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 Array with keys:
  47          *   servers           Required. Array of server info structures.
  48          *   loadMonitor       Name of a class used to fetch server lag and load.
  49          * @throws MWException
  50          */
  51         function __construct( $params ) {
  52                 if ( !isset( $params['servers'] ) ) {
  53                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  54                 }
  55                 $this->mServers = $params['servers'];
  56                 $this->mWaitTimeout = 10;
  57
  58                 $this->mReadIndex = -1;
  59                 $this->mWriteIndex = -1;
  60                 $this->mConns = array(
  61                         'local' => array(),
  62                         'foreignUsed' => array(),
  63                         'foreignFree' => array() );
  64                 $this->mLoads = array();
  65                 $this->mWaitForPos = false;
  66                 $this->mLaggedSlaveMode = false;
  67                 $this->mErrorConnection = false;
  68                 $this->mAllowLagged = false;
  69
  70                 if ( isset( $params['loadMonitor'] ) ) {
  71                         $this->mLoadMonitorClass = $params['loadMonitor'];
  72                 } else {
  73                         $master = reset( $params['servers'] );
  74                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  75                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
  76                         } else {
  77                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
  78                         }
  79                 }
  80
  81                 foreach ( $params['servers'] as $i => $server ) {
  82                         $this->mLoads[$i] = $server['load'];
  83                         if ( isset( $server['groupLoads'] ) ) {
  84                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
  85                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
  86                                                 $this->mGroupLoads[$group] = array();
  87                                         }
  88                                         $this->mGroupLoads[$group][$i] = $ratio;
  89                                 }
  90                         }
  91                 }
  92         }
  93
  94         /**
  95          * Get a LoadMonitor instance
  96          *
  97          * @return LoadMonitor
  98          */
  99         function getLoadMonitor() {
 100                 if ( !isset( $this->mLoadMonitor ) ) {
 101                         $class = $this->mLoadMonitorClass;
 102                         $this->mLoadMonitor = new $class( $this );
 103                 }
 104
 105                 return $this->mLoadMonitor;
 106         }
 107
 108         /**
 109          * Get or set arbitrary data used by the parent object, usually an LBFactory
 110          * @param mixed $x
 111          * @return mixed
 112          */
 113         function parentInfo( $x = null ) {
 114                 return wfSetVar( $this->mParentInfo, $x );
 115         }
 116
 117         /**
 118          * Given an array of non-normalised probabilities, this function will select
 119          * an element and return the appropriate key
 120          *
 121          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 122          *
 123          * @param array $weights
 124          * @return bool|int|string
 125          */
 126         function pickRandom( $weights ) {
 127                 return ArrayUtils::pickRandom( $weights );
 128         }
 129
 130         /**
 131          * @param array $loads
 132          * @param bool|string $wiki Wiki to get non-lagged for
 133          * @return bool|int|string
 134          */
 135         function getRandomNonLagged( $loads, $wiki = false ) {
 136                 # Unset excessively lagged servers
 137                 $lags = $this->getLagTimes( $wiki );
 138                 foreach ( $lags as $i => $lag ) {
 139                         if ( $i != 0 ) {
 140                                 if ( $lag === false ) {
 141                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 142                                         unset( $loads[$i] );
 143                                 } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 144                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 145                                         unset( $loads[$i] );
 146                                 }
 147                         }
 148                 }
 149
 150                 # Find out if all the slaves with non-zero load are lagged
 151                 $sum = 0;
 152                 foreach ( $loads as $load ) {
 153                         $sum += $load;
 154                 }
 155                 if ( $sum == 0 ) {
 156                         # No appropriate DB servers except maybe the master and some slaves with zero load
 157                         # Do NOT use the master
 158                         # Instead, this function will return false, triggering read-only mode,
 159                         # and a lagged slave will be used instead.
