being available for reuse under a different
 554          * DB name or prefix. This mechanism is reference-counted, and must be called
 555          * the same number of times as getConnection() to work.
 556          *
 557          * @param DatabaseBase $conn
 558          * @throws MWException
 559          */
 560         public function reuseConnection( $conn ) {
 561                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 562                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 563                 if ( $serverIndex === null || $refCount === null ) {
 564                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 565
 566                         /**
 567                          * This can happen in code like:
 568                          *   foreach ( $dbs as $db ) {
 569                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 570                          *     ...
 571                          *     $lb->reuseConnection( $conn );
 572                          *   }
 573                          * When a connection to the local DB is opened in this way, reuseConnection()
 574                          * should be ignored
 575                          */
 576
 577                         return;
 578                 }
 579
 580                 $dbName = $conn->getDBname();
 581                 $prefix = $conn->tablePrefix();
 582                 if ( strval( $prefix ) !== '' ) {
 583                         $wiki = "$dbName-$prefix";
 584                 } else {
 585                         $wiki = $dbName;
 586                 }
 587                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 588                         throw new MWException( __METHOD__ . ": connection not found, has " .
 589                                 "the connection been freed already?" );
 590                 }
 591                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 592                 if ( $refCount <= 0 ) {
 593                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 594                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 595                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 596                 } else {
 597                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 598                 }
 599         }
 600
 601         /**
 602          * Get a database connection handle reference
 603          *
 604          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 605          *
 606          * @see LoadBalancer::getConnection() for parameter information
 607          *
 608          * @param int $db
 609          * @param array|string|bool $groups Query group(s), or false for the generic reader
 610          * @param string|bool $wiki Wiki ID, or false for the current wiki
 611          * @return DBConnRef
 612          */
 613         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 614                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 615         }
 616
 617         /**
 618          * Get a database connection handle reference without connecting yet
 619          *
 620          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 621          *
 622          * @see LoadBalancer::getConnection() for parameter information
 623          *
 624          * @param int $db
 625          * @param array|string|bool $groups Query group(s), or false for the generic reader
 626          * @param string|bool $wiki Wiki ID, or false for the current wiki
 627          * @return DBConnRef
 628          */
 629         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 630                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 631         }
 632
 633         /**
 634          * Open a connection to the server given by the specified index
 635          * Index must be an actual index into the array.
 636          * If the server is already open, returns it.
 637          *
 638          * On error, returns false, and the connection which caused the
 639          * error will be available via $this->mErrorConnection.
 640          *
 641          * @param int $i Server index
 642          * @param string|bool $wiki Wiki ID, or false for the current wiki
 643          * @return DatabaseBase
 644          *
 645          * @access private
 646          */
 647         public function openConnection( $i, $wiki = false ) {
 648                 if ( $wiki !== false ) {
 649                         $conn = $this->openForeignConnection( $i, $wiki );
 650                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 651                         $conn = $this->mConns['local'][$i][0];
 652                 } else {
 653                         $server = $this->mServers[$i];
 654                         $server['serverIndex'] = $i;
 655                         $conn = $this->reallyOpenConnection( $server, false );
 656                         $serverName = $this->getServerName( $i );
 657                         if ( $conn->isOpen() ) {
 658                                 wfDebug( "Connected to database $i at $serverName\n" );
 659                                 $this->mConns['local'][$i][0] = $conn;
 660                         } else {
 661                                 wfDebug( "Failed to connect to database $i at $serverName\n" );
 662                                 $this->mErrorConnection = $conn;
 663                                 $conn = false;
 664                         }
 665                 }
 666
 667                 if ( $conn && !$conn->isOpen() ) {
 668                         // Connection was made but later unrecoverably lost for some reason.
 669                         // Do not return a handle that will just throw exceptions on use,
 670                         // but let the calling code (e.g. getReaderIndex) try another server.
 671                         // See DatabaseMyslBase::ping() for how this can happen.
 672                         $this->mErrorConnection = $conn;
 673                         $conn = false;
 674                 }
 675
 676                 return $conn;
 677         }
 678
 679         /**
 680          * Open a connection to a foreign DB, or return one if it is already open.
 681          *
 682          * Increments a reference count on the returned connection which locks the
 683          * connection to the requested wiki. This reference count can be
 684          * decremented by calling reuseConnection().
 685          *
 686          * If a connection is open to the appropriate server already, but with the wrong
 687          * database, it will be switched to the right database and returned, as long as
 688          * it has been freed first with reuseConnection().
