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Matt,<br>
<br>
What jdk release are you using?<br>
<br>
Can you send the GC log for a few of the young generation collections <br>
before the initial mark (the very long pause of ~ 4secs)? For a few
young<br>
generation collections after the end of the CMS cycle may be<br>
interesting too.<br>
<br>
Does the long pause occur with every initial mark (CMS-initial-mark)<br>
or just the first one?<br>
<br>
What type of platform are you running on?<br>
<br>
Why are you using CMSIncrementalMode?<br>
<br>
You seem to have decided to promote (copy to the tenured<br>
generation) everything that survives a young gen collection<br>
(small MaxTenuringThreshold, small survivor spaces).<br>
Is that to minimize the young gen collection pauses?<font color="navy"
face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial; color: navy;"></span></font><br>
<br>
Jon<br>
<br>
<br>
On 04/14/10 04:28, Matt Khan wrote:
<blockquote
cite="mid:OFF2843927.0084A8CF-ON80257705.003E2F96-80257705.003EFE1F@db.com"
type="cite">
<pre wrap="">Hi
I have been experimenting with larger heap sizes to see if I can reduce
the frequency of my pauses, the switches I have used are;
-Xms16192m
-Xmx16192m
-Xmn16000m
-XX:+UseCompressedOops
-XX:+UseConcMarkSweepGC
-XX:+CMSIncrementalMode
-XX:+CMSIncrementalPacing
-XX:+UseParNewGC
-XX:MaxTenuringThreshold=1
-XX:+PrintTenuringDistribution
-XX:SurvivorRatio=1022
-XX:TargetSurvivorRatio=90
-XX:+DisableExplicitGC
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-XX:+PrintGCApplicationStoppedTime
-XX:+PrintGCApplicationConcurrentTime
This works quite well in that our average pause time is ~4ms every 30s or
so (albeit in the range 5-60s but most commonly about every 30s).
There is one wrinkle and that is an initial, v long CMS pause. It happens
about ~40mins after start
2010-04-13T23:05:29.072+0000: 3342.854: [GC [1 CMS-initial-mark:
12018K(196608K)] 7811496K(16564608K), 4.2147116 secs] [Times: user=4.15
sys=0.06, real=4.22 secs]
Total time for which application threads were stopped: 4.2243800 seconds
2010-04-13T23:05:33.288+0000: 3347.070: [CMS-concurrent-mark-start]
Application time: 0.0021391 seconds
Total time for which application threads were stopped: 0.0046091 seconds
2010-04-13T23:05:33.343+0000: 3347.125: [CMS-concurrent-mark: 0.048/0.056
secs] [Times: user=0.35 sys=0.15, real=0.06 secs]
2010-04-13T23:05:33.344+0000: 3347.126: [CMS-concurrent-preclean-start]
2010-04-13T23:05:33.347+0000: 3347.128: [CMS-concurrent-preclean:
0.003/0.003 secs] [Times: user=0.01 sys=0.01, real=0.00 secs]
2010-04-13T23:05:33.347+0000: 3347.129:
[CMS-concurrent-abortable-preclean-start]
CMS: abort preclean due to time 2010-04-13T23:05:38.456+0000: 3352.238:
[CMS-concurrent-abortable-preclean: 0.573/5.109 secs] [Times: user=0.94
sys=0.24, real=5.11 secs]
Application time: 4.1574245 seconds
2010-04-13T23:05:38.461+0000: 3352.243: [GC[YG occupancy: 7824966 K
(16368000 K)]3352.243: [Rescan (parallel) , 4.2295340 secs]3356.473: [weak
refs processing, 0.0000422 secs] [1 CMS-remark: 12018K(196608K)]
7836984K(16564608K), 4.2298963 secs] [Times: user=36.56 sys=1.65,
real=4.23 secs]
Total time for which application threads were stopped: 4.2351364 seconds
2010-04-13T23:05:42.692+0000: 3356.473: [CMS-concurrent-sweep-start]
Application time: 0.0003415 seconds
What I would like to understand is why there is such a long pause when the
tenured is nowhere near full (~12m of 192m occupied)? and hence whether
this can be avoided?
Cheers
Matt
Matt Khan
--------------------------------------------------
GFFX Auto Trading
Deutsche Bank, London
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</pre>
</blockquote>
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