 160                         return false;
 161                 }
 162
 163                 if ( count( $loads ) == 0 ) {
 164                         return false;
 165                 }
 166
 167                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 168
 169                 # Return a random representative of the remainder
 170                 return ArrayUtils::pickRandom( $loads );
 171         }
 172
 173         /**
 174          * Get the index of the reader connection, which may be a slave
 175          * This takes into account load ratios and lag times. It should
 176          * always return a consistent index during a given invocation
 177          *
 178          * Side effect: opens connections to databases
 179          * @param bool|string $group
 180          * @param bool|string $wiki
 181          * @throws MWException
 182          * @return bool|int|string
 183          */
 184         function getReaderIndex( $group = false, $wiki = false ) {
 185                 global $wgReadOnly, $wgDBtype;
 186
 187                 # @todo FIXME: For now, only go through all this for mysql databases
 188                 if ( $wgDBtype != 'mysql' ) {
 189                         return $this->getWriterIndex();
 190                 }
 191
 192                 if ( count( $this->mServers ) == 1 ) {
 193                         # Skip the load balancing if there's only one server
 194                         return 0;
 195                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 196                         # Shortcut if generic reader exists already
 197                         return $this->mReadIndex;
 198                 }
 199
 200                 $section = new ProfileSection( __METHOD__ );
 201
 202                 # Find the relevant load array
 203                 if ( $group !== false ) {
 204                         if ( isset( $this->mGroupLoads[$group] ) ) {
 205                                 $nonErrorLoads = $this->mGroupLoads[$group];
 206                         } else {
 207                                 # No loads for this group, return false and the caller can use some other group
 208                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 209
 210                                 return false;
 211                         }
 212                 } else {
 213                         $nonErrorLoads = $this->mLoads;
 214                 }
 215
 216                 if ( !count( $nonErrorLoads ) ) {
 217                         throw new MWException( "Empty server array given to LoadBalancer" );
 218                 }
 219
 220                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 221                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 222
 223                 $laggedSlaveMode = false;
 224
 225                 # No server found yet
 226                 $i = false;
 227                 # First try quickly looking through the available servers for a server that
 228                 # meets our criteria
 229                 $currentLoads = $nonErrorLoads;
 230                 while ( count( $currentLoads ) ) {
 231                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 232                                 $i = ArrayUtils::pickRandom( $currentLoads );
 233                         } else {
 234                                 $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 235                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 236                                         # All slaves lagged. Switch to read-only mode
 237                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 238                                         $wgReadOnly = 'The database has been automatically locked ' .
 239                                                 'while the slave database servers catch up to the master';
 240                                         $i = ArrayUtils::pickRandom( $currentLoads );
 241                                         $laggedSlaveMode = true;
 242                                 }
 243                         }
 244
 245                         if ( $i === false ) {
 246                                 # pickRandom() returned false
 247                                 # This is permanent and means the configuration or the load monitor
 248                                 # wants us to return false.
 249                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 250
 251                                 return false;
 252                         }
 253
 254                         wfDebugLog( 'connect', __METHOD__ .
 255                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 256
 257                         $conn = $this->openConnection( $i, $wiki );
 258                         if ( !$conn ) {
 259                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 260                                 unset( $nonErrorLoads[$i] );
 261                                 unset( $currentLoads[$i] );
 262                                 $i = false;
 263                                 continue;
 264                         }
 265
 266                         // Decrement reference counter, we are finished with this connection.
 267                         // It will be incremented for the caller later.
 268                         if ( $wiki !== false ) {
 269                                 $this->reuseConnection( $conn );
 270                         }
 271
 272                         # Return this server
 273                         break;
 274                 }
 275
 276                 # If all servers were down, quit now
 277                 if ( !count( $nonErrorLoads ) ) {
 278                         wfDebugLog( 'connect', "All servers down" );
 279                 }
 280
 281                 if ( $i !== false ) {
 282                         # Slave connection successful
 283                         # Wait for the session master pos for a short time
 284                         if ( $this->mWaitForPos && $i > 0 ) {
 285                                 if ( !$this->doWait( $i ) ) {
 286                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 287                                 }
 288                         }
 289                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group !== false ) {
 290                                 $this->mReadIndex = $i;
 291                         }
 292                 }
 293
 294                 return $i;
 295         }
 296
 297         /**
 298          * Wait for a specified number of microseconds, and return the period waited
 299          * @param int $t
 300          * @return int
 301          */
 302         function sleep( $t ) {
 303                 wfProfileIn( __METHOD__ );
 304                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 305                 usleep( $t );
 306                 wfProfileOut( __METHOD__ );
 307
 308                 return $t;
