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         private $mServers, $mConns, $mLoads, $mGroupLoads;
  32
  33         /** @var bool|DatabaseBase Database connection that caused a problem */
  34         private $mErrorConnection;
  35         private $mReadIndex, $mAllowLagged;
  36
  37         /** @var bool|DBMasterPos False if not set */
  38         private $mWaitForPos;
  39
  40         private $mWaitTimeout;
  41         private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  42         private $mParentInfo, $mLagTimes;
  43         private $mLoadMonitorClass, $mLoadMonitor;
  44
  45         /**
  46          * @param array $params with keys:
  47          *   servers           Required. Array of server info structures.
  48          *   masterWaitTimeout Replication lag wait timeout
  49          *   loadMonitor       Name of a class used to fetch server lag and load.
  50          * @throws MWException
  51          */
  52         function __construct( $params ) {
  53                 if ( !isset( $params['servers'] ) ) {
  54                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  55                 }
  56                 $this->mServers = $params['servers'];
  57
  58                 if ( isset( $params['waitTimeout'] ) ) {
  59                         $this->mWaitTimeout = $params['waitTimeout'];
  60                 } else {
  61                         $this->mWaitTimeout = 10;
  62                 }
  63
  64                 $this->mReadIndex = -1;
  65                 $this->mWriteIndex = -1;
  66                 $this->mConns = array(
  67                         'local' => array(),
  68                         'foreignUsed' => array(),
  69                         'foreignFree' => array() );
  70                 $this->mLoads = array();
  71                 $this->mWaitForPos = false;
  72                 $this->mLaggedSlaveMode = false;
  73                 $this->mErrorConnection = false;
  74                 $this->mAllowLagged = false;
  75
  76                 if ( isset( $params['loadMonitor'] ) ) {
  77                         $this->mLoadMonitorClass = $params['loadMonitor'];
  78                 } else {
  79                         $master = reset( $params['servers'] );
  80                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  81                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  82                         } else {
  83                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
  84                         }
  85                 }
  86
  87                 foreach ( $params['servers'] as $i => $server ) {
  88                         $this->mLoads[$i] = $server['load'];
  89                         if ( isset( $server['groupLoads'] ) ) {
  90                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  91                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  92                                                 $this->mGroupLoads[$group] = array();
  93                                         }
  94                                         $this->mGroupLoads[$group][$i] = $ratio;
  95                                 }
  96                         }
  97                 }
  98         }
  99
 100         /**
 101          * Get a LoadMonitor instance
 102          *
 103          * @return LoadMonitor
 104          */
 105         function getLoadMonitor() {
 106                 if ( !isset( $this->mLoadMonitor ) ) {
 107                         $class = $this->mLoadMonitorClass;
 108                         $this->mLoadMonitor = new $class( $this );
 109                 }
 110
 111                 return $this->mLoadMonitor;
 112         }
 113
 114         /**
 115          * Get or set arbitrary data used by the parent object, usually an LBFactory
 116          * @param $x
 117          * @return mixed
 118          */
 119         function parentInfo( $x = null ) {
 120                 return wfSetVar( $this->mParentInfo, $x );
 121         }
 122
 123         /**
 124          * Given an array of non-normalised probabilities, this function will select
 125          * an element and return the appropriate key
 126          *
 127          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 128          *
 129          * @param array $weights
 130          * @return bool|int|string
 131          */
 132         function pickRandom( $weights ) {
 133                 return ArrayUtils::pickRandom( $weights );
 134         }
 135
 136         /**
 137          * @param array $loads
 138          * @param bool|string $wiki Wiki to get non-lagged for
 139          * @return bool|int|string
 140          */
 141         function getRandomNonLagged( $loads, $wiki = false ) {
 142                 # Unset excessively lagged servers
 143                 $lags = $this->getLagTimes( $wiki );
 144                 foreach ( $lags as $i => $lag ) {
 145                         if ( $i != 0 ) {
 146                                 if ( $lag === false ) {
 147                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 148                                         unset( $loads[$i] );
 149                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 150                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 151                                         unset( $loads[$i] );
 152                                 }
 153                         }
 154                 }
 155
 156                 # Find out if all the slaves with non-zero load are lagged
 157                 $sum = 0;
 158                 foreach ( $loads as $load ) {
 159                         $sum += $load;
 160                 }
 161                 if ( $sum == 0 ) {
 162                         # No appropriate DB servers except maybe the master and some slaves with zero load
 163                         # Do NOT use the master
 164                         # Instead, this function will return false, triggering read-only mode,
 165                         # and a lagged slave will be used instead.