 689          *
 690          * On error, returns false, and the connection which caused the
 691          * error will be available via $this->mErrorConnection.
 692          *
 693          * @param int $i Server index
 694          * @param string $wiki Wiki ID to open
 695          * @return DatabaseBase
 696          */
 697         private function openForeignConnection( $i, $wiki ) {
 698                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 699                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 700                         // Reuse an already-used connection
 701                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 702                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 703                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 704                         // Reuse a free connection for the same wiki
 705                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 706                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 707                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 708                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 709                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 710                         // Reuse a connection from another wiki
 711                         $conn = reset( $this->mConns['foreignFree'][$i] );
 712                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 713
 714                         // The empty string as a DB name means "don't care".
 715                         // DatabaseMysqlBase::open() already handle this on connection.
 716                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 717                                 $this->mLastError = "Error selecting database $dbName on server " .
 718                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 719                                 $this->mErrorConnection = $conn;
 720                                 $conn = false;
 721                         } else {
 722                                 $conn->tablePrefix( $prefix );
 723                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 724                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 725                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 726                         }
 727                 } else {
 728                         // Open a new connection
 729                         $server = $this->mServers[$i];
 730                         $server['serverIndex'] = $i;
 731                         $server['foreignPoolRefCount'] = 0;
 732                         $server['foreign'] = true;
 733                         $conn = $this->reallyOpenConnection( $server, $dbName );
 734                         if ( !$conn->isOpen() ) {
 735                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 736                                 $this->mErrorConnection = $conn;
 737                                 $conn = false;
 738                         } else {
 739                                 $conn->tablePrefix( $prefix );
 740                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 741                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 742                         }
 743                 }
 744
 745                 // Increment reference count
 746                 if ( $conn ) {
 747                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 748                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 749                 }
 750
 751                 return $conn;
 752         }
 753
 754         /**
 755          * Test if the specified index represents an open connection
 756          *
 757          * @param int $index Server index
 758          * @access private
 759          * @return bool
 760          */
 761         private function isOpen( $index ) {
 762                 if ( !is_integer( $index ) ) {
 763                         return false;
 764                 }
 765
 766                 return (bool)$this->getAnyOpenConnection( $index );
 767         }
 768
 769         /**
 770          * Really opens a connection. Uncached.
 771          * Returns a Database object whether or not the connection was successful.
 772          * @access private
 773          *
 774          * @param array $server
 775          * @param bool $dbNameOverride
 776          * @throws MWException
 777          * @return DatabaseBase
 778          */
 779         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 780                 if ( !is_array( $server ) ) {
 781                         throw new MWException( 'You must update your load-balancing configuration. ' .
 782                                 'See DefaultSettings.php entry for $wgDBservers.' );
 783                 }
 784
 785                 if ( $dbNameOverride !== false ) {
 786                         $server['dbname'] = $dbNameOverride;
 787                 }
 788
 789                 // Log when many connection are made on requests
 790                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 791                         $masterAddr = $this->getServerName( 0 );
 792                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 793                                 "{$this->connsOpened}+ connections made (master=$masterAddr)\n" .
 794                                 wfBacktrace( true ) );
 795                 }
 796
 797                 # Create object
 798                 try {
 799                         $db = DatabaseBase::factory( $server['type'], $server );
 800                 } catch ( DBConnectionError $e ) {
 801                         // FIXME: This is probably the ugliest thing I have ever done to
 802                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 803                         $db = $e->db;
 804                 }
 805
 806                 $db->setLBInfo( $server );
 807
 808                 return $db;
 809         }
 810
 811         /**
 812          * @throws DBConnectionError
 813          * @return bool
 814          */
 815         private function reportConnectionError() {
 816                 $conn = $this->mErrorConnection; // The connection which caused the error
 817                 $context = array(
 818                         'method' => __METHOD__,
 819                         'last_error' => $this->mLastError,
 820                 );
 821
 822                 if ( !is_object( $conn ) ) {
 823                         // No last connection, probably due to all servers being too busy
 824                         wfLogDBError(
 825                                 "LB failure with no last connection. Connection error: {last_error}",
 826                                 $context
 827                         );
 828
 829                         // If all servers were busy, mLastError will contain something sensible
 830                         throw new DBConnectionError( null, $this->mLastError );
 831                 } else {
 832                         $context['db_server'] = $conn->getProperty( 'mServer' );
 833                         wfLogDBError(
 834                                 "Connection error: {last_error} ({db_server})",
 835                                 $context
 836                         );
 837
 838                         // throws DBConnectionError
 839                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 840                 }
 841
 842                 return false; /* not reached */
 843         }
 844
 845         /**
 846          * @return int
 847          * @since 1.26
 848          */
 849         public function getWriterIndex() {
 850                 return 0;
 851         }
 852
 853         /**
 854          * Returns true if the specified index is a valid server index
 855          *
 856          * @param string $i
 857          * @return bool
 858          */
 859         public function haveIndex( $i ) {
 860                 return array_key_exists( $i, $this->mServers );
 861         }
 862
 863         /**
 864          * Returns true if the specified index is valid and has non-zero load
 865          *
 866          * @param string $i
 867          * @return bool
 868          */
 869         public function isNonZeroLoad( $i ) {
 870                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 871         }
 872
 873         /**
 874          * Get the number of defined servers (not the number of open connections)
 875          *
 876          * @return int
 877          */
 878         public function getServerCount() {
 879                 return count( $this->mServers );
 880         }
 881
 882         /**
 883          * Get the host name or IP address of the server with the specified index
 884          * Prefer a readable name if available.
