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https://issues.apache.org/jira/browse/SOLR-7585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14557576#comment-14557576
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Shawn Heisey commented on SOLR-7585:
------------------------------------

Apparently 6 threads is not enough to trigger the bug.  When I ran the test 
(without the fix) on a system with three cores, the test passed.  When I 
hard-coded the number of threads in the test to 8, then the test failed as 
expected.

[~maciej.zasada], should we hard-code the number of threads in the test to a 
number like 8 or 10?


> 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, 
> 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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