includes/deferred/WANCacheReapUpdate.php

   1 <?php
   2
   3 use Psr\Log\LoggerInterface;
   4 use Wikimedia\Rdbms\IDatabase;
   5
   6 /**
   7  * Class for fixing stale WANObjectCache keys using a purge event source
   8  *
   9  * This is useful for expiring keys that missed fire-and-forget purges. This uses the
  10  * recentchanges table as a reliable stream to make certain keys reach consistency
  11  * as soon as the underlying replica database catches up. These means that critical
  12  * keys will not escape getting purged simply due to brief hiccups in the network,
  13  * which are more prone to happen accross datacenters.
  14  *
  15  * ----
  16  * "I was trying to cheat death. I was only trying to surmount for a little while the
  17  * darkness that all my life I surely knew was going to come rolling in on me some day
  18  * and obliterate me. I was only to stay alive a little brief while longer, after I was
  19  * already gone. To stay in the light, to be with the living, a little while past my time."
  20  *   -- Notes for "Blues of a Lifetime", by [[Cornell Woolrich]]
  21  *
  22  * @since 1.28
  23  */
  24 class WANCacheReapUpdate implements DeferrableUpdate {
  25         /** @var IDatabase */
  26         private $db;
  27         /** @var LoggerInterface */
  28         private $logger;
  29
  30         /**
  31          * @param IDatabase $db
  32          * @param LoggerInterface $logger
  33          */
  34         public function __construct( IDatabase $db, LoggerInterface $logger ) {
  35                 $this->db = $db;
  36                 $this->logger = $logger;
  37         }
  38
  39         function doUpdate() {
  40                 $reaper = new WANObjectCacheReaper(
  41                         ObjectCache::getMainWANInstance(),
  42                         ObjectCache::getLocalClusterInstance(),
  43                         [ $this, 'getTitleChangeEvents' ],
  44                         [ $this, 'getEventAffectedKeys' ],
  45                         [
  46                                 'channel' => 'table:recentchanges:' . $this->db->getWikiID(),
  47                                 'logger' => $this->logger
  48                         ]
  49                 );
  50
  51                 $reaper->invoke( 100 );
  52         }
  53
  54         /**
  55          * @see WANObjectCacheRepear
  56          *
  57          * @param int $start
  58          * @param int $id
  59          * @param int $end
  60          * @param int $limit
  61          * @return TitleValue[]
  62          */
  63         public function getTitleChangeEvents( $start, $id, $end, $limit ) {
  64                 $db = $this->db;
  65                 $encStart = $db->addQuotes( $db->timestamp( $start ) );
  66                 $encEnd = $db->addQuotes( $db->timestamp( $end ) );
  67                 $id = (int)$id; // cast NULL => 0 since rc_id is an integer
  68
  69                 $res = $db->select(
  70                         'recentchanges',
  71                         [ 'rc_namespace', 'rc_title', 'rc_timestamp', 'rc_id' ],
  72                         [
  73                                 $db->makeList( [
  74                                         "rc_timestamp > $encStart",
  75                                         "rc_timestamp = $encStart AND rc_id > " . $db->addQuotes( $id )
  76                                 ], LIST_OR ),
  77                                 "rc_timestamp < $encEnd"
  78                         ],
  79                         __METHOD__,
  80                         [ 'ORDER BY' => 'rc_timestamp ASC, rc_id ASC', 'LIMIT' => $limit ]
  81                 );
  82
  83                 $events = [];
  84                 foreach ( $res as $row ) {
  85                         $events[] = [
  86                                 'id' => (int)$row->rc_id,
  87                                 'pos' => (int)wfTimestamp( TS_UNIX, $row->rc_timestamp ),
  88                                 'item' => new TitleValue( (int)$row->rc_namespace, $row->rc_title )
  89                         ];
  90                 }
  91
  92                 return $events;
  93         }
  94
  95         /**
  96          * Gets a list of important cache keys associated with a title
  97          *
  98          * @see WANObjectCacheRepear
  99          * @param WANObjectCache $cache
 100          * @param TitleValue $t
 101          * @returns string[]
 102          */
 103         public function getEventAffectedKeys( WANObjectCache $cache, TitleValue $t ) {
 104                 /** @var WikiPage[]|LocalFile[]|User[] $entities */
 105                 $entities = [];
 106
 107                 // You can't create a WikiPage for special pages (-1) or other virtual
 108                 // namespaces, but special pages do appear in RC sometimes, e.g. for logs
 109                 // of AbuseFilter filter changes.
 110                 if ( $t->getNamespace() >= 0 ) {
 111                         $entities[] = WikiPage::factory( Title::newFromTitleValue( $t ) );
 112                 }
 113
 114                 if ( $t->inNamespace( NS_FILE ) ) {
 115                         $entities[] = wfLocalFile( $t->getText() );
 116                 }
 117                 if ( $t->inNamespace( NS_USER ) ) {
 118                         $entities[] = User::newFromName( $t->getText(), false );
 119                 }
 120
 121                 $keys = [];
 122                 foreach ( $entities as $entity ) {
 123                         if ( $entity ) {
 124                                 $keys = array_merge( $keys, $entity->getMutableCacheKeys( $cache ) );
 125                         }
 126                 }
 127                 if ( $keys ) {
 128                         $this->logger->debug( __CLASS__ . ': got key(s) ' . implode( ', ', $keys ) );
 129                 }
 130
 131                 return $keys;
 132         }
 133 }