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<?php
use Psr\Log\LoggerInterface;
use Wikimedia\Rdbms\IDatabase;
/**
* Class for fixing stale WANObjectCache keys using a purge event source
*
* This is useful for expiring keys that missed fire-and-forget purges. This uses the
* recentchanges table as a reliable stream to make certain keys reach consistency
* as soon as the underlying replica database catches up. These means that critical
* keys will not escape getting purged simply due to brief hiccups in the network,
* which are more prone to happen accross datacenters.
*
* ----
* "I was trying to cheat death. I was only trying to surmount for a little while the
* darkness that all my life I surely knew was going to come rolling in on me some day
* and obliterate me. I was only to stay alive a little brief while longer, after I was
* already gone. To stay in the light, to be with the living, a little while past my time."
* -- Notes for "Blues of a Lifetime", by [[Cornell Woolrich]]
*
* @since 1.28
*/
class WANCacheReapUpdate implements DeferrableUpdate {
/** @var IDatabase */
private $db;
/** @var LoggerInterface */
private $logger;
/**
* @param IDatabase $db
* @param LoggerInterface $logger
*/
public function __construct( IDatabase $db, LoggerInterface $logger ) {
$this->db = $db;
$this->logger = $logger;
}
function doUpdate() {
$reaper = new WANObjectCacheReaper(
ObjectCache::getMainWANInstance(),
ObjectCache::getLocalClusterInstance(),
[ $this, 'getTitleChangeEvents' ],
[ $this, 'getEventAffectedKeys' ],
[
'channel' => 'table:recentchanges:' . $this->db->getDomainID(),
'logger' => $this->logger
]
);
$reaper->invoke( 100 );
}
/**
* @see WANObjectCacheRepear
*
* @param int $start
* @param int $id
* @param int $end
* @param int $limit
* @return TitleValue[]
*/
public function getTitleChangeEvents( $start, $id, $end, $limit ) {
$db = $this->db;
$encStart = $db->addQuotes( $db->timestamp( $start ) );
$encEnd = $db->addQuotes( $db->timestamp( $end ) );
$id = (int)$id; // cast NULL => 0 since rc_id is an integer
$res = $db->select(
'recentchanges',
[ 'rc_namespace', 'rc_title', 'rc_timestamp', 'rc_id' ],
[
$db->makeList( [
"rc_timestamp > $encStart",
"rc_timestamp = $encStart AND rc_id > " . $db->addQuotes( $id )
], LIST_OR ),
"rc_timestamp < $encEnd"
],
__METHOD__,
[ 'ORDER BY' => 'rc_timestamp ASC, rc_id ASC', 'LIMIT' => $limit ]
);
$events = [];
foreach ( $res as $row ) {
$events[] = [
'id' => (int)$row->rc_id,
'pos' => (int)wfTimestamp( TS_UNIX, $row->rc_timestamp ),
'item' => new TitleValue( (int)$row->rc_namespace, $row->rc_title )
];
}
return $events;
}
/**
* Gets a list of important cache keys associated with a title
*
* @see WANObjectCacheRepear
* @param WANObjectCache $cache
* @param TitleValue $t
* @return string[]
*/
public function getEventAffectedKeys( WANObjectCache $cache, TitleValue $t ) {
/** @var WikiPage[]|LocalFile[]|User[] $entities */
$entities = [];
// You can't create a WikiPage for special pages (-1) or other virtual
// namespaces, but special pages do appear in RC sometimes, e.g. for logs
// of AbuseFilter filter changes.
if ( $t->getNamespace() >= 0 ) {
$entities[] = WikiPage::factory( Title::newFromTitleValue( $t ) );
}
if ( $t->inNamespace( NS_FILE ) ) {
$entities[] = wfLocalFile( $t->getText() );
}
if ( $t->inNamespace( NS_USER ) ) {
$entities[] = User::newFromName( $t->getText(), false );
}
$keys = [];
foreach ( $entities as $entity ) {
if ( $entity ) {
$keys = array_merge( $keys, $entity->getMutableCacheKeys( $cache ) );
}
}
if ( $keys ) {
$this->logger->debug( __CLASS__ . ': got key(s) ' . implode( ', ', $keys ) );
}
return $keys;
}
}
|
