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From Flavio Pompermaier <pomperma...@okkam.it>
Subject Re: Flink and swapping question
Date Tue, 06 Jun 2017 17:42:12 GMT
Hi Stephan,
I also think that the error is more related to netty.
The only suspicious library I use are parquet or thrift.
I'm not using off-heap memory.
What do you mean for "crazy high number of concurrent network shuffles"?how
can I count that?
We're using java 8.

Thanks a lot,
Flavio



On 6 Jun 2017 7:13 pm, "Stephan Ewen" <sewen@apache.org> wrote:

Hi!

I would actually be surprised if this is an issue in core Flink.

  - The MaxDirectMemory parameter is pretty meaningless, it really is a max
and does not have an impact on how much is actually allocated.

  - In most cases we had reported so far, the leak was in a library that
was used in the user code

  - If you do not use offheap memory in Flink, then there are few other
culprits that can cause high virtual memory consumption:
      - Netty, if you bumped the Netty version in a custom build
      - Flink's Netty, if the job has a crazy high number of concurrent
network shuffles (we are talking 1000s here)
      - Some old Java versions have I/O memory leaks (I think some older
Java 6 and Java 7 versions were affected)


To diagnose that better:

  - Are these batch or streaming jobs?
  - If it is streaming, which state backend are you using?

Stephan


On Tue, Jun 6, 2017 at 12:00 PM, Fabian Hueske <fhueske@gmail.com> wrote:

