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          *   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          */
 335         public function waitForAll( $pos ) {
 336                 wfProfileIn( __METHOD__ );
 337                 $this->mWaitForPos = $pos;
 338                 $serverCount = count( $this->mServers );
 339                 for ( $i = 1; $i < $serverCount; $i++ ) {
 340                         if ( $this->mLoads[$i] > 0 ) {
 341                                 $this->doWait( $i, true );
 342                         }
 343                 }
 344                 wfProfileOut( __METHOD__ );
 345         }
 346
 347         /**
 348          * Get any open connection to a given server index, local or foreign
 349          * Returns false if there is no connection open
 350          *
 351          * @param int $i
 352          * @return DatabaseBase|bool False on failure
 353          */
 354         function getAnyOpenConnection( $i ) {
 355                 foreach ( $this->mConns as $conns ) {
 356                         if ( !empty( $conns[$i] ) ) {
 357                                 return reset( $conns[$i] );
 358                         }
 359                 }
 360
 361                 return false;
 362         }
 363
 364         /**
 365          * Wait for a given slave to catch up to the master pos stored in $this
 366          * @param int $index
 367          * @param bool $open
 368          * @return bool
 369          */
 370         protected function doWait( $index, $open = false ) {
 371                 # Find a connection to wait on
 372                 $conn = $this->getAnyOpenConnection( $index );
 373                 if ( !$conn ) {
 374                         if ( !$open ) {
 375                                 wfDebug( __METHOD__ . ": no connection open\n" );
 376
 377                                 return false;
 378                         } else {
 379                                 $conn = $this->openConnection( $index, '' );
 380                                 if ( !$conn ) {
 381                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 382
 383                                         return false;
 384                                 }
 385                         }
 386                 }
 387
 388                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 389                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 390
 391                 if ( $result == -1 || is_null( $result ) ) {
 392                         # Timed out waiting for slave, use master instead
 393                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 394
 395                         return false;
 396                 } else {
 397                         wfDebug( __METHOD__ . ": Done\n" );
 398
 399                         return true;
 400                 }
 401         }
 402
 403         /**
 404          * Get a connection by index
 405          * This is the main entry point for this class.
 406          *
 407          * @param int $i Server index
 408          * @param array $groups Query groups
 409          * @param bool|string $wiki Wiki ID
 410          *
 411          * @throws MWException
 412          * @return DatabaseBase
 413          */
 414         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 415                 wfProfileIn( __METHOD__ );
 416
 417                 if ( $i == DB_LAST ) {
 418                         wfProfileOut( __METHOD__ );
 419                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 420                                 ' with deprecated server index DB_LAST' );
 421                 } elseif ( $i === null || $i === false ) {
 422                         wfProfileOut( __METHOD__ );
 423                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 424                                 ' with invalid server index' );
 425                 }
 426
 427                 if ( $wiki === wfWikiID() ) {
 428                         $wiki = false;
 429                 }
 430
 431                 # Query groups
 432                 if ( $i == DB_MASTER ) {
 433                         $i = $this->getWriterIndex();
 434                 } elseif ( !is_array( $groups ) ) {
 435                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 436                         if ( $groupIndex !== false ) {
 437                                 $serverName = $this->getServerName( $groupIndex );
 438                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 439                                 $i = $groupIndex;
 440                         }
 441                 } else {
 442                         foreach ( $groups as $group ) {
 443                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 444                                 if ( $groupIndex !== false ) {
 445                                         $serverName = $this->getServerName( $groupIndex );
 446                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 447                                         $i = $groupIndex;
 448                                         break;
 449                                 }
 450                         }
 451                 }
 452
 453                 # Operation-based index
 454                 if ( $i == DB_SLAVE ) {
 455                         $this->mLastError = 'Unknown error'; // reset error string
 456                         $i = $this->getReaderIndex( false, $wiki );
 457                         # Couldn't find a working server in getReaderIndex()?
 458                         if ( $i === false ) {
 459                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 460                                 wfProfileOut( __METHOD__ );
 461
 462                                 return $this->reportConnectionError();
 463                         }
 464                 }
 465
 466                 # Now we have an explicit index into the servers array
 467                 $conn = $this->openConnection( $i, $wiki );
 468                 if ( !$conn ) {
 469                         wfProfileOut( __METHOD__ );
 470
 471                         return $this->reportConnectionError();
 472                 }
 473
 474                 wfProfileOut( __METHOD__ );
 475
 476                 return $conn;
 477         }
 478
 479         /**
 480          * Mark a foreign connection as being available for reuse under a different
 481          * DB name or prefix. This mechanism is reference-counted, and must be called
 482          * the same number of times as getConnection() to work.
