[infinispan-dev] Eviction thread and purging expired entries

[Galder Zamarreño]

On Jul 22, 2010, at 3:49 AM, Mircea Markus wrote:

> 
> On 21 Jul 2010, at 19:29, Galder Zamarreño wrote:
> 
>> 
>> On Jul 21, 2010, at 3:24 PM, Mircea Markus wrote:
>> 
>>> Hi,
>>> 
>>> Eviction thread does two things right now:
>>> - evict stuff from DataContainer
>>> - purge entries from a CacheStore
>>> 
>>> CacheStore.purge might slow down eviction as it is generally an expensive operation. It might not even be needed, if the users don't use expiration. 
>> 
>> It's not considered here, but I think it'd be hard to figure out that expiration is not in use at runtime. You'd have to track calls with expiration and make sure there's at least one expiration that has not expired. Probably not practical.
> well spotted! Not hard to implement, and definitely simple for the users, as doesn't need an additional config.

Not hard to implement? You'd need a separate collection to track those nodes to which expiration has been set, including those nodes that might have evicted from memory but are still present in the cache store (imagine a node with expire=1 day, but for eviction +passivation reasons, it has been moved to cache store after 1 min). On top of that, you'd need to update the collection everytime a node is expired to remove it from there. Then, in every call to purge entries from a cache store, you'd have to check this collection to see whether it's empty or not to decide whether to call purge entries on cache store. The latter is not difficult, but the tracking can get complicated v easily. IMO, not worth it. 

>> 
>>> What about: 
>>> a) making EvictionThread.purgeCacheStore configurable. 
>>> or/and
>>> b) use another thread for purging the store. 
>>> 
>>> This doesn't came out of the blue, there's a user that has eviction+cache store configured with eviction thread wakeup set to 1 sec - he still gets OOM.
>>> 
>>> Wdyt?
>> 
>> I think both are valid actually but let me be more precise.
>> 
>> More than making EvictionThread.purgeCacheStore configurable, I'd make expiration as a whole configurable. So, if user does not use expiration, having expiration=false would:
>> - Disallow calls to overloaded cache methods taking expiration
>> - Do not check for expiration when entries are retrieved from memory/cachestore
>> - Don't do EvictionThread.purgeCacheStore 
> This would also make sure that the user won't add expiry stuff by mistake.
> I like both solutions :)
> 
>> 
>> 
>>> 
>>> Cheers,
>>> Mircea
>>> _______________________________________________
>>> infinispan-dev mailing list
>>> infinispan-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>> 
>> --
>> Galder Zamarreño
>> Sr. Software Engineer
>> Infinispan, JBoss Cache
>> 
>> 
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> 
> 
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--
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache