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https://issues.apache.org/jira/browse/LUCENE-6096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14242670#comment-14242670
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ASF subversion and git services commented on LUCENE-6096:
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Commit 1644672 from [~jpountz] in branch 'dev/branches/branch_5x'
[ https://svn.apache.org/r1644672 ]
LUCENE-6096: Avoid CMS which can close segments while we are measuring ram
usage of the filter cache.
> Improve FilterCache.ramBytesUsed
> --------------------------------
>
> Key: LUCENE-6096
> URL: https://issues.apache.org/jira/browse/LUCENE-6096
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Assignee: Adrien Grand
> Priority: Minor
> Fix For: 5.0, Trunk
>
> Attachments: LUCENE-6096.patch
>
>
> I worked on some tests to improve ram usage estimation of LRUFilterCache and
> found some issues:
> 1. It currently only takes into account filters and DocIdSets, not the
> internal overhead of the various hash tables and linked lists that are being
> maintained. If the filter cache mostly stores sparse doc id sets (or even
> worse DocIdSet.EMPTY instances that require 0 bytes since it's a singleton)
> then the memory usage can be significantly under-estimated.
> 2. It treats all filters as if they were singletons. The filter cache is
> essentially a Map<SegmentCoreReaders, Map<Filter, DocIdSet>> and it treats
> filters as if all filters that are equal are the same instance when it comes
> to memory usage. But this is not the case actually since the map on the
> second level uses the first-seen filter as a key, which might be different on
> different segments because of merging.
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