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         private $mErrorConnection;
  33         private $mReadIndex, $mAllowLagged;
  34         private $mWaitForPos, $mWaitTimeout;
  35         private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  36         private $mParentInfo, $mLagTimes;
  37         private $mLoadMonitorClass, $mLoadMonitor;
  38
  39         /**
  40          * @param array $params with keys:
  41          *    servers           Required. Array of server info structures.
  42          *    masterWaitTimeout Replication lag wait timeout
  43          *    loadMonitor       Name of a class used to fetch server lag and load.
  44          * @throws MWException
  45          */
  46         function __construct( $params ) {
  47                 if ( !isset( $params['servers'] ) ) {
  48                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  49                 }
  50                 $this->mServers = $params['servers'];
  51
  52                 if ( isset( $params['waitTimeout'] ) ) {
  53                         $this->mWaitTimeout = $params['waitTimeout'];
  54                 } else {
  55                         $this->mWaitTimeout = 10;
  56                 }
  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 = 'LoadMonitor_MySQL';
  76                         } else {
  77                                 $this->mLoadMonitorClass = 'LoadMonitor_Null';
  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                 return $this->mLoadMonitor;
 105         }
 106
 107         /**
 108          * Get or set arbitrary data used by the parent object, usually an LBFactory
 109          * @param $x
 110          * @return Mixed
 111          */
 112         function parentInfo( $x = null ) {
 113                 return wfSetVar( $this->mParentInfo, $x );
 114         }
 115
 116         /**
 117          * Given an array of non-normalised probabilities, this function will select
 118          * an element and return the appropriate key
 119          *
 120          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 121          *
 122          * @param $weights array
 123          *
 124          * @return bool|int|string
 125          */
 126         function pickRandom( $weights ) {
 127                 return ArrayUtils::pickRandom( $weights );
 128         }
 129
 130         /**
 131          * @param $loads array
 132          * @param $wiki bool
 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\n" );
 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)\n" );
 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 $group bool
 180          * @param $wiki bool
 181          * @throws MWException
 182          * @return bool|int|string
 183          */
 184         function getReaderIndex( $group = false, $wiki = false ) {
 185                 global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $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 and $this->mReadIndex >= 0 ) {
 196                         # Shortcut if generic reader exists already
 197                         return $this->mReadIndex;
 198                 }
 199
 200                 wfProfileIn( __METHOD__ );
 201
 202                 $totalElapsed = 0;
 203
 204                 # convert from seconds to microseconds
 205                 $timeout = $wgDBClusterTimeout * 1e6;
 206
 207                 # Find the relevant load array
 208                 if ( $group !== false ) {
 209                         if ( isset( $this->mGroupLoads[$group] ) ) {
 210                                 $nonErrorLoads = $this->mGroupLoads[$group];
 211                         } else {
 212                                 # No loads for this group, return false and the caller can use some other group
 213                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 214                                 wfProfileOut( __METHOD__ );
 215                                 return false;
 216                         }
 217                 } else {
 218                         $nonErrorLoads = $this->mLoads;
 219                 }
 220
 221                 if ( !$nonErrorLoads ) {
 222                         wfProfileOut( __METHOD__ );
 223                         throw new MWException( "Empty server array given to LoadBalancer" );
 224                 }
 225
 226                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 227                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 228
 229                 $laggedSlaveMode = false;
 230
 231                 # First try quickly looking through the available servers for a server that
 232                 # meets our criteria
 233                 do {
 234                         $totalThreadsConnected = 0;
 235                         $overloadedServers = 0;
 236                         $currentLoads = $nonErrorLoads;
 237                         while ( count( $currentLoads ) ) {
 238                                 if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 239                                         $i = ArrayUtils::pickRandom( $currentLoads );
 240                                 } else {
 241                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 242                                         if ( $i === false && count( $currentLoads ) != 0 ) {
 243                                                 # All slaves lagged. Switch to read-only mode
 244                                                 wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 245                                                 $wgReadOnly = 'The database has been automatically locked ' .
