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                 wfProfileIn( __METHOD__ );
 344                 $this->mWaitForPos = $pos;
 345                 $i = $this->mReadIndex;
 346
 347                 if ( $i > 0 ) {
 348                         if ( !$this->doWait( $i ) ) {
 349                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 350                                 $this->mLaggedSlaveMode = true;
 351                         }
 352                 }
 353                 wfProfileOut( __METHOD__ );
 354         }
 355
 356         /**
 357          * Set the master wait position and wait for ALL slaves to catch up to it
 358          * @param DBMasterPos $pos
 359          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 360          * @return bool Success (able to connect and no timeouts reached)
 361          */
 362         public function waitForAll( $pos, $timeout = null ) {
 363                 wfProfileIn( __METHOD__ );
 364                 $this->mWaitForPos = $pos;
 365                 $serverCount = count( $this->mServers );
 366
 367                 $ok = true;
 368                 for ( $i = 1; $i < $serverCount; $i++ ) {
 369                         if ( $this->mLoads[$i] > 0 ) {
 370                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 371                         }
 372                 }
 373                 wfProfileOut( __METHOD__ );
 374
 375                 return $ok;
 376         }
 377
 378         /**
 379          * Get any open connection to a given server index, local or foreign
 380          * Returns false if there is no connection open
 381          *
 382          * @param int $i
 383          * @return DatabaseBase|bool False on failure
 384          */
 385         public function getAnyOpenConnection( $i ) {
 386                 foreach ( $this->mConns as $conns ) {
 387                         if ( !empty( $conns[$i] ) ) {
 388                                 return reset( $conns[$i] );
 389                         }
 390                 }
 391
 392                 return false;
 393         }
 394
 395         /**
 396          * Wait for a given slave to catch up to the master pos stored in $this
 397          * @param int $index Server index
 398          * @param bool $open Check the server even if a new connection has to be made
 399          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 400          * @return bool
 401          */
 402         protected function doWait( $index, $open = false, $timeout = null ) {
 403                 $close = false; // close the connection afterwards
 404
 405                 # Find a connection to wait on, creating one if needed and allowed
 406                 $conn = $this->getAnyOpenConnection( $index );
 407                 if ( !$conn ) {
 408                         if ( !$open ) {
 409                                 wfDebug( __METHOD__ . ": no connection open\n" );
 410
 411                                 return false;
 412                         } else {
 413                                 $conn = $this->openConnection( $index, '' );
 414                                 if ( !$conn ) {
 415                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 416
 417                                         return false;
 418                                 }
 419                                 // Avoid connection spam in waitForAll() when connections
 420                                 // are made just for the sake of doing this lag check.
 421                                 $close = true;
 422                         }
 423                 }
 424
 425                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 426                 $timeout = $timeout ?: $this->mWaitTimeout;
 427                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 428
 429                 if ( $result == -1 || is_null( $result ) ) {
 430                         # Timed out waiting for slave, use master instead
 431                         $server = $this->mServers[$index]['host'];
 432                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 433                         wfDebug( "$msg\n" );
 434                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 435                         $ok = false;
 436                 } else {
 437                         wfDebug( __METHOD__ . ": Done\n" );
 438                         $ok = true;
 439                 }
 440
 441                 if ( $close ) {
 442                         $this->closeConnection( $conn );
 443                 }
 444
 445                 return $ok;
 446         }
 447
 448         /**
 449          * Get a connection by index
 450          * This is the main entry point for this class.
