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         function __construct( $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         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         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         function pickRandom( $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          * @return bool|int|string
 155          */
 156         function getRandomNonLagged( $loads, $wiki = false ) {
 157                 # Unset excessively lagged servers
 158                 $lags = $this->getLagTimes( $wiki );
 159                 foreach ( $lags as $i => $lag ) {
 160                         if ( $i != 0 ) {
 161                                 if ( $lag === false ) {
 162                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 163                                         unset( $loads[$i] );
 164                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 165                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 166                                         unset( $loads[$i] );
 167                                 }
 168                         }
 169                 }
 170
 171                 # Find out if all the slaves with non-zero load are lagged
 172                 $sum = 0;
 173                 foreach ( $loads as $load ) {
 174                         $sum += $load;
 175                 }
 176                 if ( $sum == 0 ) {
 177                         # No appropriate DB servers except maybe the master and some slaves with zero load
 178                         # Do NOT use the master
 179                         # Instead, this function will return false, triggering read-only mode,
 180                         # and a lagged slave will be used instead.
 181                         return false;
 182                 }
 183
 184                 if ( count( $loads ) == 0 ) {
 185                         return false;
 186                 }
 187
 188                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 189
 190                 # Return a random representative of the remainder
 191                 return ArrayUtils::pickRandom( $loads );
 192         }
 193
 194         /**
 195          * Get the index of the reader connection, which may be a slave
 196          * This takes into account load ratios and lag times. It should
 197          * always return a consistent index during a given invocation
 198          *
 199          * Side effect: opens connections to databases
 200          * @param bool|string $group
 201          * @param bool|string $wiki
 202          * @throws MWException
 203          * @return bool|int|string
 204          */
 205         function getReaderIndex( $group = false, $wiki = false ) {
 206                 global $wgReadOnly, $wgDBtype;
 207
 208                 # @todo FIXME: For now, only go through all this for mysql databases
 209                 if ( $wgDBtype != 'mysql' ) {
 210                         return $this->getWriterIndex();
 211                 }
 212
 213                 if ( count( $this->mServers ) == 1 ) {
 214                         # Skip the load balancing if there's only one server
 215                         return 0;
 216                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 217                         # Shortcut if generic reader exists already
 218                         return $this->mReadIndex;
 219                 }
 220
 221                 $section = new ProfileSection( __METHOD__ );
 222
 223                 # Find the relevant load array
 224                 if ( $group !== false ) {
 225                         if ( isset( $this->mGroupLoads[$group] ) ) {
 226                                 $nonErrorLoads = $this->mGroupLoads[$group];
 227                         } else {
 228                                 # No loads for this group, return false and the caller can use some other group
 229                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 230
 231                                 return false;
 232                         }
 233                 } else {
 234                         $nonErrorLoads = $this->mLoads;
 235                 }
 236
 237                 if ( !count( $nonErrorLoads ) ) {
 238                         throw new MWException( "Empty server array given to LoadBalancer" );
 239                 }
 240
 241                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 242                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 243
 244                 $laggedSlaveMode = false;
 245
 246                 # No server found yet
 247                 $i = false;
 248                 # First try quickly looking through the available servers for a server that
 249                 # meets our criteria
 250                 $currentLoads = $nonErrorLoads;
 251                 while ( count( $currentLoads ) ) {
 252                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 253                                 $i = ArrayUtils::pickRandom( $currentLoads );
 254                         } else {
 255                                 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 256                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 257                                         # All slaves lagged. Switch to read-only mode
 258                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 259                                         $wgReadOnly = 'The database has been automatically locked ' .
 260                                                 'while the slave database servers catch up to the master';
 261                                         $i = ArrayUtils::pickRandom( $currentLoads );
 262                                         $laggedSlaveMode = true;
 263                                 }
 264                         }
 265
 266                         if ( $i === false ) {
 267                                 # pickRandom() returned false
 268                                 # This is permanent and means the configuration or the load monitor
 269                                 # wants us to return false.
 270                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 271
 272                                 return false;
 273                         }
 274
 275                         wfDebugLog( 'connect', __METHOD__ .
 276                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 277
 278                         $conn = $this->openConnection( $i, $wiki );
 279                         if ( !$conn ) {
 280                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 281                                 unset( $nonErrorLoads[$i] );
 282                                 unset( $currentLoads[$i] );
 283                                 $i = false;
 284                                 continue;
 285                         }
 286
 287                         // Decrement reference counter, we are finished with this connection.