 885          * @param string $i
 886          * @return string
 887          */
 888         public function getServerName( $i ) {
 889                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 890                         $name = $this->mServers[$i]['hostName'];
 891                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 892                         $name = $this->mServers[$i]['host'];
 893                 } else {
 894                         $name = '';
 895                 }
 896
 897                 return ( $name != '' ) ? $name : 'localhost';
 898         }
 899
 900         /**
 901          * Return the server info structure for a given index, or false if the index is invalid.
 902          * @param int $i
 903          * @return array|bool
 904          */
 905         public function getServerInfo( $i ) {
 906                 if ( isset( $this->mServers[$i] ) ) {
 907                         return $this->mServers[$i];
 908                 } else {
 909                         return false;
 910                 }
 911         }
 912
 913         /**
 914          * Sets the server info structure for the given index. Entry at index $i
 915          * is created if it doesn't exist
 916          * @param int $i
 917          * @param array $serverInfo
 918          */
 919         public function setServerInfo( $i, array $serverInfo ) {
 920                 $this->mServers[$i] = $serverInfo;
 921         }
 922
 923         /**
 924          * Get the current master position for chronology control purposes
 925          * @return mixed
 926          */
 927         public function getMasterPos() {
 928                 # If this entire request was served from a slave without opening a connection to the
 929                 # master (however unlikely that may be), then we can fetch the position from the slave.
 930                 $masterConn = $this->getAnyOpenConnection( 0 );
 931                 if ( !$masterConn ) {
 932                         $serverCount = count( $this->mServers );
 933                         for ( $i = 1; $i < $serverCount; $i++ ) {
 934                                 $conn = $this->getAnyOpenConnection( $i );
 935                                 if ( $conn ) {
 936                                         wfDebug( "Master pos fetched from slave\n" );
 937
 938                                         return $conn->getSlavePos();
 939                                 }
 940                         }
 941                 } else {
 942                         wfDebug( "Master pos fetched from master\n" );
 943
 944                         return $masterConn->getMasterPos();
 945                 }
 946
 947                 return false;
 948         }
 949
 950         /**
 951          * Close all open connections
 952          */
 953         public function closeAll() {
 954                 foreach ( $this->mConns as $conns2 ) {
 955                         foreach ( $conns2 as $conns3 ) {
 956                                 /** @var DatabaseBase $conn */
 957                                 foreach ( $conns3 as $conn ) {
 958                                         $conn->close();
 959                                 }
 960                         }
 961                 }
 962                 $this->mConns = array(
 963                         'local' => array(),
 964                         'foreignFree' => array(),
 965                         'foreignUsed' => array(),
 966                 );
 967                 $this->connsOpened = 0;
 968         }
 969
 970         /**
 971          * Close a connection
 972          * Using this function makes sure the LoadBalancer knows the connection is closed.
 973          * If you use $conn->close() directly, the load balancer won't update its state.