 483          *
 484          * @param DatabaseBase $conn
 485          * @throws MWException
 486          */
 487         public function reuseConnection( $conn ) {
 488                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 489                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 490                 if ( $serverIndex === null || $refCount === null ) {
 491                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 492
 493                         /**
 494                          * This can happen in code like:
 495                          *   foreach ( $dbs as $db ) {
 496                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 497                          *     ...
 498                          *     $lb->reuseConnection( $conn );
 499                          *   }
 500                          * When a connection to the local DB is opened in this way, reuseConnection()
 501                          * should be ignored
 502                          */
 503
 504                         return;
 505                 }
 506
 507                 $dbName = $conn->getDBname();
 508                 $prefix = $conn->tablePrefix();
 509                 if ( strval( $prefix ) !== '' ) {
 510                         $wiki = "$dbName-$prefix";
 511                 } else {
 512                         $wiki = $dbName;
 513                 }
 514                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 515                         throw new MWException( __METHOD__ . ": connection not found, has " .
 516                                 "the connection been freed already?" );
 517                 }
 518                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 519                 if ( $refCount <= 0 ) {
 520                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 521                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 522                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 523                 } else {
 524                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 525                 }
 526         }
 527
 528         /**
 529          * Get a database connection handle reference
 530          *
 531          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 532          *
 533          * @see LoadBalancer::getConnection() for parameter information
 534          *
 535          * @param int $db
 536          * @param mixed $groups
 537          * @param bool|string $wiki
 538          * @return DBConnRef
 539          */
 540         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 541                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 542         }
 543
 544         /**
 545          * Get a database connection handle reference without connecting yet
 546          *
 547          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 548          *
 549          * @see LoadBalancer::getConnection() for parameter information
 550          *
 551          * @param int $db
 552          * @param mixed $groups
 553          * @param bool|string $wiki
 554          * @return DBConnRef
 555          */
 556         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 557                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 558         }
 559
 560         /**
 561          * Open a connection to the server given by the specified index
 562          * Index must be an actual index into the array.
 563          * If the server is already open, returns it.
 564          *
 565          * On error, returns false, and the connection which caused the
 566          * error will be available via $this->mErrorConnection.
 567          *
 568          * @param int $i Server index
 569          * @param bool|string $wiki Wiki ID to open
 570          * @return DatabaseBase
 571          *
 572          * @access private
 573          */
 574         function openConnection( $i, $wiki = false ) {
 575                 wfProfileIn( __METHOD__ );
 576                 if ( $wiki !== false ) {
 577                         $conn = $this->openForeignConnection( $i, $wiki );
 578                         wfProfileOut( __METHOD__ );
 579
 580                         return $conn;
 581                 }
 582                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 583                         $conn = $this->mConns['local'][$i][0];
 584                 } else {
 585                         $server = $this->mServers[$i];
 586                         $server['serverIndex'] = $i;
 587                         $conn = $this->reallyOpenConnection( $server, false );
 588                         if ( $conn->isOpen() ) {
 589                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 590                                 $this->mConns['local'][$i][0] = $conn;
 591                         } else {
 592                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 593                                 $this->mErrorConnection = $conn;
 594                                 $conn = false;
 595                         }
 596                 }
 597                 wfProfileOut( __METHOD__ );
 598
 599                 return $conn;
 600         }
 601
 602         /**
 603          * Open a connection to a foreign DB, or return one if it is already open.
 604          *
 605          * Increments a reference count on the returned connection which locks the
 606          * connection to the requested wiki. This reference count can be
 607          * decremented by calling reuseConnection().
 608          *
 609          * If a connection is open to the appropriate server already, but with the wrong
 610          * database, it will be switched to the right database and returned, as long as
 611          * it has been freed first with reuseConnection().
 612          *
 613          * On error, returns false, and the connection which caused the
 614          * error will be available via $this->mErrorConnection.