 451          *
 452          * @param int $i Server index
 453          * @param array|string|bool $groups Query group(s), or false for the generic reader
 454          * @param string|bool $wiki Wiki ID, or false for the current wiki
 455          *
 456          * @throws MWException
 457          * @return DatabaseBase
 458          */
 459         public function getConnection( $i, $groups = array(), $wiki = false ) {
 460                 wfProfileIn( __METHOD__ );
 461
 462                 if ( $i === null || $i === false ) {
 463                         wfProfileOut( __METHOD__ );
 464                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 465                                 ' with invalid server index' );
 466                 }
 467
 468                 if ( $wiki === wfWikiID() ) {
 469                         $wiki = false;
 470                 }
 471
 472                 $groups = ( $groups === false || $groups === array() )
 473                         ? array( false ) // check one "group": the generic pool
 474                         : (array)$groups;
 475
 476                 if ( $i == DB_MASTER ) {
 477                         $i = $this->getWriterIndex();
 478                 } else {
 479                         # Try to find an available server in any the query groups (in order)
 480                         foreach ( $groups as $group ) {
 481                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 482                                 if ( $groupIndex !== false ) {
 483                                         $serverName = $this->getServerName( $groupIndex );
 484                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 485                                         $i = $groupIndex;
 486                                         break;
 487                                 }
 488                         }
 489                 }
 490
 491                 # Operation-based index
 492                 if ( $i == DB_SLAVE ) {
 493                         $this->mLastError = 'Unknown error'; // reset error string
 494                         # Try the general server pool if $groups are unavailable.
 495                         $i = in_array( false, $groups, true )
 496                                 ? false // don't bother with this if that is what was tried above
 497                                 : $this->getReaderIndex( false, $wiki );
 498                         # Couldn't find a working server in getReaderIndex()?
 499                         if ( $i === false ) {
 500                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 501                                 wfProfileOut( __METHOD__ );
 502
 503                                 return $this->reportConnectionError();
 504                         }
 505                 }
 506
 507                 # Now we have an explicit index into the servers array
 508                 $conn = $this->openConnection( $i, $wiki );
 509                 if ( !$conn ) {
 510                         wfProfileOut( __METHOD__ );
 511
 512                         return $this->reportConnectionError();
 513                 }
 514
 515                 wfProfileOut( __METHOD__ );
 516
 517                 return $conn;
 518         }
 519
 520         /**
 521          * Mark a foreign connection as being available for reuse under a different
 522          * DB name or prefix. This mechanism is reference-counted, and must be called
 523          * the same number of times as getConnection() to work.
 524          *
 525          * @param DatabaseBase $conn
 526          * @throws MWException
 527          */
 528         public function reuseConnection( $conn ) {
 529                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 530                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 531                 if ( $serverIndex === null || $refCount === null ) {
 532                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 533
 534                         /**
 535                          * This can happen in code like:
 536                          *   foreach ( $dbs as $db ) {
 537                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 538                          *     ...
 539                          *     $lb->reuseConnection( $conn );
 540                          *   }
 541                          * When a connection to the local DB is opened in this way, reuseConnection()
 542                          * should be ignored
 543                          */
 544
 545                         return;
 546                 }
 547
 548                 $dbName = $conn->getDBname();
 549                 $prefix = $conn->tablePrefix();
 550                 if ( strval( $prefix ) !== '' ) {
 551                         $wiki = "$dbName-$prefix";
 552                 } else {
 553                         $wiki = $dbName;
 554                 }
 555                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 556                         throw new MWException( __METHOD__ . ": connection not found, has " .
 557                                 "the connection been freed already?" );
 558                 }
 559                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 560                 if ( $refCount <= 0 ) {
 561                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 562                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 563                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 564                 } else {
 565                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 566                 }
 567         }
 568
 569         /**
 570          * Get a database connection handle reference
 571          *
 572          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 573          *
 574          * @see LoadBalancer::getConnection() for parameter information
 575          *
 576          * @param int $db
 577          * @param array|string|bool $groups Query group(s), or false for the generic reader
 578          * @param string|bool $wiki Wiki ID, or false for the current wiki
 579          * @return DBConnRef
 580          */
 581         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 582                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 583         }
 584
 585         /**
 586          * Get a database connection handle reference without connecting yet
 587          *
 588          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 589          *
 590          * @see LoadBalancer::getConnection() for parameter information
 591          *
 592          * @param int $db
 593          * @param array|string|bool $groups Query group(s), or false for the generic reader
 594          * @param string|bool $wiki Wiki ID, or false for the current wiki
 595          * @return DBConnRef
 596          */
 597         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 598                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 599         }
 600
 601         /**
 602          * Open a connection to the server given by the specified index
 603          * Index must be an actual index into the array.