 246                                                         'while the slave database servers catch up to the master';
 247                                                 $i = ArrayUtils::pickRandom( $currentLoads );
 248                                                 $laggedSlaveMode = true;
 249                                         }
 250                                 }
 251
 252                                 if ( $i === false ) {
 253                                         # pickRandom() returned false
 254                                         # This is permanent and means the configuration or the load monitor
 255                                         # wants us to return false.
 256                                         wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 257                                         wfProfileOut( __METHOD__ );
 258                                         return false;
 259                                 }
 260
 261                                 wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 262                                 $conn = $this->openConnection( $i, $wiki );
 263
 264                                 if ( !$conn ) {
 265                                         wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 266                                         unset( $nonErrorLoads[$i] );
 267                                         unset( $currentLoads[$i] );
 268                                         continue;
 269                                 }
 270
 271                                 // Perform post-connection backoff
 272                                 $threshold = isset( $this->mServers[$i]['max threads'] )
 273                                         ? $this->mServers[$i]['max threads'] : false;
 274                                 $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 275
 276                                 // Decrement reference counter, we are finished with this connection.
 277                                 // It will be incremented for the caller later.
 278                                 if ( $wiki !== false ) {
 279                                         $this->reuseConnection( $conn );
 280                                 }
 281
 282                                 if ( $backoff ) {
 283                                         # Post-connection overload, don't use this server for now
 284                                         $totalThreadsConnected += $backoff;
 285                                         $overloadedServers++;
 286                                         unset( $currentLoads[$i] );
 287                                 } else {
 288                                         # Return this server
 289                                         break 2;
 290                                 }
 291                         }
 292
 293                         # No server found yet
 294                         $i = false;
 295
 296                         # If all servers were down, quit now
 297                         if ( !count( $nonErrorLoads ) ) {
 298                                 wfDebugLog( 'connect', "All servers down\n" );
 299                                 break;
 300                         }
 301
 302                         # Some servers must have been overloaded
 303                         if ( $overloadedServers == 0 ) {
 304                                 throw new MWException( __METHOD__ . ": unexpectedly found no overloaded servers" );
 305                         }
 306                         # Back off for a while
 307                         # Scale the sleep time by the number of connected threads, to produce a
 308                         # roughly constant global poll rate
 309                         $avgThreads = $totalThreadsConnected / $overloadedServers;
 310                         $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 311                 } while ( $totalElapsed < $timeout );
 312
 313                 if ( $totalElapsed >= $timeout ) {
 314                         wfDebugLog( 'connect', "All servers busy\n" );
 315                         $this->mErrorConnection = false;
 316                         $this->mLastError = 'All servers busy';
 317                 }
 318
 319                 if ( $i !== false ) {
 320                         # Slave connection successful
 321                         # Wait for the session master pos for a short time
 322                         if ( $this->mWaitForPos && $i > 0 ) {
 323                                 if ( !$this->doWait( $i ) ) {
 324                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 325                                 }
 326                         }
 327                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
 328                                 $this->mReadIndex = $i;
 329                         }
 330                 }
 331                 wfProfileOut( __METHOD__ );
 332                 return $i;
 333         }
 334
 335         /**
 336          * Wait for a specified number of microseconds, and return the period waited
 337          * @param $t int
 338          * @return int
 339          */
 340         function sleep( $t ) {
 341                 wfProfileIn( __METHOD__ );
 342                 wfDebug( __METHOD__ . ": waiting $t us\n" );
 343                 usleep( $t );
 344                 wfProfileOut( __METHOD__ );
 345                 return $t;
 346         }
 347
 348         /**
 349          * Set the master wait position
 350          * If a DB_SLAVE connection has been opened already, waits
 351          * Otherwise sets a variable telling it to wait if such a connection is opened
 352          * @param $pos DBMasterPos
 353          */
 354         public function waitFor( $pos ) {
 355                 wfProfileIn( __METHOD__ );
 356                 $this->mWaitForPos = $pos;