 615          *
 616          * @param int $i Server index
 617          * @param string $wiki Wiki ID to open
 618          * @return DatabaseBase
 619          */
 620         function openForeignConnection( $i, $wiki ) {
 621                 wfProfileIn( __METHOD__ );
 622                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 623                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 624                         // Reuse an already-used connection
 625                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 626                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 627                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 628                         // Reuse a free connection for the same wiki
 629                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 630                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 631                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 632                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 633                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 634                         // Reuse a connection from another wiki
 635                         $conn = reset( $this->mConns['foreignFree'][$i] );
 636                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 637
 638                         if ( !$conn->selectDB( $dbName ) ) {
 639                                 $this->mLastError = "Error selecting database $dbName on server " .
 640                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 641                                 $this->mErrorConnection = $conn;
 642                                 $conn = false;
 643                         } else {
 644                                 $conn->tablePrefix( $prefix );
 645                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 646                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 647                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 648                         }
 649                 } else {
 650                         // Open a new connection
 651                         $server = $this->mServers[$i];
 652                         $server['serverIndex'] = $i;
 653                         $server['foreignPoolRefCount'] = 0;
 654                         $server['foreign'] = true;
 655                         $conn = $this->reallyOpenConnection( $server, $dbName );
 656                         if ( !$conn->isOpen() ) {
 657                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 658                                 $this->mErrorConnection = $conn;
 659                                 $conn = false;
 660                         } else {
 661                                 $conn->tablePrefix( $prefix );
 662                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 663                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 664                         }
 665                 }
 666
 667                 // Increment reference count
 668                 if ( $conn ) {
 669                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 670                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 671                 }
 672                 wfProfileOut( __METHOD__ );
 673
 674                 return $conn;
 675         }
 676
 677         /**
 678          * Test if the specified index represents an open connection
 679          *
 680          * @param int $index Server index
 681          * @access private
 682          * @return bool
 683          */
 684         function isOpen( $index ) {
 685                 if ( !is_integer( $index ) ) {
 686                         return false;
 687                 }
 688
 689                 return (bool)$this->getAnyOpenConnection( $index );
 690         }
 691
 692         /**
 693          * Really opens a connection. Uncached.
 694          * Returns a Database object whether or not the connection was successful.
 695          * @access private
 696          *
 697          * @param array $server
 698          * @param bool $dbNameOverride
 699          * @throws MWException
 700          * @return DatabaseBase
 701          */
 702         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 703                 if ( !is_array( $server ) ) {
 704                         throw new MWException( 'You must update your load-balancing configuration. ' .
 705                                 'See DefaultSettings.php entry for $wgDBservers.' );
 706                 }
 707
 708                 if ( $dbNameOverride !== false ) {
 709                         $server['dbname'] = $dbNameOverride;
 710                 }
 711
 712                 # Create object
 713                 try {
 714                         $db = DatabaseBase::factory( $server['type'], $server );
 715                 } catch ( DBConnectionError $e ) {
 716                         // FIXME: This is probably the ugliest thing I have ever done to
 717                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 718                         $db = $e->db;
 719                 }
 720
 721                 $db->setLBInfo( $server );
 722                 if ( isset( $server['fakeSlaveLag'] ) ) {
 723                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 724                 }
 725                 if ( isset( $server['fakeMaster'] ) ) {
 726                         $db->setFakeMaster( true );
 727                 }
 728
 729                 return $db;
 730         }
 731
 732         /**
 733          * @throws DBConnectionError
 734          * @return bool
 735          */
 736         private function reportConnectionError() {
 737                 $conn = $this->mErrorConnection; // The connection which caused the error
 738
 739                 if ( !is_object( $conn ) ) {
 740                         // No last connection, probably due to all servers being too busy
 741                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}" );
 742
 743                         // If all servers were busy, mLastError will contain something sensible
 744                         throw new DBConnectionError( null, $this->mLastError );
 745                 } else {
 746                         $server = $conn->getProperty( 'mServer' );
 747                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})" );
 748                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 749                 }
 750
 751                 return false; /* not reached */
 752         }
 753
 754         /**
 755          * @return int
 756          */
 757         function getWriterIndex() {
 758                 return 0;
 759         }
 760
 761         /**
 762          * Returns true if the specified index is a valid server index
 763          *
 764          * @param string $i
 765          * @return bool
 766          */
 767         function haveIndex( $i ) {
 768                 return array_key_exists( $i, $this->mServers );
 769         }
 770
 771         /**
 772          * Returns true if the specified index is valid and has non-zero load
 773          *
 774          * @param string $i
 775          * @return bool
 776          */
 777         function isNonZeroLoad( $i ) {
 778                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 779         }
 780
 781         /**
 782          * Get the number of defined servers (not the number of open connections)
 783          *
 784          * @return int
 785          */
 786         function getServerCount() {
 787                 return count( $this->mServers );
 788         }
 789
 790         /**
 791          * Get the host name or IP address of the server with the specified index
 792          * Prefer a readable name if available.