 288                         // It will be incremented for the caller later.
 289                         if ( $wiki !== false ) {
 290                                 $this->reuseConnection( $conn );
 291                         }
 292
 293                         # Return this server
 294                         break;
 295                 }
 296
 297                 # If all servers were down, quit now
 298                 if ( !count( $nonErrorLoads ) ) {
 299                         wfDebugLog( 'connect', "All servers down" );
 300                 }
 301
 302                 if ( $i !== false ) {
 303                         # Slave connection successful
 304                         # Wait for the session master pos for a short time
 305                         if ( $this->mWaitForPos && $i > 0 ) {
 306                                 if ( !$this->doWait( $i ) ) {
 307                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 308                                 }
 309                         }
 310                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group !== false ) {
 311                                 $this->mReadIndex = $i;
 312                         }
 313                 }
 314
 315                 return $i;
 316         }
 317
 318         /**
 319          * Wait for a specified number of microseconds, and return the period waited
 320          * @param int $t
 321          * @return int
 322          */
 323         function sleep( $t ) {
 324                 wfProfileIn( __METHOD__ );
 325                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 326                 usleep( $t );
 327                 wfProfileOut( __METHOD__ );
 328
 329                 return $t;
 330         }
 331
 332         /**
 333          * Set the master wait position
 334          * If a DB_SLAVE connection has been opened already, waits
 335          * Otherwise sets a variable telling it to wait if such a connection is opened
 336          * @param DBMasterPos $pos
 337          */
 338         public function waitFor( $pos ) {
 339                 wfProfileIn( __METHOD__ );
 340                 $this->mWaitForPos = $pos;
 341                 $i = $this->mReadIndex;
 342
 343                 if ( $i > 0 ) {
 344                         if ( !$this->doWait( $i ) ) {
 345                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 346                                 $this->mLaggedSlaveMode = true;
 347                         }
 348                 }
 349                 wfProfileOut( __METHOD__ );
 350         }
 351
 352         /**
 353          * Set the master wait position and wait for ALL slaves to catch up to it
 354          * @param DBMasterPos $pos
 355          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 356          * @return bool Success (able to connect and no timeouts reached)
 357          */
 358         public function waitForAll( $pos, $timeout = null ) {
 359                 wfProfileIn( __METHOD__ );
 360                 $this->mWaitForPos = $pos;
 361                 $serverCount = count( $this->mServers );
 362
 363                 $ok = true;
 364                 for ( $i = 1; $i < $serverCount; $i++ ) {
 365                         if ( $this->mLoads[$i] > 0 ) {
 366                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 367                         }
 368                 }
 369                 wfProfileOut( __METHOD__ );
 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         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( $result ) ) {
 426                         # Timed out waiting for slave, use master instead
 427                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 428                         $ok = false;
 429                 } else {
 430                         wfDebug( __METHOD__ . ": Done\n" );
 431                         $ok = true;
 432                 }
 433
 434                 if ( $close ) {
 435                         $this->closeConnection( $conn );
 436                 }
 437
 438                 return $ok;
 439         }
 440
 441         /**
 442          * Get a connection by index
 443          * This is the main entry point for this class.
 444          *
 445          * @param int $i Server index
 446          * @param array $groups Query groups
 447          * @param bool|string $wiki Wiki ID
 448          *
 449          * @throws MWException
 450          * @return DatabaseBase
 451          */
 452         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 453                 wfProfileIn( __METHOD__ );
 454
 455                 if ( $i === null || $i === false ) {
 456                         wfProfileOut( __METHOD__ );
 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                 # Query groups
 466                 if ( $i == DB_MASTER ) {
 467                         $i = $this->getWriterIndex();
 468                 } elseif ( !is_array( $groups ) ) {
 469                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 470                         if ( $groupIndex !== false ) {
 471                                 $serverName = $this->getServerName( $groupIndex );
 472                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 473                                 $i = $groupIndex;
 474                         }
 475                 } else {
 476                         foreach ( $groups as $group ) {
 477                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 478                                 if ( $groupIndex !== false ) {
 479                                         $serverName = $this->getServerName( $groupIndex );
 480                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 481                                         $i = $groupIndex;
 482                                         break;
 483                                 }
 484                         }
 485                 }
 486
 487                 # Operation-based index
 488                 if ( $i == DB_SLAVE ) {
 489                         $this->mLastError = 'Unknown error'; // reset error string
 490                         $i = $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                                 wfProfileOut( __METHOD__ );
 495
 496                                 return $this->reportConnectionError();
 497                         }
 498                 }
 499
 500                 # Now we have an explicit index into the servers array
 501                 $conn = $this->openConnection( $i, $wiki );
 502                 if ( !$conn ) {
 503                         wfProfileOut( __METHOD__ );
 504
 505                         return $this->reportConnectionError();
 506                 }
 507
 508                 wfProfileOut( __METHOD__ );
 509
 510                 return $conn;
 511         }
 512
 513         /**
 514          * Mark a foreign connection as being available for reuse under a different
 515          * DB name or prefix. This mechanism is reference-counted, and must be called
 516          * the same number of times as getConnection() to work.
