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 === null || $i === false ) {
 418                         wfProfileOut( __METHOD__ );
 419                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 420                                 ' with invalid server index' );
 421                 }
 422
 423                 if ( $wiki === wfWikiID() ) {
 424                         $wiki = false;
 425                 }
 426
 427                 # Query groups
 428                 if ( $i == DB_MASTER ) {
 429                         $i = $this->getWriterIndex();
 430                 } elseif ( !is_array( $groups ) ) {
 431                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 432                         if ( $groupIndex !== false ) {
 433                                 $serverName = $this->getServerName( $groupIndex );
 434                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 435                                 $i = $groupIndex;
 436                         }
 437                 } else {
 438                         foreach ( $groups as $group ) {
 439                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 440                                 if ( $groupIndex !== false ) {
 441                                         $serverName = $this->getServerName( $groupIndex );
 442                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 443                                         $i = $groupIndex;
 444                                         break;
 445                                 }
 446                         }
 447                 }
 448
 449                 # Operation-based index
 450                 if ( $i == DB_SLAVE ) {
 451                         $this->mLastError = 'Unknown error'; // reset error string
 452                         $i = $this->getReaderIndex( false, $wiki );
 453                         # Couldn't find a working server in getReaderIndex()?
 454                         if ( $i === false ) {
 455                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 456                                 wfProfileOut( __METHOD__ );
 457
 458                                 return $this->reportConnectionError();
 459                         }
 460                 }
 461
 462                 # Now we have an explicit index into the servers array
 463                 $conn = $this->openConnection( $i, $wiki );
 464                 if ( !$conn ) {
 465                         wfProfileOut( __METHOD__ );
 466
 467                         return $this->reportConnectionError();
 468                 }
 469
 470                 wfProfileOut( __METHOD__ );
 471
 472                 return $conn;
 473         }
 474
 475         /**
 476          * Mark a foreign connection as being available for reuse under a different
 477          * DB name or prefix. This mechanism is reference-counted, and must be called
 478          * the same number of times as getConnection() to work.
 479          *
 480          * @param DatabaseBase $conn
 481          * @throws MWException
 482          */
 483         public function reuseConnection( $conn ) {
 484                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 485                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 486                 if ( $serverIndex === null || $refCount === null ) {
 487                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 488
 489                         /**
 490                          * This can happen in code like:
 491                          *   foreach ( $dbs as $db ) {
 492                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 493                          *     ...
 494                          *     $lb->reuseConnection( $conn );
 495                          *   }
 496                          * When a connection to the local DB is opened in this way, reuseConnection()
 497                          * should be ignored
 498                          */
 499
 500                         return;
 501                 }
 502
 503                 $dbName = $conn->getDBname();
 504                 $prefix = $conn->tablePrefix();
 505                 if ( strval( $prefix ) !== '' ) {
 506                         $wiki = "$dbName-$prefix";
 507                 } else {
 508                         $wiki = $dbName;
 509                 }
 510                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 511                         throw new MWException( __METHOD__ . ": connection not found, has " .
 512                                 "the connection been freed already?" );
 513                 }
 514                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 515                 if ( $refCount <= 0 ) {
 516                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 517                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 518                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 519                 } else {
 520                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 521                 }
 522         }
 523
 524         /**
 525          * Get a database connection handle reference
 526          *
 527          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 528          *
 529          * @see LoadBalancer::getConnection() for parameter information
 530          *
 531          * @param int $db
 532          * @param mixed $groups
 533          * @param bool|string $wiki
 534          * @return DBConnRef
 535          */
 536         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 537                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 538         }
 539
 540         /**
 541          * Get a database connection handle reference without connecting yet
 542          *
 543          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 544          *
 545          * @see LoadBalancer::getConnection() for parameter information
 546          *
 547          * @param int $db
 548          * @param mixed $groups
 549          * @param bool|string $wiki
 550          * @return DBConnRef
 551          */
 552         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 553                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 554         }
 555
 556         /**
 557          * Open a connection to the server given by the specified index
 558          * Index must be an actual index into the array.