 309         }
 310
 311         /**
 312          * Set the master wait position
 313          * If a DB_SLAVE connection has been opened already, waits
 314          * Otherwise sets a variable telling it to wait if such a connection is opened
 315          * @param DBMasterPos $pos
 316          */
 317         public function waitFor( $pos ) {
 318                 wfProfileIn( __METHOD__ );
 319                 $this->mWaitForPos = $pos;
 320                 $i = $this->mReadIndex;
 321
 322                 if ( $i > 0 ) {
 323                         if ( !$this->doWait( $i ) ) {
 324                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 325                                 $this->mLaggedSlaveMode = true;
 326                         }
 327                 }
 328                 wfProfileOut( __METHOD__ );
 329         }
 330
 331         /**
 332          * Set the master wait position and wait for ALL slaves to catch up to it
 333          * @param DBMasterPos $pos
 334          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 335          * @return bool Success (able to connect and no timeouts reached)
 336          */
 337         public function waitForAll( $pos, $timeout = null ) {
 338                 wfProfileIn( __METHOD__ );
 339                 $this->mWaitForPos = $pos;
 340                 $serverCount = count( $this->mServers );
 341
 342                 $ok = true;
 343                 for ( $i = 1; $i < $serverCount; $i++ ) {
 344                         if ( $this->mLoads[$i] > 0 ) {
 345                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 346                         }
 347                 }
 348                 wfProfileOut( __METHOD__ );
 349
 350                 return $ok;
 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 int $index Server index
 373          * @param bool $open Check the server even if a new connection has to be made
 374          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 375          * @return bool
 376          */
 377         protected function doWait( $index, $open = false, $timeout = null ) {
 378                 # Find a connection to wait on
 379                 $conn = $this->getAnyOpenConnection( $index );
 380                 if ( !$conn ) {
 381                         if ( !$open ) {
 382                                 wfDebug( __METHOD__ . ": no connection open\n" );
 383
 384                                 return false;
 385                         } else {
 386                                 $conn = $this->openConnection( $index, '' );
 387                                 if ( !$conn ) {
 388                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 389
 390                                         return false;
 391                                 }
 392                         }
 393                 }
 394
 395                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 396                 $timeout = $timeout ?: $this->mWaitTimeout;
 397                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 398
 399                 if ( $result == -1 || is_null( $result ) ) {
 400                         # Timed out waiting for slave, use master instead
 401                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 402
 403                         return false;
 404                 } else {
 405                         wfDebug( __METHOD__ . ": Done\n" );
 406
 407                         return true;
 408                 }
 409         }
 410
 411         /**
 412          * Get a connection by index
 413          * This is the main entry point for this class.
 414          *
 415          * @param int $i Server index
 416          * @param array $groups Query groups
 417          * @param bool|string $wiki Wiki ID
 418          *
 419          * @throws MWException
 420          * @return DatabaseBase
 421          */
 422         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 423                 wfProfileIn( __METHOD__ );
 424
 425                 if ( $i === null || $i === false ) {
 426                         wfProfileOut( __METHOD__ );
 427                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 428                                 ' with invalid server index' );
 429                 }
 430
 431                 if ( $wiki === wfWikiID() ) {
 432                         $wiki = false;
 433                 }
 434
 435                 # Query groups
 436                 if ( $i == DB_MASTER ) {
 437                         $i = $this->getWriterIndex();
 438                 } elseif ( !is_array( $groups ) ) {
 439                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 440                         if ( $groupIndex !== false ) {
 441                                 $serverName = $this->getServerName( $groupIndex );
 442                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 443                                 $i = $groupIndex;
 444                         }
 445                 } else {
 446                         foreach ( $groups as $group ) {
 447                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 448                                 if ( $groupIndex !== false ) {
 449                                         $serverName = $this->getServerName( $groupIndex );
 450                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 451                                         $i = $groupIndex;
 452                                         break;
 453                                 }
 454                         }
 455                 }
 456
 457                 # Operation-based index
 458                 if ( $i == DB_SLAVE ) {
 459                         $this->mLastError = 'Unknown error'; // reset error string
 460                         $i = $this->getReaderIndex( false, $wiki );
 461                         # Couldn't find a working server in getReaderIndex()?
 462                         if ( $i === false ) {
 463                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 464                                 wfProfileOut( __METHOD__ );
 465
 466                                 return $this->reportConnectionError();
 467                         }
 468                 }
 469
 470                 # Now we have an explicit index into the servers array
 471                 $conn = $this->openConnection( $i, $wiki );
 472                 if ( !$conn ) {
 473                         wfProfileOut( __METHOD__ );
 474
 475                         return $this->reportConnectionError();
 476                 }
 477
 478                 wfProfileOut( __METHOD__ );
 479
 480                 return $conn;
 481         }
 482
 483         /**
 484          * Mark a foreign connection as being available for reuse under a different
 485          * DB name or prefix. This mechanism is reference-counted, and must be called
 486          * the same number of times as getConnection() to work.
