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 ProcessCacheLRU */
  62         private $mProcCache;
  63
  64         /**
  65          * @param array $params Array with keys:
  66          *   servers           Required. Array of server info structures.
  67          *   loadMonitor       Name of a class used to fetch server lag and load.
  68          * @throws MWException
  69          */
  70         public function __construct( array $params ) {
  71                 if ( !isset( $params['servers'] ) ) {
  72                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  73                 }
  74                 $this->mServers = $params['servers'];
  75                 $this->mWaitTimeout = 10;
  76
  77                 $this->mReadIndex = -1;
  78                 $this->mWriteIndex = -1;
  79                 $this->mConns = array(
  80                         'local' => array(),
  81                         'foreignUsed' => array(),
  82                         'foreignFree' => array() );
  83                 $this->mLoads = array();
  84                 $this->mWaitForPos = false;
  85                 $this->mLaggedSlaveMode = false;
  86                 $this->mErrorConnection = false;
  87                 $this->mAllowLagged = false;
  88
  89                 if ( isset( $params['loadMonitor'] ) ) {
  90                         $this->mLoadMonitorClass = $params['loadMonitor'];
  91                 } else {
  92                         $master = reset( $params['servers'] );
  93                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  94                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  95                         } else {
  96                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
  97                         }
  98                 }
  99
 100                 foreach ( $params['servers'] as $i => $server ) {
 101                         $this->mLoads[$i] = $server['load'];
 102                         if ( isset( $server['groupLoads'] ) ) {
 103                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 104                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 105                                                 $this->mGroupLoads[$group] = array();
 106                                         }
 107                                         $this->mGroupLoads[$group][$i] = $ratio;
 108                                 }
 109                         }
 110                 }
 111
 112                 $this->mProcCache = new ProcessCacheLRU( 30 );
 113         }
 114
 115         /**
 116          * Get a LoadMonitor instance
 117          *
 118          * @return LoadMonitor
 119          */
 120         private function getLoadMonitor() {
 121                 if ( !isset( $this->mLoadMonitor ) ) {
 122                         $class = $this->mLoadMonitorClass;
 123                         $this->mLoadMonitor = new $class( $this );
 124                 }
 125
 126                 return $this->mLoadMonitor;
 127         }
 128
 129         /**
 130          * Get or set arbitrary data used by the parent object, usually an LBFactory
 131          * @param mixed $x
 132          * @return mixed
 133          */
 134         public function parentInfo( $x = null ) {
 135                 return wfSetVar( $this->mParentInfo, $x );
 136         }
 137
 138         /**
 139          * Given an array of non-normalised probabilities, this function will select
 140          * an element and return the appropriate key
 141          *
 142          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 143          *
 144          * @param array $weights
 145          * @return bool|int|string
 146          */
 147         public function pickRandom( array $weights ) {
 148                 return ArrayUtils::pickRandom( $weights );
 149         }
 150
 151         /**
 152          * @param array $loads
 153          * @param bool|string $wiki Wiki to get non-lagged for
 154          * @param float $maxLag Restrict the maximum allowed lag to this many seconds
 155          * @return bool|int|string
 156          */
 157         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 158                 $lags = $this->getLagTimes( $wiki );
 159
 160                 # Unset excessively lagged servers
 161                 foreach ( $lags as $i => $lag ) {
 162                         if ( $i != 0 ) {
 163                                 $maxServerLag = $maxLag;
 164                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 165                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 166                                 }
 167                                 if ( $lag === false ) {
 168                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 169                                         unset( $loads[$i] );
 170                                 } elseif ( $lag > $maxServerLag ) {
 171                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 172                                         unset( $loads[$i] );
 173                                 }
 174                         }
 175                 }
 176
 177                 # Find out if all the slaves with non-zero load are lagged
 178                 $sum = 0;
 179                 foreach ( $loads as $load ) {
 180                         $sum += $load;
 181                 }
 182                 if ( $sum == 0 ) {
 183                         # No appropriate DB servers except maybe the master and some slaves with zero load
 184                         # Do NOT use the master
 185                         # Instead, this function will return false, triggering read-only mode,
 186                         # and a lagged slave will be used instead.
