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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Reopened] (CASSANDRA-7486) Migrate to G1GC by default
Date Sat, 19 Sep 2015 18:50:07 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-7486?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Benedict reopened CASSANDRA-7486:
---------------------------------

We should revert this patch until we can do further analysis. We have significantly worse
throughput and latency figures in 3.0, and much of this can be explained by the new GC settings.
This is with more realistic workloads than we have previously benchmarked, and also with the
current state of 3.0.

[These graphs|http://cstar.datastax.com/graph?stats=518e5484-5ee3-11e5-b421-42010af0688f&metric=op_rate&operation=3_user&smoothing=1&show_aggregates=true&xmin=0&xmax=113.3&ymin=0&ymax=159847.6]
paint a bleak picture. Throughput takes a 33% hit for point queries (Interestingly, there
is a reduction in GC _work_ done, presumably indicating that card marking / GC store barriers
are to blame). Latency is much worse, and much less consistent, as is throughput, for all
runs.

We may be able to use this information to counteract the problem, but releasing 3.0 GA with
this change as stands seems premature.

> Migrate to G1GC by default
> --------------------------
>
>                 Key: CASSANDRA-7486
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7486
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Config
>            Reporter: Jonathan Ellis
>            Assignee: Albert P Tobey
>             Fix For: 3.0 alpha 1
>
>
> See http://www.slideshare.net/MonicaBeckwith/garbage-first-garbage-collector-g1-7486gc-migration-to-expectations-and-advanced-tuning
and https://twitter.com/rbranson/status/482113561431265281
> May want to default 2.1 to G1.
> 2.1 is a different animal from 2.0 after moving most of memtables off heap.  Suspect
this will help G1 even more than CMS.  (NB this is off by default but needs to be part of
the test.)



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