 487          *
 488          * @param DatabaseBase $conn
 489          * @throws MWException
 490          */
 491         public function reuseConnection( $conn ) {
 492                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 493                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 494                 if ( $serverIndex === null || $refCount === null ) {
 495                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 496
 497                         /**
 498                          * This can happen in code like:
 499                          *   foreach ( $dbs as $db ) {
 500                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 501                          *     ...
 502                          *     $lb->reuseConnection( $conn );
 503                          *   }
 504                          * When a connection to the local DB is opened in this way, reuseConnection()
 505                          * should be ignored
 506                          */
 507
 508                         return;
 509                 }
 510
 511                 $dbName = $conn->getDBname();
 512                 $prefix = $conn->tablePrefix();
 513                 if ( strval( $prefix ) !== '' ) {
 514                         $wiki = "$dbName-$prefix";
 515                 } else {
 516                         $wiki = $dbName;
 517                 }
 518                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 519                         throw new MWException( __METHOD__ . ": connection not found, has " .
 520                                 "the connection been freed already?" );
 521                 }
 522                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 523                 if ( $refCount <= 0 ) {
 524                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 525                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 526                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 527                 } else {
 528                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 529                 }
 530         }
 531
 532         /**
 533          * Get a database connection handle reference
 534          *
 535          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 536          *
 537          * @see LoadBalancer::getConnection() for parameter information
 538          *
 539          * @param int $db
 540          * @param mixed $groups
 541          * @param bool|string $wiki
 542          * @return DBConnRef
 543          */
 544         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 545                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 546         }
 547
 548         /**
 549          * Get a database connection handle reference without connecting yet
 550          *
 551          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 552          *
 553          * @see LoadBalancer::getConnection() for parameter information
 554          *
 555          * @param int $db
 556          * @param mixed $groups
 557          * @param bool|string $wiki
 558          * @return DBConnRef
 559          */
 560         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 561                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 562         }
 563
 564         /**
 565          * Open a connection to the server given by the specified index
 566          * Index must be an actual index into the array.
 567          * If the server is already open, returns it.
 568          *
 569          * On error, returns false, and the connection which caused the
 570          * error will be available via $this->mErrorConnection.
 571          *
 572          * @param int $i Server index
 573          * @param bool|string $wiki Wiki ID to open
 574          * @return DatabaseBase
 575          *
 576          * @access private
 577          */
 578         function openConnection( $i, $wiki = false ) {
 579                 wfProfileIn( __METHOD__ );
 580                 if ( $wiki !== false ) {
 581                         $conn = $this->openForeignConnection( $i, $wiki );
 582                         wfProfileOut( __METHOD__ );
 583
 584                         return $conn;
 585                 }
 586                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 587                         $conn = $this->mConns['local'][$i][0];
 588                 } else {
 589                         $server = $this->mServers[$i];
 590                         $server['serverIndex'] = $i;
 591                         $conn = $this->reallyOpenConnection( $server, false );
 592                         if ( $conn->isOpen() ) {
 593                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 594                                 $this->mConns['local'][$i][0] = $conn;
 595                         } else {
 596                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 597                                 $this->mErrorConnection = $conn;
 598                                 $conn = false;
 599                         }
 600                 }
 601                 wfProfileOut( __METHOD__ );
 602
 603                 return $conn;
 604         }
 605
 606         /**
 607          * Open a connection to a foreign DB, or return one if it is already open.
 608          *
 609          * Increments a reference count on the returned connection which locks the
 610          * connection to the requested wiki. This reference count can be
 611          * decremented by calling reuseConnection().
 612          *
 613          * If a connection is open to the appropriate server already, but with the wrong
 614          * database, it will be switched to the right database and returned, as long as
 615          * it has been freed first with reuseConnection().
 616          *
 617          * On error, returns false, and the connection which caused the
 618          * error will be available via $this->mErrorConnection.
