includes/db/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         /** @var ProcessCacheLRU */
  64         private $mProcCache;
  65
  66         /** @var integer Warn when this many connection are held */
  67         const CONN_HELD_WARN_THRESHOLD = 10;
  68
  69         /**
  70          * @param array $params Array with keys:
  71          *   servers           Required. Array of server info structures.
  72          *   loadMonitor       Name of a class used to fetch server lag and load.
  73          * @throws MWException
  74          */
  75         public function __construct( array $params ) {
  76                 if ( !isset( $params['servers'] ) ) {
  77                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  78                 }
  79                 $this->mServers = $params['servers'];
  80                 $this->mWaitTimeout = 10;
  81
  82                 $this->mReadIndex = -1;
  83                 $this->mWriteIndex = -1;
  84                 $this->mConns = array(
  85                         'local' => array(),
  86                         'foreignUsed' => array(),
  87                         'foreignFree' => array() );
  88                 $this->mLoads = array();
  89                 $this->mWaitForPos = false;
  90                 $this->mLaggedSlaveMode = false;
  91                 $this->mErrorConnection = false;
  92                 $this->mAllowLagged = false;
  93
  94                 if ( isset( $params['loadMonitor'] ) ) {
  95                         $this->mLoadMonitorClass = $params['loadMonitor'];
  96                 } else {
  97                         $master = reset( $params['servers'] );
  98                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  99                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 100                         } else {
 101                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 102                         }
 103                 }
 104
 105                 foreach ( $params['servers'] as $i => $server ) {
 106                         $this->mLoads[$i] = $server['load'];
 107                         if ( isset( $server['groupLoads'] ) ) {
 108                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 109                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 110                                                 $this->mGroupLoads[$group] = array();
 111                                         }
 112                                         $this->mGroupLoads[$group][$i] = $ratio;
 113                                 }
 114                         }
 115                 }
 116
 117                 $this->mProcCache = new ProcessCacheLRU( 30 );
 118         }
 119
 120         /**
 121          * Get a LoadMonitor instance
 122          *
 123          * @return LoadMonitor
 124          */
 125         private function getLoadMonitor() {
 126                 if ( !isset( $this->mLoadMonitor ) ) {
 127                         $class = $this->mLoadMonitorClass;
 128                         $this->mLoadMonitor = new $class( $this );
 129                 }
 130
 131                 return $this->mLoadMonitor;
 132         }
 133
 134         /**
 135          * Get or set arbitrary data used by the parent object, usually an LBFactory
 136          * @param mixed $x
 137          * @return mixed
 138          */
 139         public function parentInfo( $x = null ) {
 140                 return wfSetVar( $this->mParentInfo, $x );
 141         }
 142
 143         /**
 144          * Given an array of non-normalised probabilities, this function will select
 145          * an element and return the appropriate key
 146          *
 147          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 148          *
 149          * @param array $weights
 150          * @return bool|int|string
 151          */
 152         public function pickRandom( array $weights ) {
 153                 return ArrayUtils::pickRandom( $weights );
 154         }
 155
 156         /**
 157          * @param array $loads
 158          * @param bool|string $wiki Wiki to get non-lagged for
 159          * @param float $maxLag Restrict the maximum allowed lag to this many seconds
 160          * @return bool|int|string
 161          */
 162         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 163                 $lags = $this->getLagTimes( $wiki );
 164
 165                 # Unset excessively lagged servers
 166                 foreach ( $lags as $i => $lag ) {
 167                         if ( $i != 0 ) {
 168                                 $maxServerLag = $maxLag;
 169                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 170                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 171                                 }
 172                                 if ( $lag === false ) {
 173                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 174                                         unset( $loads[$i] );
 175                                 } elseif ( $lag > $maxServerLag ) {
 176                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 177                                         unset( $loads[$i] );
 178                                 }
 179                         }
 180                 }
 181
 182                 # Find out if all the slaves with non-zero load are lagged
 183                 $sum = 0;
 184                 foreach ( $loads as $load ) {
 185                         $sum += $load;
 186                 }
 187                 if ( $sum == 0 ) {
 188                         # No appropriate DB servers except maybe the master and some slaves with zero load
 189                         # Do NOT use the master
 190                         # Instead, this function will return false, triggering read-only mode,
 191                         # and a lagged slave will be used instead.
