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https://issues.apache.org/jira/browse/SOLR-7585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14557517#comment-14557517
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Maciej Zasada commented on SOLR-7585:
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Yes, I saw SOLR-3393 before, but I assumed it will take a while to deprecate
and remove the old class, and we're currently experiencing some exceptions
because of this race condition :) Having in mind that you're working on more
performant LFU cache, I tried to make changes as small and noninvasive as
possible.
bq. it looks like markAndSweep was designed to reduce the cache size to
lowerWaterMark.
Exactly. I believe that your change will actually reduce (sometimes) the cache
size to be equal to {{lowerWaterMark -1}}, instead of equal to
{{lowerWaterMark}}.
bq. Is it acceptable to avoid eviction if the current cache size is somewhere
between the two watermarks?
Eviction will be only avoided if the size was less than or equal to
{{upperWaterMark}}, which is exactly the same condition as in
{{org.apache.solr.util.ConcurrentLFUCache#put}} method (L#139), where it's
decided whether to call {{markAndSweep}} at all or not. Essentially, the same
condition is checked after acquiring a lock to mitigate a race condition.
> 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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