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