 357                 $i = $this->mReadIndex;
 358
 359                 if ( $i > 0 ) {
 360                         if ( !$this->doWait( $i ) ) {
 361                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 362                                 $this->mLaggedSlaveMode = true;
 363                         }
 364                 }
 365                 wfProfileOut( __METHOD__ );
 366         }
 367
 368         /**
 369          * Set the master wait position and wait for ALL slaves to catch up to it
 370          * @param $pos DBMasterPos
 371          */
 372         public function waitForAll( $pos ) {
 373                 wfProfileIn( __METHOD__ );
 374                 $this->mWaitForPos = $pos;
 375                 $serverCount = count( $this->mServers );
 376                 for ( $i = 1; $i < $serverCount; $i++ ) {
 377                         if ( $this->mLoads[$i] > 0 ) {
 378                                 $this->doWait( $i, true );
 379                         }
 380                 }
 381                 wfProfileOut( __METHOD__ );
 382         }
 383
 384         /**
 385          * Get any open connection to a given server index, local or foreign
 386          * Returns false if there is no connection open
 387          *
 388          * @param $i int
 389          * @return DatabaseBase|bool False on failure
 390          */
 391         function getAnyOpenConnection( $i ) {
 392                 foreach ( $this->mConns as $conns ) {
 393                         if ( !empty( $conns[$i] ) ) {
 394                                 return reset( $conns[$i] );
 395                         }
 396                 }
 397                 return false;
 398         }
 399
 400         /**
 401          * Wait for a given slave to catch up to the master pos stored in $this
 402          * @param $index
 403          * @param $open bool
 404          * @return bool
 405          */
 406         protected function doWait( $index, $open = false ) {
 407                 # Find a connection to wait on
 408                 $conn = $this->getAnyOpenConnection( $index );
 409                 if ( !$conn ) {
 410                         if ( !$open ) {
 411                                 wfDebug( __METHOD__ . ": no connection open\n" );
 412                                 return false;
 413                         } else {
 414                                 $conn = $this->openConnection( $index, '' );
 415                                 if ( !$conn ) {
 416                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 417                                         return false;
 418                                 }
 419                         }
 420                 }
 421
 422                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 423                 $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 424
 425                 if ( $result == -1 || is_null( $result ) ) {
 426                         # Timed out waiting for slave, use master instead
 427                         wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 428                         return false;
 429                 } else {
 430                         wfDebug( __METHOD__ . ": Done\n" );
 431                         return true;
 432                 }
 433         }
 434
 435         /**
 436          * Get a connection by index
 437          * This is the main entry point for this class.
 438          *
 439          * @param $i Integer: server index
 440          * @param array $groups query groups
 441          * @param bool|string $wiki Wiki ID
 442          *
 443          * @throws MWException
 444          * @return DatabaseBase
 445          */
 446         public function &getConnection( $i, $groups = array(), $wiki = false ) {
 447                 wfProfileIn( __METHOD__ );
 448
 449                 if ( $i == DB_LAST ) {
 450                         wfProfileOut( __METHOD__ );
 451                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 452                 } elseif ( $i === null || $i === false ) {
 453                         wfProfileOut( __METHOD__ );
 454                         throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 455                 }
 456
 457                 if ( $wiki === wfWikiID() ) {
 458                         $wiki = false;
 459                 }
 460
 461                 # Query groups
 462                 if ( $i == DB_MASTER ) {
 463                         $i = $this->getWriterIndex();
 464                 } elseif ( !is_array( $groups ) ) {
 465                         $groupIndex = $this->getReaderIndex( $groups, $wiki );
 466                         if ( $groupIndex !== false ) {
 467                                 $serverName = $this->getServerName( $groupIndex );
 468                                 wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 469                                 $i = $groupIndex;
 470                         }
 471                 } else {
 472                         foreach ( $groups as $group ) {
 473                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 474                                 if ( $groupIndex !== false ) {
 475                                         $serverName = $this->getServerName( $groupIndex );
 476                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 477                                         $i = $groupIndex;
 478                                         break;
 479                                 }
 480                         }
 481                 }
 482
 483                 # Operation-based index
 484                 if ( $i == DB_SLAVE ) {
 485                         $this->mLastError = 'Unknown error'; // reset error string
 486                         $i = $this->getReaderIndex( false, $wiki );
 487                         # Couldn't find a working server in getReaderIndex()?
