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From "Ferenczi Jim (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-7319) Workaround the "Four Month Bug" causing GC pause problems
Date Tue, 31 Mar 2015 07:06:54 GMT

    [ https://issues.apache.org/jira/browse/SOLR-7319?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14388154#comment-14388154
] 

Ferenczi Jim commented on SOLR-7319:
------------------------------------

Most of the java options in the solr.in.cmd should not be activated by default. The tenuring
threshold, the numbers of threads for the GC, ..., they all depend on the type of deployment
you have, the size of the heap and the machine hosting the Solr node. In my company we are
using a custom script full of java options that we added over the years. Most of the options
are here because somebody added this with the assertion that the performance are better. Most
of the time, we don't know what the option is for but nobody wants to remove it because the
urban legend says it's useful. The solr startup script should be almost empty (at least for
the java options), maybe one or two options to set up the garbage collector and that's it.

> 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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