 517          *
 518          * @param DatabaseBase $conn
 519          * @throws MWException
 520          */
 521         public function reuseConnection( $conn ) {
 522                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 523                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 524                 if ( $serverIndex === null || $refCount === null ) {
 525                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 526
 527                         /**
 528                          * This can happen in code like:
 529                          *   foreach ( $dbs as $db ) {
 530                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 531                          *     ...
 532                          *     $lb->reuseConnection( $conn );
 533                          *   }
 534                          * When a connection to the local DB is opened in this way, reuseConnection()
 535                          * should be ignored
 536                          */
 537
 538                         return;
 539                 }
 540
 541                 $dbName = $conn->getDBname();
 542                 $prefix = $conn->tablePrefix();
 543                 if ( strval( $prefix ) !== '' ) {
 544                         $wiki = "$dbName-$prefix";
 545                 } else {
 546                         $wiki = $dbName;
 547                 }
 548                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 549                         throw new MWException( __METHOD__ . ": connection not found, has " .
 550                                 "the connection been freed already?" );
 551                 }
 552                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 553                 if ( $refCount <= 0 ) {
 554                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 555                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 556                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 557                 } else {
 558                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 559                 }
 560         }
 561
 562         /**
 563          * Get a database connection handle reference
 564          *
 565          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 566          *
 567          * @see LoadBalancer::getConnection() for parameter information
 568          *
 569          * @param int $db
 570          * @param mixed $groups
 571          * @param bool|string $wiki
 572          * @return DBConnRef
 573          */
 574         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 575                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 576         }
 577
 578         /**
 579          * Get a database connection handle reference without connecting yet
 580          *
 581          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 582          *
 583          * @see LoadBalancer::getConnection() for parameter information
 584          *
 585          * @param int $db
 586          * @param mixed $groups
 587          * @param bool|string $wiki
 588          * @return DBConnRef
 589          */
 590         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 591                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 592         }
 593
 594         /**
 595          * Open a connection to the server given by the specified index
 596          * Index must be an actual index into the array.
 597          * If the server is already open, returns it.
 598          *
 599          * On error, returns false, and the connection which caused the
 600          * error will be available via $this->mErrorConnection.
 601          *
 602          * @param int $i Server index
 603          * @param bool|string $wiki Wiki ID to open
 604          * @return DatabaseBase
 605          *
 606          * @access private
 607          */
 608         function openConnection( $i, $wiki = false ) {
 609                 wfProfileIn( __METHOD__ );
 610                 if ( $wiki !== false ) {
 611                         $conn = $this->openForeignConnection( $i, $wiki );
 612                         wfProfileOut( __METHOD__ );
 613
 614                         return $conn;
 615                 }
 616                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 617                         $conn = $this->mConns['local'][$i][0];
 618                 } else {
 619                         $server = $this->mServers[$i];
 620                         $server['serverIndex'] = $i;
 621                         $conn = $this->reallyOpenConnection( $server, false );
 622                         if ( $conn->isOpen() ) {
 623                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 624                                 $this->mConns['local'][$i][0] = $conn;
 625                         } else {
 626                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 627                                 $this->mErrorConnection = $conn;
 628                                 $conn = false;
 629                         }
 630                 }
 631                 wfProfileOut( __METHOD__ );
 632
 633                 return $conn;
 634         }
 635
 636         /**
 637          * Open a connection to a foreign DB, or return one if it is already open.
 638          *
 639          * Increments a reference count on the returned connection which locks the
 640          * connection to the requested wiki. This reference count can be
 641          * decremented by calling reuseConnection().
