1 files changed, 133 insertions, 0 deletions
diff --git a/www/wiki/includes/deferred/WANCacheReapUpdate.php b/www/wiki/includes/deferred/WANCacheReapUpdate.php
new file mode 100644
index 00000000..5ffc9388
--- /dev/null
+++ b/www/wiki/includes/deferred/WANCacheReapUpdate.php
@@ -0,0 +1,133 @@
+<?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;
+	}
+}