 187                         return false;
 188                 }
 189
 190                 if ( count( $loads ) == 0 ) {
 191                         return false;
 192                 }
 193
 194                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 195
 196                 # Return a random representative of the remainder
 197                 return ArrayUtils::pickRandom( $loads );
 198         }
 199
 200         /**
 201          * Get the index of the reader connection, which may be a slave
 202          * This takes into account load ratios and lag times. It should
 203          * always return a consistent index during a given invocation
 204          *
 205          * Side effect: opens connections to databases
 206          * @param string|bool $group Query group, or false for the generic reader
 207          * @param string|bool $wiki Wiki ID, or false for the current wiki
 208          * @throws MWException
 209          * @return bool|int|string
 210          */
 211         public function getReaderIndex( $group = false, $wiki = false ) {
 212                 global $wgReadOnly, $wgDBtype;
 213
 214                 # @todo FIXME: For now, only go through all this for mysql databases
 215                 if ( $wgDBtype != 'mysql' ) {
 216                         return $this->getWriterIndex();
 217                 }
 218
 219                 if ( count( $this->mServers ) == 1 ) {
 220                         # Skip the load balancing if there's only one server
 221                         return 0;
 222                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 223                         # Shortcut if generic reader exists already
 224                         return $this->mReadIndex;
 225                 }
 226
 227                 new ProfileSection( __METHOD__ );
 228
 229                 # Find the relevant load array
 230                 if ( $group !== false ) {
 231                         if ( isset( $this->mGroupLoads[$group] ) ) {
 232                                 $nonErrorLoads = $this->mGroupLoads[$group];
 233                         } else {
 234                                 # No loads for this group, return false and the caller can use some other group
 235                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 236
 237                                 return false;
 238                         }
 239                 } else {
 240                         $nonErrorLoads = $this->mLoads;
 241                 }
 242
 243                 if ( !count( $nonErrorLoads ) ) {
 244                         throw new MWException( "Empty server array given to LoadBalancer" );
 245                 }
 246
 247                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 248                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 249
 250                 $laggedSlaveMode = false;
 251
 252                 # No server found yet
 253                 $i = 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 ( $wgReadOnly || $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                                         $wgReadOnly = 'The database has been automatically locked ' .
 278                                                 'while the slave database servers catch up to the master';
 279                                         $i = ArrayUtils::pickRandom( $currentLoads );
 280                                         $laggedSlaveMode = true;
 281                                 }
 282                         }
 283
 284                         if ( $i === false ) {
 285                                 # pickRandom() returned false
 286                                 # This is permanent and means the configuration or the load monitor
 287                                 # wants us to return false.
 288                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 289
 290                                 return false;
 291                         }
 292
 293                         wfDebugLog( 'connect', __METHOD__ .
 294                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 295
 296                         $conn = $this->openConnection( $i, $wiki );
 297                         if ( !$conn ) {
 298                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 299                                 unset( $nonErrorLoads[$i] );
 300                                 unset( $currentLoads[$i] );
 301                                 $i = false;
 302                                 continue;
 303                         }
 304
 305                         // Decrement reference counter, we are finished with this connection.
 306                         // It will be incremented for the caller later.
 307                         if ( $wiki !== false ) {
 308                                 $this->reuseConnection( $conn );
 309                         }
 310
 311                         # Return this server
 312                         break;
 313                 }
 314
 315                 # If all servers were down, quit now
 316                 if ( !count( $nonErrorLoads ) ) {
 317                         wfDebugLog( 'connect', "All servers down" );
 318                 }
 319
 320                 if ( $i !== false ) {
 321                         # Slave connection successful
 322                         # Wait for the session master pos for a short time
 323                         if ( $this->mWaitForPos && $i > 0 ) {
 324                                 if ( !$this->doWait( $i ) ) {
 325                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 326                                 }
 327                         }
 328                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group !== false ) {
 329                                 $this->mReadIndex = $i;
 330                         }
 331                 }
 332
 333                 return $i;
 334         }
 335
 336         /**
 337          * Set the master wait position
 338          * If a DB_SLAVE connection has been opened already, waits
 339          * Otherwise sets a variable telling it to wait if such a connection is opened
 340          * @param DBMasterPos $pos
 341          */
 342         public function waitFor( $pos ) {
 343                 $this->mWaitForPos = $pos;
 344                 $i = $this->mReadIndex;
 345
 346                 if ( $i > 0 ) {
 347                         if ( !$this->doWait( $i ) ) {
 348                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 349                                 $this->mLaggedSlaveMode = true;