 166                         return false;
 167                 }
 168
 169                 if ( count( $loads ) == 0 ) {
 170                         return false;
 171                 }
 172
 173                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 174
 175                 # Return a random representative of the remainder
 176                 return ArrayUtils::pickRandom( $loads );
 177         }
 178
 179         /**
 180          * Get the index of the reader connection, which may be a slave
 181          * This takes into account load ratios and lag times. It should
 182          * always return a consistent index during a given invocation
 183          *
 184          * Side effect: opens connections to databases
 185          * @param bool|string $group
 186          * @param bool|string $wiki
 187          * @throws MWException
 188          * @return bool|int|string
 189          */
 190         function getReaderIndex( $group = false, $wiki = false ) {
 191                 global $wgReadOnly, $wgDBtype;
 192
 193                 # @todo FIXME: For now, only go through all this for mysql databases
 194                 if ( $wgDBtype != 'mysql' ) {
 195                         return $this->getWriterIndex();
 196                 }
 197
 198                 if ( count( $this->mServers ) == 1 ) {
 199                         # Skip the load balancing if there's only one server
 200                         return 0;
 201                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 202                         # Shortcut if generic reader exists already
 203                         return $this->mReadIndex;
 204                 }
 205
 206                 $section = new ProfileSection( __METHOD__ );
 207
 208                 # Find the relevant load array
 209                 if ( $group !== false ) {
 210                         if ( isset( $this->mGroupLoads[$group] ) ) {
 211                                 $nonErrorLoads = $this->mGroupLoads[$group];
 212                         } else {
 213                                 # No loads for this group, return false and the caller can use some other group
 214                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 215
 216                                 return false;
 217                         }
 218                 } else {
 219                         $nonErrorLoads = $this->mLoads;
 220                 }
 221
 222                 if ( !count( $nonErrorLoads ) ) {
 223                         throw new MWException( "Empty server array given to LoadBalancer" );
 224                 }
 225
 226                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 227                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 228
 229                 $laggedSlaveMode = false;
 230
 231                 # No server found yet
 232                 $i = false;
 233                 # First try quickly looking through the available servers for a server that
 234                 # meets our criteria
 235                 $currentLoads = $nonErrorLoads;
 236                 while ( count( $currentLoads ) ) {
 237                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 238                                 $i = ArrayUtils::pickRandom( $currentLoads );
 239                         } else {
 240                                 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 241                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 242                                         # All slaves lagged. Switch to read-only mode
 243                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 244                                         $wgReadOnly = 'The database has been automatically locked ' .
 245                                                 'while the slave database servers catch up to the master';
 246                                         $i = ArrayUtils::pickRandom( $currentLoads );
 247                                         $laggedSlaveMode = true;
 248                                 }
 249                         }
 250
 251                         if ( $i === false ) {
 252                                 # pickRandom() returned false
 253                                 # This is permanent and means the configuration or the load monitor
 254                                 # wants us to return false.
 255                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 256
 257                                 return false;
 258                         }
 259
 260                         wfDebugLog( 'connect', __METHOD__ .
 261                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 262
 263                         $conn = $this->openConnection( $i, $wiki );
 264                         if ( !$conn ) {
 265                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 266                                 unset( $nonErrorLoads[$i] );
 267                                 unset( $currentLoads[$i] );
 268                                 $i = false;
 269                                 continue;
 270                         }
 271
 272                         // Decrement reference counter, we are finished with this connection.
 273                         // It will be incremented for the caller later.
