edeis53 commented on issue #1704: Redis cache TTL
URL: 
https://github.com/apache/incubator-pagespeed-mod/issues/1704#issuecomment-387566711
 
 
   I would suggest a default -1 expiry to match current pagespeed config 
behaviour, and yes we'd probably use a long TTL like 1 year in our config.
   
   The default LRU for Redis and also most desirable for our use case is 
`volatile-lru`: evict keys by trying to remove the less recently used (LRU) 
keys first, but only among keys that have an expire set, in order to make space 
for the new data added.
   
   Without a TTL set from pagespeed, the pagespeed cached keys will never be 
purged using a volatile-lru policy.
   
   To prevent running out of memory, redis imlementations are forced to use 
`allkeys-lru`: evict keys by trying to remove the less recently used (LRU) keys 
first, in order to make space for the new data added.
   
   `allkeys-lru` policy is a problem if there are keys that you wish to persist 
as they may be purged before some ephemeral keys.
   
   By defining a ttl and using `volatile-lru` you can explicitly declare which 
keys you want to evict as the cache fills up.
   
   
   
   
   
   
   
   

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