 642          *
 643          * If a connection is open to the appropriate server already, but with the wrong
 644          * database, it will be switched to the right database and returned, as long as
 645          * it has been freed first with reuseConnection().
 646          *
 647          * On error, returns false, and the connection which caused the
 648          * error will be available via $this->mErrorConnection.
 649          *
 650          * @param int $i Server index
 651          * @param string $wiki Wiki ID to open
 652          * @return DatabaseBase
 653          */
 654         function openForeignConnection( $i, $wiki ) {
 655                 wfProfileIn( __METHOD__ );
 656                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 657                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 658                         // Reuse an already-used connection
 659                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 660                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 661                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 662                         // Reuse a free connection for the same wiki
 663                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 664                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 665                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 666                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 667                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 668                         // Reuse a connection from another wiki
 669                         $conn = reset( $this->mConns['foreignFree'][$i] );
 670                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 671
 672                         if ( !$conn->selectDB( $dbName ) ) {
 673                                 $this->mLastError = "Error selecting database $dbName on server " .
 674                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 675                                 $this->mErrorConnection = $conn;
 676                                 $conn = false;
 677                         } else {
 678                                 $conn->tablePrefix( $prefix );
 679                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 680                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 681                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 682                         }
 683                 } else {
 684                         // Open a new connection
 685                         $server = $this->mServers[$i];
 686                         $server['serverIndex'] = $i;
 687                         $server['foreignPoolRefCount'] = 0;
 688                         $server['foreign'] = true;
 689                         $conn = $this->reallyOpenConnection( $server, $dbName );
 690                         if ( !$conn->isOpen() ) {
 691                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 692                                 $this->mErrorConnection = $conn;
 693                                 $conn = false;
 694                         } else {
 695                                 $conn->tablePrefix( $prefix );
 696                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 697                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 698                         }
 699                 }
 700
 701                 // Increment reference count
 702                 if ( $conn ) {
 703                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 704                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 705                 }
 706                 wfProfileOut( __METHOD__ );
 707
 708                 return $conn;
 709         }
 710
 711         /**
 712          * Test if the specified index represents an open connection
 713          *
 714          * @param int $index Server index
 715          * @access private
 716          * @return bool
 717          */
 718         function isOpen( $index ) {
 719                 if ( !is_integer( $index ) ) {
 720                         return false;
 721                 }
 722
 723                 return (bool)$this->getAnyOpenConnection( $index );
 724         }
 725
 726         /**
 727          * Really opens a connection. Uncached.
 728          * Returns a Database object whether or not the connection was successful.
 729          * @access private
 730          *
 731          * @param array $server
 732          * @param bool $dbNameOverride
 733          * @throws MWException
 734          * @return DatabaseBase
 735          */
 736         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 737                 if ( !is_array( $server ) ) {
 738                         throw new MWException( 'You must update your load-balancing configuration. ' .
 739                                 'See DefaultSettings.php entry for $wgDBservers.' );
 740                 }
 741
 742                 if ( $dbNameOverride !== false ) {
 743                         $server['dbname'] = $dbNameOverride;
 744                 }
 745
 746                 # Create object
 747                 try {
 748                         $db = DatabaseBase::factory( $server['type'], $server );
 749                 } catch ( DBConnectionError $e ) {
 750                         // FIXME: This is probably the ugliest thing I have ever done to
 751                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 752                         $db = $e->db;
 753                 }
 754
 755                 $db->setLBInfo( $server );
 756                 if ( isset( $server['fakeSlaveLag'] ) ) {
 757                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 758                 }
 759                 if ( isset( $server['fakeMaster'] ) ) {
 760                         $db->setFakeMaster( true );
 761                 }
 762
 763                 return $db;
 764         }
 765
 766         /**
 767          * @throws DBConnectionError
 768          * @return bool
 769          */
 770         private function reportConnectionError() {
 771                 $conn = $this->mErrorConnection; // The connection which caused the error
 772
 773                 if ( !is_object( $conn ) ) {
 774                         // No last connection, probably due to all servers being too busy
 775                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}" );
 776
 777                         // If all servers were busy, mLastError will contain something sensible
 778                         throw new DBConnectionError( null, $this->mLastError );
 779                 } else {
 780                         $server = $conn->getProperty( 'mServer' );
 781                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})" );
 782                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 783                 }
 784
 785                 return false; /* not reached */
 786         }
 787
 788         /**
 789          * @return int
 790          */
 791         function getWriterIndex() {
 792                 return 0;
 793         }
 794
 795         /**
 796          * Returns true if the specified index is a valid server index
 797          *
 798          * @param string $i
 799          * @return bool
 800          */
 801         function haveIndex( $i ) {
 802                 return array_key_exists( $i, $this->mServers );
 803         }
 804
 805         /**
 806          * Returns true if the specified index is valid and has non-zero load
 807          *
 808          * @param string $i
 809          * @return bool
 810          */
 811         function isNonZeroLoad( $i ) {
 812                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 813         }
 814
 815         /**
 816          * Get the number of defined servers (not the number of open connections)
 817          *
 818          * @return int
 819          */
 820         function getServerCount() {
 821                 return count( $this->mServers );
 822         }
 823
 824         /**
 825          * Get the host name or IP address of the server with the specified index
 826          * Prefer a readable name if available.