 274                         if ( $wiki !== false ) {
 275                                 $this->reuseConnection( $conn );
 276                         }
 277
 278                         # Return this server
 279                         break;
 280                 }
 281
 282                 # If all servers were down, quit now
 283                 if ( !count( $nonErrorLoads ) ) {
 284                         wfDebugLog( 'connect', "All servers down" );
 285                 }
 286
 287                 if ( $i !== false ) {
 288                         # Slave connection successful
 289                         # Wait for the session master pos for a short time
 290                         if ( $this->mWaitForPos && $i > 0 ) {
 291                                 if ( !$this->doWait( $i ) ) {
 292                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 293                                 }
 294                         }
 295                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group !== false ) {
 296                                 $this->mReadIndex = $i;
 297                         }
 298                 }
 299
 300                 return $i;
 301         }
 302
 303         /**
 304          * Wait for a specified number of microseconds, and return the period waited
 305          * @param int $t
 306          * @return int
 307          */
 308         function sleep( $t ) {
 309                 wfProfileIn( __METHOD__ );
 310                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 311                 usleep( $t );
 312                 wfProfileOut( __METHOD__ );
 313
 314                 return $t;
 315         }
 316
 317         /**
 318          * Set the master wait position
 319          * If a DB_SLAVE connection has been opened already, waits
 320          * Otherwise sets a variable telling it to wait if such a connection is opened
 321          * @param DBMasterPos $pos
 322          */
 323         public function waitFor( $pos ) {
 324                 wfProfileIn( __METHOD__ );
 325                 $this->mWaitForPos = $pos;
 326                 $i = $this->mReadIndex;
 327
 328                 if ( $i > 0 ) {
 329                         if ( !$this->doWait( $i ) ) {
 330                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 331                                 $this->mLaggedSlaveMode = true;
 332                         }
 333                 }
 334                 wfProfileOut( __METHOD__ );
 335         }
 336
 337         /**
 338          * Set the master wait position and wait for ALL slaves to catch up to it
 339          * @param DBMasterPos $pos
 340          */
 341         public function waitForAll( $pos ) {
 342                 wfProfileIn( __METHOD__ );
 343                 $this->mWaitForPos = $pos;
 344                 $serverCount = count( $this->mServers );
 345                 for ( $i = 1; $i < $serverCount; $i++ ) {
 346                         if ( $this->mLoads[$i] > 0 ) {
 347                                 $this->doWait( $i, true );
 348                         }
 349                 }
 350                 wfProfileOut( __METHOD__ );
 351         }
 352
 353         /**
 354          * Get any open connection to a given server index, local or foreign
 355          * Returns false if there is no connection open
 356          *
 357          * @param int $i
 358          * @return DatabaseBase|bool False on failure
 359          */
 360         function getAnyOpenConnection( $i ) {
 361                 foreach ( $this->mConns as $conns ) {
 362                         if ( !empty( $conns[$i] ) ) {
 363                                 return reset( $conns[$i] );
 364                         }
 365                 }
 366
 367                 return false;
 368         }
 369
 370         /**
 371          * Wait for a given slave to catch up to the master pos stored in $this
 372          * @param $index
 373          * @param $open bool
 374          * @return bool
 375          */
 376         protected function doWait( $index, $open = false ) {
 377                 # Find a connection to wait on
 378                 $conn = $this->getAnyOpenConnection( $index );
 379                 if ( !$conn ) {
 380                         if ( !$open ) {
 381                                 wfDebug( __METHOD__ . ": no connection open\n" );
 382
 383                                 return false;
 384                         } else {
 385                                 $conn = $this->openConnection( $index, '' );
 386                                 if ( !$conn ) {
 387                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 388
 389                                         return false;
 390                                 }
 391                         }
 392                 }
 393
 394                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 395                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 396
 397                 if ( $result == -1 || is_null( $result ) ) {
 398                         # Timed out waiting for slave, use master instead
 399                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 400
 401                         return false;
 402                 } else {
 403                         wfDebug( __METHOD__ . ": Done\n" );
 404
 405                         return true;
 406                 }
 407         }
 408
 409         /**
 410          * Get a connection by index
 411          * This is the main entry point for this class.