 559          * If the server is already open, returns it.
 560          *
 561          * On error, returns false, and the connection which caused the
 562          * error will be available via $this->mErrorConnection.
 563          *
 564          * @param int $i Server index
 565          * @param bool|string $wiki Wiki ID to open
 566          * @return DatabaseBase
 567          *
 568          * @access private
 569          */
 570         function openConnection( $i, $wiki = false ) {
 571                 wfProfileIn( __METHOD__ );
 572                 if ( $wiki !== false ) {
 573                         $conn = $this->openForeignConnection( $i, $wiki );
 574                         wfProfileOut( __METHOD__ );
 575
 576                         return $conn;
 577                 }
 578                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 579                         $conn = $this->mConns['local'][$i][0];
 580                 } else {
 581                         $server = $this->mServers[$i];
 582                         $server['serverIndex'] = $i;
 583                         $conn = $this->reallyOpenConnection( $server, false );
 584                         if ( $conn->isOpen() ) {
 585                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 586                                 $this->mConns['local'][$i][0] = $conn;
 587                         } else {
 588                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 589                                 $this->mErrorConnection = $conn;
 590                                 $conn = false;
 591                         }
 592                 }
 593                 wfProfileOut( __METHOD__ );
 594
 595                 return $conn;
 596         }
 597
 598         /**
 599          * Open a connection to a foreign DB, or return one if it is already open.
 600          *
 601          * Increments a reference count on the returned connection which locks the
 602          * connection to the requested wiki. This reference count can be
 603          * decremented by calling reuseConnection().
 604          *
 605          * If a connection is open to the appropriate server already, but with the wrong
 606          * database, it will be switched to the right database and returned, as long as
 607          * it has been freed first with reuseConnection().
 608          *
 609          * On error, returns false, and the connection which caused the
 610          * error will be available via $this->mErrorConnection.
 611          *
 612          * @param int $i Server index
 613          * @param string $wiki Wiki ID to open
 614          * @return DatabaseBase
 615          */
 616         function openForeignConnection( $i, $wiki ) {
 617                 wfProfileIn( __METHOD__ );
 618                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 619                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 620                         // Reuse an already-used connection
 621                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 622                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 623                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 624                         // Reuse a free connection for the same wiki
 625                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 626                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 627                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 628                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 629                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 630                         // Reuse a connection from another wiki
 631                         $conn = reset( $this->mConns['foreignFree'][$i] );
 632                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 633
 634                         if ( !$conn->selectDB( $dbName ) ) {
 635                                 $this->mLastError = "Error selecting database $dbName on server " .
 636                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 637                                 $this->mErrorConnection = $conn;
 638                                 $conn = false;
 639                         } else {
 640                                 $conn->tablePrefix( $prefix );
 641                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 642                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 643                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 644                         }
 645                 } else {
 646                         // Open a new connection
 647                         $server = $this->mServers[$i];
 648                         $server['serverIndex'] = $i;
 649                         $server['foreignPoolRefCount'] = 0;
 650                         $server['foreign'] = true;
 651                         $conn = $this->reallyOpenConnection( $server, $dbName );
 652                         if ( !$conn->isOpen() ) {
 653                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 654                                 $this->mErrorConnection = $conn;
 655                                 $conn = false;
 656                         } else {
 657                                 $conn->tablePrefix( $prefix );
 658                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 659                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 660                         }
 661                 }
 662
 663                 // Increment reference count
 664                 if ( $conn ) {
 665                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 666                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 667                 }
 668                 wfProfileOut( __METHOD__ );
 669
 670                 return $conn;
 671         }
 672
 673         /**
 674          * Test if the specified index represents an open connection
 675          *
 676          * @param int $index Server index
 677          * @access private
 678          * @return bool
 679          */
 680         function isOpen( $index ) {
 681                 if ( !is_integer( $index ) ) {
 682                         return false;
 683                 }
 684
 685                 return (bool)$this->getAnyOpenConnection( $index );
 686         }
 687
 688         /**
 689          * Really opens a connection. Uncached.
