CMS initial mark pauses
Y. S. Ramakrishna
y.s.ramakrishna at oracle.com
Thu Oct 14 11:56:31 PDT 2010
Hi Adam --
Do you have a fuller GC log (perhaps including
PrintCMSStatistics=2) to help make a sharper diagnosis?
It could be:-
6412968 CMS: Long initial mark pauses
which we have unfortunately not gotten to addressing yet:
CMS initial mark work is (still) done single-threaded.
Usually there is little such work so we are usually fine,
but if survivor spaces are large and full and/or if CMS triggering
occupancy is such that CMS runs frequently then you can
be affected by long serial initial mark pauses because
the work is non-trivial. (CMS-remark and scavenges on
the other hand are done by several worker threads working
Here's an excerpt from the "workaround" section of that bug
(reproduced here because i cannot seem to get bugs.sun.com
to display it) :-
> This is not really a viable workaround since it might lead to suboptimal
> heap configuration:
> (1) use no survivor spaces (at the risk of larger scavenge pauses, larger remark pauses,
> even concurrent mode failures)
> (2) use a sufficiently large heap so as to be able to afford to set a
> mark initiation threshold above the low water-mark (after a major
> collection cycle). This will keep init-mark's riding on the coat-tails
> of scavenges.
> *** (#1 of 2): 2006-04-13 09:53:14 PDT xxxx at oracle.com
> Also, if using iCMS (Inceremental CMS), drop the Incremental mode and revert to
> vanilla CMS.
> *** (#2 of 2): 2010-04-14 11:02:03 PDT xxxx at oracle.com
If you have support, you can try escalating it via your support channels
to get this addressed, especially if the workaround/retuning doesn't
do the job.
On 10/14/10 11:31, Adam Hawthorne wrote:
> Hi all,
> I'm seeing a customer running CMS with some fairly long initial mark
> pauses, especially relative to all the other pauses. The machine is (I
> believe) an Itanium 6-way running HP-UX, with HP's version of Hotspot,
> version 1.6.0.06 .
> What I'm seeing is that all the remark and young gc pauses are less than
> 500ms, and very consistent. There are a lot of initial mark pauses that
> also fall in this range. That's our target, and things look really
> good. The problem is that there are occasional pauses of up to 1.5s,
> which is unacceptable for the customer. Does anyone have any ideas what
> can cause (seemingly random) long initial mark pauses?
> Here's an example of one of the long mark pauses:
> 45946.930: [GC [1 CMS-initial-mark: 957254K(1598236K)]
> 1473999K(2151196K), 1.3505680 secs] [Times: user=1.34 sys=0.00,
> real=1.35 secs]
> Here's an example of one of the more typical pauses:
> 45954.362: [GC [1 CMS-initial-mark: 963824K(1598236K)]
> 1001370K(2151196K), 0.1579016 secs] [Times: user=0.16 sys=0.00,
> real=0.16 secs]
> From my understanding, initial mark pauses are supposed to be
> relatively short, and usually shorter than remark pauses, but I don't
> have a remark pause greater than 300ms.
> Any help is appreciated. Thanks,
> Adam Hawthorne
> Software Engineer
> BASIS International Ltd.
> www.basis.com <http://www.basis.com>
> +1.505.345.5232 Phone
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