 619          *
 620          * @param int $i Server index
 621          * @param string $wiki Wiki ID to open
 622          * @return DatabaseBase
 623          */
 624         function openForeignConnection( $i, $wiki ) {
 625                 wfProfileIn( __METHOD__ );
 626                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 627                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 628                         // Reuse an already-used connection
 629                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 630                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 631                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 632                         // Reuse a free connection for the same wiki
 633                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 634                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 635                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 636                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 637                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 638                         // Reuse a connection from another wiki
 639                         $conn = reset( $this->mConns['foreignFree'][$i] );
 640                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 641
 642                         if ( !$conn->selectDB( $dbName ) ) {
 643                                 $this->mLastError = "Error selecting database $dbName on server " .
 644                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 645                                 $this->mErrorConnection = $conn;
 646                                 $conn = false;
 647                         } else {
 648                                 $conn->tablePrefix( $prefix );
 649                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 650                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 651                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 652                         }
 653                 } else {
 654                         // Open a new connection
 655                         $server = $this->mServers[$i];
 656                         $server['serverIndex'] = $i;
 657                         $server['foreignPoolRefCount'] = 0;
 658                         $server['foreign'] = true;
 659                         $conn = $this->reallyOpenConnection( $server, $dbName );
 660                         if ( !$conn->isOpen() ) {
 661                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 662                                 $this->mErrorConnection = $conn;
 663                                 $conn = false;
 664                         } else {
 665                                 $conn->tablePrefix( $prefix );
 666                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 667                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 668                         }
 669                 }
 670
 671                 // Increment reference count
 672                 if ( $conn ) {
 673                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 674                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 675                 }
 676                 wfProfileOut( __METHOD__ );
 677
 678                 return $conn;
 679         }
 680
 681         /**
 682          * Test if the specified index represents an open connection
 683          *
 684          * @param int $index Server index
 685          * @access private
 686          * @return bool
 687          */
 688         function isOpen( $index ) {
 689                 if ( !is_integer( $index ) ) {
 690                         return false;
 691                 }
 692
 693                 return (bool)$this->getAnyOpenConnection( $index );
 694         }
 695
 696         /**
 697          * Really opens a connection. Uncached.
 698          * Returns a Database object whether or not the connection was successful.
 699          * @access private
 700          *
 701          * @param array $server
 702          * @param bool $dbNameOverride
 703          * @throws MWException
 704          * @return DatabaseBase
 705          */
 706         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 707                 if ( !is_array( $server ) ) {
 708                         throw new MWException( 'You must update your load-balancing configuration. ' .
 709                                 'See DefaultSettings.php entry for $wgDBservers.' );
 710                 }
 711
 712                 if ( $dbNameOverride !== false ) {
 713                         $server['dbname'] = $dbNameOverride;
 714                 }
 715
 716                 # Create object
 717                 try {
 718                         $db = DatabaseBase::factory( $server['type'], $server );
 719                 } catch ( DBConnectionError $e ) {
 720                         // FIXME: This is probably the ugliest thing I have ever done to
 721                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 722                         $db = $e->db;
 723                 }
 724
 725                 $db->setLBInfo( $server );
 726                 if ( isset( $server['fakeSlaveLag'] ) ) {
 727                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 728                 }
 729                 if ( isset( $server['fakeMaster'] ) ) {
 730                         $db->setFakeMaster( true );
 731                 }
 732
 733                 return $db;
 734         }
 735
 736         /**
 737          * @throws DBConnectionError
 738          * @return bool
 739          */
 740         private function reportConnectionError() {
 741                 $conn = $this->mErrorConnection; // The connection which caused the error
 742
 743                 if ( !is_object( $conn ) ) {
 744                         // No last connection, probably due to all servers being too busy
 745                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}" );
 746
 747                         // If all servers were busy, mLastError will contain something sensible
 748                         throw new DBConnectionError( null, $this->mLastError );
 749                 } else {
 750                         $server = $conn->getProperty( 'mServer' );
 751                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})" );
 752                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 753                 }
 754
 755                 return false; /* not reached */
 756         }
 757
 758         /**
 759          * @return int
 760          */
 761         function getWriterIndex() {
 762                 return 0;
 763         }
 764
 765         /**
 766          * Returns true if the specified index is a valid server index
 767          *
 768          * @param string $i
 769          * @return bool
 770          */
 771         function haveIndex( $i ) {
 772                 return array_key_exists( $i, $this->mServers );
 773         }
 774
 775         /**
 776          * Returns true if the specified index is valid and has non-zero load
 777          *
 778          * @param string $i
 779          * @return bool
 780          */
 781         function isNonZeroLoad( $i ) {
 782                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 783         }
 784
 785         /**
 786          * Get the number of defined servers (not the number of open connections)
 787          *
 788          * @return int
 789          */
 790         function getServerCount() {
 791                 return count( $this->mServers );
 792         }
 793
 794         /**
 795          * Get the host name or IP address of the server with the specified index
 796          * Prefer a readable name if available.
