From: Aaron Schulz <aschulz@wikimedia.org>
Date: Wed, 11 Jul 2018 21:29:51 +0000 (+0100)
Subject: objectcache: add "epoch" parameter to WANObjectCache
X-Git-Tag: 1.34.0-rc.0~4517^2
X-Git-Url: http://git.heureux-cyclage.org/?a=commitdiff_plain;h=4af7fbd76a50c1c578f2af2c9a779cf1db35c3cd;p=lhc%2Fweb%2Fwiklou.git

objectcache: add "epoch" parameter to WANObjectCache

This can be used to discard all values before a certain point in
time, such as periods of severe network problems or misconfiguration
that resulted in missed purges.

Change-Id: I612db8f91a5960b912e9f35645a3d3872df47460
---

diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php
index e30e061815..ed791284f3 100644
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -107,6 +107,8 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
 	protected $useInterimHoldOffCaching = true;
 	/** @var callable|null Function that takes a WAN cache callback and runs it later */
 	protected $asyncHandler;
+	/** @var float Unix timestamp of the oldest possible valid values */
+	protected $epoch;
 
 	/** @var int ERR_* constant for the "last error" registry */
 	protected $lastRelayError = self::ERR_NONE;
@@ -223,6 +225,7 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
 	 *   - mcrouterAware: set as true if mcrouter is the backing store proxy and mcrouter
 	 *       is configured to interpret /<region>/<cluster>/ key prefixes as routes. This
 	 *       requires that "region" and "cluster" are both set above. [optional]
+	 *   - epoch: lowest UNIX timestamp a value/tombstone must have to be valid. [optional]
 	 */
 	public function __construct( array $params ) {
 		$this->cache = $params['cache'];
@@ -231,6 +234,7 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
 		$this->region = $params['region'] ?? 'main';
 		$this->cluster = $params['cluster'] ?? 'wan-main';
 		$this->mcrouterAware = !empty( $params['mcrouterAware'] );
+		$this->epoch = $params['epoch'] ?? 1.0;
 
 		$this->setLogger( $params['logger'] ?? new NullLogger() );
 		$this->stats = $params['stats'] ?? new NullStatsdDataFactory();
@@ -2040,6 +2044,11 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
 			$curTTL = INF;
 		}
 
+		if ( $wrapped[self::FLD_TIME] < $this->epoch ) {
+			// Values this old are ignored
+			return [ false, null ];
+		}
+
 		return [ $wrapped[self::FLD_VALUE], $curTTL ];
 	}
 
@@ -2068,7 +2077,7 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
 	}
 
 	/**
-	 * @param string $value Wrapped value like "PURGED:<timestamp>:<holdoff>"
+	 * @param string|array|bool $value Possible string of the form "PURGED:<timestamp>:<holdoff>"
 	 * @return array|bool Array containing a UNIX timestamp (float) and holdoff period (integer),
 	 *  or false if value isn't a valid purge value
 	 */
@@ -2076,16 +2085,24 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
 		if ( !is_string( $value ) ) {
 			return false;
 		}
+
 		$segments = explode( ':', $value, 3 );
 		if ( !isset( $segments[0] ) || !isset( $segments[1] )
 			|| "{$segments[0]}:" !== self::PURGE_VAL_PREFIX
 		) {
 			return false;
 		}
+
 		if ( !isset( $segments[2] ) ) {
 			// Back-compat with old purge values without holdoff
 			$segments[2] = self::HOLDOFF_TTL;
 		}
+
+		if ( $segments[1] < $this->epoch ) {
+			// Values this old are ignored
+			return false;
+		}
+
 		return [
 			self::FLD_TIME => (float)$segments[1],
 			self::FLD_HOLDOFF => (int)$segments[2],
diff --git a/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php b/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
index 662bb9617c..22aa6671bb 100644
--- a/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
+++ b/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
@@ -1569,6 +1569,44 @@ class WANObjectCacheTest extends PHPUnit\Framework\TestCase {
 		$wanCache->resetCheckKey( 'test' );
 	}
 
+	public function testEpoch() {
+		$bag = new HashBagOStuff();
+		$cache = new WANObjectCache( [ 'cache' => $bag, 'pool' => 'testcache-hash' ] );
+		$key = $cache->makeGlobalKey( 'The whole of the Law' );
+
+		$now = microtime( true );
+		$cache->setMockTime( $now );
+
+		$cache->set( $key, 'Do what thou Wilt' );
+		$cache->touchCheckKey( $key );
+
+		$then = $now;
+		$now += 30;
+		$this->assertEquals( 'Do what thou Wilt', $cache->get( $key ) );
+		$this->assertEquals( $then, $cache->getCheckKeyTime( $key ), 'Check key init', 0.01 );
+
+		$cache = new WANObjectCache( [
+			'cache' => $bag,
+			'pool' => 'testcache-hash',
+			'epoch' => $now - 3600
+		] );
+		$cache->setMockTime( $now );
+
+		$this->assertEquals( 'Do what thou Wilt', $cache->get( $key ) );
+		$this->assertEquals( $then, $cache->getCheckKeyTime( $key ), 'Check key kept', 0.01 );
+
+		$now += 30;
+		$cache = new WANObjectCache( [
+			'cache' => $bag,
+			'pool' => 'testcache-hash',
+			'epoch' => $now + 3600
+		] );
+		$cache->setMockTime( $now );
+
+		$this->assertFalse( $cache->get( $key ), 'Key rejected due to epoch' );
+		$this->assertEquals( $now, $cache->getCheckKeyTime( $key ), 'Check key reset', 0.01 );
+	}
+
 	/**
 	 * @dataProvider provideAdaptiveTTL
 	 * @covers WANObjectCache::adaptiveTTL()