jenkins-bot has submitted this change and it was merged. (
https://gerrit.wikimedia.org/r/393571 )
Change subject: objectcache: add "graceTTL" option to
WANObjectCache::getWithSetCallback()
......................................................................
objectcache: add "graceTTL" option to WANObjectCache::getWithSetCallback()
Also made worthRefreshExpiring() fully match the method documentation.
Change-Id: I48a4b1b9d006de100389b47c03c1185a9316abfc
---
M includes/libs/objectcache/WANObjectCache.php
M tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
2 files changed, 100 insertions(+), 19 deletions(-)
Approvals:
Krinkle: Looks good to me, approved
jenkins-bot: Verified
diff --git a/includes/libs/objectcache/WANObjectCache.php
b/includes/libs/objectcache/WANObjectCache.php
index f5c561f..a55d21c 100644
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -137,6 +137,8 @@
const HOLDOFF_NONE = 0;
/** Idiom for set()/getWithSetCallback() for "do not augment the
storage medium TTL" */
const STALE_TTL_NONE = 0;
+ /** Idiom for set()/getWithSetCallback() for "no post-expired grace
period" */
+ const GRACE_TTL_NONE = 0;
/** Idiom for getWithSetCallback() for "no minimum required as-of
timestamp" */
const MIN_TIMESTAMP_NONE = 0.0;
@@ -820,6 +822,12 @@
* - checkKeys: List of "check" keys. The key at $key will be seen as
invalid when either
* touchCheckKey() or resetCheckKey() is called on any of these
keys.
* Default: [].
+ * - graceTTL: Consider reusing expired values instead of refreshing
them if they expired
+ * less than this many seconds ago. The odds of a refresh becomes
more likely over time,
+ * becoming certain once the grace period is reached. This can
reduce traffic spikes
+ * when millions of keys are compared to the same "check" key and
touchCheckKey()
+ * or resetCheckKey() is called on that "check" key.
+ * Default: WANObjectCache::GRACE_TTL_NONE.
* - lockTSE: If the key is tombstoned or expired (by checkKeys) less
than this many seconds
* ago, then try to have a single thread handle cache regeneration
at any given time.
* Other threads will try to use stale values if possible. If, on
miss, the time since
@@ -854,13 +862,13 @@
* This is useful if the source of a key is suspected of having
possibly changed
* recently, and the caller wants any such changes to be reflected.
* Default: WANObjectCache::MIN_TIMESTAMP_NONE.
- * - hotTTR: Expected time-till-refresh (TTR) for keys that average
~1 hit/second (1 Hz).
- * Keys with a hit rate higher than 1Hz will refresh sooner than
this TTR and vise versa.
- * Such refreshes won't happen until keys are "ageNew" seconds
old. The TTR is useful at
- * reducing the impact of missed cache purges, since the effect of
a heavily referenced
- * key being stale is worse than that of a rarely referenced key.
Unlike simply lowering
- * $ttl, seldomly used keys are largely unaffected by this option,
which makes it possible
- * to have a high hit rate for the "long-tail" of less-used keys.
+ * - hotTTR: Expected time-till-refresh (TTR) in seconds for keys
that average ~1 hit per
+ * second (e.g. 1Hz). Keys with a hit rate higher than 1Hz will
refresh sooner than this
+ * TTR and vise versa. Such refreshes won't happen until keys are
"ageNew" seconds old.
+ * The TTR is useful at reducing the impact of missed cache
purges, since the effect of
+ * a heavily referenced key being stale is worse than that of a
rarely referenced key.
+ * Unlike simply lowering $ttl, seldomly used keys are largely
unaffected by this option,
+ * which makes it possible to have a high hit rate for the
"long-tail" of less-used keys.
* Default: WANObjectCache::HOT_TTR.
* - lowTTL: Consider pre-emptive updates when the current TTL
(seconds) of the key is less
* than this. It becomes more likely over time, becoming certain
once the key is expired.