 797          * @param string $i
 798          * @return string
 799          */
 800         function getServerName( $i ) {
 801                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 802                         return $this->mServers[$i]['hostName'];
 803                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 804                         return $this->mServers[$i]['host'];
 805                 } else {
 806                         return '';
 807                 }
 808         }
 809
 810         /**
 811          * Return the server info structure for a given index, or false if the index is invalid.
 812          * @param int $i
 813          * @return array|bool
 814          */
 815         function getServerInfo( $i ) {
 816                 if ( isset( $this->mServers[$i] ) ) {
 817                         return $this->mServers[$i];
 818                 } else {
 819                         return false;
 820                 }
 821         }
 822
 823         /**
 824          * Sets the server info structure for the given index. Entry at index $i
 825          * is created if it doesn't exist
 826          * @param int $i
 827          * @param array $serverInfo
 828          */
 829         function setServerInfo( $i, $serverInfo ) {
 830                 $this->mServers[$i] = $serverInfo;
 831         }
 832
 833         /**
 834          * Get the current master position for chronology control purposes
 835          * @return mixed
 836          */
 837         function getMasterPos() {
 838                 # If this entire request was served from a slave without opening a connection to the
 839                 # master (however unlikely that may be), then we can fetch the position from the slave.
 840                 $masterConn = $this->getAnyOpenConnection( 0 );
 841                 if ( !$masterConn ) {
 842                         $serverCount = count( $this->mServers );
 843                         for ( $i = 1; $i < $serverCount; $i++ ) {
 844                                 $conn = $this->getAnyOpenConnection( $i );
 845                                 if ( $conn ) {
 846                                         wfDebug( "Master pos fetched from slave\n" );
 847
 848                                         return $conn->getSlavePos();
 849                                 }
 850                         }
 851                 } else {
 852                         wfDebug( "Master pos fetched from master\n" );
 853
 854                         return $masterConn->getMasterPos();
 855                 }
 856
 857                 return false;
 858         }
 859
 860         /**
 861          * Close all open connections
 862          */
 863         function closeAll() {
 864                 foreach ( $this->mConns as $conns2 ) {
 865                         foreach ( $conns2 as $conns3 ) {
 866                                 /** @var DatabaseBase $conn */
 867                                 foreach ( $conns3 as $conn ) {
 868                                         $conn->close();
 869                                 }
 870                         }
 871                 }
 872                 $this->mConns = array(
 873                         'local' => array(),
 874                         'foreignFree' => array(),
 875                         'foreignUsed' => array(),
 876                 );
 877         }
 878
 879         /**
 880          * Close a connection
 881          * Using this function makes sure the LoadBalancer knows the connection is closed.
 882          * If you use $conn->close() directly, the load balancer won't update its state.
 883          * @param DatabaseBase $conn
 884          */
 885         function closeConnection( $conn ) {
 886                 $done = false;
 887                 foreach ( $this->mConns as $i1 => $conns2 ) {
 888                         foreach ( $conns2 as $i2 => $conns3 ) {
 889                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 890                                         if ( $conn === $candidateConn ) {
 891                                                 $conn->close();
 892                                                 unset( $this->mConns[$i1][$i2][$i3] );
 893                                                 $done = true;
 894                                                 break;
 895                                         }
 896                                 }
 897                         }
 898                 }
 899                 if ( !$done ) {
 900                         $conn->close();
 901                 }
 902         }
 903
 904         /**
 905          * Commit transactions on all open connections
 906          */
 907         function commitAll() {
 908                 foreach ( $this->mConns as $conns2 ) {
 909                         foreach ( $conns2 as $conns3 ) {
 910                                 /** @var DatabaseBase[] $conns3 */
 911                                 foreach ( $conns3 as $conn ) {
 912                                         if ( $conn->trxLevel() ) {
 913                                                 $conn->commit( __METHOD__, 'flush' );
 914                                         }
 915                                 }
 916                         }
