includes/db/ChronologyProtector.php

   1 <?php
   2 /**
   3  * Generator of database load balancing objects.
   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  * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
  26  * Kind of like Hawking's [[Chronology Protection Agency]].
  27  */
  28 class ChronologyProtector {
  29         var $startupPos;
  30         var $shutdownPos = array();
  31
  32         /**
  33          * Initialise a LoadBalancer to give it appropriate chronology protection.
  34          *
  35          * @param $lb LoadBalancer
  36          */
  37         function initLB( $lb ) {
  38                 if ( $this->startupPos === null ) {
  39                         if ( !empty( $_SESSION[__CLASS__] ) ) {
  40                                 $this->startupPos = $_SESSION[__CLASS__];
  41                         }
  42                 }
  43                 if ( !$this->startupPos ) {
  44                         return;
  45                 }
  46                 $masterName = $lb->getServerName( 0 );
  47
  48                 if ( $lb->getServerCount() > 1 && !empty( $this->startupPos[$masterName] ) ) {
  49                         $info = $lb->parentInfo();
  50                         $pos = $this->startupPos[$masterName];
  51                         wfDebug( __METHOD__ . ": LB " . $info['id'] . " waiting for master pos $pos\n" );
  52                         $lb->waitFor( $this->startupPos[$masterName] );
  53                 }
  54         }
  55
  56         /**
  57          * Notify the ChronologyProtector that the LoadBalancer is about to shut
  58          * down. Saves replication positions.
  59          *
  60          * @param $lb LoadBalancer
  61          */
  62         function shutdownLB( $lb ) {
  63                 // Don't start a session, don't bother with non-replicated setups
  64                 if ( strval( session_id() ) == '' || $lb->getServerCount() <= 1 ) {
  65                         return;
  66                 }
  67                 $masterName = $lb->getServerName( 0 );
  68                 if ( isset( $this->shutdownPos[$masterName] ) ) {
  69                         // Already done
  70                         return;
  71                 }
  72                 // Only save the position if writes have been done on the connection
  73                 $db = $lb->getAnyOpenConnection( 0 );
  74                 $info = $lb->parentInfo();
  75                 if ( !$db || !$db->doneWrites() ) {
  76                         wfDebug( __METHOD__ . ": LB {$info['id']}, no writes done\n" );
  77                         return;
  78                 }
  79                 $pos = $db->getMasterPos();
  80                 wfDebug( __METHOD__ . ": LB {$info['id']} has master pos $pos\n" );
  81                 $this->shutdownPos[$masterName] = $pos;
  82         }
  83
  84         /**
  85          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
  86          * May commit chronology data to persistent storage.
  87          */
  88         function shutdown() {
  89                 if ( session_id() != '' && count( $this->shutdownPos ) ) {
  90                         wfDebug( __METHOD__ . ": saving master pos for " .
  91                                 count( $this->shutdownPos ) . " master(s)\n" );
  92                         $_SESSION[__CLASS__] = $this->shutdownPos;
  93                 }
  94         }
  95 }