 192                         return false;
 193                 }
 194
 195                 if ( count( $loads ) == 0 ) {
 196                         return false;
 197                 }
 198
 199                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 200
 201                 # Return a random representative of the remainder
 202                 return ArrayUtils::pickRandom( $loads );
 203         }
 204
 205         /**
 206          * Get the index of the reader connection, which may be a slave
 207          * This takes into account load ratios and lag times. It should
 208          * always return a consistent index during a given invocation
 209          *
 210          * Side effect: opens connections to databases
 211          * @param string|bool $group Query group, or false for the generic reader
 212          * @param string|bool $wiki Wiki ID, or false for the current wiki
 213          * @throws MWException
 214          * @return bool|int|string
 215          */
 216         public function getReaderIndex( $group = false, $wiki = false ) {
 217                 global $wgDBtype;
 218
 219                 # @todo FIXME: For now, only go through all this for mysql databases
 220                 if ( $wgDBtype != 'mysql' ) {
 221                         return $this->getWriterIndex();
 222                 }
 223
 224                 if ( count( $this->mServers ) == 1 ) {
 225                         # Skip the load balancing if there's only one server
 226                         return 0;
 227                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 228                         # Shortcut if generic reader exists already
 229                         return $this->mReadIndex;
 230                 }
 231
 232                 # Find the relevant load array
 233                 if ( $group !== false ) {
 234                         if ( isset( $this->mGroupLoads[$group] ) ) {
 235                                 $nonErrorLoads = $this->mGroupLoads[$group];
 236                         } else {
 237                                 # No loads for this group, return false and the caller can use some other group
 238                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 239
 240                                 return false;
 241                         }
 242                 } else {
 243                         $nonErrorLoads = $this->mLoads;
 244                 }
 245
 246                 if ( !count( $nonErrorLoads ) ) {
 247                         throw new MWException( "Empty server array given to LoadBalancer" );
 248                 }
 249
 250                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 251                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 252
 253                 $laggedSlaveMode = false;
 254
 255                 # No server found yet
 256                 $i = false;
 257                 # First try quickly looking through the available servers for a server that
 258                 # meets our criteria
 259                 $currentLoads = $nonErrorLoads;
 260                 while ( count( $currentLoads ) ) {
 261                         if ( $this->mAllowLagged || $laggedSlaveMode ) {
 262                                 $i = ArrayUtils::pickRandom( $currentLoads );
 263                         } else {
 264                                 $i = false;
 265                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 266                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 267                                         # This triggers doWait() after connect, so it's especially good to
 268                                         # avoid lagged servers so as to avoid just blocking in that method.
 269                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 270                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 271                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 272                                 }
 273                                 if ( $i === false ) {
 274                                         # Any server with less lag than it's 'max lag' param is preferable
 275                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 276                                 }
 277                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 278                                         # All slaves lagged. Switch to read-only mode
 279                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 280                                         $i = ArrayUtils::pickRandom( $currentLoads );
 281                                         $laggedSlaveMode = true;
 282                                 }
 283                         }
 284
 285                         if ( $i === false ) {
 286                                 # pickRandom() returned false
 287                                 # This is permanent and means the configuration or the load monitor
 288                                 # wants us to return false.
 289                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 290
 291                                 return false;
 292                         }
 293
 294                         wfDebugLog( 'connect', __METHOD__ .
 295                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 296
 297                         $conn = $this->openConnection( $i, $wiki );
 298                         if ( !$conn ) {
 299                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 300                                 unset( $nonErrorLoads[$i] );
 301                                 unset( $currentLoads[$i] );
 302                                 $i = false;
 303                                 continue;
 304                         }
 305
 306                         // Decrement reference counter, we are finished with this connection.
 307                         // It will be incremented for the caller later.
 308                         if ( $wiki !== false ) {
 309                                 $this->reuseConnection( $conn );
 310                         }
 311
 312                         # Return this server
 313                         break;
 314                 }
 315
 316                 # If all servers were down, quit now
 317                 if ( !count( $nonErrorLoads ) ) {
 318                         wfDebugLog( 'connect', "All servers down" );
 319                 }
 320
 321                 if ( $i !== false ) {
 322                         # Slave connection successful
 323                         # Wait for the session master pos for a short time
 324                         if ( $this->mWaitForPos && $i > 0 ) {
 325                                 if ( !$this->doWait( $i ) ) {
 326                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 327                                 }
 328                         }
 329                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 330                                 $this->mReadIndex = $i;
 331                                 # Record if the generic reader index is in "lagged slave" mode
 332                                 if ( $laggedSlaveMode ) {
 333                                         $this->mLaggedSlaveMode = true;
 334                                 }
 335                         }
 336                         $serverName = $this->getServerName( $i );
 337                         wfDebug( __METHOD__ . ": using server $serverName for group '$group'\n" );
 338                 }
 339
 340                 return $i;
 341         }
 342
 343         /**
 344          * Set the master wait position
 345          * If a DB_SLAVE connection has been opened already, waits
 346          * Otherwise sets a variable telling it to wait if such a connection is opened
 347          * @param DBMasterPos $pos
 348          */
 349         public function waitFor( $pos ) {
 350                 $this->mWaitForPos = $pos;
 351                 $i = $this->mReadIndex;
 352
 353                 if ( $i > 0 ) {
 354                         if ( !$this->doWait( $i ) ) {
 355                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 356                                 $this->mLaggedSlaveMode = true;
 357                         }
 358                 }
 359         }
 360
 361         /**
 362          * Set the master wait position and wait for a "generic" slave to catch up to it
 363          *
 364          * This can be used a faster proxy for waitForAll()
 365          *
 366          * @param DBMasterPos $pos
 367          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 368          * @return bool Success (able to connect and no timeouts reached)
 369          * @since 1.26
 370          */
 371         public function waitForOne( $pos, $timeout = null ) {
 372                 $this->mWaitForPos = $pos;
 373
 374                 $i = $this->mReadIndex;
 375                 if ( $i <= 0 ) {
 376                         // Pick a generic slave if there isn't one yet
 377                         $readLoads = $this->mLoads;
 378                         unset( $readLoads[$this->getWriterIndex()] ); // slaves only
 379                         $readLoads = array_filter( $readLoads ); // with non-zero load
 380                         $i = ArrayUtils::pickRandom( $readLoads );
 381                 }
 382
 383                 if ( $i > 0 ) {
 384                         $ok = $this->doWait( $i, true, $timeout );
 385                 } else {
 386                         $ok = true; // no applicable loads
 387                 }
 388
 389                 return $ok;
 390         }
 391
 392         /**
 393          * Set the master wait position and wait for ALL slaves to catch up to it
 394          * @param DBMasterPos $pos
 395          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 396          * @return bool Success (able to connect and no timeouts reached)
 397          */
 398         public function waitForAll( $pos, $timeout = null ) {
 399                 $this->mWaitForPos = $pos;
 400                 $serverCount = count( $this->mServers );
 401
 402                 $ok = true;
 403                 for ( $i = 1; $i < $serverCount; $i++ ) {
 404                         if ( $this->mLoads[$i] > 0 ) {
 405                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 406                         }
 407                 }
 408
 409                 return $ok;
 410         }
 411
 412         /**
 413          * Get any open connection to a given server index, local or foreign
 414          * Returns false if there is no connection open
 415          *
 416          * @param int $i
 417          * @return DatabaseBase|bool False on failure
 418          */
 419         public function getAnyOpenConnection( $i ) {
 420                 foreach ( $this->mConns as $conns ) {
 421                         if ( !empty( $conns[$i] ) ) {
 422                                 return reset( $conns[$i] );
 423                         }
 424                 }
 425
 426                 return false;
 427         }
 428
 429         /**
 430          * Wait for a given slave to catch up to the master pos stored in $this
 431          * @param int $index Server index
 432          * @param bool $open Check the server even if a new connection has to be made
 433          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 434          * @return bool
 435          */
 436         protected function doWait( $index, $open = false, $timeout = null ) {
 437                 $close = false; // close the connection afterwards
 438
 439                 # Find a connection to wait on, creating one if needed and allowed
 440                 $conn = $this->getAnyOpenConnection( $index );
 441                 if ( !$conn ) {
 442                         if ( !$open ) {
 443                                 wfDebug( __METHOD__ . ": no connection open\n" );
 444
 445                                 return false;
 446                         } else {
 447                                 $conn = $this->openConnection( $index, '' );
 448                                 if ( !$conn ) {
 449                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 450
 451                                         return false;
 452                                 }
 453                                 // Avoid connection spam in waitForAll() when connections
 454                                 // are made just for the sake of doing this lag check.
 455                                 $close = true;
 456                         }
 457                 }
 458
 459                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 460                 $timeout = $timeout ?: $this->mWaitTimeout;
 461                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 462
 463                 if ( $result == -1 || is_null( $result ) ) {
 464                         # Timed out waiting for slave, use master instead
 465                         $server = $this->mServers[$index]['host'];
 466                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 467                         wfDebug( "$msg\n" );
 468                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 469                         $ok = false;
 470                 } else {
 471                         wfDebug( __METHOD__ . ": Done\n" );
 472                         $ok = true;
 473                 }
 474
 475                 if ( $close ) {
 476                         $this->closeConnection( $conn );
 477                 }
 478
 479                 return $ok;
 480         }
 481
 482         /**
 483          * Get a connection by index
 484          * This is the main entry point for this class.
