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https://issues.apache.org/jira/browse/SOLR-7585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14557504#comment-14557504
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Maciej Zasada commented on SOLR-7585:
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Personally I like exiting the code early. If I understand correctly, new
implementation will always evict at least one entry, which means cache size may
drop below {{lowerWaterMark}} (which somehow brakes a contract). To fix
underlying problem we should get rid of a race condition at all, but I haven't
measure the performance impact of such change. Moreover, first approach has 2
additional benefits:
* not producing additional garbage
* not executing unnecessary code (if cache size is below {{upperWaterMark}},
there's no need to evict anything)
both seem to be important for a cache. WDYT?
> ConcurrentLFUCache throws NoSuchElementException under a write-heavy load
> -------------------------------------------------------------------------
>
> Key: SOLR-7585
> URL: https://issues.apache.org/jira/browse/SOLR-7585
> Project: Solr
> Issue Type: Bug
> Affects Versions: 5.1
> Reporter: Maciej Zasada
> Priority: Minor
> Attachments: SOLR-7585.patch, SOLR-7585.patch, SOLR-7585.patch
>
>
> Under a write-heavy load {{ConcurrentLFUCache}} throws
> {{NoSuchElementException}}. The problem lies within
> {{org.apache.solr.util.ConcurrentLFUCache#put}} method, which allows for a
> race condition between the check and the call to {{markAndSweep}} method.
> Despite that a thread must acquire a lock to perform sweeping, it's still
> possible that multiple threads successfully detected a need for calling
> markAndSweep. If they execute it sequentially, subsequent runs will fail with
> {{NoSuchElementException}}.
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