 827          * @param string $i
 828          * @return string
 829          */
 830         function getServerName( $i ) {
 831                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 832                         return $this->mServers[$i]['hostName'];
 833                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 834                         return $this->mServers[$i]['host'];
 835                 } else {
 836                         return '';
 837                 }
 838         }
 839
 840         /**
 841          * Return the server info structure for a given index, or false if the index is invalid.
 842          * @param int $i
 843          * @return array|bool
 844          */
 845         function getServerInfo( $i ) {
 846                 if ( isset( $this->mServers[$i] ) ) {
 847                         return $this->mServers[$i];
 848                 } else {
 849                         return false;
 850                 }
 851         }
 852
 853         /**
 854          * Sets the server info structure for the given index. Entry at index $i
 855          * is created if it doesn't exist
 856          * @param int $i
 857          * @param array $serverInfo
 858          */
 859         function setServerInfo( $i, $serverInfo ) {
 860                 $this->mServers[$i] = $serverInfo;
 861         }
 862
 863         /**
 864          * Get the current master position for chronology control purposes
 865          * @return mixed
 866          */
 867         function getMasterPos() {
 868                 # If this entire request was served from a slave without opening a connection to the
 869                 # master (however unlikely that may be), then we can fetch the position from the slave.
 870                 $masterConn = $this->getAnyOpenConnection( 0 );
 871                 if ( !$masterConn ) {
 872                         $serverCount = count( $this->mServers );
 873                         for ( $i = 1; $i < $serverCount; $i++ ) {
 874                                 $conn = $this->getAnyOpenConnection( $i );
 875                                 if ( $conn ) {
 876                                         wfDebug( "Master pos fetched from slave\n" );
 877
 878                                         return $conn->getSlavePos();
 879                                 }
 880                         }
 881                 } else {
 882                         wfDebug( "Master pos fetched from master\n" );
 883
 884                         return $masterConn->getMasterPos();
 885                 }
 886
 887                 return false;
 888         }
 889
 890         /**
 891          * Close all open connections
 892          */
 893         function closeAll() {
 894                 foreach ( $this->mConns as $conns2 ) {
 895                         foreach ( $conns2 as $conns3 ) {
 896                                 /** @var DatabaseBase $conn */
 897                                 foreach ( $conns3 as $conn ) {
 898                                         $conn->close();
 899                                 }
 900                         }
 901                 }
 902                 $this->mConns = array(
 903                         'local' => array(),
 904                         'foreignFree' => array(),
 905                         'foreignUsed' => array(),
 906                 );
 907         }
 908
 909         /**
 910          * Close a connection
 911          * Using this function makes sure the LoadBalancer knows the connection is closed.
 912          * If you use $conn->close() directly, the load balancer won't update its state.