 412          *
 413          * @param $i Integer: server index
 414          * @param array $groups query groups
 415          * @param bool|string $wiki Wiki ID
 416          *
 417          * @throws MWException
 418          * @return DatabaseBase
 419          */
 420         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 421                 wfProfileIn( __METHOD__ );
 422
 423                 if ( $i == DB_LAST ) {
 424                         wfProfileOut( __METHOD__ );
 425                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 426                                 ' with deprecated server index DB_LAST' );
 427                 } elseif ( $i === null || $i === false ) {
 428                         wfProfileOut( __METHOD__ );
 429                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 430                                 ' with invalid server index' );
 431                 }
 432
 433                 if ( $wiki === wfWikiID() ) {
 434                         $wiki = false;
 435                 }
 436
 437                 # Query groups
 438                 if ( $i == DB_MASTER ) {
 439                         $i = $this->getWriterIndex();
 440                 } elseif ( !is_array( $groups ) ) {
 441                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 442                         if ( $groupIndex !== false ) {
 443                                 $serverName = $this->getServerName( $groupIndex );
 444                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 445                                 $i = $groupIndex;
 446                         }
 447                 } else {
 448                         foreach ( $groups as $group ) {
 449                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 450                                 if ( $groupIndex !== false ) {
 451                                         $serverName = $this->getServerName( $groupIndex );
 452                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 453                                         $i = $groupIndex;
 454                                         break;
 455                                 }
 456                         }
 457                 }
 458
 459                 # Operation-based index
 460                 if ( $i == DB_SLAVE ) {
 461                         $this->mLastError = 'Unknown error'; // reset error string
 462                         $i = $this->getReaderIndex( false, $wiki );
 463                         # Couldn't find a working server in getReaderIndex()?
 464                         if ( $i === false ) {
 465                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 466                                 wfProfileOut( __METHOD__ );
 467
 468                                 return $this->reportConnectionError();
 469                         }
 470                 }
 471
 472                 # Now we have an explicit index into the servers array
 473                 $conn = $this->openConnection( $i, $wiki );
 474                 if ( !$conn ) {
 475                         wfProfileOut( __METHOD__ );
 476
 477                         return $this->reportConnectionError();
 478                 }
 479
 480                 wfProfileOut( __METHOD__ );
 481
 482                 return $conn;
 483         }
 484
 485         /**
 486          * Mark a foreign connection as being available for reuse under a different
 487          * DB name or prefix. This mechanism is reference-counted, and must be called
 488          * the same number of times as getConnection() to work.
 489          *
 490          * @param DatabaseBase $conn
 491          * @throws MWException
 492          */
 493         public function reuseConnection( $conn ) {
 494                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 495                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 496                 $dbName = $conn->getDBname();
 497                 $prefix = $conn->tablePrefix();
 498                 if ( strval( $prefix ) !== '' ) {
 499                         $wiki = "$dbName-$prefix";
 500                 } else {
 501                         $wiki = $dbName;
 502                 }
 503                 if ( $serverIndex === null || $refCount === null ) {
 504                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 505
 506                         /**
 507                          * This can happen in code like:
 508                          *   foreach ( $dbs as $db ) {
 509                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 510                          *     ...
 511                          *     $lb->reuseConnection( $conn );
 512                          *   }
 513                          * When a connection to the local DB is opened in this way, reuseConnection()
 514                          * should be ignored
 515                          */
 516
 517                         return;
 518                 }
 519                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 520                         throw new MWException( __METHOD__ . ": connection not found, has " .
 521                                 "the connection been freed already?" );
 522                 }
 523                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 524                 if ( $refCount <= 0 ) {
 525                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 526                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 527                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 528                 } else {
 529                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 530                 }
 531         }
 532
 533         /**
 534          * Get a database connection handle reference
 535          *
 536          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 537          *
 538          * @see LoadBalancer::getConnection() for parameter information
 539          *
 540          * @param integer $db
 541          * @param mixed $groups
 542          * @param bool|string $wiki
 543          * @return DBConnRef
 544          */
 545         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 546                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 547         }
 548
 549         /**
 550          * Get a database connection handle reference without connecting yet
 551          *
 552          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 553          *
 554          * @see LoadBalancer::getConnection() for parameter information
 555          *
 556          * @param integer $db
 557          * @param mixed $groups
 558          * @param bool|string $wiki
 559          * @return DBConnRef
 560          */
 561         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 562                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 563         }
 564
 565         /**
 566          * Open a connection to the server given by the specified index
 567          * Index must be an actual index into the array.
 568          * If the server is already open, returns it.
 569          *
 570          * On error, returns false, and the connection which caused the
 571          * error will be available via $this->mErrorConnection.
