Appreciate the information.
From: "ryangardner [via Artifactory]"
<[email protected]<mailto:[email protected]>>
Date: Tuesday, June 3, 2014 at 1:50 PM
To: Ryan Goodwin <[email protected]<mailto:[email protected]>>
Subject: Re: Artifactory 3.0.4 performance tuning and G1GC vs CMS
goody wrote
What I haven’t found is any hard evidence from performance tests showing that
G1 beats out a properly tuned CMS config. I am not basing my statements on the
sole findings of the test results I linked to. I’ve found multiple sources
which all state the same thing, specifically some tests done against JIRA with
default configurations of the various jvm collectors showing CMS still on top.
The performance on G1 just isn’t there yet.
The key phrase there is "properly tuned" CMS. CMS is an absolute nightmare to
tune. When you tune CMS, you have to tune a lot of knobs that are all based on
the object allocation rate and how long the objects live for.
If you have an application, such as a cache server, that has a warming period
(where it is primarily filling its heap with cached objects, but also serving
up content) and then a longer state where it is mainly serving up those
requests (but with some of the cache being invalidated over time) - you have
two massively different object allocation rates. There is no proper way to tune
CMS for that - you have to either choose to have optimal settings for one of
those scenarios or have a set of compromised settings that are kind of "okish"
for both of them.
G1 can handle both large and small heaps just fine, but the areas you are going
to find G1 used exclusively are apps that make use of lots of heap. Getting CMS
to perform well with a 50 or 60GB heap is an exercise in futility - but G1 can
handle that with ease.
There was an article published by linked in a while ago where they claim they
had better performance from CMS than G1 - but that article also had a bunch of
incorrect statements in it (I was going to offer suggestions to them on how to
re-run their tests or fix their G1 cases, but their blog didn't allow comments
so their article will likely live on forever with incorrect statements and be
referenced by others who assume that the people at linkedIn know what they are
doing)
If you want to talk about GC tuning - I would suggest the hotspot-gc-users
mailing list. It is frequented by the hotspot developers (who are experts in
both CMS and G1) and also by GC tuning enthusiasts.
Another good source would be Charlie Hunt and Monica Beckwith's presentations
on G1 tuning.
Charlie Hunt you may recognize as probably one of the leading experts on GC
tuning. He has written probably the best book on the market about how to tune
the CMS garbage collector - "Java Performance" - and in his presentation at
Java One, _he_ openly admitted how much he hates tuning CMS (it really is a
_massive_ pain in the rear to get right) and suggests people try using G1.
The default tuning for G1 is going to behave far better and with less surprises
than the default tuning for CMS - so for them to ship with G1 by default is a
very good decision.
http://www.infoq.com/presentations/java-g1
http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html
A very good video presentation on G1:
https://www.parleys.com/share_channel.html#play/525528dbe4b0a43ac12124d7
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