 913          * @param DatabaseBase $conn
 914          */
 915         function closeConnection( $conn ) {
 916                 $done = false;
 917                 foreach ( $this->mConns as $i1 => $conns2 ) {
 918                         foreach ( $conns2 as $i2 => $conns3 ) {
 919                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 920                                         if ( $conn === $candidateConn ) {
 921                                                 $conn->close();
 922                                                 unset( $this->mConns[$i1][$i2][$i3] );
 923                                                 $done = true;
 924                                                 break;
 925                                         }
 926                                 }
 927                         }
 928                 }
 929                 if ( !$done ) {
 930                         $conn->close();
 931                 }
 932         }
 933
 934         /**
 935          * Commit transactions on all open connections
 936          */
 937         function commitAll() {
 938                 foreach ( $this->mConns as $conns2 ) {
 939                         foreach ( $conns2 as $conns3 ) {
 940                                 /** @var DatabaseBase[] $conns3 */
 941                                 foreach ( $conns3 as $conn ) {
 942                                         if ( $conn->trxLevel() ) {
 943                                                 $conn->commit( __METHOD__, 'flush' );
 944                                         }
 945                                 }
 946                         }
 947                 }
 948         }
 949
 950         /**
 951          *  Issue COMMIT only on master, only if queries were done on connection
 952          */
 953         function commitMasterChanges() {
 954                 // Always 0, but who knows.. :)
 955                 $masterIndex = $this->getWriterIndex();
 956                 foreach ( $this->mConns as $conns2 ) {
 957                         if ( empty( $conns2[$masterIndex] ) ) {
 958                                 continue;
 959                         }
 960                         /** @var DatabaseBase $conn */
 961                         foreach ( $conns2[$masterIndex] as $conn ) {
 962                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 963                                         $conn->commit( __METHOD__, 'flush' );
 964                                 }
 965                         }
 966                 }
 967         }
 968
 969         /**
 970          * Issue ROLLBACK only on master, only if queries were done on connection
 971          * @since 1.23
 972          */
 973         function rollbackMasterChanges() {
 974                 // Always 0, but who knows.. :)
 975                 $masterIndex = $this->getWriterIndex();
 976                 foreach ( $this->mConns as $conns2 ) {
 977                         if ( empty( $conns2[$masterIndex] ) ) {
 978                                 continue;
 979                         }
 980                         /** @var DatabaseBase $conn */
 981                         foreach ( $conns2[$masterIndex] as $conn ) {
 982                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 983                                         $conn->rollback( __METHOD__, 'flush' );
 984                                 }
 985                         }
 986                 }
 987         }
 988
 989         /**
 990          * @return bool Whether a master connection is already open
 991          * @since 1.24
 992          */
 993         function hasMasterConnection() {
 994                 return $this->isOpen( $this->getWriterIndex() );
 995         }
 996
 997         /**
 998          * Determine if there are any pending changes that need to be rolled back
 999          * or committed.
1000          * @since 1.23
1001          * @return bool
1002          */
1003         function hasMasterChanges() {
1004                 // Always 0, but who knows.. :)
1005                 $masterIndex = $this->getWriterIndex();
1006                 foreach ( $this->mConns as $conns2 ) {
1007                         if ( empty( $conns2[$masterIndex] ) ) {
1008                                 continue;
1009                         }
1010                         /** @var DatabaseBase $conn */
1011                         foreach ( $conns2[$masterIndex] as $conn ) {
1012                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1013                                         return true;
1014                                 }
1015                         }
1016                 }
1017                 return false;
1018         }
1019
1020         /**
1021          * @param mixed $value
1022          * @return mixed
1023          */
1024         function waitTimeout( $value = null ) {
1025                 return wfSetVar( $this->mWaitTimeout, $value );
1026         }
1027
1028         /**
1029          * @return bool
1030          */
1031         function getLaggedSlaveMode() {
1032                 return $this->mLaggedSlaveMode;
1033         }
1034
1035         /**
1036          * Disables/enables lag checks
1037          * @param null|bool $mode
1038          * @return bool
1039          */
1040         function allowLagged( $mode = null ) {
1041                 if ( $mode === null ) {
1042                         return $this->mAllowLagged;
1043                 }
1044                 $this->mAllowLagged = $mode;
1045
1046                 return $this->mAllowLagged;
1047         }
1048
1049         /**
1050          * @return bool
1051          */
1052         function pingAll() {
1053                 $success = true;
1054                 foreach ( $this->mConns as $conns2 ) {
1055                         foreach ( $conns2 as $conns3 ) {
1056                                 /** @var DatabaseBase[] $conns3 */
1057                                 foreach ( $conns3 as $conn ) {
1058                                         if ( !$conn->ping() ) {
1059                                                 $success = false;
1060                                         }
1061                                 }
1062                         }
1063                 }
1064
1065                 return $success;
1066         }
1067
1068         /**
1069          * Call a function with each open connection object
1070          * @param callable $callback
1071          * @param array $params
1072          */
1073         function forEachOpenConnection( $callback, $params = array() ) {
1074                 foreach ( $this->mConns as $conns2 ) {
1075                         foreach ( $conns2 as $conns3 ) {
1076                                 foreach ( $conns3 as $conn ) {
1077                                         $mergedParams = array_merge( array( $conn ), $params );
1078                                         call_user_func_array( $callback, $mergedParams );
1079                                 }
1080                         }
1081                 }
1082         }
1083
1084         /**
1085          * Get the hostname and lag time of the most-lagged slave
1086          *
1087          * This is useful for maintenance scripts that need to throttle their updates.
