Aaron Schulz has uploaded a new change for review. (
https://gerrit.wikimedia.org/r/393516 )
Change subject: objectcache: add more comments to WANObjectCache
getWithSetCallback()
......................................................................
objectcache: add more comments to WANObjectCache getWithSetCallback()
Change-Id: I567f45fa7b33226b0ccf7d80440802eab71ff753
---
M includes/libs/objectcache/WANObjectCache.php
1 file changed, 7 insertions(+), 5 deletions(-)
git pull ssh://gerrit.wikimedia.org:29418/mediawiki/core
refs/changes/16/393516/1
diff --git a/includes/libs/objectcache/WANObjectCache.php
b/includes/libs/objectcache/WANObjectCache.php
index e63b32e..d6a850e 100644
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -857,14 +857,16 @@
* 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.
+ * Such refreshes won't happen until keys are "ageNew" seconds
old. This also uses
+ * randomization to avoid triggering stampedes. 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.
+ * This helps avoid stampedes that might be triggered due to the
key expiring.
* Default: WANObjectCache::LOW_TTL.
* - ageNew: Consider popularity refreshes only once a key reaches
this age in seconds.
* Default: WANObjectCache::AGE_NEW.
--
To view, visit https://gerrit.wikimedia.org/r/393516
To unsubscribe, visit https://gerrit.wikimedia.org/r/settings
Gerrit-MessageType: newchange
Gerrit-Change-Id: I567f45fa7b33226b0ccf7d80440802eab71ff753
Gerrit-PatchSet: 1
Gerrit-Project: mediawiki/core
Gerrit-Branch: master
Gerrit-Owner: Aaron Schulz <[email protected]>
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