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From vinay patil <vinay18.pa...@gmail.com>
Subject Re: Frequent Full GC's in case of FSStateBackend
Date Thu, 09 Mar 2017 02:21:19 GMT
Hi Sai,

If you are sure that your state will not exceed the memory limit of nodes
then you should consider FSStatebackend otherwise you should go for RocksDB

What is the configuration of your cluster ?

On Mar 9, 2017 7:31 AM, "saiprasad mishra [via Apache Flink User Mailing
List archive.]" <ml-node+s2336050n12126h58@n4.nabble.com> wrote:

> Hi All
>
> I am also seeing issues with FsStateBackend as it stalls coz of full gc.
> We have very large state,
> Does this mean the below doc should not claim that FsStateBackend is
> encouraged for large state.
>
> https://ci.apache.org/projects/flink/flink-docs-release-1.2/ops/state_
> backends.html#the-fsstatebackend
>
> Regards
> Sai
>
> On Fri, Feb 10, 2017 at 6:19 AM, Stefan Richter <[hidden email]
> <http:///user/SendEmail.jtp?type=node&node=12126&i=0>> wrote:
>
>> Async snapshotting is the default.
>>
>> Am 10.02.2017 um 14:03 schrieb vinay patil <[hidden email]
>> <http:///user/SendEmail.jtp?type=node&node=12126&i=1>>:
>>
>> Hi Stephan,
>>
>> Thank you for the clarification.
>> Yes with RocksDB I don't see Full GC happening, also I am using Flink
>> 1.2.0 version and I have set the statebackend in flink-conf.yaml file to
>> rocksdb, so by default does this do asynchronous checkpointing or I have to
>> specify it at the job level  ?
>>
>> Regards,
>> Vinay Patil
>>
>> On Fri, Feb 10, 2017 at 4:16 PM, Stefan Richter [via Apache Flink User
>> Mailing List archive.] <[hidden email]> wrote:
>>
>>> Hi,
>>>
>>> FSStateBackend operates completely on-heap and only snapshots for
>>> checkpoints go against the file system. This is why the backend is
>>> typically faster for small states, but can become problematic for larger
>>> states. If your state exceeds a certain size, you should strongly consider
>>> to use RocksDB as backend. In particular, RocksDB also offers asynchronous
>>> snapshots which is very valuable to keep stream processing running for
>>> large state. RocksDB works on native memory/disk, so there is no GC to
>>> observe. For cases in which your state fits in memory but GC is a problem
>>> you could try using the G1 garbage collector which offers better
>>> performance for the FSStateBackend than the default.
>>>
>>> Best,
>>> Stefan
>>>
>>>
>>> Am 10.02.2017 um 11:16 schrieb Vinay Patil <[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11565&i=0>>:
>>>
>>> Hi,
>>>
>>> I am doing performance test for my pipeline keeping FSStateBackend, I
>>> have observed frequent Full GC's after processing 20M records.
>>>
>>> When I did memory analysis using MAT, it showed that the many objects
>>> maintained by Flink state are live.
>>>
>>> Flink keeps the state in memory even after checkpointing , when does
>>> this state gets removed / GC. (I am using window operator in which the DTO
>>> comes as input)
>>>
>>> Also why does Flink keep the state in memory after checkpointing ?
>>>
>>> P.S Using RocksDB is not causing Full GC at all.
>>>
>>> Regards,
>>> Vinay Patil
>>>
>>>
>>>
>>>
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