 488                         if ( $i === false ) {
 489                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 490                                 wfProfileOut( __METHOD__ );
 491                                 return $this->reportConnectionError();
 492                         }
 493                 }
 494
 495                 # Now we have an explicit index into the servers array
 496                 $conn = $this->openConnection( $i, $wiki );
 497                 if ( !$conn ) {
 498                         wfProfileOut( __METHOD__ );
 499                         return $this->reportConnectionError();
 500                 }
 501
 502                 wfProfileOut( __METHOD__ );
 503                 return $conn;
 504         }
 505
 506         /**
 507          * Mark a foreign connection as being available for reuse under a different
 508          * DB name or prefix. This mechanism is reference-counted, and must be called
 509          * the same number of times as getConnection() to work.
 510          *
 511          * @param DatabaseBase $conn
 512          * @throws MWException
 513          */
 514         public function reuseConnection( $conn ) {
 515                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 516                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 517                 $dbName = $conn->getDBname();
 518                 $prefix = $conn->tablePrefix();
 519                 if ( strval( $prefix ) !== '' ) {
 520                         $wiki = "$dbName-$prefix";
 521                 } else {
 522                         $wiki = $dbName;
 523                 }
 524                 if ( $serverIndex === null || $refCount === null ) {
 525                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 526                         /**
 527                          * This can happen in code like:
 528                          *   foreach ( $dbs as $db ) {
 529                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 530                          *     ...
 531                          *     $lb->reuseConnection( $conn );
 532                          *   }
 533                          * When a connection to the local DB is opened in this way, reuseConnection()
 534                          * should be ignored
 535                          */
 536                         return;
 537                 }
 538                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 539                         throw new MWException( __METHOD__ . ": connection not found, has the connection been freed already?" );
 540                 }
 541                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 542                 if ( $refCount <= 0 ) {
 543                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 544                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 545                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 546                 } else {
 547                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 548                 }
 549         }
 550
 551         /**
 552          * Get a database connection handle reference
 553          *
 554          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 555          *
 556          * @see LoadBalancer::getConnection() for parameter information
 557          *
 558          * @param integer $db
 559          * @param mixed $groups
 560          * @param string $wiki
 561          * @return DBConnRef
 562          */
 563         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 564                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 565         }
 566
 567         /**
 568          * Get a database connection handle reference without connecting yet
 569          *
 570          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 571          *
 572          * @see LoadBalancer::getConnection() for parameter information
 573          *
 574          * @param integer $db
 575          * @param mixed $groups
 576          * @param string $wiki
 577          * @return DBConnRef
 578          */
 579         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 580                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 581         }
 582
 583         /**
 584          * Open a connection to the server given by the specified index
 585          * Index must be an actual index into the array.
 586          * If the server is already open, returns it.
 587          *
 588          * On error, returns false, and the connection which caused the
 589          * error will be available via $this->mErrorConnection.
 590          *
 591          * @param $i Integer server index
 592          * @param string $wiki wiki ID to open
 593          * @return DatabaseBase
 594          *
 595          * @access private
 596          */
 597         function openConnection( $i, $wiki = false ) {
 598                 wfProfileIn( __METHOD__ );
 599                 if ( $wiki !== false ) {
 600                         $conn = $this->openForeignConnection( $i, $wiki );
 601                         wfProfileOut( __METHOD__ );
 602                         return $conn;
 603                 }
 604                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 605                         $conn = $this->mConns['local'][$i][0];
 606                 } else {
 607                         $server = $this->mServers[$i];
 608                         $server['serverIndex'] = $i;
 609                         $conn = $this->reallyOpenConnection( $server, false );
 610                         if ( $conn->isOpen() ) {
 611                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 612                                 $this->mConns['local'][$i][0] = $conn;
 613                         } else {
 614                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 615                                 $this->mErrorConnection = $conn;
 616                                 $conn = false;
 617                         }
 618                 }
 619                 wfProfileOut( __METHOD__ );
 620                 return $conn;
 621         }
 622
 623         /**
 624          * Open a connection to a foreign DB, or return one if it is already open.