 350                         }
 351                 }
 352         }
 353
 354         /**
 355          * Set the master wait position and wait for ALL slaves to catch up to it
 356          * @param DBMasterPos $pos
 357          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 358          * @return bool Success (able to connect and no timeouts reached)
 359          */
 360         public function waitForAll( $pos, $timeout = null ) {
 361                 $this->mWaitForPos = $pos;
 362                 $serverCount = count( $this->mServers );
 363
 364                 $ok = true;
 365                 for ( $i = 1; $i < $serverCount; $i++ ) {
 366                         if ( $this->mLoads[$i] > 0 ) {
 367                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 368                         }
 369                 }
 370
 371                 return $ok;
 372         }
 373
 374         /**
 375          * Get any open connection to a given server index, local or foreign
 376          * Returns false if there is no connection open
 377          *
 378          * @param int $i
 379          * @return DatabaseBase|bool False on failure
 380          */
 381         public function getAnyOpenConnection( $i ) {
 382                 foreach ( $this->mConns as $conns ) {
 383                         if ( !empty( $conns[$i] ) ) {
 384                                 return reset( $conns[$i] );
 385                         }
 386                 }
 387
 388                 return false;
 389         }
 390
 391         /**
 392          * Wait for a given slave to catch up to the master pos stored in $this
 393          * @param int $index Server index
 394          * @param bool $open Check the server even if a new connection has to be made
 395          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 396          * @return bool
 397          */
 398         protected function doWait( $index, $open = false, $timeout = null ) {
 399                 $close = false; // close the connection afterwards
 400
 401                 # Find a connection to wait on, creating one if needed and allowed
 402                 $conn = $this->getAnyOpenConnection( $index );
 403                 if ( !$conn ) {
 404                         if ( !$open ) {
 405                                 wfDebug( __METHOD__ . ": no connection open\n" );
 406
 407                                 return false;
 408                         } else {
 409                                 $conn = $this->openConnection( $index, '' );
 410                                 if ( !$conn ) {
 411                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 412
 413                                         return false;
 414                                 }
 415                                 // Avoid connection spam in waitForAll() when connections
 416                                 // are made just for the sake of doing this lag check.
 417                                 $close = true;
 418                         }
 419                 }
 420
 421                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 422                 $timeout = $timeout ?: $this->mWaitTimeout;
 423                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 424
 425                 if ( $result == -1 || is_null( $result ) ) {
 426                         # Timed out waiting for slave, use master instead
 427                         $server = $this->mServers[$index]['host'];
 428                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 429                         wfDebug( "$msg\n" );
 430                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 431                         $ok = false;
 432                 } else {
 433                         wfDebug( __METHOD__ . ": Done\n" );
 434                         $ok = true;
 435                 }
 436
 437                 if ( $close ) {
 438                         $this->closeConnection( $conn );
 439                 }
 440
 441                 return $ok;
 442         }
 443
 444         /**
 445          * Get a connection by index
 446          * This is the main entry point for this class.
 447          *
 448          * @param int $i Server index
 449          * @param array|string|bool $groups Query group(s), or false for the generic reader
 450          * @param string|bool $wiki Wiki ID, or false for the current wiki
 451          *
 452          * @throws MWException
 453          * @return DatabaseBase
 454          */
 455         public function getConnection( $i, $groups = array(), $wiki = false ) {
 456                 if ( $i === null || $i === false ) {
 457                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 458                                 ' with invalid server index' );
 459                 }
 460
 461                 if ( $wiki === wfWikiID() ) {
 462                         $wiki = false;
 463                 }
 464
 465                 $groups = ( $groups === false || $groups === array() )
 466                         ? array( false ) // check one "group": the generic pool
 467                         : (array)$groups;
 468
 469                 if ( $i == DB_MASTER ) {
 470                         $i = $this->getWriterIndex();
 471                 } else {
 472                         # Try to find an available server in any the query groups (in order)
 473                         foreach ( $groups as $group ) {
 474                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 475                                 if ( $groupIndex !== false ) {
 476                                         $serverName = $this->getServerName( $groupIndex );
 477                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 478                                         $i = $groupIndex;
 479                                         break;
 480                                 }
 481                         }
 482                 }
 483
 484                 # Operation-based index
 485                 if ( $i == DB_SLAVE ) {
 486                         $this->mLastError = 'Unknown error'; // reset error string
 487                         # Try the general server pool if $groups are unavailable.
 488                         $i = in_array( false, $groups, true )
 489                                 ? false // don't bother with this if that is what was tried above
 490                                 : $this->getReaderIndex( false, $wiki );
 491                         # Couldn't find a working server in getReaderIndex()?