 485          *
 486          * @param int $i Server index
 487          * @param array|string|bool $groups Query group(s), or false for the generic reader
 488          * @param string|bool $wiki Wiki ID, or false for the current wiki
 489          *
 490          * @throws MWException
 491          * @return DatabaseBase
 492          */
 493         public function getConnection( $i, $groups = array(), $wiki = false ) {
 494                 if ( $i === null || $i === false ) {
 495                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 496                                 ' with invalid server index' );
 497                 }
 498
 499                 if ( $wiki === wfWikiID() ) {
 500                         $wiki = false;
 501                 }
 502
 503                 $groups = ( $groups === false || $groups === array() )
 504                         ? array( false ) // check one "group": the generic pool
 505                         : (array)$groups;
 506
 507                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 508                 $oldConnsOpened = $this->connsOpened; // connections open now
 509
 510                 if ( $i == DB_MASTER ) {
 511                         $i = $this->getWriterIndex();
 512                 } else {
 513                         # Try to find an available server in any the query groups (in order)
 514                         foreach ( $groups as $group ) {
 515                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 516                                 if ( $groupIndex !== false ) {
 517                                         $i = $groupIndex;
 518                                         break;
 519                                 }
 520                         }
 521                 }
 522
 523                 # Operation-based index
 524                 if ( $i == DB_SLAVE ) {
 525                         $this->mLastError = 'Unknown error'; // reset error string
 526                         # Try the general server pool if $groups are unavailable.
 527                         $i = in_array( false, $groups, true )
 528                                 ? false // don't bother with this if that is what was tried above
 529                                 : $this->getReaderIndex( false, $wiki );
 530                         # Couldn't find a working server in getReaderIndex()?
 531                         if ( $i === false ) {
 532                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 533
 534                                 return $this->reportConnectionError();
 535                         }
 536                 }
 537
 538                 # Now we have an explicit index into the servers array
 539                 $conn = $this->openConnection( $i, $wiki );
 540                 if ( !$conn ) {
 541
 542                         return $this->reportConnectionError();
 543                 }
 544
 545                 # Profile any new connections that happen
 546                 if ( $this->connsOpened > $oldConnsOpened ) {
 547                         $host = $conn->getServer();
 548                         $dbname = $conn->getDBname();
 549                         $trxProf = Profiler::instance()->getTransactionProfiler();
 550                         $trxProf->recordConnection( $host, $dbname, $masterOnly );
 551                 }
 552
 553                 return $conn;
 554         }
 555
 556         /**
 557          * Mark a foreign connection as being available for reuse under a different
 558          * DB name or prefix. This mechanism is reference-counted, and must be called
 559          * the same number of times as getConnection() to work.
 560          *
 561          * @param DatabaseBase $conn
 562          * @throws MWException
 563          */
 564         public function reuseConnection( $conn ) {
 565                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 566                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 567                 if ( $serverIndex === null || $refCount === null ) {
 568                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 569
 570                         /**
 571                          * This can happen in code like:
 572                          *   foreach ( $dbs as $db ) {
 573                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 574                          *     ...
 575                          *     $lb->reuseConnection( $conn );
 576                          *   }
 577                          * When a connection to the local DB is opened in this way, reuseConnection()
 578                          * should be ignored
 579                          */
 580
 581                         return;
 582                 }
 583
 584                 $dbName = $conn->getDBname();
 585                 $prefix = $conn->tablePrefix();
 586                 if ( strval( $prefix ) !== '' ) {
 587                         $wiki = "$dbName-$prefix";
 588                 } else {
 589                         $wiki = $dbName;
 590                 }
 591                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 592                         throw new MWException( __METHOD__ . ": connection not found, has " .
 593                                 "the connection been freed already?" );
 594                 }
 595                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 596                 if ( $refCount <= 0 ) {
 597                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 598                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 599                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 600                 } else {
 601                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 602                 }
 603         }
 604
 605         /**
 606          * Get a database connection handle reference
 607          *
 608          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 609          *
 610          * @see LoadBalancer::getConnection() for parameter information
 611          *
 612          * @param int $db
 613          * @param array|string|bool $groups Query group(s), or false for the generic reader
 614          * @param string|bool $wiki Wiki ID, or false for the current wiki
 615          * @return DBConnRef
 616          */
 617         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 618                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 619         }
 620
 621         /**
 622          * Get a database connection handle reference without connecting yet
 623          *
 624          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 625          *
 626          * @see LoadBalancer::getConnection() for parameter information
 627          *
 628          * @param int $db
 629          * @param array|string|bool $groups Query group(s), or false for the generic reader
 630          * @param string|bool $wiki Wiki ID, or false for the current wiki
 631          * @return DBConnRef
 632          */
 633         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 634                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 635         }
 636
 637         /**
 638          * Open a connection to the server given by the specified index
 639          * Index must be an actual index into the array.
 640          * If the server is already open, returns it.
 641          *
 642          * On error, returns false, and the connection which caused the
 643          * error will be available via $this->mErrorConnection.