 604          * If the server is already open, returns it.
 605          *
 606          * On error, returns false, and the connection which caused the
 607          * error will be available via $this->mErrorConnection.
 608          *
 609          * @param int $i Server index
 610          * @param string|bool $wiki Wiki ID, or false for the current wiki
 611          * @return DatabaseBase
 612          *
 613          * @access private
 614          */
 615         public function openConnection( $i, $wiki = false ) {
 616                 wfProfileIn( __METHOD__ );
 617                 if ( $wiki !== false ) {
 618                         $conn = $this->openForeignConnection( $i, $wiki );
 619                         wfProfileOut( __METHOD__ );
 620
 621                         return $conn;
 622                 }
 623                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 624                         $conn = $this->mConns['local'][$i][0];
 625                 } else {
 626                         $server = $this->mServers[$i];
 627                         $server['serverIndex'] = $i;
 628                         $conn = $this->reallyOpenConnection( $server, false );
 629                         if ( $conn->isOpen() ) {
 630                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 631                                 $this->mConns['local'][$i][0] = $conn;
 632                         } else {
 633                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 634                                 $this->mErrorConnection = $conn;
 635                                 $conn = false;
 636                         }
 637                 }
 638                 wfProfileOut( __METHOD__ );
 639
 640                 return $conn;
 641         }
 642
 643         /**
 644          * Open a connection to a foreign DB, or return one if it is already open.
 645          *
 646          * Increments a reference count on the returned connection which locks the
 647          * connection to the requested wiki. This reference count can be
 648          * decremented by calling reuseConnection().
 649          *
 650          * If a connection is open to the appropriate server already, but with the wrong
 651          * database, it will be switched to the right database and returned, as long as
 652          * it has been freed first with reuseConnection().
 653          *
 654          * On error, returns false, and the connection which caused the
 655          * error will be available via $this->mErrorConnection.
 656          *
 657          * @param int $i Server index
 658          * @param string $wiki Wiki ID to open
 659          * @return DatabaseBase
 660          */
 661         private function openForeignConnection( $i, $wiki ) {
 662                 wfProfileIn( __METHOD__ );
 663                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 664                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 665                         // Reuse an already-used connection
 666                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 667                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 668                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 669                         // Reuse a free connection for the same wiki
 670                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 671                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 672                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 673                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 674                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 675                         // Reuse a connection from another wiki
 676                         $conn = reset( $this->mConns['foreignFree'][$i] );
 677                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 678
 679                         // The empty string as a DB name means "don't care".
 680                         // DatabaseMysqlBase::open() already handle this on connection.
 681                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 682                                 $this->mLastError = "Error selecting database $dbName on server " .
 683                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 684                                 $this->mErrorConnection = $conn;
 685                                 $conn = false;
 686                         } else {
 687                                 $conn->tablePrefix( $prefix );
 688                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 689                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 690                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 691                         }
 692                 } else {
 693                         // Open a new connection
 694                         $server = $this->mServers[$i];
 695                         $server['serverIndex'] = $i;
 696                         $server['foreignPoolRefCount'] = 0;
 697                         $server['foreign'] = true;
 698                         $conn = $this->reallyOpenConnection( $server, $dbName );
 699                         if ( !$conn->isOpen() ) {
 700                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 701                                 $this->mErrorConnection = $conn;
 702                                 $conn = false;
 703                         } else {
 704                                 $conn->tablePrefix( $prefix );
 705                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 706                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 707                         }
 708                 }
 709
 710                 // Increment reference count
 711                 if ( $conn ) {
 712                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 713                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 714                 }
 715                 wfProfileOut( __METHOD__ );
 716
 717                 return $conn;
 718         }
 719
 720         /**
 721          * Test if the specified index represents an open connection
 722          *
 723          * @param int $index Server index
 724          * @access private
 725          * @return bool
 726          */
 727         private function isOpen( $index ) {
 728                 if ( !is_integer( $index ) ) {
 729                         return false;
 730                 }
 731
 732                 return (bool)$this->getAnyOpenConnection( $index );
 733         }
 734
 735         /**
 736          * Really opens a connection. Uncached.
 737          * Returns a Database object whether or not the connection was successful.
 738          * @access private
 739          *
 740          * @param array $server
 741          * @param bool $dbNameOverride
 742          * @throws MWException
 743          * @return DatabaseBase
 744          */
 745         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 746                 if ( !is_array( $server ) ) {
 747                         throw new MWException( 'You must update your load-balancing configuration. ' .
 748                                 'See DefaultSettings.php entry for $wgDBservers.' );
 749                 }
 750
 751                 if ( $dbNameOverride !== false ) {
 752                         $server['dbname'] = $dbNameOverride;
 753                 }
 754
 755                 # Create object
 756                 try {
 757                         $db = DatabaseBase::factory( $server['type'], $server );
 758                 } catch ( DBConnectionError $e ) {
 759                         // FIXME: This is probably the ugliest thing I have ever done to
 760                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 761                         $db = $e->db;
 762                 }
 763
 764                 $db->setLBInfo( $server );
 765                 if ( isset( $server['fakeSlaveLag'] ) ) {
 766                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 767                 }
 768                 if ( isset( $server['fakeMaster'] ) ) {
 769                         $db->setFakeMaster( true );
 770                 }
 771
 772                 return $db;
 773         }
 774
 775         /**
 776          * @throws DBConnectionError
 777          * @return bool
 778          */
 779         private function reportConnectionError() {
 780                 $conn = $this->mErrorConnection; // The connection which caused the error
 781                 $context = array(
 782                         'method' => __METHOD__,
 783                         'last_error' => $this->mLastError,
 784                 );
 785
 786                 if ( !is_object( $conn ) ) {
 787                         // No last connection, probably due to all servers being too busy
 788                         wfLogDBError(
 789                                 "LB failure with no last connection. Connection error: {last_error}",
 790                                 $context
 791                         );
 792
 793                         // If all servers were busy, mLastError will contain something sensible
 794                         throw new DBConnectionError( null, $this->mLastError );
 795                 } else {
 796                         $context['db_server'] = $conn->getProperty( 'mServer' );
 797                         wfLogDBError(
 798                                 "Connection error: {last_error} ({db_server})",
 799                                 $context
 800                         );
 801                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
 802                 }
 803
 804                 return false; /* not reached */
 805         }
 806
 807         /**
 808          * @return int
 809          */
 810         private function getWriterIndex() {
 811                 return 0;
 812         }
 813
 814         /**
 815          * Returns true if the specified index is a valid server index
 816          *
 817          * @param string $i
 818          * @return bool
 819          */
 820         public function haveIndex( $i ) {
 821                 return array_key_exists( $i, $this->mServers );
 822         }
 823
 824         /**
 825          * Returns true if the specified index is valid and has non-zero load
 826          *
 827          * @param string $i
 828          * @return bool
 829          */
 830         public function isNonZeroLoad( $i ) {
 831                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 832         }
 833
 834         /**
 835          * Get the number of defined servers (not the number of open connections)
 836          *
 837          * @return int
 838          */
 839         public function getServerCount() {
 840                 return count( $this->mServers );
 841         }
 842
 843         /**
 844          * Get the host name or IP address of the server with the specified index
 845          * Prefer a readable name if available.
 846          * @param string $i
 847          * @return string
 848          */
 849         public function getServerName( $i ) {
 850                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 851                         return $this->mServers[$i]['hostName'];
 852                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 853                         return $this->mServers[$i]['host'];
 854                 } else {
 855                         return '';
 856                 }
 857         }
 858
 859         /**
 860          * Return the server info structure for a given index, or false if the index is invalid.