 492                         if ( $i === false ) {
 493                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 494
 495                                 return $this->reportConnectionError();
 496                         }
 497                 }
 498
 499                 # Now we have an explicit index into the servers array
 500                 $conn = $this->openConnection( $i, $wiki );
 501                 if ( !$conn ) {
 502
 503                         return $this->reportConnectionError();
 504                 }
 505
 506
 507                 return $conn;
 508         }
 509
 510         /**
 511          * Mark a foreign connection as being available for reuse under a different
 512          * DB name or prefix. This mechanism is reference-counted, and must be called
 513          * the same number of times as getConnection() to work.
 514          *
 515          * @param DatabaseBase $conn
 516          * @throws MWException
 517          */
 518         public function reuseConnection( $conn ) {
 519                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 520                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 521                 if ( $serverIndex === null || $refCount === null ) {
 522                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 523
 524                         /**
 525                          * This can happen in code like:
 526                          *   foreach ( $dbs as $db ) {
 527                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 528                          *     ...
 529                          *     $lb->reuseConnection( $conn );
 530                          *   }
 531                          * When a connection to the local DB is opened in this way, reuseConnection()
 532                          * should be ignored
 533                          */
 534
 535                         return;
 536                 }
 537
 538                 $dbName = $conn->getDBname();
 539                 $prefix = $conn->tablePrefix();
 540                 if ( strval( $prefix ) !== '' ) {
 541                         $wiki = "$dbName-$prefix";
 542                 } else {
 543                         $wiki = $dbName;
 544                 }
 545                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 546                         throw new MWException( __METHOD__ . ": connection not found, has " .
 547                                 "the connection been freed already?" );
 548                 }
 549                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 550                 if ( $refCount <= 0 ) {
 551                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 552                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 553                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 554                 } else {
 555                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 556                 }
 557         }
 558
 559         /**
 560          * Get a database connection handle reference
 561          *
 562          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 563          *
 564          * @see LoadBalancer::getConnection() for parameter information
 565          *
 566          * @param int $db
 567          * @param array|string|bool $groups Query group(s), or false for the generic reader
 568          * @param string|bool $wiki Wiki ID, or false for the current wiki
 569          * @return DBConnRef
 570          */
 571         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 572                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 573         }
 574
 575         /**
 576          * Get a database connection handle reference without connecting yet
 577          *
 578          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 579          *
 580          * @see LoadBalancer::getConnection() for parameter information
 581          *
 582          * @param int $db
 583          * @param array|string|bool $groups Query group(s), or false for the generic reader
 584          * @param string|bool $wiki Wiki ID, or false for the current wiki
 585          * @return DBConnRef
 586          */
 587         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 588                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 589         }
 590
 591         /**
 592          * Open a connection to the server given by the specified index
 593          * Index must be an actual index into the array.
 594          * If the server is already open, returns it.
 595          *
 596          * On error, returns false, and the connection which caused the
 597          * error will be available via $this->mErrorConnection.
 598          *
 599          * @param int $i Server index
 600          * @param string|bool $wiki Wiki ID, or false for the current wiki
 601          * @return DatabaseBase
 602          *
 603          * @access private
 604          */
 605         public function openConnection( $i, $wiki = false ) {
 606                 if ( $wiki !== false ) {
 607                         $conn = $this->openForeignConnection( $i, $wiki );
 608
 609                         return $conn;
 610                 }
 611                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 612                         $conn = $this->mConns['local'][$i][0];
 613                 } else {
 614                         $server = $this->mServers[$i];
 615                         $server['serverIndex'] = $i;
 616                         $conn = $this->reallyOpenConnection( $server, false );
 617                         if ( $conn->isOpen() ) {
 618                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 619                                 $this->mConns['local'][$i][0] = $conn;
 620                         } else {
 621                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 622                                 $this->mErrorConnection = $conn;
 623                                 $conn = false;
 624                         }
 625                 }
 626
 627                 return $conn;
 628         }
 629
 630         /**
 631          * Open a connection to a foreign DB, or return one if it is already open.
 632          *
 633          * Increments a reference count on the returned connection which locks the
 634          * connection to the requested wiki. This reference count can be
 635          * decremented by calling reuseConnection().
 636          *
 637          * If a connection is open to the appropriate server already, but with the wrong
 638          * database, it will be switched to the right database and returned, as long as
 639          * it has been freed first with reuseConnection().