 644          *
 645          * @param int $i Server index
 646          * @param string|bool $wiki Wiki ID, or false for the current wiki
 647          * @return DatabaseBase
 648          *
 649          * @access private
 650          */
 651         public function openConnection( $i, $wiki = false ) {
 652                 if ( $wiki !== false ) {
 653                         $conn = $this->openForeignConnection( $i, $wiki );
 654
 655                         return $conn;
 656                 }
 657                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 658                         $conn = $this->mConns['local'][$i][0];
 659                 } else {
 660                         $server = $this->mServers[$i];
 661                         $server['serverIndex'] = $i;
 662                         $conn = $this->reallyOpenConnection( $server, false );
 663                         if ( $conn->isOpen() ) {
 664                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 665                                 $this->mConns['local'][$i][0] = $conn;
 666                         } else {
 667                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 668                                 $this->mErrorConnection = $conn;
 669                                 $conn = false;
 670                         }
 671                 }
 672
 673                 return $conn;
 674         }
 675
 676         /**
 677          * Open a connection to a foreign DB, or return one if it is already open.
 678          *
 679          * Increments a reference count on the returned connection which locks the
 680          * connection to the requested wiki. This reference count can be
 681          * decremented by calling reuseConnection().
 682          *
 683          * If a connection is open to the appropriate server already, but with the wrong
 684          * database, it will be switched to the right database and returned, as long as
 685          * it has been freed first with reuseConnection().
 686          *
 687          * On error, returns false, and the connection which caused the
 688          * error will be available via $this->mErrorConnection.
 689          *
 690          * @param int $i Server index
 691          * @param string $wiki Wiki ID to open
 692          * @return DatabaseBase
 693          */
 694         private function openForeignConnection( $i, $wiki ) {
 695                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 696                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 697                         // Reuse an already-used connection
 698                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 699                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 700                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 701                         // Reuse a free connection for the same wiki
 702                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 703                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 704                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 705                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 706                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 707                         // Reuse a connection from another wiki
 708                         $conn = reset( $this->mConns['foreignFree'][$i] );
 709                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 710
 711                         // The empty string as a DB name means "don't care".
 712                         // DatabaseMysqlBase::open() already handle this on connection.
 713                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 714                                 $this->mLastError = "Error selecting database $dbName on server " .
 715                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 716                                 $this->mErrorConnection = $conn;
 717                                 $conn = false;
 718                         } else {
 719                                 $conn->tablePrefix( $prefix );
 720                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 721                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 722                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 723                         }
 724                 } else {
 725                         // Open a new connection
 726                         $server = $this->mServers[$i];
 727                         $server['serverIndex'] = $i;
 728                         $server['foreignPoolRefCount'] = 0;
 729                         $server['foreign'] = true;
 730                         $conn = $this->reallyOpenConnection( $server, $dbName );
 731                         if ( !$conn->isOpen() ) {
 732                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 733                                 $this->mErrorConnection = $conn;
 734                                 $conn = false;
 735                         } else {
 736                                 $conn->tablePrefix( $prefix );
 737                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 738                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 739                         }
 740                 }
 741
 742                 // Increment reference count
 743                 if ( $conn ) {
 744                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 745                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 746                 }
 747
 748                 return $conn;
 749         }
 750
 751         /**
 752          * Test if the specified index represents an open connection
 753          *
 754          * @param int $index Server index
 755          * @access private
 756          * @return bool
 757          */
 758         private function isOpen( $index ) {
 759                 if ( !is_integer( $index ) ) {
 760                         return false;
 761                 }
 762
 763                 return (bool)$this->getAnyOpenConnection( $index );
 764         }
 765
 766         /**
 767          * Really opens a connection. Uncached.
 768          * Returns a Database object whether or not the connection was successful.
 769          * @access private
 770          *
 771          * @param array $server
 772          * @param bool $dbNameOverride
 773          * @throws MWException
 774          * @return DatabaseBase
 775          */
 776         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 777                 if ( !is_array( $server ) ) {
 778                         throw new MWException( 'You must update your load-balancing configuration. ' .
 779                                 'See DefaultSettings.php entry for $wgDBservers.' );
 780                 }
 781
 782                 if ( $dbNameOverride !== false ) {
 783                         $server['dbname'] = $dbNameOverride;
 784                 }
 785
 786                 // Log when many connection are made on requests
 787                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 788                         $masterAddr = $this->getServerName( 0 );
 789                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 790                                 "{$this->connsOpened}+ connections made (master=$masterAddr)\n" .
