[infinispan-issues] [JBoss JIRA] (ISPN-6706) Purging cache writers is [mostly] redundant when eviction is disabled and preload is enabled

[William Burns (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-6706?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13242587#comment-13242587 ] 

William Burns commented on ISPN-6706:
-------------------------------------

If you are running a cluster I just noticed we don't have a very simple optimization of only running purge on the coordinator node when a shared store is used.  This means that without this all nodes may be hitting the DB server at approximately the same time, which is probably why it is killing your DB response times.  Another thing I would suggest is to limit how often the cache writer purge is performed in comparison to in memory (it could be ran every 5th memory purge for example).

And looking closer at the JPAStore and Jdbc*Store implementations they should be using a simple select that only returns expired entries.  I am not sure if we have indexes on these fields or not though, I haven't looked too closely at these classes (which may be causing your full table scan).

Also the optimization you have right now could still be used but we would have to limit it as the following:
# Only supported with 1 cache loader/writer (note we can have multiple configured)
# Store state in the persistence manager to guarantee evict was never called

> Purging cache writers is [mostly] redundant when eviction is disabled and preload is enabled
> --------------------------------------------------------------------------------------------
>
>                 Key: ISPN-6706
>                 URL: https://issues.jboss.org/browse/ISPN-6706
>             Project: Infinispan
>          Issue Type: Enhancement
>          Components: Loaders and Stores
>    Affects Versions: 8.2.2.Final
>            Reporter: Krzysztof Sobolewski
>
> This issue arised when I was testing a cluster with about 16 million entries. Our configuration is that all the data is also kept in memory, so eviction is disabled in this cache. But expiration is enabled. During the test I noticed pauses that started small but increased while the test was progressing, reaching more than 20 seconds at one point. After ruling out maintenance tasks in MySQL that could interfere, I discovered that the pause is caused by the expiration thread purging the database for expired entries. This was a huge and unnecessary drag so I hacked Infinispan to skip the purge of persistent state in cases when it's likely to be redundant with purging the transient state. I say "likely" because entries evicted maually via the evict() call poke a huge hole in the underlying assumptions :) Anyway, our cluster no longer regularly pauses for half a minute, so here's something for your consideration.



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