 861          * @param int $i
 862          * @return array|bool
 863          */
 864         public function getServerInfo( $i ) {
 865                 if ( isset( $this->mServers[$i] ) ) {
 866                         return $this->mServers[$i];
 867                 } else {
 868                         return false;
 869                 }
 870         }
 871
 872         /**
 873          * Sets the server info structure for the given index. Entry at index $i
 874          * is created if it doesn't exist
 875          * @param int $i
 876          * @param array $serverInfo
 877          */
 878         public function setServerInfo( $i, array $serverInfo ) {
 879                 $this->mServers[$i] = $serverInfo;
 880         }
 881
 882         /**
 883          * Get the current master position for chronology control purposes
 884          * @return mixed
 885          */
 886         public function getMasterPos() {
 887                 # If this entire request was served from a slave without opening a connection to the
 888                 # master (however unlikely that may be), then we can fetch the position from the slave.
 889                 $masterConn = $this->getAnyOpenConnection( 0 );
 890                 if ( !$masterConn ) {
 891                         $serverCount = count( $this->mServers );
 892                         for ( $i = 1; $i < $serverCount; $i++ ) {
 893                                 $conn = $this->getAnyOpenConnection( $i );
 894                                 if ( $conn ) {
 895                                         wfDebug( "Master pos fetched from slave\n" );
 896
 897                                         return $conn->getSlavePos();
 898                                 }
 899                         }
 900                 } else {
 901                         wfDebug( "Master pos fetched from master\n" );
 902
 903                         return $masterConn->getMasterPos();
 904                 }
 905
 906                 return false;
 907         }
 908
 909         /**
 910          * Close all open connections
 911          */
 912         public function closeAll() {
 913                 foreach ( $this->mConns as $conns2 ) {
 914                         foreach ( $conns2 as $conns3 ) {
 915                                 /** @var DatabaseBase $conn */
 916                                 foreach ( $conns3 as $conn ) {
 917                                         $conn->close();
 918                                 }
 919                         }
 920                 }
 921                 $this->mConns = array(
 922                         'local' => array(),
 923                         'foreignFree' => array(),
 924                         'foreignUsed' => array(),
 925                 );
 926         }
 927
 928         /**
 929          * Close a connection
 930          * Using this function makes sure the LoadBalancer knows the connection is closed.
 931          * If you use $conn->close() directly, the load balancer won't update its state.
 932          * @param DatabaseBase $conn
 933          */
 934         public function closeConnection( $conn ) {
 935                 $done = false;
 936                 foreach ( $this->mConns as $i1 => $conns2 ) {
 937                         foreach ( $conns2 as $i2 => $conns3 ) {
 938                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 939                                         if ( $conn === $candidateConn ) {
 940                                                 $conn->close();
 941                                                 unset( $this->mConns[$i1][$i2][$i3] );
 942                                                 $done = true;
 943                                                 break;
 944                                         }
 945                                 }
 946                         }
 947                 }
 948                 if ( !$done ) {
 949                         $conn->close();
 950                 }
 951         }
 952
 953         /**
 954          * Commit transactions on all open connections
 955          */
 956         public function commitAll() {
 957                 foreach ( $this->mConns as $conns2 ) {
 958                         foreach ( $conns2 as $conns3 ) {
 959                                 /** @var DatabaseBase[] $conns3 */
 960                                 foreach ( $conns3 as $conn ) {
 961                                         if ( $conn->trxLevel() ) {
 962                                                 $conn->commit( __METHOD__, 'flush' );
 963                                         }
 964                                 }
 965                         }
 966                 }
 967         }
 968
 969         /**
 970          *  Issue COMMIT only on master, only if queries were done on connection
 971          */
 972         public function commitMasterChanges() {
 973                 // Always 0, but who knows.. :)
 974                 $masterIndex = $this->getWriterIndex();
 975                 foreach ( $this->mConns as $conns2 ) {
 976                         if ( empty( $conns2[$masterIndex] ) ) {
 977                                 continue;