 690          * Returns a Database object whether or not the connection was successful.
 691          * @access private
 692          *
 693          * @param array $server
 694          * @param bool $dbNameOverride
 695          * @throws MWException
 696          * @return DatabaseBase
 697          */
 698         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 699                 if ( !is_array( $server ) ) {
 700                         throw new MWException( 'You must update your load-balancing configuration. ' .
 701                                 'See DefaultSettings.php entry for $wgDBservers.' );
 702                 }
 703
 704                 if ( $dbNameOverride !== false ) {
 705                         $server['dbname'] = $dbNameOverride;
 706                 }
 707
 708                 # Create object
 709                 try {
 710                         $db = DatabaseBase::factory( $server['type'], $server );
 711                 } catch ( DBConnectionError $e ) {
 712                         // FIXME: This is probably the ugliest thing I have ever done to
 713                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 714                         $db = $e->db;
 715                 }
 716
 717                 $db->setLBInfo( $server );
 718                 if ( isset( $server['fakeSlaveLag'] ) ) {
 719                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 720                 }
 721                 if ( isset( $server['fakeMaster'] ) ) {
 722                         $db->setFakeMaster( true );
 723                 }
 724
 725                 return $db;
 726         }
 727
 728         /**
 729          * @throws DBConnectionError
 730          * @return bool
 731          */
 732         private function reportConnectionError() {
 733                 $conn = $this->mErrorConnection; // The connection which caused the error
 734
 735                 if ( !is_object( $conn ) ) {
 736                         // No last connection, probably due to all servers being too busy
 737                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}" );
 738
 739                         // If all servers were busy, mLastError will contain something sensible
 740                         throw new DBConnectionError( null, $this->mLastError );
 741                 } else {
 742                         $server = $conn->getProperty( 'mServer' );
 743                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})" );
 744                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 745                 }
 746
 747                 return false; /* not reached */
 748         }
 749
 750         /**
 751          * @return int
 752          */
 753         function getWriterIndex() {
 754                 return 0;
 755         }
 756
 757         /**
 758          * Returns true if the specified index is a valid server index
 759          *
 760          * @param string $i
 761          * @return bool
 762          */
 763         function haveIndex( $i ) {
 764                 return array_key_exists( $i, $this->mServers );
 765         }
 766
 767         /**
 768          * Returns true if the specified index is valid and has non-zero load
 769          *
 770          * @param string $i
 771          * @return bool
 772          */
 773         function isNonZeroLoad( $i ) {
 774                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 775         }
 776
 777         /**
 778          * Get the number of defined servers (not the number of open connections)
 779          *
 780          * @return int
 781          */
 782         function getServerCount() {
 783                 return count( $this->mServers );
 784         }
 785
 786         /**
 787          * Get the host name or IP address of the server with the specified index
 788          * Prefer a readable name if available.
 789          * @param string $i
 790          * @return string
 791          */
 792         function getServerName( $i ) {
 793                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 794                         return $this->mServers[$i]['hostName'];
 795                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 796                         return $this->mServers[$i]['host'];
 797                 } else {
 798                         return '';
 799                 }
 800         }
 801
 802         /**
 803          * Return the server info structure for a given index, or false if the index is invalid.
 804          * @param int $i
 805          * @return array|bool
 806          */
 807         function getServerInfo( $i ) {
 808                 if ( isset( $this->mServers[$i] ) ) {
 809                         return $this->mServers[$i];
 810                 } else {
 811                         return false;
 812                 }
 813         }
 814
 815         /**
 816          * Sets the server info structure for the given index. Entry at index $i
 817          * is created if it doesn't exist
 818          * @param int $i
 819          * @param array $serverInfo
 820          */
 821         function setServerInfo( $i, $serverInfo ) {
 822                 $this->mServers[$i] = $serverInfo;
 823         }
 824
 825         /**
 826          * Get the current master position for chronology control purposes
 827          * @return mixed
 828          */
 829         function getMasterPos() {
 830                 # If this entire request was served from a slave without opening a connection to the
 831                 # master (however unlikely that may be), then we can fetch the position from the slave.