 974          * @param DatabaseBase $conn
 975          */
 976         public function closeConnection( $conn ) {
 977                 $done = false;
 978                 foreach ( $this->mConns as $i1 => $conns2 ) {
 979                         foreach ( $conns2 as $i2 => $conns3 ) {
 980                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 981                                         if ( $conn === $candidateConn ) {
 982                                                 $conn->close();
 983                                                 unset( $this->mConns[$i1][$i2][$i3] );
 984                                                 --$this->connsOpened;
 985                                                 $done = true;
 986                                                 break;
 987                                         }
 988                                 }
 989                         }
 990                 }
 991                 if ( !$done ) {
 992                         $conn->close();
 993                 }
 994         }
 995
 996         /**
 997          * Commit transactions on all open connections
 998          */
 999         public function commitAll() {
1000                 foreach ( $this->mConns as $conns2 ) {
1001                         foreach ( $conns2 as $conns3 ) {
1002                                 /** @var DatabaseBase[] $conns3 */
1003                                 foreach ( $conns3 as $conn ) {
1004                                         if ( $conn->trxLevel() ) {
1005                                                 $conn->commit( __METHOD__, 'flush' );
1006                                         }
1007                                 }
1008                         }
1009                 }
1010         }
1011
1012         /**
1013          *  Issue COMMIT only on master, only if queries were done on connection
1014          */
1015         public function commitMasterChanges() {
1016                 $masterIndex = $this->getWriterIndex();
1017                 foreach ( $this->mConns as $conns2 ) {
1018                         if ( empty( $conns2[$masterIndex] ) ) {
1019                                 continue;
1020                         }
1021                         /** @var DatabaseBase $conn */
1022                         foreach ( $conns2[$masterIndex] as $conn ) {
1023                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1024                                         $conn->commit( __METHOD__, 'flush' );
1025                                 }
1026                         }
1027                 }
1028         }
1029
1030         /**
1031          * Issue ROLLBACK only on master, only if queries were done on connection
1032          * @since 1.23
1033          */
1034         public function rollbackMasterChanges() {
1035                 $failedServers = array();
1036
1037                 $masterIndex = $this->getWriterIndex();
1038                 foreach ( $this->mConns as $conns2 ) {
1039                         if ( empty( $conns2[$masterIndex] ) ) {
1040                                 continue;
1041                         }
1042                         /** @var DatabaseBase $conn */
1043                         foreach ( $conns2[$masterIndex] as $conn ) {
1044                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1045                                         try {
1046                                                 $conn->rollback( __METHOD__, 'flush' );
1047                                         } catch ( DBError $e ) {
1048                                                 MWExceptionHandler::logException( $e );
1049                                                 $failedServers[] = $conn->getServer();
1050                                         }
1051                                 }
1052                         }
1053                 }
1054
1055                 if ( $failedServers ) {
1056                         throw new DBExpectedError( null, "Rollback failed on server(s) " .
1057                                 implode( ', ', array_unique( $failedServers ) ) );
1058                 }
1059         }
1060
1061         /**
1062          * @return bool Whether a master connection is already open
1063          * @since 1.24
1064          */
1065         public function hasMasterConnection() {
1066                 return $this->isOpen( $this->getWriterIndex() );
1067         }
1068
1069         /**
1070          * Determine if there are pending changes in a transaction by this thread
1071          * @since 1.23
1072          * @return bool
1073          */
1074         public function hasMasterChanges() {
1075                 $masterIndex = $this->getWriterIndex();
1076                 foreach ( $this->mConns as $conns2 ) {
1077                         if ( empty( $conns2[$masterIndex] ) ) {
1078                                 continue;
1079                         }
1080                         /** @var DatabaseBase $conn */
1081                         foreach ( $conns2[$masterIndex] as $conn ) {
1082                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1083                                         return true;
1084                                 }
1085                         }
1086                 }
1087                 return false;
1088         }
1089
1090         /**
1091          * Get the timestamp of the latest write query done by this thread
1092          * @since 1.25
1093          * @return float|bool UNIX timestamp or false
1094          */
1095         public function lastMasterChangeTimestamp() {
1096                 $lastTime = false;
1097                 $masterIndex = $this->getWriterIndex();
1098                 foreach ( $this->mConns as $conns2 ) {
1099                         if ( empty( $conns2[$masterIndex] ) ) {
1100                                 continue;
1101                         }
1102                         /** @var DatabaseBase $conn */
1103                         foreach ( $conns2[$masterIndex] as $conn ) {
1104                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1105                         }
1106                 }
1107                 return $lastTime;
1108         }
1109
1110         /**
1111          * Check if this load balancer object had any recent or still
1112          * pending writes issued against it by this PHP thread
1113          *