> Hi Flavio,
>
> can you post the all memory configuration parameters of your workers?
> Did you investigate which whether the direct or heap memory grew?
>
> Thanks, Fabian
>
> 2017-05-29 20:53 GMT+02:00 Flavio Pompermaier <pompermaier@okkam.it>:
>
>> Hi to all,
>> I'm still trying to understand what's going on our production Flink
>> cluster.
>> The facts are:
>>
>> 1. The Flink cluster runs on 5 VMWare VMs managed by ESXi
>> 2. On a specific  job we have, without limiting the direct memory to 5g,
>> the TM gets killed by the OS almost immediately because the memory required
>> by the TM, at some point, becomes huge, like > 100 GB (others jobs seem to
>> be less affected by the problem )
>> 3. Although the memory consumption is much better this way, the Flink TM
>> memory continuously grow job after job (of this problematic type): we set
>> TM max heap to 14 GB and the JVM required memory can be ~ 30 Gb. How is
>> that possible?
>>
>> My fear is that there's some annoying memory leak / bad memory allocation
>> in the Flink network level, but I can't have any evidence of this (except
>> the fact that the vm which doesn't have a hdfs datanode underneath the
>> Flink TM is the one with the biggest TM virtual memory consumption).
>>
>> Thanks for the help ,
>> Flavio
>>
>> On 29 May 2017 15:37, "Nico Kruber" <nico@data-artisans.com> wrote:
>>
>>> FYI: taskmanager.sh sets this parameter but also states the following:
>>>
>>>   # Long.MAX_VALUE in TB: This is an upper bound, much less direct
>>> memory will
>>> be used
>>>   TM_MAX_OFFHEAP_SIZE="8388607T"
>>>
>>>
>>> Nico
>>>
>>> On Monday, 29 May 2017 15:19:47 CEST Aljoscha Krettek wrote:
>>> > Hi Flavio,
>>> >
>>> > Is this running on YARN or bare metal? Did you manage to find out
>>> where this
>>> > insanely large parameter is coming from?
>>> >
>>> > Best,
>>> > Aljoscha
>>> >
>>> > > On 25. May 2017, at 19:36, Flavio Pompermaier <pompermaier@okkam.it>
>>> > > wrote:
>>> > >
>>> > > Hi to all,
>>> > > I think we found the root cause of all the problems. Looking ad dmesg
>>> > > there was a "crazy" total-vm size associated to the OOM error, a LOT
>>> much
>>> > > bigger than the TaskManager's available memory. In our case, the TM
>>> had a
>>> > > max heap of 14 GB while the dmsg error was reporting a required
>>> amount of
>>> > > memory in the order of 60 GB!
>>> > >
>>> > > [ 5331.992539] Out of memory: Kill process 24221 (java) score 937 or
>>> > > sacrifice child [ 5331.992619] Killed process 24221 (java)
>>> > > total-vm:64800680kB, anon-rss:31387544kB, file-rss:6064kB,
>>> shmem-rss:0kB
>>> > >
>>> > > That wasn't definitively possible usin an ordinary JVM (and our TM
>>> was
>>> > > running without off-heap settings) so we've looked at the parameters
>>> used
>>> > > to run the TM JVM and indeed there was a reall huge amount of memory
>>> > > given to MaxDirectMemorySize. With my big surprise Flink runs a TM
>>> with
>>> > > this parameter set to 8.388.607T..does it make any sense?? Is it
>>> > > documented anywhere the importance of this parameter (and why it is
>>> used
>>> > > in non off-heap mode as well)? Is it related to network buffers? It
>>> > > should also be documented that this parameter should be added to the
>>> TM
>>> > > heap when reserving memory to Flin (IMHO).
>>> > >
>>> > > I hope that this painful sessions of Flink troubleshooting could be
>>> an
>>> > > added value sooner or later..
>>> > >
>>> > > Best,
>>> > > Flavio
>>> > >
>>> > > On Thu, May 25, 2017 at 10:21 AM, Flavio Pompermaier <
>>> pompermaier@okkam.it
>>> > > <mailto:pompermaier@okkam.it>> wrote: I can confirm that after
>>> giving
>>> > > less memory to the Flink TM the job was able to run successfully.
>>> After
>>> > > almost 2 weeks of pain, we summarize here our experience with Fink
in
>>> > > virtualized environments (such as VMWare ESXi): Disable the
>>> > > virtualization "feature" that transfer a VM from a (heavy loaded)
>>> > > physical machine to another one (to balance the resource consumption)
>>> > > Check dmesg when a TM dies without logging anything (usually it goes
>>> OOM
>>> > > and the OS kills it but there you can find the log of this thing)
>>> CentOS
>>> > > 7 on ESXi seems to start swapping VERY early (in my case I see the
OS
>>> > > starting swapping also if there are 12 out of 32 GB of free memory)!
>>> > > We're still investigating how this behavior could be fixed: the
>>> problem
>>> > > is that it's better not to disable swapping because otherwise VMWare
>>> > > could start ballooning (that is definitely worse...).
>>> > >
>>> > > I hope this tips could save someone else's day..
>>> > >
>>> > > Best,
>>> > > Flavio
>>> > >
>>> > > On Wed, May 24, 2017 at 4:28 PM, Flavio Pompermaier <
>>> pompermaier@okkam.it
>>> > > <mailto:pompermaier@okkam.it>> wrote: Hi Greg, you were right!
After
>>> > > typing dmsg I found "Out of memory: Kill process 13574 (java)". This
>>> is
>>> > > really strange because the JVM of the TM is very calm.
>>> > > Moreover, there are 7 GB of memory available (out of 32) but somehow
>>> the
>>> > > OS decides to start swapping and, when it runs out of available swap
>>> > > memory, the OS decides to kill the Flink TM :(
>>> > >
>>> > > Any idea of what's going on here?
>>> > >
>>> > > On Wed, May 24, 2017 at 2:32 PM, Flavio Pompermaier <
>>> pompermaier@okkam.it
>>> > > <mailto:pompermaier@okkam.it>> wrote: Hi Greg,
>>> > > I carefully monitored all TM memory with jstat -gcutil and there'no
>>> full
>>> > > gc, only .>
>>> > > The initial situation on the dying TM is:
>>> > >   S0     S1     E      O      M     CCS    YGC     YGCT    FGC
>>> FGCT
>>> > >   GCT 0.00 100.00  33.57  88.74  98.42  97.17    159    2.508     1
>>> > >   0.255    2.763 0.00 100.00  90.14  88.80  98.67  97.17    197
>>> 2.617
>>> > >      1    0.255    2.873 0.00 100.00  27.00  88.82  98.75  97.17
>>> 234
>>> > >    2.730     1    0.255    2.986>
>>> > > After about 10 hours of processing is:
>>> > >   0.00 100.00  21.74  83.66  98.52  96.94   5519   33.011     1
>>> 0.255
>>> > >   33.267 0.00 100.00  21.74  83.66  98.52  96.94   5519   33.011
>>>  1
>>> > >   0.255   33.267 0.00 100.00  21.74  83.66  98.52  96.94   5519
>>>  33.011
>>> > >      1    0.255   33.267>
>>> > > So I don't think thta OOM could be an option.
>>> > >
>>> > > However, the cluster is running on ESXi vSphere VMs and we already
>>> > > experienced unexpected crash of jobs because of ESXi moving a
>>> > > heavy-loaded VM to another (less loaded) physical machine..I would't
>>> be
>>> > > surprised if swapping is also handled somehow differently.. Looking
>>> at
>>> > > Cloudera widgets I see that the crash is usually preceded by an
>>> intense
>>> > > cpu_iowait period. I fear that Flink unsafe access to memory could
>>> be a
>>> > > problem in those scenarios. Am I wrong?
>>> > >
>>> > > Any insight or debugging technique is  greatly appreciated.
>>> > > Best,
>>> > > Flavio
>>> > >
>>> > >
>>> > > On Wed, May 24, 2017 at 2:11 PM, Greg Hogan <code@greghogan.com
>>> > > <mailto:code@greghogan.com>> wrote: Hi Flavio,
>>> > >
>>> > > Flink handles interrupts so the only silent killer I am aware of is
>>> > > Linux's OOM killer. Are you seeing such a message in dmesg?
>>> > >
>>> > > Greg
>>> > >
>>> > > On Wed, May 24, 2017 at 3:18 AM, Flavio Pompermaier <
>>> pompermaier@okkam.it
>>> > > <mailto:pompermaier@okkam.it>> wrote: Hi to all,
>>> > > I'd like to know whether memory swapping could cause a taskmanager
>>> crash.
>>> > > In my cluster of virtual machines 'm seeing this strange behavior in
>>> my
>>> > > Flink cluster: sometimes, if memory get swapped the taskmanager (on
>>> that
>>> > > machine) dies unexpectedly without any log about the error.
>>> > >
>>> > > Is that possible or not?
>>> > >
>>> > > Best,
>>> > > Flavio
>>>
>>>
>

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