 793          * @param string $i
 794          * @return string
 795          */
 796         function getServerName( $i ) {
 797                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 798                         return $this->mServers[$i]['hostName'];
 799                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 800                         return $this->mServers[$i]['host'];
 801                 } else {
 802                         return '';
 803                 }
 804         }
 805
 806         /**
 807          * Return the server info structure for a given index, or false if the index is invalid.
 808          * @param int $i
 809          * @return array|bool
 810          */
 811         function getServerInfo( $i ) {
 812                 if ( isset( $this->mServers[$i] ) ) {
 813                         return $this->mServers[$i];
 814                 } else {
 815                         return false;
 816                 }
 817         }
 818
 819         /**
 820          * Sets the server info structure for the given index. Entry at index $i
 821          * is created if it doesn't exist
 822          * @param int $i
 823          * @param array $serverInfo
 824          */
 825         function setServerInfo( $i, $serverInfo ) {
 826                 $this->mServers[$i] = $serverInfo;
 827         }
 828
 829         /**
 830          * Get the current master position for chronology control purposes
 831          * @return mixed
 832          */
 833         function getMasterPos() {
 834                 # If this entire request was served from a slave without opening a connection to the
 835                 # master (however unlikely that may be), then we can fetch the position from the slave.
 836                 $masterConn = $this->getAnyOpenConnection( 0 );
 837                 if ( !$masterConn ) {
 838                         $serverCount = count( $this->mServers );
 839                         for ( $i = 1; $i < $serverCount; $i++ ) {
 840                                 $conn = $this->getAnyOpenConnection( $i );
 841                                 if ( $conn ) {
 842                                         wfDebug( "Master pos fetched from slave\n" );
 843
 844                                         return $conn->getSlavePos();
 845                                 }
 846                         }
 847                 } else {
 848                         wfDebug( "Master pos fetched from master\n" );
 849
 850                         return $masterConn->getMasterPos();
 851                 }
 852
 853                 return false;
 854         }
 855
 856         /**
 857          * Close all open connections
 858          */
 859         function closeAll() {
 860                 foreach ( $this->mConns as $conns2 ) {
 861                         foreach ( $conns2 as $conns3 ) {
 862                                 /** @var DatabaseBase $conn */
 863                                 foreach ( $conns3 as $conn ) {
 864                                         $conn->close();
 865                                 }
 866                         }
 867                 }
 868                 $this->mConns = array(
 869                         'local' => array(),
 870                         'foreignFree' => array(),
 871                         'foreignUsed' => array(),
 872                 );
 873         }
 874
 875         /**
 876          * Deprecated function, typo in function name
 877          *
 878          * @deprecated since 1.18
 879          * @param DatabaseBase $conn
 880          */
 881         function closeConnecton( $conn ) {
 882                 wfDeprecated( __METHOD__, '1.18' );
 883                 $this->closeConnection( $conn );
 884         }
 885
 886         /**
 887          * Close a connection
 888          * Using this function makes sure the LoadBalancer knows the connection is closed.
 889          * If you use $conn->close() directly, the load balancer won't update its state.