1114          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1115          * @return bool
1116          * @since 1.25
1117          */
1118         public function hasOrMadeRecentMasterChanges( $age = null ) {
1119                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1120
1121                 return ( $this->hasMasterChanges()
1122                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1123         }
1124
1125         /**
1126          * @param mixed $value
1127          * @return mixed
1128          */
1129         public function waitTimeout( $value = null ) {
1130                 return wfSetVar( $this->mWaitTimeout, $value );
1131         }
1132
1133         /**
1134          * @return bool Whether the generic connection for reads is highly "lagged"
1135          */
1136         public function getLaggedSlaveMode() {
1137                 # Get a generic reader connection
1138                 $this->getConnection( DB_SLAVE );
1139
1140                 return $this->mLaggedSlaveMode;
1141         }
1142
1143         /**
1144          * Disables/enables lag checks
1145          * @param null|bool $mode
1146          * @return bool
1147          */
1148         public function allowLagged( $mode = null ) {
1149                 if ( $mode === null ) {
1150                         return $this->mAllowLagged;
1151                 }
1152                 $this->mAllowLagged = $mode;
1153
1154                 return $this->mAllowLagged;
1155         }
1156
1157         /**
1158          * @return bool
1159          */
1160         public function pingAll() {
1161                 $success = true;
1162                 foreach ( $this->mConns as $conns2 ) {
1163                         foreach ( $conns2 as $conns3 ) {
1164                                 /** @var DatabaseBase[] $conns3 */
1165                                 foreach ( $conns3 as $conn ) {
1166                                         if ( !$conn->ping() ) {
1167                                                 $success = false;
1168                                         }
1169                                 }
1170                         }
1171                 }
1172
1173                 return $success;
1174         }
1175
1176         /**
1177          * Call a function with each open connection object
1178          * @param callable $callback
1179          * @param array $params
1180          */
1181         public function forEachOpenConnection( $callback, array $params = array() ) {
1182                 foreach ( $this->mConns as $conns2 ) {
1183                         foreach ( $conns2 as $conns3 ) {
1184                                 foreach ( $conns3 as $conn ) {
1185                                         $mergedParams = array_merge( array( $conn ), $params );
1186                                         call_user_func_array( $callback, $mergedParams );
1187                                 }
1188                         }
1189                 }
1190         }
1191
1192         /**
1193          * Get the hostname and lag time of the most-lagged slave
1194          *
1195          * This is useful for maintenance scripts that need to throttle their updates.
1196          * May attempt to open connections to slaves on the default DB. If there is
1197          * no lag, the maximum lag will be reported as -1.
1198          *
1199          * @param bool|string $wiki Wiki ID, or false for the default database
1200          * @return array ( host, max lag, index of max lagged host )
1201          */
1202         public function getMaxLag( $wiki = false ) {
1203                 $maxLag = -1;
1204                 $host = '';
1205                 $maxIndex = 0;
1206
1207                 if ( $this->getServerCount() <= 1 ) {
1208                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1209                 }
1210
1211                 $lagTimes = $this->getLagTimes( $wiki );
1212                 foreach ( $lagTimes as $i => $lag ) {
1213                         if ( $lag > $maxLag ) {
1214                                 $maxLag = $lag;
1215                                 $host = $this->mServers[$i]['host'];
1216                                 $maxIndex = $i;
1217                         }
1218                 }
1219
1220                 return array( $host, $maxLag, $maxIndex );
1221         }
1222
1223         /**
1224          * Get an estimate of replication lag (in seconds) for each server
1225          *
1226          * Results are cached for a short time in memcached/process cache
1227          *
1228          * Values may be "false" if replication is too broken to estimate
1229          *
1230          * @param string|bool $wiki
1231          * @return int[] Map of (server index => float|int|bool)
1232          */
1233         public function getLagTimes( $wiki = false ) {
1234                 if ( $this->getServerCount() <= 1 ) {
1235                         return array( 0 => 0 ); // no replication = no lag
1236                 }
1237
1238                 # Send the request to the load monitor
1239                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1240         }
1241
1242         /**
1243          * Get the lag in seconds for a given connection, or zero if this load
1244          * balancer does not have replication enabled.
1245          *
1246          * This should be used in preference to Database::getLag() in cases where
1247          * replication may not be in use, since there is no way to determine if
1248          * replication is in use at the connection level without running
1249          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1250          * function instead of Database::getLag() avoids a fatal error in this
1251          * case on many installations.
1252          *
1253          * @param DatabaseBase $conn
1254          * @return int
1255          */
1256         public function safeGetLag( $conn ) {
1257                 if ( $this->getServerCount() == 1 ) {
1258                         return 0;
1259                 } else {
1260                         return $conn->getLag();
1261                 }
1262         }
1263
1264         /**
1265          * Clear the cache for slag lag delay times
1266          *
1267          * This is only used for testing
1268          */
1269         public function clearLagTimeCache() {
1270                 $this->getLoadMonitor()->clearCaches();
1271         }
1272 }