 640          *
 641          * On error, returns false, and the connection which caused the
 642          * error will be available via $this->mErrorConnection.
 643          *
 644          * @param int $i Server index
 645          * @param string $wiki Wiki ID to open
 646          * @return DatabaseBase
 647          */
 648         private function openForeignConnection( $i, $wiki ) {
 649                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 650                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 651                         // Reuse an already-used connection
 652                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 653                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 654                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 655                         // Reuse a free connection for the same wiki
 656                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 657                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 658                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 659                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 660                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 661                         // Reuse a connection from another wiki
 662                         $conn = reset( $this->mConns['foreignFree'][$i] );
 663                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 664
 665                         // The empty string as a DB name means "don't care".
 666                         // DatabaseMysqlBase::open() already handle this on connection.
 667                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 668                                 $this->mLastError = "Error selecting database $dbName on server " .
 669                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 670                                 $this->mErrorConnection = $conn;
 671                                 $conn = false;
 672                         } else {
 673                                 $conn->tablePrefix( $prefix );
 674                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 675                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 676                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 677                         }
 678                 } else {
 679                         // Open a new connection
 680                         $server = $this->mServers[$i];
 681                         $server['serverIndex'] = $i;
 682                         $server['foreignPoolRefCount'] = 0;
 683                         $server['foreign'] = true;
 684                         $conn = $this->reallyOpenConnection( $server, $dbName );
 685                         if ( !$conn->isOpen() ) {
 686                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 687                                 $this->mErrorConnection = $conn;
 688                                 $conn = false;
 689                         } else {
 690                                 $conn->tablePrefix( $prefix );
 691                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 692                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 693                         }
 694                 }
 695
 696                 // Increment reference count
 697                 if ( $conn ) {
 698                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 699                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 700                 }
 701
 702                 return $conn;
 703         }
 704
 705         /**
 706          * Test if the specified index represents an open connection
 707          *
 708          * @param int $index Server index
 709          * @access private
 710          * @return bool
 711          */
 712         private function isOpen( $index ) {
 713                 if ( !is_integer( $index ) ) {
 714                         return false;
 715                 }
 716
 717                 return (bool)$this->getAnyOpenConnection( $index );
 718         }
 719
 720         /**
 721          * Really opens a connection. Uncached.
 722          * Returns a Database object whether or not the connection was successful.
 723          * @access private
 724          *
 725          * @param array $server
 726          * @param bool $dbNameOverride
 727          * @throws MWException
 728          * @return DatabaseBase
 729          */
 730         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 731                 if ( !is_array( $server ) ) {
 732                         throw new MWException( 'You must update your load-balancing configuration. ' .
 733                                 'See DefaultSettings.php entry for $wgDBservers.' );
 734                 }
 735
 736                 if ( $dbNameOverride !== false ) {
 737                         $server['dbname'] = $dbNameOverride;
 738                 }
 739
 740                 # Create object
 741                 try {
 742                         $db = DatabaseBase::factory( $server['type'], $server );
 743                 } catch ( DBConnectionError $e ) {
 744                         // FIXME: This is probably the ugliest thing I have ever done to
 745                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 746                         $db = $e->db;
 747                 }
 748
 749                 $db->setLBInfo( $server );
 750                 if ( isset( $server['fakeSlaveLag'] ) ) {
 751                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 752                 }
 753                 if ( isset( $server['fakeMaster'] ) ) {
 754                         $db->setFakeMaster( true );
 755                 }
 756
 757                 return $db;
 758         }
 759
 760         /**
 761          * @throws DBConnectionError
 762          * @return bool
 763          */
 764         private function reportConnectionError() {
 765                 $conn = $this->mErrorConnection; // The connection which caused the error
 766                 $context = array(
 767                         'method' => __METHOD__,
 768                         'last_error' => $this->mLastError,
 769                 );
 770
 771                 if ( !is_object( $conn ) ) {
 772                         // No last connection, probably due to all servers being too busy
 773                         wfLogDBError(
 774                                 "LB failure with no last connection. Connection error: {last_error}",
 775                                 $context
 776                         );
 777
 778                         // If all servers were busy, mLastError will contain something sensible
 779                         throw new DBConnectionError( null, $this->mLastError );
 780                 } else {
 781                         $context['db_server'] = $conn->getProperty( 'mServer' );
 782                         wfLogDBError(
 783                                 "Connection error: {last_error} ({db_server})",
 784                                 $context
 785                         );
 786                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
 787                 }
 788
 789                 return false; /* not reached */
 790         }
 791
 792         /**
 793          * @return int
 794          */
 795         private function getWriterIndex() {
 796                 return 0;
 797         }
 798
 799         /**
 800          * Returns true if the specified index is a valid server index
 801          *
 802          * @param string $i
 803          * @return bool
 804          */
 805         public function haveIndex( $i ) {
 806                 return array_key_exists( $i, $this->mServers );
 807         }
 808
 809         /**
 810          * Returns true if the specified index is valid and has non-zero load
 811          *
 812          * @param string $i
 813          * @return bool
 814          */
 815         public function isNonZeroLoad( $i ) {
 816                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 817         }
 818
 819         /**
 820          * Get the number of defined servers (not the number of open connections)
 821          *
 822          * @return int
 823          */
 824         public function getServerCount() {
 825                 return count( $this->mServers );
 826         }
 827
 828         /**
 829          * Get the host name or IP address of the server with the specified index
 830          * Prefer a readable name if available.
