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Add migration docs for GC logging #27631

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Dec 8, 2017
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Add migration docs for GC logging #27631

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28 changes: 28 additions & 0 deletions docs/reference/migration/migrate_6_2.asciidoc
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Expand Up @@ -23,3 +23,31 @@ existing <<jvm-options,`jvm.options`>>, you should add the line
`-Djava.io.tmpdir=${ES_TMPDIR}`. It is safe to do this on all OS as we preserve
using a private temporary directory on non-Linux systems with the same
mechanism.

=== GC logging

Starting in Elasticsearch 6.2.0, JVM <<gc-logging,GC logging>> is enabled out of
the box. This lightweight facility gives insight into GC issues. The settings
for this are in <<jvm-options,`jvm.options`>> and default to keeping 2 GB worth
(rotating every 64 MB) of logs in the default logs directory. If you are
upgrading from a previous version of Elasticsearch and preserve your existing
<<jvm-options,`jvm.options`>>, you should add the following GC logging settings
so that this valuable debugging information is available:

[source,sh]
--------------------------------------------------
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-XX:+PrintTenuringDistribution
-XX:+PrintGCApplicationStoppedTime
-Xloggc:logs/gc.log or /var/log/elasticsearch/gc.log <1>
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@rjernst rjernst Dec 5, 2017

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I would put the "or" part in the description below, so that this can more easily be copy/pasted?

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@jasontedor jasontedor Dec 8, 2017

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I would rather copy-pasting not be encouraged here because the right value of this setting depends on whether or not a user is using a package distribution versus an archive distribution?

-XX:+UseGCLogFileRotation
-XX:NumberOfGCLogFiles=32
-XX:GCLogFileSize=64m
--------------------------------------------------

<1> If you have installed Elasticsearch from the RPM or the Debian packaging
distributions and use the default logging location use `/var/log/elasticsearch`
otherwise if you have installed from the `tar.gz` or `zip` archive distributions
and use the default logging location use `logs/gc.log`; otherwise, set the
location to the absolute path to your log files.