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https://issues.apache.org/jira/browse/SOLR-7319?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14386877#comment-14386877
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Timothy Potter commented on SOLR-7319:
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That's correct - MMap is only for reading the index, so maybe instead of
enabling this by default, we document it in bin/solr.in.(sh|cmd) and users can
turn it on if they so choose. I've already been ding'd a few times on adding
Java flags as defaults in those scripts because they helped my prod env. but
weren't deemed generally applicable for all Solr users. So I vote for leaving
it out by default, but documenting it as something for operators to enable if
they experience this issue.
> Workaround the "Four Month Bug" causing GC pause problems
> ---------------------------------------------------------
>
> Key: SOLR-7319
> URL: https://issues.apache.org/jira/browse/SOLR-7319
> Project: Solr
> Issue Type: Bug
> Components: scripts and tools
> Affects Versions: 5.0
> Reporter: Shawn Heisey
> Assignee: Shawn Heisey
> Fix For: 5.1
>
> Attachments: SOLR-7319.patch, SOLR-7319.patch, SOLR-7319.patch
>
>
> A twitter engineer found a bug in the JVM that contributes to GC pause
> problems:
> http://www.evanjones.ca/jvm-mmap-pause.html
> Problem summary (in case the blog post disappears): The JVM calculates
> statistics on things like garbage collection and writes them to a file in the
> temp directory using MMAP. If there is a lot of other MMAP write activity,
> which is precisely how Lucene accomplishes indexing and merging, it can
> result in a GC pause because the mmap write to the temp file is delayed.
> We should implement the workaround in the solr start scripts (disable
> creation of the mmap statistics tempfile) and document the impact in
> CHANGES.txt.
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