 831          * @param string $i
 832          * @return string
 833          */
 834         public function getServerName( $i ) {
 835                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 836                         return $this->mServers[$i]['hostName'];
 837                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 838                         return $this->mServers[$i]['host'];
 839                 } else {
 840                         return '';
 841                 }
 842         }
 843
 844         /**
 845          * Return the server info structure for a given index, or false if the index is invalid.
 846          * @param int $i
 847          * @return array|bool
 848          */
 849         public function getServerInfo( $i ) {
 850                 if ( isset( $this->mServers[$i] ) ) {
 851                         return $this->mServers[$i];
 852                 } else {
 853                         return false;
 854                 }
 855         }
 856
 857         /**
 858          * Sets the server info structure for the given index. Entry at index $i
 859          * is created if it doesn't exist
 860          * @param int $i
 861          * @param array $serverInfo
 862          */
 863         public function setServerInfo( $i, array $serverInfo ) {
 864                 $this->mServers[$i] = $serverInfo;
 865         }
 866
 867         /**
 868          * Get the current master position for chronology control purposes
 869          * @return mixed
 870          */
 871         public function getMasterPos() {
 872                 # If this entire request was served from a slave without opening a connection to the
 873                 # master (however unlikely that may be), then we can fetch the position from the slave.
 874                 $masterConn = $this->getAnyOpenConnection( 0 );
 875                 if ( !$masterConn ) {
 876                         $serverCount = count( $this->mServers );
 877                         for ( $i = 1; $i < $serverCount; $i++ ) {
 878                                 $conn = $this->getAnyOpenConnection( $i );
 879                                 if ( $conn ) {
 880                                         wfDebug( "Master pos fetched from slave\n" );
 881
 882                                         return $conn->getSlavePos();
 883                                 }
 884                         }
 885                 } else {
 886                         wfDebug( "Master pos fetched from master\n" );
 887
 888                         return $masterConn->getMasterPos();
 889                 }
 890
 891                 return false;
 892         }
 893
 894         /**
 895          * Close all open connections
 896          */
 897         public function closeAll() {
 898                 foreach ( $this->mConns as $conns2 ) {
 899                         foreach ( $conns2 as $conns3 ) {
 900                                 /** @var DatabaseBase $conn */
 901                                 foreach ( $conns3 as $conn ) {
 902                                         $conn->close();
 903                                 }
 904                         }
 905                 }
 906                 $this->mConns = array(
 907                         'local' => array(),
 908                         'foreignFree' => array(),
 909                         'foreignUsed' => array(),
 910                 );
 911         }
 912
 913         /**
 914          * Close a connection
 915          * Using this function makes sure the LoadBalancer knows the connection is closed.
 916          * If you use $conn->close() directly, the load balancer won't update its state.