 572          *
 573          * @param $i Integer server index
 574          * @param bool|string $wiki wiki ID to open
 575          * @return DatabaseBase
 576          *
 577          * @access private
 578          */
 579         function openConnection( $i, $wiki = false ) {
 580                 wfProfileIn( __METHOD__ );
 581                 if ( $wiki !== false ) {
 582                         $conn = $this->openForeignConnection( $i, $wiki );
 583                         wfProfileOut( __METHOD__ );
 584
 585                         return $conn;
 586                 }
 587                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 588                         $conn = $this->mConns['local'][$i][0];
 589                 } else {
 590                         $server = $this->mServers[$i];
 591                         $server['serverIndex'] = $i;
 592                         $conn = $this->reallyOpenConnection( $server, false );
 593                         if ( $conn->isOpen() ) {
 594                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 595                                 $this->mConns['local'][$i][0] = $conn;
 596                         } else {
 597                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 598                                 $this->mErrorConnection = $conn;
 599                                 $conn = false;
 600                         }
 601                 }
 602                 wfProfileOut( __METHOD__ );
 603
 604                 return $conn;
 605         }
 606
 607         /**
 608          * Open a connection to a foreign DB, or return one if it is already open.
 609          *
 610          * Increments a reference count on the returned connection which locks the
 611          * connection to the requested wiki. This reference count can be
 612          * decremented by calling reuseConnection().
 613          *
 614          * If a connection is open to the appropriate server already, but with the wrong
 615          * database, it will be switched to the right database and returned, as long as
 616          * it has been freed first with reuseConnection().
 617          *
 618          * On error, returns false, and the connection which caused the
 619          * error will be available via $this->mErrorConnection.
 620          *
 621          * @param $i Integer: server index
 622          * @param string $wiki wiki ID to open
 623          * @return DatabaseBase
 624          */
 625         function openForeignConnection( $i, $wiki ) {
 626                 wfProfileIn( __METHOD__ );
 627                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 628                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 629                         // Reuse an already-used connection
 630                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 631                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 632                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 633                         // Reuse a free connection for the same wiki
 634                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 635                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 636                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 637                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 638                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 639                         // Reuse a connection from another wiki
 640                         $conn = reset( $this->mConns['foreignFree'][$i] );
 641                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 642
 643                         if ( !$conn->selectDB( $dbName ) ) {
 644                                 $this->mLastError = "Error selecting database $dbName on server " .
 645                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 646                                 $this->mErrorConnection = $conn;
 647                                 $conn = false;
 648                         } else {
 649                                 $conn->tablePrefix( $prefix );
 650                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 651                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 652                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 653                         }
 654                 } else {
 655                         // Open a new connection
 656                         $server = $this->mServers[$i];
 657                         $server['serverIndex'] = $i;
 658                         $server['foreignPoolRefCount'] = 0;
 659                         $server['foreign'] = true;
 660                         $conn = $this->reallyOpenConnection( $server, $dbName );
 661                         if ( !$conn->isOpen() ) {
 662                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 663                                 $this->mErrorConnection = $conn;
 664                                 $conn = false;
 665                         } else {
 666                                 $conn->tablePrefix( $prefix );
 667                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 668                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 669                         }
 670                 }
 671
 672                 // Increment reference count
 673                 if ( $conn ) {
 674                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 675                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 676                 }
 677                 wfProfileOut( __METHOD__ );
 678
 679                 return $conn;
 680         }
 681
 682         /**
 683          * Test if the specified index represents an open connection
 684          *
 685          * @param $index Integer: server index
 686          * @access private
 687          * @return bool
 688          */
 689         function isOpen( $index ) {
 690                 if ( !is_integer( $index ) ) {
 691                         return false;
 692                 }
 693
 694                 return (bool)$this->getAnyOpenConnection( $index );
 695         }
 696
 697         /**
 698          * Really opens a connection. Uncached.
 699          * Returns a Database object whether or not the connection was successful.
 700          * @access private
 701          *
 702          * @param $server
 703          * @param $dbNameOverride bool
 704          * @throws MWException
 705          * @return DatabaseBase
 706          */
 707         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 708                 if ( !is_array( $server ) ) {
 709                         throw new MWException( 'You must update your load-balancing configuration. ' .
