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From Leon Rosenberg <rosenberg.l...@gmail.com>
Subject What is the healthy interval length for young gc?
Date Mon, 03 Jan 2011 11:12:57 GMT
Hi,

First of all Happy and Successful New Year to all subscribers.

I understand that this is a very application specific issue, but I'm
wondering which interval is perceived as 'healthy' for young
collections?
I have one customer's system which, at peak time, performs a young gc
every 15 seconds. Parallel the response time goes incredibly high (>30
seconds).
Here a log sniplet:

2010-12-30T21:34:07.500+0100: 818132.148: [Full GC [PSYoungGen:
289802K->0K(3838208K)] [PSOldGen: 8366132K->7958635K(8388608K)]
8655935K->7958635K(12226816K) [PSPermGen: 152897K->152281K(262144K)],
79.1738980 secs] [Times: user=79.04 sys=0.02, real=79.18 secs]
2010-12-30T21:35:36.748+0100: 818221.397: [GC [PSYoungGen:
3487936K->106067K(3794752K)] 11446571K->8064702K(12183360K), 0.3410450
secs] [Times: user=1.83 sys=0.01, real=0.34 secs]
2010-12-30T21:35:43.792+0100: 818228.441: [GC [PSYoungGen:
3555155K->129828K(3578944K)] 11513790K->8088464K(11967552K), 0.2955760
secs] [Times: user=1.39 sys=0.02, real=0.30 secs]
2010-12-30T21:35:58.512+0100: 818243.160: [GC [PSYoungGen:
3578617K->154016K(3795456K)] 11537253K->8112652K(12184064K), 0.3276970
secs] [Times: user=1.57 sys=0.07, real=0.33 secs]
2010-12-30T21:36:28.126+0100: 818272.774: [GC [PSYoungGen:
3561760K->143668K(3551424K)] 11520396K->8102304K(11940032K), 0.3682730
secs] [Times: user=1.56 sys=0.12, real=0.37 secs]

So my questions are:

Could it be that the long liveness of the objects in the young space,
combined with often young collections lead to heap pollution on the
old gen, cause request bound objects live to long?

Do I understand it correctly that the size of the young space doesn't
influence the collection time (as long as the amount of living objects
remains the same) and does it make sense to increase the young space
in our case?

tomcat: 6.0.20
java 1.6.0.16

regards
Leon

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