 917          * @param DatabaseBase $conn
 918          */
 919         public function closeConnection( $conn ) {
 920                 $done = false;
 921                 foreach ( $this->mConns as $i1 => $conns2 ) {
 922                         foreach ( $conns2 as $i2 => $conns3 ) {
 923                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 924                                         if ( $conn === $candidateConn ) {
 925                                                 $conn->close();
 926                                                 unset( $this->mConns[$i1][$i2][$i3] );
 927                                                 $done = true;
 928                                                 break;
 929                                         }
 930                                 }
 931                         }
 932                 }
 933                 if ( !$done ) {
 934                         $conn->close();
 935                 }
 936         }
 937
 938         /**
 939          * Commit transactions on all open connections
 940          */
 941         public function commitAll() {
 942                 foreach ( $this->mConns as $conns2 ) {
 943                         foreach ( $conns2 as $conns3 ) {
 944                                 /** @var DatabaseBase[] $conns3 */
 945                                 foreach ( $conns3 as $conn ) {
 946                                         if ( $conn->trxLevel() ) {
 947                                                 $conn->commit( __METHOD__, 'flush' );
 948                                         }
 949                                 }
 950                         }
 951                 }
 952         }
 953
 954         /**
 955          *  Issue COMMIT only on master, only if queries were done on connection
 956          */
 957         public function commitMasterChanges() {
 958                 // Always 0, but who knows.. :)
 959                 $masterIndex = $this->getWriterIndex();
 960                 foreach ( $this->mConns as $conns2 ) {
 961                         if ( empty( $conns2[$masterIndex] ) ) {
 962                                 continue;
 963                         }
 964                         /** @var DatabaseBase $conn */
 965                         foreach ( $conns2[$masterIndex] as $conn ) {
 966                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 967                                         $conn->commit( __METHOD__, 'flush' );
 968                                 }
 969                         }
 970                 }
 971         }
 972
 973         /**
 974          * Issue ROLLBACK only on master, only if queries were done on connection
 975          * @since 1.23
 976          */
 977         public function rollbackMasterChanges() {
 978                 // Always 0, but who knows.. :)
 979                 $masterIndex = $this->getWriterIndex();
 980                 foreach ( $this->mConns as $conns2 ) {
 981                         if ( empty( $conns2[$masterIndex] ) ) {
 982                                 continue;
 983                         }
 984                         /** @var DatabaseBase $conn */
 985                         foreach ( $conns2[$masterIndex] as $conn ) {
 986                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 987                                         $conn->rollback( __METHOD__, 'flush' );
 988                                 }
 989                         }
 990                 }
 991         }
 992
 993         /**
 994          * @return bool Whether a master connection is already open
 995          * @since 1.24
 996          */
 997         public function hasMasterConnection() {
 998                 return $this->isOpen( $this->getWriterIndex() );
 999         }
1000
1001         /**
1002          * Determine if there are any pending changes that need to be rolled back
1003          * or committed.
1004          * @since 1.23
1005          * @return bool
1006          */
1007         public function hasMasterChanges() {
1008                 // Always 0, but who knows.. :)
1009                 $masterIndex = $this->getWriterIndex();
1010                 foreach ( $this->mConns as $conns2 ) {
1011                         if ( empty( $conns2[$masterIndex] ) ) {
1012                                 continue;
1013                         }
1014                         /** @var DatabaseBase $conn */
1015                         foreach ( $conns2[$masterIndex] as $conn ) {
1016                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1017                                         return true;
1018                                 }
1019                         }
1020                 }
1021                 return false;
1022         }
1023
1024         /**
1025          * @param mixed $value
1026          * @return mixed
1027          */
1028         public function waitTimeout( $value = null ) {
1029                 return wfSetVar( $this->mWaitTimeout, $value );
1030         }
1031
1032         /**
1033          * @return bool
1034          */
1035         public function getLaggedSlaveMode() {
1036                 return $this->mLaggedSlaveMode;
1037         }
1038
1039         /**
1040          * Disables/enables lag checks
1041          * @param null|bool $mode
1042          * @return bool
1043          */
1044         public function allowLagged( $mode = null ) {
1045                 if ( $mode === null ) {
1046                         return $this->mAllowLagged;
1047                 }
1048                 $this->mAllowLagged = $mode;
1049
1050                 return $this->mAllowLagged;
1051         }
1052
1053         /**
1054          * @return bool
1055          */
1056         public function pingAll() {
1057                 $success = true;
1058                 foreach ( $this->mConns as $conns2 ) {
1059                         foreach ( $conns2 as $conns3 ) {
1060                                 /** @var DatabaseBase[] $conns3 */
1061                                 foreach ( $conns3 as $conn ) {
1062                                         if ( !$conn->ping() ) {
1063                                                 $success = false;
1064                                         }
1065                                 }
1066                         }
1067                 }
1068
1069                 return $success;
1070         }
1071
1072         /**
1073          * Call a function with each open connection object
1074          * @param callable $callback
1075          * @param array $params
1076          */
1077         public function forEachOpenConnection( $callback, array $params = array() ) {
1078                 foreach ( $this->mConns as $conns2 ) {
1079                         foreach ( $conns2 as $conns3 ) {
1080                                 foreach ( $conns3 as $conn ) {
1081                                         $mergedParams = array_merge( array( $conn ), $params );
1082                                         call_user_func_array( $callback, $mergedParams );
1083                                 }
1084                         }
1085                 }
1086         }
1087
1088         /**
1089          * Get the hostname and lag time of the most-lagged slave
1090          *
1091          * This is useful for maintenance scripts that need to throttle their updates.
