includes/deferred/WANCacheReapUpdate.php

   1 <?php
   2
   3 use Psr\Log\LoggerInterface;
   4
   5 /**
   6  * Class for fixing stale WANObjectCache keys using a purge event source
   7  *
   8  * This is useful for expiring keys that missed fire-and-forget purges. This uses the
   9  * recentchanges table as a reliable stream to make certain keys reach consistency
  10  * as soon as the underlying replica database catches up. These means that critical
  11  * keys will not escape getting purged simply due to brief hiccups in the network,
  12  * which are more prone to happen accross datacenters.
  13  *
  14  * ----
  15  * "I was trying to cheat death. I was only trying to surmount for a little while the
  16  * darkness that all my life I surely knew was going to come rolling in on me some day
  17  * and obliterate me. I was only to stay alive a little brief while longer, after I was
  18  * already gone. To stay in the light, to be with the living, a little while past my time."
  19  *   -- Notes for "Blues of a Lifetime", by [[Cornell Woolrich]]
  20  *
  21  * @since 1.28
  22  */
  23 class WANCacheReapUpdate implements DeferrableUpdate {
  24         /** @var IDatabase */
  25         private $db;
  26         /** @var LoggerInterface */
  27         private $logger;
  28
  29         /**
  30          * @param IDatabase $db
  31          * @param LoggerInterface $logger
  32          */
  33         public function __construct( IDatabase $db, LoggerInterface $logger ) {
  34                 $this->db = $db;
  35                 $this->logger = $logger;
  36         }
  37
  38         function doUpdate() {
  39                 $reaper = new WANObjectCacheReaper(
  40                         ObjectCache::getMainWANInstance(),
  41                         ObjectCache::getLocalClusterInstance(),
  42                         [ $this, 'getTitleChangeEvents' ],
  43                         [ $this, 'getEventAffectedKeys' ],
  44                         [
  45                                 'channel' => 'table:recentchanges:' . $this->db->getWikiID(),
  46                                 'logger' => $this->logger
  47                         ]
  48                 );
  49
  50                 $reaper->invoke( 100 );
  51         }
  52
  53         /**
  54          * @see WANObjectCacheRepear
  55          *
  56          * @param int $start
  57          * @param int $id
  58          * @param int $end
  59          * @param int $limit
  60          * @return TitleValue[]
  61          */
  62         public function getTitleChangeEvents( $start, $id, $end, $limit ) {
  63                 $db = $this->db;
  64                 $encStart = $db->addQuotes( $db->timestamp( $start ) );
  65                 $encEnd = $db->addQuotes( $db->timestamp( $end ) );
  66                 $id = (int)$id; // cast NULL => 0 since rc_id is an integer
  67
  68                 $res = $db->select(
  69                         'recentchanges',
  70                         [ 'rc_namespace', 'rc_title', 'rc_timestamp', 'rc_id' ],
  71                         [
  72                                 $db->makeList( [
  73                                         "rc_timestamp > $encStart",
  74                                         "rc_timestamp = $encStart AND rc_id > " . $db->addQuotes( $id )
  75                                 ], LIST_OR ),
  76                                 "rc_timestamp < $encEnd"
  77                         ],
  78                         __METHOD__,
  79                         [ 'ORDER BY' => 'rc_timestamp ASC, rc_id ASC', 'LIMIT' => $limit ]
  80                 );
  81
  82                 $events = [];
  83                 foreach ( $res as $row ) {
  84                         $events[] = [
  85                                 'id' => (int)$row->rc_id,
  86                                 'pos' => (int)wfTimestamp( TS_UNIX, $row->rc_timestamp ),
  87                                 'item' => new TitleValue( (int)$row->rc_namespace, $row->rc_title )
  88                         ];
  89                 }
  90
  91                 return $events;
  92         }
  93
  94         /**
  95          * Gets a list of important cache keys associated with a title
  96          *
  97          * @see WANObjectCacheRepear
  98          * @param WANObjectCache $cache
  99          * @param TitleValue $t
 100          * @returns string[]
 101          */
 102         public function getEventAffectedKeys( WANObjectCache $cache, TitleValue $t ) {
 103                 /** @var WikiPage[]|LocalFile[]|User[] $entities */
 104                 $entities = [];
 105
 106                 $entities[] = WikiPage::factory( Title::newFromTitleValue( $t ) );
 107                 if ( $t->inNamespace( NS_FILE ) ) {
 108                         $entities[] = wfLocalFile( $t->getText() );
 109                 }
 110                 if ( $t->inNamespace( NS_USER ) ) {
 111                         $entities[] = User::newFromName( $t->getText(), false );
 112                 }
 113
 114                 $keys = [];
 115                 foreach ( $entities as $entity ) {
 116                         if ( $entity ) {
 117                                 $keys = array_merge( $keys, $entity->getMutableCacheKeys( $cache ) );
 118                         }
 119                 }
 120                 if ( $keys ) {
 121                         $this->logger->debug( __CLASS__ . ': got key(s) ' . implode( ', ', $keys ) );
 122                 }
 123
 124                 return $keys;
 125         }
 126 }