 710                                 'See DefaultSettings.php entry for $wgDBservers.' );
 711                 }
 712
 713                 if ( $dbNameOverride !== false ) {
 714                         $server['dbname'] = $dbNameOverride;
 715                 }
 716
 717                 # Create object
 718                 try {
 719                         $db = DatabaseBase::factory( $server['type'], $server );
 720                 } catch ( DBConnectionError $e ) {
 721                         // FIXME: This is probably the ugliest thing I have ever done to
 722                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 723                         $db = $e->db;
 724                 }
 725
 726                 $db->setLBInfo( $server );
 727                 if ( isset( $server['fakeSlaveLag'] ) ) {
 728                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 729                 }
 730                 if ( isset( $server['fakeMaster'] ) ) {
 731                         $db->setFakeMaster( true );
 732                 }
 733
 734                 return $db;
 735         }
 736
 737         /**
 738          * @throws DBConnectionError
 739          * @return bool
 740          */
 741         private function reportConnectionError() {
 742                 $conn = $this->mErrorConnection; // The connection which caused the error
 743
 744                 if ( !is_object( $conn ) ) {
 745                         // No last connection, probably due to all servers being too busy
 746                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 747
 748                         // If all servers were busy, mLastError will contain something sensible
 749                         throw new DBConnectionError( null, $this->mLastError );
 750                 } else {
 751                         $server = $conn->getProperty( 'mServer' );
 752                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 753                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 754                 }
 755
 756                 return false; /* not reached */
 757         }
 758
 759         /**
 760          * @return int
 761          */
 762         function getWriterIndex() {
 763                 return 0;
 764         }
 765
 766         /**
 767          * Returns true if the specified index is a valid server index
 768          *
 769          * @param string $i
 770          * @return bool
 771          */
 772         function haveIndex( $i ) {
 773                 return array_key_exists( $i, $this->mServers );
 774         }
 775
 776         /**
 777          * Returns true if the specified index is valid and has non-zero load
 778          *
 779          * @param string $i
 780          * @return bool
 781          */
 782         function isNonZeroLoad( $i ) {
 783                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 784         }
 785
 786         /**
 787          * Get the number of defined servers (not the number of open connections)
 788          *
 789          * @return int
 790          */
 791         function getServerCount() {
 792                 return count( $this->mServers );
 793         }
 794
 795         /**
 796          * Get the host name or IP address of the server with the specified index
 797          * Prefer a readable name if available.
 798          * @param string $i
 799          * @return string
 800          */
 801         function getServerName( $i ) {
 802                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 803                         return $this->mServers[$i]['hostName'];
 804                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 805                         return $this->mServers[$i]['host'];
 806                 } else {
 807                         return '';
 808                 }
 809         }
 810
 811         /**
 812          * Return the server info structure for a given index, or false if the index is invalid.
 813          * @param $i
 814          * @return bool
 815          */
 816         function getServerInfo( $i ) {
 817                 if ( isset( $this->mServers[$i] ) ) {
 818                         return $this->mServers[$i];
 819                 } else {
 820                         return false;
 821                 }
 822         }
 823
 824         /**
 825          * Sets the server info structure for the given index. Entry at index $i
 826          * is created if it doesn't exist
 827          * @param $i
 828          * @param $serverInfo
 829          */
 830         function setServerInfo( $i, $serverInfo ) {
 831                 $this->mServers[$i] = $serverInfo;
 832         }
 833
 834         /**
 835          * Get the current master position for chronology control purposes
 836          * @return mixed
 837          */
 838         function getMasterPos() {
 839                 # If this entire request was served from a slave without opening a connection to the
 840                 # master (however unlikely that may be), then we can fetch the position from the slave.
 841                 $masterConn = $this->getAnyOpenConnection( 0 );
 842                 if ( !$masterConn ) {
 843                         $serverCount = count( $this->mServers );
 844                         for ( $i = 1; $i < $serverCount; $i++ ) {
 845                                 $conn = $this->getAnyOpenConnection( $i );
 846                                 if ( $conn ) {
 847                                         wfDebug( "Master pos fetched from slave\n" );
 848
 849                                         return $conn->getSlavePos();
 850                                 }
 851                         }
 852                 } else {
 853                         wfDebug( "Master pos fetched from master\n" );
 854
 855                         return $masterConn->getMasterPos();
 856                 }
 857
 858                 return false;
 859         }
 860
 861         /**
 862          * Close all open connections
 863          */
 864         function closeAll() {
 865                 foreach ( $this->mConns as $conns2 ) {
 866                         foreach ( $conns2 as $conns3 ) {
 867                                 /** @var DatabaseBase $conn */
 868                                 foreach ( $conns3 as $conn ) {
 869                                         $conn->close();
 870                                 }
 871                         }
 872                 }
 873                 $this->mConns = array(
 874                         'local' => array(),
 875                         'foreignFree' => array(),
 876                         'foreignUsed' => array(),
 877                 );
 878         }
 879
 880         /**
 881          * Deprecated function, typo in function name
 882          *
 883          * @deprecated in 1.18
 884          * @param DatabaseBase $conn
 885          */
 886         function closeConnecton( $conn ) {
 887                 wfDeprecated( __METHOD__, '1.18' );
 888                 $this->closeConnection( $conn );
 889         }
 890
 891         /**
 892          * Close a connection
 893          * Using this function makes sure the LoadBalancer knows the connection is closed.