 625          *
 626          * Increments a reference count on the returned connection which locks the
 627          * connection to the requested wiki. This reference count can be
 628          * decremented by calling reuseConnection().
 629          *
 630          * If a connection is open to the appropriate server already, but with the wrong
 631          * database, it will be switched to the right database and returned, as long as
 632          * it has been freed first with reuseConnection().
 633          *
 634          * On error, returns false, and the connection which caused the
 635          * error will be available via $this->mErrorConnection.
 636          *
 637          * @param $i Integer: server index
 638          * @param string $wiki wiki ID to open
 639          * @return DatabaseBase
 640          */
 641         function openForeignConnection( $i, $wiki ) {
 642                 wfProfileIn( __METHOD__ );
 643                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 644                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 645                         // Reuse an already-used connection
 646                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 647                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 648                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 649                         // Reuse a free connection for the same wiki
 650                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 651                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 652                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 653                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 654                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 655                         // Reuse a connection from another wiki
 656                         $conn = reset( $this->mConns['foreignFree'][$i] );
 657                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 658
 659                         if ( !$conn->selectDB( $dbName ) ) {
 660                                 $this->mLastError = "Error selecting database $dbName on server " .
 661                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 662                                 $this->mErrorConnection = $conn;
 663                                 $conn = false;
 664                         } else {
 665                                 $conn->tablePrefix( $prefix );
 666                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 667                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 668                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 669                         }
 670                 } else {
 671                         // Open a new connection
 672                         $server = $this->mServers[$i];
 673                         $server['serverIndex'] = $i;
 674                         $server['foreignPoolRefCount'] = 0;
 675                         $server['foreign'] = true;
 676                         $conn = $this->reallyOpenConnection( $server, $dbName );
 677                         if ( !$conn->isOpen() ) {
 678                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 679                                 $this->mErrorConnection = $conn;
 680                                 $conn = false;
 681                         } else {
 682                                 $conn->tablePrefix( $prefix );
 683                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 684                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 685                         }
 686                 }
 687
 688                 // Increment reference count
 689                 if ( $conn ) {
 690                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 691                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 692                 }
 693                 wfProfileOut( __METHOD__ );
 694                 return $conn;
 695         }
 696
 697         /**
 698          * Test if the specified index represents an open connection
 699          *
 700          * @param $index Integer: server index
 701          * @access private
 702          * @return bool
 703          */
 704         function isOpen( $index ) {
 705                 if ( !is_integer( $index ) ) {
 706                         return false;
 707                 }
 708                 return (bool)$this->getAnyOpenConnection( $index );
 709         }
 710
 711         /**
 712          * Really opens a connection. Uncached.
 713          * Returns a Database object whether or not the connection was successful.
 714          * @access private
 715          *
 716          * @param $server
 717          * @param $dbNameOverride bool
 718          * @throws MWException
 719          * @return DatabaseBase
 720          */
 721         function reallyOpenConnection( $server, $dbNameOverride = false ) {
 722                 if ( !is_array( $server ) ) {
 723                         throw new MWException( 'You must update your load-balancing configuration. ' .
