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From "Erick Erickson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-8906) Make transient core cache pluggable.
Date Tue, 05 Apr 2016 21:13:25 GMT

    [ https://issues.apache.org/jira/browse/SOLR-8906?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15227136#comment-15227136
] 

Erick Erickson commented on SOLR-8906:
--------------------------------------

So I did hack together a PoC and it doesn't disrupt CoreContainer too much. I'm not really
ready to put it up since it's too crude. The "interface" is just selected interfaces from
LinkedHashMap for instance, but it works enough to decouple internal locking of objects in
CoreContainer from the plugin code which was my first concern.

Thinking about this some more, I started asking myself why should only transient cores be
manipulated by the plugin? CoreContainer shouldn't really need to care whether the core is
transient or not for its purposes. Gotta think about that some more. Once the state of the
core is removed from being so intertwined with CoreContainer, it seems like it would be adaptable
to  using ZK as "the one source of truth" pretty easily...

> 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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