 894          * If you use $conn->close() directly, the load balancer won't update its state.
 895          * @param DatabaseBase $conn
 896          */
 897         function closeConnection( $conn ) {
 898                 $done = false;
 899                 foreach ( $this->mConns as $i1 => $conns2 ) {
 900                         foreach ( $conns2 as $i2 => $conns3 ) {
 901                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 902                                         if ( $conn === $candidateConn ) {
 903                                                 $conn->close();
 904                                                 unset( $this->mConns[$i1][$i2][$i3] );
 905                                                 $done = true;
 906                                                 break;
 907                                         }
 908                                 }
 909                         }
 910                 }
 911                 if ( !$done ) {
 912                         $conn->close();
 913                 }
 914         }
 915
 916         /**
 917          * Commit transactions on all open connections
 918          */
 919         function commitAll() {
 920                 foreach ( $this->mConns as $conns2 ) {
 921                         foreach ( $conns2 as $conns3 ) {
 922                                 /** @var DatabaseBase[] $conns3 */
 923                                 foreach ( $conns3 as $conn ) {
 924                                         if ( $conn->trxLevel() ) {
 925                                                 $conn->commit( __METHOD__, 'flush' );
 926                                         }
 927                                 }
 928                         }
 929                 }
 930         }
 931
 932         /**
 933          *  Issue COMMIT only on master, only if queries were done on connection
 934          */
 935         function commitMasterChanges() {
 936                 // Always 0, but who knows.. :)
 937                 $masterIndex = $this->getWriterIndex();
 938                 foreach ( $this->mConns as $conns2 ) {
 939                         if ( empty( $conns2[$masterIndex] ) ) {
 940                                 continue;
 941                         }
 942                         /** @var DatabaseBase $conn */
 943                         foreach ( $conns2[$masterIndex] as $conn ) {
 944                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 945                                         $conn->commit( __METHOD__, 'flush' );
 946                                 }
 947                         }
 948                 }
 949         }
 950
 951         /**
 952          * @param $value null
 953          * @return Mixed
 954          */
 955         function waitTimeout( $value = null ) {
 956                 return wfSetVar( $this->mWaitTimeout, $value );
 957         }
 958
 959         /**
 960          * @return bool
 961          */
 962         function getLaggedSlaveMode() {
 963                 return $this->mLaggedSlaveMode;
 964         }
 965
 966         /**
 967          * Disables/enables lag checks
 968          * @param null|bool $mode
 969          * @return bool
 970          */
 971         function allowLagged( $mode = null ) {
 972                 if ( $mode === null ) {
 973                         return $this->mAllowLagged;
 974                 }
 975                 $this->mAllowLagged = $mode;
 976
 977                 return $this->mAllowLagged;
 978         }
 979
 980         /**
 981          * @return bool
 982          */
 983         function pingAll() {
 984                 $success = true;
 985                 foreach ( $this->mConns as $conns2 ) {
 986                         foreach ( $conns2 as $conns3 ) {
 987                                 /** @var DatabaseBase[] $conns3 */
 988                                 foreach ( $conns3 as $conn ) {
 989                                         if ( !$conn->ping() ) {
 990                                                 $success = false;
 991                                         }
 992                                 }
 993                         }
 994                 }
 995
 996                 return $success;
 997         }
 998
 999         /**
1000          * Call a function with each open connection object
1001          * @param callable $callback
1002          * @param array $params
1003          */
1004         function forEachOpenConnection( $callback, $params = array() ) {
1005                 foreach ( $this->mConns as $conns2 ) {
1006                         foreach ( $conns2 as $conns3 ) {
1007                                 foreach ( $conns3 as $conn ) {
1008                                         $mergedParams = array_merge( array( $conn ), $params );
1009                                         call_user_func_array( $callback, $mergedParams );
1010                                 }
1011                         }
1012                 }
1013         }
1014
1015         /**
1016          * Get the hostname and lag time of the most-lagged slave.