@@ -962,6 +970,7 @@
$lowTTL = isset( $opts['lowTTL'] ) ? $opts['lowTTL'] : min(
self::LOW_TTL, $ttl );
$lockTSE = isset( $opts['lockTSE'] ) ? $opts['lockTSE'] :
self::TSE_NONE;
$staleTTL = isset( $opts['staleTTL'] ) ? $opts['staleTTL'] :
self::STALE_TTL_NONE;
+ $graceTTL = isset( $opts['graceTTL'] ) ? $opts['graceTTL'] :
self::GRACE_TTL_NONE;
$checkKeys = isset( $opts['checkKeys'] ) ? $opts['checkKeys'] :
[];
$busyValue = isset( $opts['busyValue'] ) ? $opts['busyValue'] :
null;
$popWindow = isset( $opts['hotTTR'] ) ? $opts['hotTTR'] :
self::HOT_TTR;
@@ -980,7 +989,7 @@
$preCallbackTime = $this->getCurrentTime();
// Determine if a cached value regeneration is needed or desired
if ( $value !== false
- && $curTTL > 0
+ && $this->isAliveOrInGracePeriod( $curTTL, $graceTTL )
&& $this->isValid( $value, $versioned, $asOf, $minTime )
&& !$this->worthRefreshExpiring( $curTTL, $lowTTL )
&& !$this->worthRefreshPopular( $asOf, $ageNew,
$popWindow, $preCallbackTime )
@@ -1632,12 +1641,40 @@
}
/**
+ * Check if a key is fresh or in the grace window and thus due for
randomized reuse
+ *
+ * If $curTTL > 0 (e.g. not expired) this returns true. Otherwise, the
chance of returning
+ * true decrease steadily from 100% to 0% as the |$curTTL| moves from 0
to $graceTTL seconds.
+ * This handles widely varying levels of cache access traffic.
+ *
+ * If $curTTL <= -$graceTTL (e.g. already expired), then this returns
false.
+ *
+ * @param float $curTTL Approximate TTL left on the key if present
+ * @param int $graceTTL Consider using stale values if $curTTL is
greater than this
+ * @return bool
+ */
+ protected function isAliveOrInGracePeriod( $curTTL, $graceTTL ) {
+ if ( $curTTL > 0 ) {
+ return true;
+ } elseif ( $graceTTL <= 0 ) {
+ return false;
+ }
+
+ $ageStale = abs( $curTTL ); // seconds of staleness
+ $curGTTL = ( $graceTTL - $ageStale ); // current
grace-time-to-live
+
+ // Chance of using a stale value is the complement of the
chance of refreshing it
+ return !$this->worthRefreshExpiring( $curGTTL, $graceTTL );
+ }
+
+ /**
* Check if a key is nearing expiration and thus due for randomized
regeneration
*
- * This returns false if $curTTL >= $lowTTL. Otherwise, the chance
- * of returning true increases steadily from 0% to 100% as the $curTTL
- * moves from $lowTTL to 0 seconds. This handles widely varying
- * levels of cache access traffic.
+ * This returns false if $curTTL >= $lowTTL. Otherwise, the chance of
returning true
+ * increases steadily from 0% to 100% as the $curTTL moves from $lowTTL
to 0 seconds.
+ * This handles widely varying levels of cache access traffic.
+ *
+ * If $curTTL <= 0 (e.g. already expired), then this returns false.
*
* @param float $curTTL Approximate TTL left on the key if present
* @param float $lowTTL Consider a refresh when $curTTL is less than
this
@@ -1649,7 +1686,7 @@
} elseif ( $curTTL >= $lowTTL ) {
return false;
} elseif ( $curTTL <= 0 ) {
- return true;
+ return false;
}
$chance = ( 1 - $curTTL / $lowTTL );
diff --git a/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
b/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
index b779231..d94c546 100644
--- a/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
+++ b/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
@@ -267,7 +267,7 @@
$this->assertEquals( $value, $v, "Value still returned after
deleted" );
$this->assertEquals( 1, $wasSet, "Value process cached while
deleted" );
- $backToTheFutureCache = new TimeAdjustableWANObjectCache( [
+ $timeyCache = new TimeAdjustableWANObjectCache( [
'cache' => new TimeAdjustableHashBagOStuff(),
'pool' => 'empty'
] );
@@ -283,29 +283,73 @@
return 'xxx' . $wasSet;
};
+ $now = microtime( true ); // reference time
+
$wasSet = 0;
$key = wfRandomString();