1088          * May attempt to open connections to slaves on the default DB. If there is
1089          * no lag, the maximum lag will be reported as -1.
1090          *
1091          * @param bool|string $wiki Wiki ID, or false for the default database
1092          * @return array ( host, max lag, index of max lagged host )
1093          */
1094         function getMaxLag( $wiki = false ) {
1095                 $maxLag = -1;
1096                 $host = '';
1097                 $maxIndex = 0;
1098
1099                 if ( $this->getServerCount() <= 1 ) {
1100                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1101                 }
1102
1103                 $lagTimes = $this->getLagTimes( $wiki );
1104                 foreach ( $lagTimes as $i => $lag ) {
1105                         if ( $lag > $maxLag ) {
1106                                 $maxLag = $lag;
1107                                 $host = $this->mServers[$i]['host'];
1108                                 $maxIndex = $i;
1109                         }
1110                 }
1111
1112                 return array( $host, $maxLag, $maxIndex );
1113         }
1114
1115         /**
1116          * Get lag time for each server
1117          *
1118          * Results are cached for a short time in memcached/process cache
1119          *
1120          * @param string|bool $wiki
1121          * @return array Map of (server index => seconds)
1122          */
1123         function getLagTimes( $wiki = false ) {
1124                 if ( $this->getServerCount() <= 1 ) {
1125                         return array( 0 => 0 ); // no replication = no lag
1126                 }
1127
1128                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1129                         return $this->mProcCache->get( 'slave_lag', 'times' );
1130                 }
1131
1132                 # Send the request to the load monitor
1133                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1134
1135                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1136
1137                 return $times;
1138         }
1139
1140         /**
1141          * Get the lag in seconds for a given connection, or zero if this load
1142          * balancer does not have replication enabled.
1143          *
1144          * This should be used in preference to Database::getLag() in cases where
1145          * replication may not be in use, since there is no way to determine if
1146          * replication is in use at the connection level without running
1147          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1148          * function instead of Database::getLag() avoids a fatal error in this
1149          * case on many installations.
1150          *
1151          * @param DatabaseBase $conn
1152          * @return int
1153          */
1154         function safeGetLag( $conn ) {
1155                 if ( $this->getServerCount() == 1 ) {
1156                         return 0;
1157                 } else {
1158                         return $conn->getLag();
1159                 }
1160         }
1161
1162         /**
1163          * Clear the cache for slag lag delay times
1164          */
1165         function clearLagTimeCache() {
1166                 $this->mProcCache->clear( 'slave_lag' );
1167         }
1168 }
1169
1170 /**
1171  * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1172  * as well handling deferring the actual network connection until the handle is used
1173  *
1174  * @ingroup Database
1175  * @since 1.22
1176  */
1177 class DBConnRef implements IDatabase {
1178         /** @var LoadBalancer */
1179         protected $lb;
1180
1181         /** @var DatabaseBase|null */
1182         protected $conn;
1183
1184         /** @var array|null */
1185         protected $params;
1186
1187         /**
1188          * @param LoadBalancer $lb
1189          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1190          */
1191         public function __construct( LoadBalancer $lb, $conn ) {
1192                 $this->lb = $lb;
1193                 if ( $conn instanceof DatabaseBase ) {
1194                         $this->conn = $conn;
1195                 } else {
1196                         $this->params = $conn;
1197                 }
1198         }
1199
1200         public function __call( $name, $arguments ) {
1201                 if ( $this->conn === null ) {
1202                         list( $db, $groups, $wiki ) = $this->params;
1203                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1204                 }
1205
1206                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1207         }
1208
1209         function __destruct() {
1210                 if ( $this->conn !== null ) {
1211                         $this->lb->reuseConnection( $this->conn );
1212                 }
1213         }
1214 }