 832                 $masterConn = $this->getAnyOpenConnection( 0 );
 833                 if ( !$masterConn ) {
 834                         $serverCount = count( $this->mServers );
 835                         for ( $i = 1; $i < $serverCount; $i++ ) {
 836                                 $conn = $this->getAnyOpenConnection( $i );
 837                                 if ( $conn ) {
 838                                         wfDebug( "Master pos fetched from slave\n" );
 839
 840                                         return $conn->getSlavePos();
 841                                 }
 842                         }
 843                 } else {
 844                         wfDebug( "Master pos fetched from master\n" );
 845
 846                         return $masterConn->getMasterPos();
 847                 }
 848
 849                 return false;
 850         }
 851
 852         /**
 853          * Close all open connections
 854          */
 855         function closeAll() {
 856                 foreach ( $this->mConns as $conns2 ) {
 857                         foreach ( $conns2 as $conns3 ) {
 858                                 /** @var DatabaseBase $conn */
 859                                 foreach ( $conns3 as $conn ) {
 860                                         $conn->close();
 861                                 }
 862                         }
 863                 }
 864                 $this->mConns = array(
 865                         'local' => array(),
 866                         'foreignFree' => array(),
 867                         'foreignUsed' => array(),
 868                 );
 869         }
 870
 871         /**
 872          * Close a connection
 873          * Using this function makes sure the LoadBalancer knows the connection is closed.
 874          * If you use $conn->close() directly, the load balancer won't update its state.
 875          * @param DatabaseBase $conn
 876          */
 877         function closeConnection( $conn ) {
 878                 $done = false;
 879                 foreach ( $this->mConns as $i1 => $conns2 ) {
 880                         foreach ( $conns2 as $i2 => $conns3 ) {
 881                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 882                                         if ( $conn === $candidateConn ) {
 883                                                 $conn->close();
 884                                                 unset( $this->mConns[$i1][$i2][$i3] );
 885                                                 $done = true;
 886                                                 break;
 887                                         }
 888                                 }
 889                         }
 890                 }
 891                 if ( !$done ) {
 892                         $conn->close();
 893                 }
 894         }
 895
 896         /**
 897          * Commit transactions on all open connections
 898          */
 899         function commitAll() {
 900                 foreach ( $this->mConns as $conns2 ) {
 901                         foreach ( $conns2 as $conns3 ) {
 902                                 /** @var DatabaseBase[] $conns3 */
 903                                 foreach ( $conns3 as $conn ) {
 904                                         if ( $conn->trxLevel() ) {
 905                                                 $conn->commit( __METHOD__, 'flush' );
 906                                         }
 907                                 }
 908                         }
 909                 }
 910         }
 911
 912         /**
 913          *  Issue COMMIT only on master, only if queries were done on connection
 914          */
 915         function commitMasterChanges() {
 916                 // Always 0, but who knows.. :)
 917                 $masterIndex = $this->getWriterIndex();
 918                 foreach ( $this->mConns as $conns2 ) {
 919                         if ( empty( $conns2[$masterIndex] ) ) {
 920                                 continue;
 921                         }
 922                         /** @var DatabaseBase $conn */
 923                         foreach ( $conns2[$masterIndex] as $conn ) {
 924                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 925                                         $conn->commit( __METHOD__, 'flush' );
 926                                 }
 927                         }
 928                 }
 929         }
 930
 931         /**
 932          * Issue ROLLBACK only on master, only if queries were done on connection
 933          * @since 1.23
 934          */
 935         function rollbackMasterChanges() {
 936                 // Always 0, but who knows.. :)
 937                 $masterIndex = $this->getWriterIndex();
 938                 foreach ( $this->mConns as $conns2 ) {
 939                         if ( empty( $conns2[$masterIndex] ) ) {
 940                                 continue;
 941                         }
 942                         /** @var DatabaseBase $conn */
 943                         foreach ( $conns2[$masterIndex] as $conn ) {
 944                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 945                                         $conn->rollback( __METHOD__, 'flush' );
 946                                 }
 947                         }
 948                 }
 949         }
 950
 951         /**
 952          * @return bool Whether a master connection is already open
 953          * @since 1.24
 954          */
 955         function hasMasterConnection() {
 956                 return $this->isOpen( $this->getWriterIndex() );
 957         }
 958
 959         /**
 960          * Determine if there are any pending changes that need to be rolled back
 961          * or committed.
