<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Sorry I didn’t do this earlier but Censum’s parsers not yet coping with Ergonomic data as well as they should be. This only reminds me that it’s been on my todo list a wee bit too long.<div class=""><br class=""></div><div class="">Kind regards,</div><div class="">Kirk</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On May 1, 2017, at 7:42 PM, nezih yigitbasi <<a href="mailto:nezihyigitbasi@gmail.com" class="">nezihyigitbasi@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Hi,<div class="">We have THP enabled for memory regions that explicitly request huge pages using madvise. We don't have swapping enabled. We run Presto (a distributed SQL engine, <a href="http://prestodb.io/" class="">http://prestodb.io</a>) on Java 1.8.0_112 and the machine has ~250GB memory and 12 physical cores.</div><div class="">I have some followup questions:</div><div class="">- I was always thinking that remembered sets were updated in the "Update RS" phase, can you please elaborate on the difference between rset update vs. object copy phases in terms of the rset processing that is being done in each?</div><div class="">- Is high system cpu time a good indicator for high contention?</div><div class=""><br class=""></div><div class="">Thanks!</div><div class="">Nezih</div><div class="gmail_extra"><br class=""><div class="gmail_quote">2017-04-28 15:44 GMT-07:00 <a href="mailto:yu.zhang@oracle.com" class="">yu.zhang@oracle.com</a> <span dir="ltr" class=""><<a href="mailto:yu.zhang@oracle.com" target="_blank" class="">yu.zhang@oracle.com</a>></span>:<br class=""><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF" class=""><p class="">Hi, Nezih,</p>
I agree with your estimation. There is not much promotion going on.<br class="">
<br class="">
Though I do not see high system cpu, if you are on a Linux system,
can you verify that the OS Transparent Huge Page is off?<br class="">
<br class="">
Remember set is the data structure that keep track of pointers from
other regions to the region we are operating on. If there are
pointers from old regions to the objects in the young regions, we
can not collect that object.<br class="">
After a gc pause, the live objects are evacuated to either the
survivor or old gen regions. Then we need to update the Remember
set. That is what I was referring to.<br class="">
It is part of object copy.<br class="">
<br class="">
Like Kirk mentioned, the parallelism of the gc threads seems fine.
Charlie.Hunt suggested maybe the object graph is very deep so that
the gc threads can not steal work and end up spinning.<br class="">
<br class="">
Some things we can try:<br class="">
-XX:MaxGCPauseMillis=<200> Maybe increase it to 400<br class="">
Maybe try to reduce the -XX:ParallelGCThreads<br class="">
<br class="">
<pre style="box-sizing:border-box;font-family:sfmono-regular,consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:normal;font-stretch:normal;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(246,248,250);border-radius:3px;color:rgb(36,41,46);letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;margin-top:0px;margin-bottom:0px" class=""><code style="box-sizing:border-box;font-family:sfmono-regular,consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0px;margin:0px;background:transparent;border-radius:3px;word-break:normal;white-space:pre-wrap;border:0px;display:inline;overflow:visible;line-height:inherit;word-wrap:normal" class="">-XX:+G1SummarizeRSetStats
-XX:<wbr class="">G1SummarizeRSetStatsPeriod=10</code></pre>
<br class="">
It is very expensive to print those statistics, for now we know
there is a lot of coarsening. We can make
G1SumarizeRSetStatsPeriod=100<br class="">
<br class="">
The RSet footprint is so big, increasing <span style="font-family:georgia;font-size:18px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline" class="">-XX:G1RSetRegionEntries
will get rid of coarsening but make the memory footprint bigger.
We can delay this for now.<br class="">
<br class="">
What is your hardware/software configuration? cpu/memory/cores?
There is no swapping, right?<br class="">
<br class="">
Thanks<span class="gmail-HOEnZb"><font color="#888888" class=""><br class="">
Jenny<br class="">
<br class="">
</font></span></span><div class=""><div class="gmail-h5">
<div class="gmail-m_2983664130649143190moz-cite-prefix">On 04/27/2017 08:52 PM, nezih yigitbasi
wrote:<br class="">
</div>
<blockquote type="cite" class="">
<div dir="ltr" class="">My first question is incorrect actually, so I am
giving a better example to rephrase my question. At time
"2017-04-26T03:12:24.259-0700" there is a young GC that
took 35.47 s, where object copy took 28983.4 ms. In that event I
see the following log:
<div class=""><br class="">
</div>
<div class="">
<div class=""> [Eden: 7168.0M(7168.0M)->0.0B(7168.<wbr class="">0M) Survivors:
1024.0M->1024.0M Heap: 153.4G(160.0G)->149.4G(160.0G)<wbr class="">]</div>
<div class=""><br class="">
</div>
<div class="">My interpretation for this is, ~4GB of garbage was
collected from heap in total and we see that eden usage goes
down by ~7GB, this means ~3GB of the eden was live objects.