 917                 }
 918         }
 919
 920         /**
 921          *  Issue COMMIT only on master, only if queries were done on connection
 922          */
 923         function commitMasterChanges() {
 924                 // Always 0, but who knows.. :)
 925                 $masterIndex = $this->getWriterIndex();
 926                 foreach ( $this->mConns as $conns2 ) {
 927                         if ( empty( $conns2[$masterIndex] ) ) {
 928                                 continue;
 929                         }
 930                         /** @var DatabaseBase $conn */
 931                         foreach ( $conns2[$masterIndex] as $conn ) {
 932                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 933                                         $conn->commit( __METHOD__, 'flush' );
 934                                 }
 935                         }
 936                 }
 937         }
 938
 939         /**
 940          * Issue ROLLBACK only on master, only if queries were done on connection
 941          * @since 1.23
 942          */
 943         function rollbackMasterChanges() {
 944                 // Always 0, but who knows.. :)
 945                 $masterIndex = $this->getWriterIndex();
 946                 foreach ( $this->mConns as $conns2 ) {
 947                         if ( empty( $conns2[$masterIndex] ) ) {
 948                                 continue;
 949                         }
 950                         /** @var DatabaseBase $conn */
 951                         foreach ( $conns2[$masterIndex] as $conn ) {
 952                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 953                                         $conn->rollback( __METHOD__, 'flush' );
 954                                 }
 955                         }
 956                 }
 957         }
 958
 959         /**
 960          * @return bool Whether a master connection is already open
 961          * @since 1.24
 962          */
 963         function hasMasterConnection() {
 964                 return $this->isOpen( $this->getWriterIndex() );
 965         }
 966
 967         /**
 968          * Determine if there are any pending changes that need to be rolled back
 969          * or committed.
 970          * @since 1.23
 971          * @return bool
 972          */
 973         function hasMasterChanges() {
 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                                         return true;
 984                                 }
 985                         }
 986                 }
 987                 return false;
 988         }
 989
 990         /**
 991          * @param mixed $value
 992          * @return mixed
 993          */
 994         function waitTimeout( $value = null ) {
 995                 return wfSetVar( $this->mWaitTimeout, $value );
 996         }
 997
 998         /**
 999          * @return bool
1000          */
1001         function getLaggedSlaveMode() {
1002                 return $this->mLaggedSlaveMode;
1003         }
1004
1005         /**
1006          * Disables/enables lag checks
1007          * @param null|bool $mode
1008          * @return bool
1009          */
1010         function allowLagged( $mode = null ) {
1011                 if ( $mode === null ) {
1012                         return $this->mAllowLagged;
1013                 }
1014                 $this->mAllowLagged = $mode;
1015
1016                 return $this->mAllowLagged;
1017         }
1018
1019         /**
1020          * @return bool
1021          */
1022         function pingAll() {
1023                 $success = true;
1024                 foreach ( $this->mConns as $conns2 ) {
1025                         foreach ( $conns2 as $conns3 ) {
1026                                 /** @var DatabaseBase[] $conns3 */
1027                                 foreach ( $conns3 as $conn ) {
1028                                         if ( !$conn->ping() ) {
1029                                                 $success = false;
1030                                         }
1031                                 }
1032                         }
1033                 }
1034
1035                 return $success;
1036         }
1037
1038         /**
1039          * Call a function with each open connection object
1040          * @param callable $callback
1041          * @param array $params
1042          */
1043         function forEachOpenConnection( $callback, $params = array() ) {
1044                 foreach ( $this->mConns as $conns2 ) {
1045                         foreach ( $conns2 as $conns3 ) {
1046                                 foreach ( $conns3 as $conn ) {
1047                                         $mergedParams = array_merge( array( $conn ), $params );
1048                                         call_user_func_array( $callback, $mergedParams );
1049                                 }
1050                         }
1051                 }
1052         }
1053
1054         /**
1055          * Get the hostname and lag time of the most-lagged slave.
1056          * This is useful for maintenance scripts that need to throttle their updates.
1057          * May attempt to open connections to slaves on the default DB. If there is
1058          * no lag, the maximum lag will be reported as -1.