 962          * @since 1.23
 963          * @return bool
 964          */
 965         function hasMasterChanges() {
 966                 // Always 0, but who knows.. :)
 967                 $masterIndex = $this->getWriterIndex();
 968                 foreach ( $this->mConns as $conns2 ) {
 969                         if ( empty( $conns2[$masterIndex] ) ) {
 970                                 continue;
 971                         }
 972                         /** @var DatabaseBase $conn */
 973                         foreach ( $conns2[$masterIndex] as $conn ) {
 974                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 975                                         return true;
 976                                 }
 977                         }
 978                 }
 979                 return false;
 980         }
 981
 982         /**
 983          * @param mixed $value
 984          * @return mixed
 985          */
 986         function waitTimeout( $value = null ) {
 987                 return wfSetVar( $this->mWaitTimeout, $value );
 988         }
 989
 990         /**
 991          * @return bool
 992          */
 993         function getLaggedSlaveMode() {
 994                 return $this->mLaggedSlaveMode;
 995         }
 996
 997         /**
 998          * Disables/enables lag checks
 999          * @param null|bool $mode
1000          * @return bool
1001          */
1002         function allowLagged( $mode = null ) {
1003                 if ( $mode === null ) {
1004                         return $this->mAllowLagged;
1005                 }
1006                 $this->mAllowLagged = $mode;
1007
1008                 return $this->mAllowLagged;
1009         }
1010
1011         /**
1012          * @return bool
1013          */
1014         function pingAll() {
1015                 $success = true;
1016                 foreach ( $this->mConns as $conns2 ) {
1017                         foreach ( $conns2 as $conns3 ) {
1018                                 /** @var DatabaseBase[] $conns3 */
1019                                 foreach ( $conns3 as $conn ) {
1020                                         if ( !$conn->ping() ) {
1021                                                 $success = false;
1022                                         }
1023                                 }
1024                         }
1025                 }
1026
1027                 return $success;
1028         }
1029
1030         /**
1031          * Call a function with each open connection object
1032          * @param callable $callback
1033          * @param array $params
1034          */
1035         function forEachOpenConnection( $callback, $params = array() ) {
1036                 foreach ( $this->mConns as $conns2 ) {
1037                         foreach ( $conns2 as $conns3 ) {
1038                                 foreach ( $conns3 as $conn ) {
1039                                         $mergedParams = array_merge( array( $conn ), $params );
1040                                         call_user_func_array( $callback, $mergedParams );
1041                                 }
1042                         }
1043                 }
1044         }
1045
1046         /**
1047          * Get the hostname and lag time of the most-lagged slave.
1048          * This is useful for maintenance scripts that need to throttle their updates.
1049          * May attempt to open connections to slaves on the default DB. If there is
1050          * no lag, the maximum lag will be reported as -1.