1092          * May attempt to open connections to slaves on the default DB. If there is
1093          * no lag, the maximum lag will be reported as -1.
1094          *
1095          * @param bool|string $wiki Wiki ID, or false for the default database
1096          * @return array ( host, max lag, index of max lagged host )
1097          */
1098         public function getMaxLag( $wiki = false ) {
1099                 $maxLag = -1;
1100                 $host = '';
1101                 $maxIndex = 0;
1102
1103                 if ( $this->getServerCount() <= 1 ) {
1104                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1105                 }
1106
1107                 $lagTimes = $this->getLagTimes( $wiki );
1108                 foreach ( $lagTimes as $i => $lag ) {
1109                         if ( $lag > $maxLag ) {
1110                                 $maxLag = $lag;
1111                                 $host = $this->mServers[$i]['host'];
1112                                 $maxIndex = $i;
1113                         }
1114                 }
1115
1116                 return array( $host, $maxLag, $maxIndex );
1117         }
1118
1119         /**
1120          * Get lag time for each server
1121          *
1122          * Results are cached for a short time in memcached/process cache
1123          *
1124          * @param string|bool $wiki
1125          * @return int[] Map of (server index => seconds)
1126          */
1127         public function getLagTimes( $wiki = false ) {
1128                 if ( $this->getServerCount() <= 1 ) {
1129                         return array( 0 => 0 ); // no replication = no lag
1130                 }
1131
1132                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1133                         return $this->mProcCache->get( 'slave_lag', 'times' );
1134                 }
1135
1136                 # Send the request to the load monitor
1137                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1138
1139                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1140
1141                 return $times;
1142         }
1143
1144         /**
1145          * Get the lag in seconds for a given connection, or zero if this load
1146          * balancer does not have replication enabled.
1147          *
1148          * This should be used in preference to Database::getLag() in cases where
1149          * replication may not be in use, since there is no way to determine if
1150          * replication is in use at the connection level without running
1151          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1152          * function instead of Database::getLag() avoids a fatal error in this
1153          * case on many installations.
1154          *
1155          * @param DatabaseBase $conn
1156          * @return int
1157          */
1158         public function safeGetLag( $conn ) {
1159                 if ( $this->getServerCount() == 1 ) {
1160                         return 0;
1161                 } else {
1162                         return $conn->getLag();
1163                 }
1164         }
1165
1166         /**
1167          * Clear the cache for slag lag delay times
1168          */
1169         public function clearLagTimeCache() {
1170                 $this->mProcCache->clear( 'slave_lag' );
1171         }
1172 }
1173
1174 /**
1175  * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1176  * as well handling deferring the actual network connection until the handle is used
1177  *
1178  * @ingroup Database
1179  * @since 1.22
1180  */
1181 class DBConnRef implements IDatabase {
1182         /** @var LoadBalancer */
1183         private $lb;
1184
1185         /** @var DatabaseBase|null */
1186         private $conn;
1187
1188         /** @var array|null */
1189         private $params;
1190
1191         /**
1192          * @param LoadBalancer $lb
1193          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1194          */
1195         public function __construct( LoadBalancer $lb, $conn ) {
1196                 $this->lb = $lb;
1197                 if ( $conn instanceof DatabaseBase ) {
1198                         $this->conn = $conn;
1199                 } else {
1200                         $this->params = $conn;
1201                 }
1202         }
1203
1204         public function __call( $name, $arguments ) {
1205                 if ( $this->conn === null ) {
1206                         list( $db, $groups, $wiki ) = $this->params;
1207                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1208                 }
1209
1210                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1211         }
1212
1213         public function __destruct() {
1214                 if ( $this->conn !== null ) {
1215                         $this->lb->reuseConnection( $this->conn );
1216                 }
1217         }
1218 }