[jira] [Commented] (SOLR-8906) Make transient core cache pluggable.

["Noble Paul (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-8906?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15898488#comment-15898488 ] 

Noble Paul commented on SOLR-8906:
----------------------------------

lazy cores itself is a vestige a of the old master-slave model where cores were not expected to be up. 

So, this is an X-Y problem. Let's ask the question , why do we want to unload a core?

We just need to ensure that the resources held by a core is kept minimal. The expensive resources are file handles & caches.(there could be others and we can ignore them for a while). So, if we manage to free up these resources for the unused core we can pretty much achieve our objective. 

> Make transient core cache pluggable.
> ------------------------------------
>
>                 Key: SOLR-8906
>                 URL: https://issues.apache.org/jira/browse/SOLR-8906
>             Project: Solr
>          Issue Type: Improvement
>            Reporter: Erick Erickson
>            Assignee: Erick Erickson
>
> The current Lazy Core stuff is pretty deeply intertwined in CoreContainer. Adding and removing active cores is based on a simple LRU mechanism, but keeping the right cores in the right internal structures involves a lot of attention to locking various objects to update internal structures. This makes it difficult/dangerous to use any other caching algorithms.
> Any single age-out algorithm will have non-optimal access patterns, so making this pluggable would allow better algorithms to be substituted in those cases.
> If we ever extend transient cores to SolrCloud, we need to have load/unload decisions that are cloud-aware rather then entirely local so in that sense this is would lay some groundwork if we ever want to go there.
> So I'm going to try to hack together a PoC. Any ideas on the most sensible pattern for this gratefully received.



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