 791                                 wfBacktrace( true ) );
 792                 }
 793
 794                 # Create object
 795                 try {
 796                         $db = DatabaseBase::factory( $server['type'], $server );
 797                 } catch ( DBConnectionError $e ) {
 798                         // FIXME: This is probably the ugliest thing I have ever done to
 799                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 800                         $db = $e->db;
 801                 }
 802
 803                 $db->setLBInfo( $server );
 804                 if ( isset( $server['fakeSlaveLag'] ) ) {
 805                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 806                 }
 807                 if ( isset( $server['fakeMaster'] ) ) {
 808                         $db->setFakeMaster( true );
 809                 }
 810
 811                 return $db;
 812         }
 813
 814         /**
 815          * @throws DBConnectionError
 816          * @return bool
 817          */
 818         private function reportConnectionError() {
 819                 $conn = $this->mErrorConnection; // The connection which caused the error
 820                 $context = array(
 821                         'method' => __METHOD__,
 822                         'last_error' => $this->mLastError,
 823                 );
 824
 825                 if ( !is_object( $conn ) ) {
 826                         // No last connection, probably due to all servers being too busy
 827                         wfLogDBError(
 828                                 "LB failure with no last connection. Connection error: {last_error}",
 829                                 $context
 830                         );
 831
 832                         // If all servers were busy, mLastError will contain something sensible
 833                         throw new DBConnectionError( null, $this->mLastError );
 834                 } else {
 835                         $context['db_server'] = $conn->getProperty( 'mServer' );
 836                         wfLogDBError(
 837                                 "Connection error: {last_error} ({db_server})",
 838                                 $context
 839                         );
 840                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
 841                 }
 842
 843                 return false; /* not reached */
 844         }
 845
 846         /**
 847          * @return int
 848          * @since 1.26
 849          */
 850         public function getWriterIndex() {
 851                 return 0;
 852         }
 853
 854         /**
 855          * Returns true if the specified index is a valid server index
 856          *
 857          * @param string $i
 858          * @return bool
 859          */
 860         public function haveIndex( $i ) {
 861                 return array_key_exists( $i, $this->mServers );
 862         }
 863
 864         /**
 865          * Returns true if the specified index is valid and has non-zero load
 866          *
 867          * @param string $i
 868          * @return bool
 869          */
 870         public function isNonZeroLoad( $i ) {
 871                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 872         }
 873
 874         /**
 875          * Get the number of defined servers (not the number of open connections)
 876          *
 877          * @return int
 878          */
 879         public function getServerCount() {
 880                 return count( $this->mServers );
 881         }
 882
 883         /**
 884          * Get the host name or IP address of the server with the specified index
 885          * Prefer a readable name if available.
 886          * @param string $i
 887          * @return string
 888          */
 889         public function getServerName( $i ) {
 890                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 891                         return $this->mServers[$i]['hostName'];
 892                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 893                         return $this->mServers[$i]['host'];
 894                 } else {
 895                         return '';
 896                 }
 897         }
 898
 899         /**
 900          * Return the server info structure for a given index, or false if the index is invalid.
 901          * @param int $i
 902          * @return array|bool
 903          */
 904         public function getServerInfo( $i ) {
 905                 if ( isset( $this->mServers[$i] ) ) {
 906                         return $this->mServers[$i];
 907                 } else {
 908                         return false;
 909                 }
 910         }
 911
 912         /**
 913          * Sets the server info structure for the given index. Entry at index $i
 914          * is created if it doesn't exist
 915          * @param int $i
 916          * @param array $serverInfo
 917          */
 918         public function setServerInfo( $i, array $serverInfo ) {
 919                 $this->mServers[$i] = $serverInfo;
 920         }
 921
 922         /**
 923          * Get the current master position for chronology control purposes
 924          * @return mixed
 925          */
 926         public function getMasterPos() {
 927                 # If this entire request was served from a slave without opening a connection to the
 928                 # master (however unlikely that may be), then we can fetch the position from the slave.
 929                 $masterConn = $this->getAnyOpenConnection( 0 );
 930                 if ( !$masterConn ) {
 931                         $serverCount = count( $this->mServers );
 932                         for ( $i = 1; $i < $serverCount; $i++ ) {
 933                                 $conn = $this->getAnyOpenConnection( $i );
 934                                 if ( $conn ) {
 935                                         wfDebug( "Master pos fetched from slave\n" );
 936
 937                                         return $conn->getSlavePos();
 938                                 }
 939                         }
 940                 } else {
 941                         wfDebug( "Master pos fetched from master\n" );
 942
 943                         return $masterConn->getMasterPos();
 944                 }
 945
 946                 return false;
 947         }
 948
 949         /**
 950          * Close all open connections
 951          */
 952         public function closeAll() {
 953                 foreach ( $this->mConns as $conns2 ) {
 954                         foreach ( $conns2 as $conns3 ) {
 955                                 /** @var DatabaseBase $conn */
 956                                 foreach ( $conns3 as $conn ) {
 957                                         $conn->close();
 958                                 }
 959                         }
 960                 }
 961                 $this->mConns = array(
 962                         'local' => array(),
 963                         'foreignFree' => array(),
 964                         'foreignUsed' => array(),
 965                 );
 966                 $this->connsOpened = 0;
 967         }
 968
 969         /**
 970          * Close a connection
 971          * Using this function makes sure the LoadBalancer knows the connection is closed.
 972          * If you use $conn->close() directly, the load balancer won't update its state.
 973          * @param DatabaseBase $conn
 974          */
 975         public function closeConnection( $conn ) {
 976                 $done = false;
 977                 foreach ( $this->mConns as $i1 => $conns2 ) {
 978                         foreach ( $conns2 as $i2 => $conns3 ) {
 979                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 980                                         if ( $conn === $candidateConn ) {
 981                                                 $conn->close();
 982                                                 unset( $this->mConns[$i1][$i2][$i3] );
 983                                                 --$this->connsOpened;
 984                                                 $done = true;
 985                                                 break;
 986                                         }
 987                                 }
 988                         }
 989                 }
 990                 if ( !$done ) {
 991                         $conn->close();
 992                 }
 993         }
 994
 995         /**
 996          * Commit transactions on all open connections
 997          */
 998         public function commitAll() {
 999                 foreach ( $this->mConns as $conns2 ) {
1000                         foreach ( $conns2 as $conns3 ) {
1001                                 /** @var DatabaseBase[] $conns3 */
1002                                 foreach ( $conns3 as $conn ) {
1003                                         if ( $conn->trxLevel() ) {
1004                                                 $conn->commit( __METHOD__, 'flush' );
1005                                         }
1006                                 }
1007                         }
1008                 }
1009         }
1010
1011         /**
1012          *  Issue COMMIT only on master, only if queries were done on connection
1013          */
1014         public function commitMasterChanges() {
1015                 $masterIndex = $this->getWriterIndex();
1016                 foreach ( $this->mConns as $conns2 ) {
1017                         if ( empty( $conns2[$masterIndex] ) ) {
1018                                 continue;
1019                         }
1020                         /** @var DatabaseBase $conn */
1021                         foreach ( $conns2[$masterIndex] as $conn ) {
1022                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1023                                         $conn->commit( __METHOD__, 'flush' );
1024                                 }
1025                         }
1026                 }
1027         }
1028
1029         /**
1030          * Issue ROLLBACK only on master, only if queries were done on connection
1031          * @since 1.23
1032          */
1033         public function rollbackMasterChanges() {
1034                 $failedServers = array();
1035
1036                 $masterIndex = $this->getWriterIndex();
1037                 foreach ( $this->mConns as $conns2 ) {
1038                         if ( empty( $conns2[$masterIndex] ) ) {
1039                                 continue;
1040                         }
1041                         /** @var DatabaseBase $conn */
1042                         foreach ( $conns2[$masterIndex] as $conn ) {
1043                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1044                                         try {
1045                                                 $conn->rollback( __METHOD__, 'flush' );
1046                                         } catch ( DBError $e ) {
1047                                                 MWExceptionHandler::logException( $e );
1048                                                 $failedServers[] = $conn->getServer();
1049                                         }
1050                                 }
1051                         }
1052                 }
1053
1054                 if ( $failedServers ) {
1055                         throw new DBExpectedError( null, "Rollback failed on server(s) " .
1056                                 implode( ', ', array_unique( $failedServers ) ) );
1057                 }
1058         }
1059
1060         /**
1061          * @return bool Whether a master connection is already open
1062          * @since 1.24
1063          */
1064         public function hasMasterConnection() {
1065                 return $this->isOpen( $this->getWriterIndex() );
1066         }
1067
1068         /**
1069          * Determine if there are pending changes in a transaction by this thread
1070          * @since 1.23
1071          * @return bool
1072          */
1073         public function hasMasterChanges() {
1074                 $masterIndex = $this->getWriterIndex();
1075                 foreach ( $this->mConns as $conns2 ) {
1076                         if ( empty( $conns2[$masterIndex] ) ) {
1077                                 continue;
1078                         }
1079                         /** @var DatabaseBase $conn */
1080                         foreach ( $conns2[$masterIndex] as $conn ) {
1081                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1082                                         return true;
1083                                 }
1084                         }
1085                 }
1086                 return false;
1087         }
1088
1089         /**
1090          * Get the timestamp of the latest write query done by this thread
1091          * @since 1.25
1092          * @return float|bool UNIX timestamp or false
1093          */
1094         public function lastMasterChangeTimestamp() {
1095                 $lastTime = false;
1096                 $masterIndex = $this->getWriterIndex();
1097                 foreach ( $this->mConns as $conns2 ) {
1098                         if ( empty( $conns2[$masterIndex] ) ) {
1099                                 continue;
1100                         }
1101                         /** @var DatabaseBase $conn */
1102                         foreach ( $conns2[$masterIndex] as $conn ) {
1103                                 $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1104                         }
1105                 }
1106                 return $lastTime;
1107         }
1108
1109         /**
1110          * Check if this load balancer object had any recent or still
1111          * pending writes issued against it by this PHP thread
1112          *
1113          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1114          * @return bool
