Hello Jaikiran,
Did you try collecting a heap dump and inspecting these ByteBuffers that
you suspect are holding on to non-heap memory? Looking at the GC roots
of these objects in the heap dump might shed some light as to why these
objects are not getting collected.
Thanks,
Poonam
On 12/3/18 7:57 PM, Jaikiran Pai wrote:
Hello Leo and Jeremy,
Thank you both for pointing me to those docs. They did help - the
ElasticSearch doc, I hadn't seen before during my search and the docs at
redhat.com developer blogs, although I had read them before a while
back, it was still useful since I found some new JVM options that I
could experiment with to get more details for the issue at hand.
Apologies for the delayed response though. I wanted to run a bunch of
experiments with various different configs to figure out what's really
going on, instead of speculating what might be going on.
After using all available/relevant JVM options and tuning the heap max
sizes and the cgroup limits and using OS level commands (that I know
off) to track the resource usage, we still ended up seeing the docker
container hitting the limit and then being killed. All the relevant
tracking tools (jconsole, the native hotspot memory tracking, the
direct/mapped buffer usage, heap usage) all kept showing that the usage
was well below the allowed limits. Yet the cgroups memory.usage_in_bytes
kept increasing over days and ultimately kept hitting the limit set at
cgroups level. At this point, it looked like we were either looking at
the wrong info or we weren't really using the right tools to figure out
what's really consuming this memory. After a bit more searching, we
finally found these issues[1][2] that match exactly to what we are
seeing (right down to the exact version of OS and docker and the nature
of configuration). So it looks like it's a known issue with docker + the
kernel version in use and apparently no known workaround (other than
downgrading to a version of docker that doesn't hit this). There appears
to be a commit[3] that has been done upstream but isn't yet released. We
will evaluate how to either try and patch/test that change or figure out
some other way (may be not set a --memory limit for now) to get past this.
Thank you all again for the helpful replies.
[1] https://github.com/opencontainers/runc/issues/1725
[2] https://github.com/moby/moby/issues/37722
[3]
https://github.com/opencontainers/runc/commit/6a2c15596845f6ff5182e2022f38a65e5dfa88eb
-Jaikiran
On 26/11/18 3:56 PM, jwhit...@redhat.com wrote:
Hi Jaikiran
Have a look at some blog posts by old friends :) These blog posts
might be helpful (along with the other replies you received) to
diagnose the root cause of the issue. In particular native memory
tracking.
https://developers.redhat.com/blog/2017/03/14/java-inside-docker/
https://developers.redhat.com/blog/2017/04/04/openjdk-and-containers/
Regards,
Jeremy
On Fri, 2018-11-23 at 19:25 +0530, Jaikiran Pai wrote:
Hi,
I'm looking for some inputs in debugging a high memory usage issue
(and
subsequently the process being killed) in one of the applications I
deal
with. Given that from what I have looked into this issue so far, this
appears to be something to do with the CMS collector, so I hope this
is
the right place to this question.
A bit of a background - The application that I'm dealing with is
ElasticSearch server version 1.7.5. We use Java 8:
java version "1.8.0_172"
Java(TM) SE Runtime Environment (build 1.8.0_172-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.172-b11, mixed mode)
To add to the complexity in debugging this issue, this runs as a
docker
container on docker version 18.03.0-ce on a CentOS 7 host VM kernel
version 3.10.0-693.5.2.el7.x86_64.
We have been noticing that this container/process keeps getting
killed
by the oom-killer every few days. The dmesg logs suggest that the
process has hit the "limits" set on the docker cgroups level. After
debugging this over past day or so, I've reached a point where I
can't
make much sense of the data I'm looking at. The JVM process is
started
using the following params (of relevance):
java -Xms2G -Xmx6G -XX:+UseParNewGC -XX:+UseConcMarkSweepGC
-XX:CMSInitiatingOccupancyFraction=75
-XX:+UseCMSInitiatingOccupancyOnly
-XX:+HeapDumpOnOutOfMemoryError -XX:+DisableExplicitGC ....
As you can see it uses CMS collector with 75% of tenured/old gen for
initiating the GC.
After a few hours/days of running I notice that even though the CMS
collector does run almost every hour or so, there are huge number of
objects _with no GC roots_ that never get collected. These objects
internally seem to hold on to ByteBuffer(s) which (from what I see)
as a
result never get released and the non-heap memory keeps building up,
till the process gets killed. To give an example, here's the jmap
-histo
output (only relevant parts):
1: 861642 196271400 [B
2: 198776 28623744
org.apache.lucene.codecs.blocktree.SegmentTermsEnumFrame
3: 676722 21655104
org.apache.lucene.store.ByteArrayDataInput
4: 202398 19430208
org.apache.lucene.codecs.lucene41.Lucene41PostingsWriter$IntBlockTerm
State
5: 261819 18850968
org.apache.lucene.util.fst.FST$Arc
6: 178661 17018376 [C
7: 31452 16856024 [I
8: 203911 8049352 [J
9: 85700 5484800 java.nio.DirectByteBufferR
10: 168935 5405920
java.util.concurrent.ConcurrentHashMap$Node
11: 89948 5105328 [Ljava.lang.Object;
12: 148514 4752448
org.apache.lucene.util.WeakIdentityMap$IdentityWeakReference
....
Total 5061244 418712248
This above output is without the "live" option. Running jmap
-histo:live
returns something like (again only relevant parts):
13: 31753 1016096
org.apache.lucene.util.WeakIdentityMap$IdentityWeakReference
...
44: 887 127728
org.apache.lucene.codecs.blocktree.SegmentTermsEnumFrame
...
50: 3054 97728
org.apache.lucene.store.ByteArrayDataInput
...
59: 888 85248
org.apache.lucene.codecs.lucene41.Lucene41PostingsWriter$IntBlockTerm
State
Total 1177783 138938920
Notice the vast difference between the live and non-live instances of
the same class. This isn't just in one "snapshot". I have been
monitoring this for more than a day and this pattern continues. Even
taking heap dumps and using tools like visualvm shows that these
instances have "no GC root" and I have even checked the gc log files
to
see that the CMS collector does occasionally run. However these
objects
never seem to get collected.
I realize this data may not be enough to narrow down the issue, but
what
I am looking for is some kind of help/input/hints/suggestions on what
I
should be trying to figure out why these instances aren't GCed. Is
this
something that's expected in certain situations?
-Jaikiran
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