 978                         }
 979                         /** @var DatabaseBase $conn */
 980                         foreach ( $conns2[$masterIndex] as $conn ) {
 981                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 982                                         $conn->commit( __METHOD__, 'flush' );
 983                                 }
 984                         }
 985                 }
 986         }
 987
 988         /**
 989          * Issue ROLLBACK only on master, only if queries were done on connection
 990          * @since 1.23
 991          */
 992         public function rollbackMasterChanges() {
 993                 // Always 0, but who knows.. :)
 994                 $masterIndex = $this->getWriterIndex();
 995                 foreach ( $this->mConns as $conns2 ) {
 996                         if ( empty( $conns2[$masterIndex] ) ) {
 997                                 continue;
 998                         }
 999                         /** @var DatabaseBase $conn */
1000                         foreach ( $conns2[$masterIndex] as $conn ) {
1001                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1002                                         $conn->rollback( __METHOD__, 'flush' );
1003                                 }
1004                         }
1005                 }
1006         }
1007
1008         /**
1009          * @return bool Whether a master connection is already open
1010          * @since 1.24
1011          */
1012         public function hasMasterConnection() {
1013                 return $this->isOpen( $this->getWriterIndex() );
1014         }
1015
1016         /**
1017          * Determine if there are any pending changes that need to be rolled back
1018          * or committed.
1019          * @since 1.23
1020          * @return bool
1021          */
1022         public function hasMasterChanges() {
1023                 // Always 0, but who knows.. :)
1024                 $masterIndex = $this->getWriterIndex();
1025                 foreach ( $this->mConns as $conns2 ) {
1026                         if ( empty( $conns2[$masterIndex] ) ) {
1027                                 continue;
1028                         }
1029                         /** @var DatabaseBase $conn */
1030                         foreach ( $conns2[$masterIndex] as $conn ) {
1031                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1032                                         return true;
1033                                 }
1034                         }
1035                 }
1036                 return false;
1037         }
1038
1039         /**
1040          * @param mixed $value
1041          * @return mixed
1042          */
1043         public function waitTimeout( $value = null ) {
1044                 return wfSetVar( $this->mWaitTimeout, $value );
1045         }
1046
1047         /**
1048          * @return bool
1049          */
1050         public function getLaggedSlaveMode() {
1051                 return $this->mLaggedSlaveMode;
1052         }
1053
1054         /**
1055          * Disables/enables lag checks
1056          * @param null|bool $mode
1057          * @return bool
1058          */
1059         public function allowLagged( $mode = null ) {
1060                 if ( $mode === null ) {
1061                         return $this->mAllowLagged;
1062                 }
1063                 $this->mAllowLagged = $mode;
1064
1065                 return $this->mAllowLagged;
1066         }
1067
1068         /**
1069          * @return bool
1070          */
1071         public function pingAll() {
1072                 $success = true;
1073                 foreach ( $this->mConns as $conns2 ) {
1074                         foreach ( $conns2 as $conns3 ) {
1075                                 /** @var DatabaseBase[] $conns3 */
1076                                 foreach ( $conns3 as $conn ) {
1077                                         if ( !$conn->ping() ) {
1078                                                 $success = false;
1079                                         }
1080                                 }
1081                         }
1082                 }
1083
1084                 return $success;
1085         }
1086
1087         /**
1088          * Call a function with each open connection object
1089          * @param callable $callback
1090          * @param array $params
1091          */
1092         public function forEachOpenConnection( $callback, array $params = array() ) {
1093                 foreach ( $this->mConns as $conns2 ) {
1094                         foreach ( $conns2 as $conns3 ) {
1095                                 foreach ( $conns3 as $conn ) {
1096                                         $mergedParams = array_merge( array( $conn ), $params );
1097                                         call_user_func_array( $callback, $mergedParams );
1098                                 }
1099                         }
1100                 }
1101         }
1102
1103         /**
1104          * Get the hostname and lag time of the most-lagged slave
1105          *
1106          * This is useful for maintenance scripts that need to throttle their updates.