1051          *
1052          * @param bool|string $wiki Wiki ID, or false for the default database
1053          * @return array ( host, max lag, index of max lagged host )
1054          */
1055         function getMaxLag( $wiki = false ) {
1056                 $maxLag = -1;
1057                 $host = '';
1058                 $maxIndex = 0;
1059
1060                 if ( $this->getServerCount() <= 1 ) { // no replication = no lag
1061                         return array( $host, $maxLag, $maxIndex );
1062                 }
1063
1064                 // Try to get the max lag info from the server cache
1065                 $key = 'loadbalancer:maxlag:cluster:' . $this->mServers[0]['host'];
1066                 $cache = ObjectCache::newAccelerator( array(), 'hash' );
1067                 $maxLagInfo = $cache->get( $key ); // (host, lag, index)
1068
1069                 // Fallback to connecting to each slave and getting the lag
1070                 if ( !$maxLagInfo ) {
1071                         foreach ( $this->mServers as $i => $conn ) {
1072                                 if ( $i == $this->getWriterIndex() ) {
1073                                         continue; // nothing to check
1074                                 }
1075                                 $conn = false;
1076                                 if ( $wiki === false ) {
1077                                         $conn = $this->getAnyOpenConnection( $i );
1078                                 }
1079                                 if ( !$conn ) {
1080                                         $conn = $this->openConnection( $i, $wiki );
1081                                 }
1082                                 if ( !$conn ) {
1083                                         continue;
1084                                 }
1085                                 $lag = $conn->getLag();
1086                                 if ( $lag > $maxLag ) {
1087                                         $maxLag = $lag;
1088                                         $host = $this->mServers[$i]['host'];
1089                                         $maxIndex = $i;
1090                                 }
1091                         }
1092                         $maxLagInfo = array( $host, $maxLag, $maxIndex );
1093                         $cache->set( $key, $maxLagInfo, 5 );
1094                 }
1095
1096                 return $maxLagInfo;
1097         }
1098
1099         /**
1100          * Get lag time for each server
1101          * Results are cached for a short time in memcached, and indefinitely in the process cache
1102          *
1103          * @param string|bool $wiki
1104          * @return array
1105          */
1106         function getLagTimes( $wiki = false ) {
1107                 # Try process cache
1108                 if ( isset( $this->mLagTimes ) ) {
1109                         return $this->mLagTimes;
1110                 }
1111                 if ( $this->getServerCount() == 1 ) {
1112                         # No replication
1113                         $this->mLagTimes = array( 0 => 0 );
1114                 } else {
1115                         # Send the request to the load monitor
1116                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1117                                 array_keys( $this->mServers ), $wiki );
1118                 }
1119
1120                 return $this->mLagTimes;
1121         }
1122
1123         /**
1124          * Get the lag in seconds for a given connection, or zero if this load
1125          * balancer does not have replication enabled.
1126          *
1127          * This should be used in preference to Database::getLag() in cases where
1128          * replication may not be in use, since there is no way to determine if
1129          * replication is in use at the connection level without running
1130          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1131          * function instead of Database::getLag() avoids a fatal error in this
1132          * case on many installations.
1133          *
1134          * @param DatabaseBase $conn
1135          * @return int
1136          */
1137         function safeGetLag( $conn ) {
1138                 if ( $this->getServerCount() == 1 ) {
1139                         return 0;
1140                 } else {
1141                         return $conn->getLag();
1142                 }
1143         }
1144
1145         /**
1146          * Clear the cache for getLagTimes
1147          */
1148         function clearLagTimeCache() {
1149                 $this->mLagTimes = null;
1150         }
1151 }
1152
1153 /**
1154  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1155  * as well handling deferring the actual network connection until the handle is used
1156  *
1157  * @ingroup Database
1158  * @since 1.22
1159  */
1160 class DBConnRef implements IDatabase {
1161         /** @var LoadBalancer */
1162         protected $lb;
1163
1164         /** @var DatabaseBase|null */
1165         protected $conn;
1166
1167         /** @var array|null */
1168         protected $params;
1169
1170         /**
1171          * @param LoadBalancer $lb
1172          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1173          */
1174         public function __construct( LoadBalancer $lb, $conn ) {
1175                 $this->lb = $lb;
1176                 if ( $conn instanceof DatabaseBase ) {
1177                         $this->conn = $conn;
1178                 } else {
1179                         $this->params = $conn;
1180                 }
1181         }
1182
1183         public function __call( $name, $arguments ) {
1184                 if ( $this->conn === null ) {
1185                         list( $db, $groups, $wiki ) = $this->params;
1186                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1187                 }
1188
1189                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1190         }
1191
1192         function __destruct() {
1193                 if ( $this->conn !== null ) {
1194                         $this->lb->reuseConnection( $this->conn );
1195                 }
1196         }
1197 }