 724                                 'See DefaultSettings.php entry for $wgDBservers.' );
 725                 }
 726
 727                 if ( $dbNameOverride !== false ) {
 728                         $server['dbname'] = $dbNameOverride;
 729                 }
 730
 731                 # Create object
 732                 try {
 733                         $db = DatabaseBase::factory( $server['type'], $server );
 734                 } catch ( DBConnectionError $e ) {
 735                         // FIXME: This is probably the ugliest thing I have ever done to
 736                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 737                         $db = $e->db;
 738                 }
 739
 740                 $db->setLBInfo( $server );
 741                 if ( isset( $server['fakeSlaveLag'] ) ) {
 742                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 743                 }
 744                 if ( isset( $server['fakeMaster'] ) ) {
 745                         $db->setFakeMaster( true );
 746                 }
 747                 return $db;
 748         }
 749
 750         /**
 751          * @throws DBConnectionError
 752          * @return bool
 753          */
 754         private function reportConnectionError() {
 755                 $conn = $this->mErrorConnection; // The connection which caused the error
 756
 757                 if ( !is_object( $conn ) ) {
 758                         // No last connection, probably due to all servers being too busy
 759                         wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 760
 761                         // If all servers were busy, mLastError will contain something sensible
 762                         throw new DBConnectionError( null, $this->mLastError );
 763                 } else {
 764                         $server = $conn->getProperty( 'mServer' );
 765                         wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 766                         $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 767                 }
 768                 return false; /* not reached */
 769         }
 770
 771         /**
 772          * @return int
 773          */
 774         function getWriterIndex() {
 775                 return 0;
 776         }
 777
 778         /**
 779          * Returns true if the specified index is a valid server index
 780          *
 781          * @param $i
 782          * @return bool
 783          */
 784         function haveIndex( $i ) {
 785                 return array_key_exists( $i, $this->mServers );
 786         }
 787
 788         /**
 789          * Returns true if the specified index is valid and has non-zero load
 790          *
 791          * @param $i
 792          * @return bool
 793          */
 794         function isNonZeroLoad( $i ) {
 795                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 796         }
 797
 798         /**
 799          * Get the number of defined servers (not the number of open connections)
 800          *
 801          * @return int
 802          */
 803         function getServerCount() {
 804                 return count( $this->mServers );
 805         }
 806
 807         /**
 808          * Get the host name or IP address of the server with the specified index
 809          * Prefer a readable name if available.
 810          * @param $i
 811          * @return string
 812          */
 813         function getServerName( $i ) {
 814                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 815                         return $this->mServers[$i]['hostName'];
 816                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 817                         return $this->mServers[$i]['host'];
 818                 } else {
 819                         return '';
 820                 }
 821         }
 822
 823         /**
 824          * Return the server info structure for a given index, or false if the index is invalid.
 825          * @param $i
 826          * @return bool
 827          */
 828         function getServerInfo( $i ) {
 829                 if ( isset( $this->mServers[$i] ) ) {
 830                         return $this->mServers[$i];
 831                 } else {
 832                         return false;
 833                 }
 834         }
 835
 836         /**
 837          * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 838          * @param $i
 839          * @param $serverInfo
 840          */
 841         function setServerInfo( $i, $serverInfo ) {
 842                 $this->mServers[$i] = $serverInfo;
 843         }
 844
 845         /**
 846          * Get the current master position for chronology control purposes
 847          * @return mixed
 848          */
 849         function getMasterPos() {
 850                 # If this entire request was served from a slave without opening a connection to the
 851                 # master (however unlikely that may be), then we can fetch the position from the slave.
 852                 $masterConn = $this->getAnyOpenConnection( 0 );
 853                 if ( !$masterConn ) {
 854                         $serverCount = count( $this->mServers );
 855                         for ( $i = 1; $i < $serverCount; $i++ ) {
 856                                 $conn = $this->getAnyOpenConnection( $i );
 857                                 if ( $conn ) {
 858                                         wfDebug( "Master pos fetched from slave\n" );
 859                                         return $conn->getSlavePos();
 860                                 }
 861                         }
 862                 } else {
 863                         wfDebug( "Master pos fetched from master\n" );
 864                         return $masterConn->getMasterPos();
 865                 }
 866                 return false;
 867         }
 868
 869         /**
 870          * Close all open connections
 871          */
 872         function closeAll() {
 873                 foreach ( $this->mConns as $conns2 ) {
 874                         foreach ( $conns2 as $conns3 ) {
 875                                 foreach ( $conns3 as $conn ) {
 876                                         $conn->close();
 877                                 }
 878                         }
 879                 }
 880                 $this->mConns = array(
 881                         'local' => array(),
 882                         'foreignFree' => array(),
 883                         'foreignUsed' => array(),
 884                 );
 885         }
 886
 887         /**
 888          * Deprecated function, typo in function name
 889          *
 890          * @deprecated in 1.18
 891          * @param $conn
 892          */
 893         function closeConnecton( $conn ) {
 894                 wfDeprecated( __METHOD__, '1.18' );
 895                 $this->closeConnection( $conn );
 896         }
 897
 898         /**
 899          * Close a connection
 900          * Using this function makes sure the LoadBalancer knows the connection is closed.