1017          * This is useful for maintenance scripts that need to throttle their updates.
1018          * May attempt to open connections to slaves on the default DB. If there is
1019          * no lag, the maximum lag will be reported as -1.
1020          *
1021          * @param bool|string $wiki Wiki ID, or false for the default database
1022          * @return array ( host, max lag, index of max lagged host )
1023          */
1024         function getMaxLag( $wiki = false ) {
1025                 $maxLag = -1;
1026                 $host = '';
1027                 $maxIndex = 0;
1028                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1029                         foreach ( $this->mServers as $i => $conn ) {
1030                                 $conn = false;
1031                                 if ( $wiki === false ) {
1032                                         $conn = $this->getAnyOpenConnection( $i );
1033                                 }
1034                                 if ( !$conn ) {
1035                                         $conn = $this->openConnection( $i, $wiki );
1036                                 }
1037                                 if ( !$conn ) {
1038                                         continue;
1039                                 }
1040                                 $lag = $conn->getLag();
1041                                 if ( $lag > $maxLag ) {
1042                                         $maxLag = $lag;
1043                                         $host = $this->mServers[$i]['host'];
1044                                         $maxIndex = $i;
1045                                 }
1046                         }
1047                 }
1048
1049                 return array( $host, $maxLag, $maxIndex );
1050         }
1051
1052         /**
1053          * Get lag time for each server
1054          * Results are cached for a short time in memcached, and indefinitely in the process cache
1055          *
1056          * @param string|bool $wiki
1057          * @return array
1058          */
1059         function getLagTimes( $wiki = false ) {
1060                 # Try process cache
1061                 if ( isset( $this->mLagTimes ) ) {
1062                         return $this->mLagTimes;
1063                 }
1064                 if ( $this->getServerCount() == 1 ) {
1065                         # No replication
1066                         $this->mLagTimes = array( 0 => 0 );
1067                 } else {
1068                         # Send the request to the load monitor
1069                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1070                                 array_keys( $this->mServers ), $wiki );
1071                 }
1072
1073                 return $this->mLagTimes;
1074         }
1075
1076         /**
1077          * Get the lag in seconds for a given connection, or zero if this load
1078          * balancer does not have replication enabled.
1079          *
1080          * This should be used in preference to Database::getLag() in cases where
1081          * replication may not be in use, since there is no way to determine if
1082          * replication is in use at the connection level without running
1083          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1084          * function instead of Database::getLag() avoids a fatal error in this
1085          * case on many installations.
1086          *
1087          * @param DatabaseBase $conn
1088          * @return int
1089          */
1090         function safeGetLag( $conn ) {
1091                 if ( $this->getServerCount() == 1 ) {
1092                         return 0;
1093                 } else {
1094                         return $conn->getLag();
1095                 }
1096         }
1097
1098         /**
1099          * Clear the cache for getLagTimes
1100          */
1101         function clearLagTimeCache() {
1102                 $this->mLagTimes = null;
1103         }
1104 }
1105
1106 /**
1107  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1108  * as well handling deferring the actual network connection until the handle is used
1109  *
1110  * @ingroup Database
1111  * @since 1.22
1112  */
1113 class DBConnRef implements IDatabase {
1114         /** @var LoadBalancer */
1115         protected $lb;
1116
1117         /** @var DatabaseBase|null */
1118         protected $conn;
1119
1120         /** @var array|null */
1121         protected $params;
1122
1123         /**
1124          * @param LoadBalancer $lb
1125          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1126          */
1127         public function __construct( LoadBalancer $lb, $conn ) {
1128                 $this->lb = $lb;
1129                 if ( $conn instanceof DatabaseBase ) {
1130                         $this->conn = $conn;
1131                 } else {
1132                         $this->params = $conn;
1133                 }
1134         }
1135
1136         public function __call( $name, $arguments ) {
1137                 if ( $this->conn === null ) {
1138                         list( $db, $groups, $wiki ) = $this->params;
1139                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1140                 }
1141
1142                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1143         }
1144
1145         function __destruct() {
1146                 if ( $this->conn !== null ) {
1147                         $this->lb->reuseConnection( $this->conn );
1148                 }
1149         }
1150 }