1107          * May attempt to open connections to slaves on the default DB. If there is
1108          * no lag, the maximum lag will be reported as -1.
1109          *
1110          * @param bool|string $wiki Wiki ID, or false for the default database
1111          * @return array ( host, max lag, index of max lagged host )
1112          */
1113         public function getMaxLag( $wiki = false ) {
1114                 $maxLag = -1;
1115                 $host = '';
1116                 $maxIndex = 0;
1117
1118                 if ( $this->getServerCount() <= 1 ) {
1119                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1120                 }
1121
1122                 $lagTimes = $this->getLagTimes( $wiki );
1123                 foreach ( $lagTimes as $i => $lag ) {
1124                         if ( $lag > $maxLag ) {
1125                                 $maxLag = $lag;
1126                                 $host = $this->mServers[$i]['host'];
1127                                 $maxIndex = $i;
1128                         }
1129                 }
1130
1131                 return array( $host, $maxLag, $maxIndex );
1132         }
1133
1134         /**
1135          * Get lag time for each server
1136          *
1137          * Results are cached for a short time in memcached/process cache
1138          *
1139          * @param string|bool $wiki
1140          * @return int[] Map of (server index => seconds)
1141          */
1142         public function getLagTimes( $wiki = false ) {
1143                 if ( $this->getServerCount() <= 1 ) {
1144                         return array( 0 => 0 ); // no replication = no lag
1145                 }
1146
1147                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1148                         return $this->mProcCache->get( 'slave_lag', 'times' );
1149                 }
1150
1151                 # Send the request to the load monitor
1152                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1153
1154                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1155
1156                 return $times;
1157         }
1158
1159         /**
1160          * Get the lag in seconds for a given connection, or zero if this load
1161          * balancer does not have replication enabled.
1162          *
1163          * This should be used in preference to Database::getLag() in cases where
1164          * replication may not be in use, since there is no way to determine if
1165          * replication is in use at the connection level without running
1166          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1167          * function instead of Database::getLag() avoids a fatal error in this
1168          * case on many installations.
1169          *
1170          * @param DatabaseBase $conn
1171          * @return int
1172          */
1173         public function safeGetLag( $conn ) {
1174                 if ( $this->getServerCount() == 1 ) {
1175                         return 0;
1176                 } else {
1177                         return $conn->getLag();
1178                 }
1179         }
1180
1181         /**
1182          * Clear the cache for slag lag delay times
1183          */
1184         public function clearLagTimeCache() {
1185                 $this->mProcCache->clear( 'slave_lag' );
1186         }
1187 }
1188
1189 /**
1190  * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1191  * as well handling deferring the actual network connection until the handle is used
1192  *
1193  * @ingroup Database
1194  * @since 1.22
1195  */
1196 class DBConnRef implements IDatabase {
1197         /** @var LoadBalancer */
1198         private $lb;
1199
1200         /** @var DatabaseBase|null */
1201         private $conn;
1202
1203         /** @var array|null */
1204         private $params;
1205
1206         /**
1207          * @param LoadBalancer $lb
1208          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1209          */
1210         public function __construct( LoadBalancer $lb, $conn ) {
1211                 $this->lb = $lb;
1212                 if ( $conn instanceof DatabaseBase ) {
1213                         $this->conn = $conn;
1214                 } else {
1215                         $this->params = $conn;
1216                 }
1217         }
1218
1219         public function __call( $name, $arguments ) {
1220                 if ( $this->conn === null ) {
1221                         list( $db, $groups, $wiki ) = $this->params;
1222                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1223                 }
1224
1225                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1226         }
1227
1228         public function __destruct() {
1229                 if ( $this->conn !== null ) {
1230                         $this->lb->reuseConnection( $this->conn );
1231                 }
1232         }
1233 }