 890          * @param DatabaseBase $conn
 891          */
 892         function closeConnection( $conn ) {
 893                 $done = false;
 894                 foreach ( $this->mConns as $i1 => $conns2 ) {
 895                         foreach ( $conns2 as $i2 => $conns3 ) {
 896                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 897                                         if ( $conn === $candidateConn ) {
 898                                                 $conn->close();
 899                                                 unset( $this->mConns[$i1][$i2][$i3] );
 900                                                 $done = true;
 901                                                 break;
 902                                         }
 903                                 }
 904                         }
 905                 }
 906                 if ( !$done ) {
 907                         $conn->close();
 908                 }
 909         }
 910
 911         /**
 912          * Commit transactions on all open connections
 913          */
 914         function commitAll() {
 915                 foreach ( $this->mConns as $conns2 ) {
 916                         foreach ( $conns2 as $conns3 ) {
 917                                 /** @var DatabaseBase[] $conns3 */
 918                                 foreach ( $conns3 as $conn ) {
 919                                         if ( $conn->trxLevel() ) {
 920                                                 $conn->commit( __METHOD__, 'flush' );
 921                                         }
 922                                 }
 923                         }
 924                 }
 925         }
 926
 927         /**
 928          *  Issue COMMIT only on master, only if queries were done on connection
 929          */
 930         function commitMasterChanges() {
 931                 // Always 0, but who knows.. :)
 932                 $masterIndex = $this->getWriterIndex();
 933                 foreach ( $this->mConns as $conns2 ) {
 934                         if ( empty( $conns2[$masterIndex] ) ) {
 935                                 continue;
 936                         }
 937                         /** @var DatabaseBase $conn */
 938                         foreach ( $conns2[$masterIndex] as $conn ) {
 939                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 940                                         $conn->commit( __METHOD__, 'flush' );
 941                                 }
 942                         }
 943                 }
 944         }
 945
 946         /**
 947          * Issue ROLLBACK only on master, only if queries were done on connection
 948          * @since 1.23
 949          */
 950         function rollbackMasterChanges() {
 951                 // Always 0, but who knows.. :)
 952                 $masterIndex = $this->getWriterIndex();
 953                 foreach ( $this->mConns as $conns2 ) {
 954                         if ( empty( $conns2[$masterIndex] ) ) {
 955                                 continue;
 956                         }
 957                         /** @var DatabaseBase $conn */
 958                         foreach ( $conns2[$masterIndex] as $conn ) {
 959                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 960                                         $conn->rollback( __METHOD__, 'flush' );
 961                                 }
 962                         }
 963                 }
 964         }
 965
 966         /**
 967          * Determine if there are any pending changes that need to be rolled back
 968          * or committed.
 969          * @since 1.23
 970          * @return bool
 971          */
 972         function hasMasterChanges() {
 973                 // Always 0, but who knows.. :)
 974                 $masterIndex = $this->getWriterIndex();
 975                 foreach ( $this->mConns as $conns2 ) {
 976                         if ( empty( $conns2[$masterIndex] ) ) {
 977                                 continue;
 978                         }
 979                         /** @var DatabaseBase $conn */
 980                         foreach ( $conns2[$masterIndex] as $conn ) {
 981                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 982                                         return true;
 983                                 }
 984                         }
 985                 }
 986                 return false;
 987         }
 988
 989         /**
 990          * @param mixed $value
 991          * @return mixed
 992          */
 993         function waitTimeout( $value = null ) {
 994                 return wfSetVar( $this->mWaitTimeout, $value );
 995         }
 996
 997         /**
 998          * @return bool
 999          */
1000         function getLaggedSlaveMode() {
1001                 return $this->mLaggedSlaveMode;
1002         }
1003
1004         /**
1005          * Disables/enables lag checks
1006          * @param null|bool $mode
1007          * @return bool
1008          */
1009         function allowLagged( $mode = null ) {
1010                 if ( $mode === null ) {
1011                         return $this->mAllowLagged;
1012                 }
1013                 $this->mAllowLagged = $mode;
1014
1015                 return $this->mAllowLagged;
1016         }
1017
1018         /**
1019          * @return bool
1020          */
1021         function pingAll() {
1022                 $success = true;
1023                 foreach ( $this->mConns as $conns2 ) {
1024                         foreach ( $conns2 as $conns3 ) {
1025                                 /** @var DatabaseBase[] $conns3 */
1026                                 foreach ( $conns3 as $conn ) {
1027                                         if ( !$conn->ping() ) {
1028                                                 $success = false;
1029                                         }
1030                                 }
1031                         }
1032                 }
1033
1034                 return $success;
1035         }
1036
1037         /**
1038          * Call a function with each open connection object
1039          * @param callable $callback
1040          * @param array $params
1041          */
1042         function forEachOpenConnection( $callback, $params = array() ) {
1043                 foreach ( $this->mConns as $conns2 ) {
1044                         foreach ( $conns2 as $conns3 ) {
1045                                 foreach ( $conns3 as $conn ) {
1046                                         $mergedParams = array_merge( array( $conn ), $params );
1047                                         call_user_func_array( $callback, $mergedParams );
1048                                 }
1049                         }
1050                 }
1051         }
1052
1053         /**
1054          * Get the hostname and lag time of the most-lagged slave.