1115          * @since 1.25
1116          */
1117         public function hasOrMadeRecentMasterChanges( $age = null ) {
1118                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1119
1120                 return ( $this->hasMasterChanges()
1121                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1122         }
1123
1124         /**
1125          * @param mixed $value
1126          * @return mixed
1127          */
1128         public function waitTimeout( $value = null ) {
1129                 return wfSetVar( $this->mWaitTimeout, $value );
1130         }
1131
1132         /**
1133          * @return bool Whether the generic connection for reads is highly "lagged"
1134          */
1135         public function getLaggedSlaveMode() {
1136                 # Get a generic reader connection
1137                 $this->getConnection( DB_SLAVE );
1138
1139                 return $this->mLaggedSlaveMode;
1140         }
1141
1142         /**
1143          * Disables/enables lag checks
1144          * @param null|bool $mode
1145          * @return bool
1146          */
1147         public function allowLagged( $mode = null ) {
1148                 if ( $mode === null ) {
1149                         return $this->mAllowLagged;
1150                 }
1151                 $this->mAllowLagged = $mode;
1152
1153                 return $this->mAllowLagged;
1154         }
1155
1156         /**
1157          * @return bool
1158          */
1159         public function pingAll() {
1160                 $success = true;
1161                 foreach ( $this->mConns as $conns2 ) {
1162                         foreach ( $conns2 as $conns3 ) {
1163                                 /** @var DatabaseBase[] $conns3 */
1164                                 foreach ( $conns3 as $conn ) {
1165                                         if ( !$conn->ping() ) {
1166                                                 $success = false;
1167                                         }
1168                                 }
1169                         }
1170                 }
1171
1172                 return $success;
1173         }
1174
1175         /**
1176          * Call a function with each open connection object
1177          * @param callable $callback
1178          * @param array $params
1179          */
1180         public function forEachOpenConnection( $callback, array $params = array() ) {
1181                 foreach ( $this->mConns as $conns2 ) {
1182                         foreach ( $conns2 as $conns3 ) {
1183                                 foreach ( $conns3 as $conn ) {
1184                                         $mergedParams = array_merge( array( $conn ), $params );
1185                                         call_user_func_array( $callback, $mergedParams );
1186                                 }
1187                         }
1188                 }
1189         }
1190
1191         /**
1192          * Get the hostname and lag time of the most-lagged slave
1193          *
1194          * This is useful for maintenance scripts that need to throttle their updates.
1195          * May attempt to open connections to slaves on the default DB. If there is
1196          * no lag, the maximum lag will be reported as -1.
1197          *
1198          * @param bool|string $wiki Wiki ID, or false for the default database
1199          * @return array ( host, max lag, index of max lagged host )
1200          */
1201         public function getMaxLag( $wiki = false ) {
1202                 $maxLag = -1;
1203                 $host = '';
1204                 $maxIndex = 0;
1205
1206                 if ( $this->getServerCount() <= 1 ) {
1207                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1208                 }
1209
1210                 $lagTimes = $this->getLagTimes( $wiki );
1211                 foreach ( $lagTimes as $i => $lag ) {
1212                         if ( $lag > $maxLag ) {
1213                                 $maxLag = $lag;
1214                                 $host = $this->mServers[$i]['host'];
1215                                 $maxIndex = $i;
1216                         }
1217                 }
1218
1219                 return array( $host, $maxLag, $maxIndex );
1220         }
1221
1222         /**
1223          * Get lag time for each server
1224          *
1225          * Results are cached for a short time in memcached/process cache
1226          *
1227          * @param string|bool $wiki
1228          * @return int[] Map of (server index => seconds)
1229          */
1230         public function getLagTimes( $wiki = false ) {
1231                 if ( $this->getServerCount() <= 1 ) {
1232                         return array( 0 => 0 ); // no replication = no lag
1233                 }
1234
1235                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1236                         return $this->mProcCache->get( 'slave_lag', 'times' );
1237                 }
1238
1239                 # Send the request to the load monitor
1240                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1241
1242                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1243
1244                 return $times;
1245         }
1246
1247         /**
1248          * Get the lag in seconds for a given connection, or zero if this load
1249          * balancer does not have replication enabled.
1250          *
1251          * This should be used in preference to Database::getLag() in cases where
1252          * replication may not be in use, since there is no way to determine if
1253          * replication is in use at the connection level without running
1254          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1255          * function instead of Database::getLag() avoids a fatal error in this
1256          * case on many installations.
1257          *
1258          * @param DatabaseBase $conn
1259          * @return int
1260          */
1261         public function safeGetLag( $conn ) {
1262                 if ( $this->getServerCount() == 1 ) {
1263                         return 0;
1264                 } else {
1265                         return $conn->getLag();
1266                 }
1267         }
1268
1269         /**
1270          * Clear the cache for slag lag delay times
1271          */
1272         public function clearLagTimeCache() {
1273                 $this->mProcCache->clear( 'slave_lag' );
1274         }
1275 }