 901          * If you use $conn->close() directly, the load balancer won't update its state.
 902          * @param $conn DatabaseBase
 903          */
 904         function closeConnection( $conn ) {
 905                 $done = false;
 906                 foreach ( $this->mConns as $i1 => $conns2 ) {
 907                         foreach ( $conns2 as $i2 => $conns3 ) {
 908                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 909                                         if ( $conn === $candidateConn ) {
 910                                                 $conn->close();
 911                                                 unset( $this->mConns[$i1][$i2][$i3] );
 912                                                 $done = true;
 913                                                 break;
 914                                         }
 915                                 }
 916                         }
 917                 }
 918                 if ( !$done ) {
 919                         $conn->close();
 920                 }
 921         }
 922
 923         /**
 924          * Commit transactions on all open connections
 925          */
 926         function commitAll() {
 927                 foreach ( $this->mConns as $conns2 ) {
 928                         foreach ( $conns2 as $conns3 ) {
 929                                 foreach ( $conns3 as $conn ) {
 930                                         if ( $conn->trxLevel() ) {
 931                                                 $conn->commit( __METHOD__, 'flush' );
 932                                         }
 933                                 }
 934                         }
 935                 }
 936         }
 937
 938         /**
 939          *  Issue COMMIT only on master, only if queries were done on connection
 940          */
 941         function commitMasterChanges() {
 942                 // Always 0, but who knows.. :)
 943                 $masterIndex = $this->getWriterIndex();
 944                 foreach ( $this->mConns as $conns2 ) {
 945                         if ( empty( $conns2[$masterIndex] ) ) {
 946                                 continue;
 947                         }
 948                         foreach ( $conns2[$masterIndex] as $conn ) {
 949                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 950                                         $conn->commit( __METHOD__, 'flush' );
 951                                 }
 952                         }
 953                 }
 954         }
 955
 956         /**
 957          * @param $value null
 958          * @return Mixed
 959          */
 960         function waitTimeout( $value = null ) {
 961                 return wfSetVar( $this->mWaitTimeout, $value );
 962         }
 963
 964         /**
 965          * @return bool
 966          */
 967         function getLaggedSlaveMode() {
 968                 return $this->mLaggedSlaveMode;
 969         }
 970
 971         /**
 972          * Disables/enables lag checks
 973          * @param $mode null
 974          * @return bool
 975          */
 976         function allowLagged( $mode = null ) {
 977                 if ( $mode === null ) {
 978                         return $this->mAllowLagged;
 979                 }
 980                 $this->mAllowLagged = $mode;
 981                 return $this->mAllowLagged;
 982         }
 983
 984         /**
 985          * @return bool
 986          */
 987         function pingAll() {
 988                 $success = true;
 989                 foreach ( $this->mConns as $conns2 ) {
 990                         foreach ( $conns2 as $conns3 ) {
 991                                 foreach ( $conns3 as $conn ) {
 992                                         if ( !$conn->ping() ) {
 993                                                 $success = false;
 994                                         }
 995                                 }
 996                         }
 997                 }
 998                 return $success;
 999         }
1000
1001         /**
1002          * Call a function with each open connection object
1003          * @param $callback
1004          * @param array $params
1005          */
1006         function forEachOpenConnection( $callback, $params = array() ) {
1007                 foreach ( $this->mConns as $conns2 ) {
1008                         foreach ( $conns2 as $conns3 ) {
1009                                 foreach ( $conns3 as $conn ) {
1010                                         $mergedParams = array_merge( array( $conn ), $params );
1011                                         call_user_func_array( $callback, $mergedParams );
1012                                 }
1013                         }
1014                 }
1015         }
1016
1017         /**
1018          * Get the hostname and lag time of the most-lagged slave.
1019          * This is useful for maintenance scripts that need to throttle their updates.
1020          * May attempt to open connections to slaves on the default DB. If there is
1021          * no lag, the maximum lag will be reported as -1.