Is this interpretation correct? If it is, how come copying
over 3GB takes ~29s? In your answer you said "most of the
object copy time is dealing with the Remember Set", can you
please give some details about what kind of operations on
rsets are done during the object copy phase, and can we see
that from these logs?</div>
<div class=""><br class="">
</div>
<div class="">Thanks again,</div>
<div class="">Nezih</div>
<div class=""><br class="">
</div>
</div>
</div>
<div class="gmail_extra"><br class="">
<div class="gmail_quote">2017-04-27 17:20 GMT-07:00 nezih
yigitbasi <span dir="ltr" class=""><<a href="mailto:nezihyigitbasi@gmail.com" target="_blank" class="">nezihyigitbasi@gmail.com</a>></span>:<br class="">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr" class="">Thanks for the suggestions. We use the
default pause time. And here is our entire set of JVM
args: <a href="https://gist.github.com/nezihyigitbasi/04f5fdb9c32ac56097011819e20602d8" target="_blank" class="">https://gist.github.com/<wbr class="">nezihyigitbasi/04f5fdb9c32ac56<wbr class="">097011819e20602d8</a>
<div class=""><br class="">
</div>
<div class="">I have some followup questions:<br class="">
<div class="">
<div class=""><br class="">
</div>
<div class="">- In some case the object copy took 39406.8 ms,
even if the remembered set is ~30GB isn't this too
slow (that's <1GB/s of data)?</div>
<div class="">- Is there any way to reduce the rset overhead?</div>
<div class="">- My initial thought when I saw the high object
copy times was there may be some sort of contention
to have such a low throughput during the copy.
Although it may not be the case here, I just wonder
whether there is a way to see the amount of
contention from the gc logs?</div>
<span class="gmail-m_2983664130649143190HOEnZb"><font color="#888888" class="">
<div class=""><br class="">
</div>
<div class="">Nezih</div>
</font></span>
<div class="">
<div class="gmail-m_2983664130649143190h5">
<div class=""><br class="">
</div>
<div class="">
<div class="">
<div class="gmail_extra"><br class="">
<div class="gmail_quote">2017-04-27 16:58
GMT-07:00 Jenny Zhang <span dir="ltr" class=""><<a href="mailto:yu.zhang@oracle.com" target="_blank" class="">yu.zhang@oracle.com</a>></span>:<br class="">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi,
Hezih,<br class="">
<br class="">
It seems this workload is very heavy on
Remember Set. It has about 31G native
memory for RSet (old gen) and still with
coarsening.<br class="">
<br class="">
What is you pause time goal? The default
(200ms) might be too small for you. Can
you increase that so G1 can increase the
young gen size? Since there is not much
promotion, I guess most of the object
copy time is dealing with the Remember
Set.<br class="">
<br class="">
There are other things you can try, like
increase the G1RSetReginEntries, but the
memory footprint will be bigger.<br class="">
<br class="">
So if you can, I suggest increase the
pause time goal first.<br class="">
<br class="">
Thanks<span class="gmail-m_2983664130649143190m_8770557251507851110gmail-HOEnZb"><font color="#888888" class=""><br class="">
<br class="">
Jenny</font></span>
<div class="gmail-m_2983664130649143190m_8770557251507851110gmail-HOEnZb">
<div class="gmail-m_2983664130649143190m_8770557251507851110gmail-h5"><br class="">
<br class="">
<br class="">
<br class="">
On 4/27/2017 9:22 AM, nezih
yigitbasi wrote:<br class="">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
Hi,<br class="">
We see huge object copy times (and
relatively high termination times)
during young GCs in our production
system running on Java
1.8.0_112-b15. You can find the GC
logs here: <a href="https://gist.github.com/nezihyigitbasi/1f7a92da7860908a611cb1197bd8626b" rel="noreferrer" target="_blank" class="">https://gist.github.com/nezihy<wbr class="">igitbasi/1f7a92da7860908a611cb<wbr class="">1197bd8626b</a><br class="">
<br class="">
The young GC times start going
high after the timestamp
"2017-04-26T03:07:22.164-0700"<wbr class="">.<br class="">
<br class="">
I will appreciate if you can give
some details about:<br class="">
- what goes into the "Object Copy"
phase during young GCs and how we
can reduce it.<br class="">
- why we see high Termination
times and what we can do about it<br class="">
<br class="">
Thanks,<br class="">
Nezih<br class="">
</blockquote>
<br class="">
</div>
</div>
</blockquote>
</div>
<br class="">
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</blockquote>
</div>
<br class="">
</div>
</blockquote>
<br class="">
</div></div></div>
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