- $v = $backToTheFutureCache->getWithSetCallback(
+ $timeyCache->setTime( $now );
+ $v = $timeyCache->getWithSetCallback(
$key, 30, $checkFunc, [ 'staleTTL' => 50 ] + $extOpts );
$this->assertEquals( 'xxx1', $v, "Value returned" );
$this->assertEquals( false, $oldValReceived, "Callback got no
stale value" );
$this->assertEquals( null, $oldAsOfReceived, "Callback got no
stale value" );
- $backToTheFutureCache->setTime( microtime( true ) + 40 );
- $v = $backToTheFutureCache->getWithSetCallback(
+ $timeyCache->setTime( $now + 40 );
+ $v = $timeyCache->getWithSetCallback(
$key, 30, $checkFunc, [ 'staleTTL' => 50 ] + $extOpts );
$this->assertEquals( 'xxx2', $v, "Value still returned after
expired" );
$this->assertEquals( 2, $wasSet, "Value recalculated while
expired" );
$this->assertEquals( 'xxx1', $oldValReceived, "Callback got
stale value" );
$this->assertNotEquals( null, $oldAsOfReceived, "Callback got
stale value" );
- $backToTheFutureCache->setTime( microtime( true ) + 300 );
- $v = $backToTheFutureCache->getWithSetCallback(
+ $timeyCache->setTime( $now + 300 );
+ $v = $timeyCache->getWithSetCallback(
$key, 30, $checkFunc, [ 'staleTTL' => 50 ] + $extOpts );
$this->assertEquals( 'xxx3', $v, "Value still returned after
expired" );
$this->assertEquals( 3, $wasSet, "Value recalculated while
expired" );
$this->assertEquals( false, $oldValReceived, "Callback got no
stale value" );
$this->assertEquals( null, $oldAsOfReceived, "Callback got no
stale value" );
+
+ $wasSet = 0;
+ $key = wfRandomString();
+ $checkKey = $timeyCache->makeKey( 'template', 'X' );
+ $timeyCache->setTime( $now - $timeyCache::HOLDOFF_TTL - 1 );
+ $timeyCache->touchCheckKey( $checkKey ); // init check key
+ $timeyCache->setTime( $now );
+ $v = $timeyCache->getWithSetCallback(
+ $key,
+ $timeyCache::TTL_WEEK,
+ $checkFunc,
+ [ 'graceTTL' => $timeyCache::TTL_DAY, 'checkKeys' => [
$checkKey ] ] + $extOpts
+ );
+ $this->assertEquals( 'xxx1', $v, "Value returned" );
+ $this->assertEquals( 1, $wasSet, "Value computed" );
+ $this->assertEquals( false, $oldValReceived, "Callback got no
stale value" );
+ $this->assertEquals( null, $oldAsOfReceived, "Callback got no
stale value" );
+
+ $timeyCache->setTime( $now + 300 ); // some time passes
+ $timeyCache->touchCheckKey( $checkKey ); // make key stale
+ $timeyCache->setTime( $now + 3600 ); // ~23 hours left of grace
+ $v = $timeyCache->getWithSetCallback(
+ $key,
+ $timeyCache::TTL_WEEK,
+ $checkFunc,
+ [ 'graceTTL' => $timeyCache::TTL_DAY, 'checkKeys' => [
$checkKey ] ] + $extOpts
+ );
+ $this->assertEquals( 'xxx1', $v, "Value still returned after
expired (in grace)" );
+ $this->assertEquals( 1, $wasSet, "Value still returned after
expired (in grace)" );
+
+ $timeyCache->setTime( $now + $timeyCache::TTL_DAY );
+ $v = $timeyCache->getWithSetCallback(
+ $key,
+ $timeyCache::TTL_WEEK,
+ $checkFunc,
+ [ 'graceTTL' => $timeyCache::TTL_DAY, 'checkKeys' => [
$checkKey ] ] + $extOpts
+ );
+ $this->assertEquals( 'xxx2', $v, "Value was recomputed (past
grace)" );
+ $this->assertEquals( 2, $wasSet, "Value was recomputed (past
grace)" );
+ $this->assertEquals( 'xxx1', $oldValReceived, "Callback got
post-grace stale value" );
+ $this->assertNotEquals( null, $oldAsOfReceived, "Callback got
post-grace stale value" );
}
public static function getWithSetCallback_provider() {
--
To view, visit https://gerrit.wikimedia.org/r/393571
To unsubscribe, visit https://gerrit.wikimedia.org/r/settings
Gerrit-MessageType: merged
Gerrit-Change-Id: I48a4b1b9d006de100389b47c03c1185a9316abfc
Gerrit-PatchSet: 7
Gerrit-Project: mediawiki/core
Gerrit-Branch: master
Gerrit-Owner: Aaron Schulz <asch...@wikimedia.org>
Gerrit-Reviewer: Krinkle <krinklem...@gmail.com>
Gerrit-Reviewer: jenkins-bot <>
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