1022          *
1023          * @param string $wiki Wiki ID, or false for the default database
1024          *
1025          * @return array ( host, max lag, index of max lagged host )
1026          */
1027         function getMaxLag( $wiki = false ) {
1028                 $maxLag = -1;
1029                 $host = '';
1030                 $maxIndex = 0;
1031                 if ( $this->getServerCount() > 1 ) { // no replication = no lag
1032                         foreach ( $this->mServers as $i => $conn ) {
1033                                 $conn = false;
1034                                 if ( $wiki === false ) {
1035                                         $conn = $this->getAnyOpenConnection( $i );
1036                                 }
1037                                 if ( !$conn ) {
1038                                         $conn = $this->openConnection( $i, $wiki );
1039                                 }
1040                                 if ( !$conn ) {
1041                                         continue;
1042                                 }
1043                                 $lag = $conn->getLag();
1044                                 if ( $lag > $maxLag ) {
1045                                         $maxLag = $lag;
1046                                         $host = $this->mServers[$i]['host'];
1047                                         $maxIndex = $i;
1048                                 }
1049                         }
1050                 }
1051                 return array( $host, $maxLag, $maxIndex );
1052         }
1053
1054         /**
1055          * Get lag time for each server
1056          * Results are cached for a short time in memcached, and indefinitely in the process cache
1057          *
1058          * @param $wiki
1059          *
1060          * @return array
1061          */
1062         function getLagTimes( $wiki = false ) {
1063                 # Try process cache
1064                 if ( isset( $this->mLagTimes ) ) {
1065                         return $this->mLagTimes;
1066                 }
1067                 if ( $this->getServerCount() == 1 ) {
1068                         # No replication
1069                         $this->mLagTimes = array( 0 => 0 );
1070                 } else {
1071                         # Send the request to the load monitor
1072                         $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1073                                 array_keys( $this->mServers ), $wiki );
1074                 }
1075                 return $this->mLagTimes;
1076         }
1077
1078         /**
1079          * Get the lag in seconds for a given connection, or zero if this load
1080          * balancer does not have replication enabled.
1081          *
1082          * This should be used in preference to Database::getLag() in cases where
1083          * replication may not be in use, since there is no way to determine if
1084          * replication is in use at the connection level without running
1085          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1086          * function instead of Database::getLag() avoids a fatal error in this
1087          * case on many installations.
1088          *
1089          * @param $conn DatabaseBase
1090          *
1091          * @return int
1092          */
1093         function safeGetLag( $conn ) {
1094                 if ( $this->getServerCount() == 1 ) {
1095                         return 0;
1096                 } else {
1097                         return $conn->getLag();
1098                 }
1099         }
1100
1101         /**
1102          * Clear the cache for getLagTimes
1103          */
1104         function clearLagTimeCache() {
1105                 $this->mLagTimes = null;
1106         }
1107 }
1108
1109 /**
1110  * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1111  * as well handling deferring the actual network connection until the handle is used
1112  *
1113  * @ingroup Database
1114  * @since 1.22
1115  */
1116 class DBConnRef implements IDatabase {
1117         /** @var LoadBalancer */
1118         protected $lb;
1119         /** @var DatabaseBase|null */
1120         protected $conn;
1121         /** @var Array|null */
1122         protected $params;
1123
1124         /**
1125          * @param $lb LoadBalancer
1126          * @param $conn DatabaseBase|array Connection or (server index, group, wiki ID) array
1127          */
1128         public function __construct( LoadBalancer $lb, $conn ) {
1129                 $this->lb = $lb;
1130                 if ( $conn instanceof DatabaseBase ) {
1131                         $this->conn = $conn;
1132                 } else {
1133                         $this->params = $conn;
1134                 }
1135         }
1136
1137         public function __call( $name, $arguments ) {
1138                 if ( $this->conn === null ) {
1139                         list( $db, $groups, $wiki ) = $this->params;
1140                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1141                 }
1142                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1143         }
1144
1145         function __destruct() {
1146                 if ( $this->conn !== null ) {
1147                         $this->lb->reuseConnection( $this->conn );
1148                 }
1149         }
1150 }