1059          *
1060          * @param bool|string $wiki Wiki ID, or false for the default database
1061          * @return array ( host, max lag, index of max lagged host )
1062          */
1063         function getMaxLag( $wiki = false ) {
1064                 $maxLag = -1;
1065                 $host = '';
1066                 $maxIndex = 0;
1067
1068                 if ( $this->getServerCount() <= 1 ) { // no replication = no lag
1069                         return array( $host, $maxLag, $maxIndex );
1070                 }
1071
1072                 // Try to get the max lag info from the server cache
1073                 $key = 'loadbalancer:maxlag:cluster:' . $this->mServers[0]['host'];
1074                 $cache = ObjectCache::newAccelerator( array(), 'hash' );
1075                 $maxLagInfo = $cache->get( $key ); // (host, lag, index)
1076
1077                 // Fallback to connecting to each slave and getting the lag
1078                 if ( !$maxLagInfo ) {
1079                         foreach ( $this->mServers as $i => $conn ) {
1080                                 if ( $i == $this->getWriterIndex() ) {
1081                                         continue; // nothing to check
1082                                 }
1083                                 $conn = false;
1084                                 if ( $wiki === false ) {
1085                                         $conn = $this->getAnyOpenConnection( $i );
1086                                 }
1087                                 if ( !$conn ) {
1088                                         $conn = $this->openConnection( $i, $wiki );
1089                                 }
1090                                 if ( !$conn ) {
1091                                         continue;
1092                                 }
1093                                 $lag = $conn->getLag();
1094                                 if ( $lag > $maxLag ) {
1095                                         $maxLag = $lag;
1096                                         $host = $this->mServers[$i]['host'];
1097                                         $maxIndex = $i;
1098                                 }
1099                         }
1100                         $maxLagInfo = array( $host, $maxLag, $maxIndex );
1101                         $cache->set( $key, $maxLagInfo, 5 );
1102                 }
1103
1104                 return $maxLagInfo;
1105         }
1106
1107         /**
1108          * Get lag time for each server
1109          * Results are cached for a short time in memcached, and indefinitely in the process cache
1110          *
1111          * @param string|bool $wiki
1112          * @return array
1113          */
1114         function getLagTimes( $wiki = false ) {
1115                 # Try process cache
1116                 if ( isset( $this->mLagTimes ) ) {
1117                         return $this->mLagTimes;
1118                 }
1119                 if ( $this->getServerCount() == 1 ) {
1120                         # No replication
1121                         $this->mLagTimes = array( 0 => 0 );
1122                 } else {
1123                         # Send the request to the load monitor
1124                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1125                                 array_keys( $this->mServers ), $wiki );
1126                 }
1127
1128                 return $this->mLagTimes;
1129         }
1130
1131         /**
1132          * Get the lag in seconds for a given connection, or zero if this load
1133          * balancer does not have replication enabled.
1134          *
1135          * This should be used in preference to Database::getLag() in cases where
1136          * replication may not be in use, since there is no way to determine if
1137          * replication is in use at the connection level without running
1138          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1139          * function instead of Database::getLag() avoids a fatal error in this
1140          * case on many installations.
1141          *
1142          * @param DatabaseBase $conn
1143          * @return int
1144          */
1145         function safeGetLag( $conn ) {
1146                 if ( $this->getServerCount() == 1 ) {
1147                         return 0;
1148                 } else {
1149                         return $conn->getLag();
1150                 }
1151         }
1152
1153         /**
1154          * Clear the cache for getLagTimes
1155          */
1156         function clearLagTimeCache() {
1157                 $this->mLagTimes = null;
1158         }
1159 }
1160
1161 /**
1162  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1163  * as well handling deferring the actual network connection until the handle is used
1164  *
1165  * @ingroup Database
1166  * @since 1.22
1167  */
1168 class DBConnRef implements IDatabase {
1169         /** @var LoadBalancer */
1170         protected $lb;
1171
1172         /** @var DatabaseBase|null */
1173         protected $conn;
1174
1175         /** @var array|null */
1176         protected $params;
1177
1178         /**
1179          * @param LoadBalancer $lb
1180          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1181          */
1182         public function __construct( LoadBalancer $lb, $conn ) {
1183                 $this->lb = $lb;
1184                 if ( $conn instanceof DatabaseBase ) {
1185                         $this->conn = $conn;
1186                 } else {
1187                         $this->params = $conn;
1188                 }
1189         }
1190
1191         public function __call( $name, $arguments ) {
1192                 if ( $this->conn === null ) {
1193                         list( $db, $groups, $wiki ) = $this->params;
1194                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1195                 }
1196
1197                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1198         }
1199
1200         function __destruct() {
1201                 if ( $this->conn !== null ) {
1202                         $this->lb->reuseConnection( $this->conn );
1203                 }
1204         }
1205 }