1055          * This is useful for maintenance scripts that need to throttle their updates.
1056          * May attempt to open connections to slaves on the default DB. If there is
1057          * no lag, the maximum lag will be reported as -1.
1058          *
1059          * @param bool|string $wiki Wiki ID, or false for the default database
1060          * @return array ( host, max lag, index of max lagged host )
1061          */
1062         function getMaxLag( $wiki = false ) {
1063                 $maxLag = -1;
1064                 $host = '';
1065                 $maxIndex = 0;
1066                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1067                         foreach ( $this->mServers as $i => $conn ) {
1068                                 $conn = false;
1069                                 if ( $wiki === false ) {
1070                                         $conn = $this->getAnyOpenConnection( $i );
1071                                 }
1072                                 if ( !$conn ) {
1073                                         $conn = $this->openConnection( $i, $wiki );
1074                                 }
1075                                 if ( !$conn ) {
1076                                         continue;
1077                                 }
1078                                 $lag = $conn->getLag();
1079                                 if ( $lag > $maxLag ) {
1080                                         $maxLag = $lag;
1081                                         $host = $this->mServers[$i]['host'];
1082                                         $maxIndex = $i;
1083                                 }
1084                         }
1085                 }
1086
1087                 return array( $host, $maxLag, $maxIndex );
1088         }
1089
1090         /**
1091          * Get lag time for each server
1092          * Results are cached for a short time in memcached, and indefinitely in the process cache
1093          *
1094          * @param string|bool $wiki
1095          * @return array
1096          */
1097         function getLagTimes( $wiki = false ) {
1098                 # Try process cache
1099                 if ( isset( $this->mLagTimes ) ) {
1100                         return $this->mLagTimes;
1101                 }
1102                 if ( $this->getServerCount() == 1 ) {
1103                         # No replication
1104                         $this->mLagTimes = array( 0 => 0 );
1105                 } else {
1106                         # Send the request to the load monitor
1107                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1108                                 array_keys( $this->mServers ), $wiki );
1109                 }
1110
1111                 return $this->mLagTimes;
1112         }
1113
1114         /**
1115          * Get the lag in seconds for a given connection, or zero if this load
1116          * balancer does not have replication enabled.
1117          *
1118          * This should be used in preference to Database::getLag() in cases where
1119          * replication may not be in use, since there is no way to determine if
1120          * replication is in use at the connection level without running
1121          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1122          * function instead of Database::getLag() avoids a fatal error in this
1123          * case on many installations.
1124          *
1125          * @param DatabaseBase $conn
1126          * @return int
1127          */
1128         function safeGetLag( $conn ) {
1129                 if ( $this->getServerCount() == 1 ) {
1130                         return 0;
1131                 } else {
1132                         return $conn->getLag();
1133                 }
1134         }
1135
1136         /**
1137          * Clear the cache for getLagTimes
1138          */
1139         function clearLagTimeCache() {
1140                 $this->mLagTimes = null;
1141         }
1142 }
1143
1144 /**
1145  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1146  * as well handling deferring the actual network connection until the handle is used
1147  *
1148  * @ingroup Database
1149  * @since 1.22
1150  */
1151 class DBConnRef implements IDatabase {
1152         /** @var LoadBalancer */
1153         protected $lb;
1154
1155         /** @var DatabaseBase|null */
1156         protected $conn;
1157
1158         /** @var array|null */
1159         protected $params;
1160
1161         /**
1162          * @param LoadBalancer $lb
1163          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1164          */
1165         public function __construct( LoadBalancer $lb, $conn ) {
1166                 $this->lb = $lb;
1167                 if ( $conn instanceof DatabaseBase ) {
1168                         $this->conn = $conn;
1169                 } else {
1170                         $this->params = $conn;
1171                 }
1172         }
1173
1174         public function __call( $name, $arguments ) {
1175                 if ( $this->conn === null ) {
1176                         list( $db, $groups, $wiki ) = $this->params;
1177                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1178                 }
1179
1180                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1181         }
1182
1183         function __destruct() {
1184                 if ( $this->conn !== null ) {
1185                         $this->lb->reuseConnection( $this->conn );
1186                 }
1187         }
1188 }