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From "Tzu-Li (Gordon) Tai" <tzuli...@apache.org>
Subject Re: A question regarding to the checkpoint mechanism
Date Mon, 17 Oct 2016 05:57:04 GMT
Users don’t need to explicitly make a copy of the state. Take checkpointing instance fields
as operator state for example [1].
You simply return your current state in `snapshotState()`, and Flink will take care of snapshotting
and persisting it to the state backend.
The persisting process does not block processing of input records if you implement the `CheckpointedAsynchronously`
interface (which is usually the more desirable case).
The same goes for key-partitioned states.

Best Regards,
Gordon

[1] https://ci.apache.org/projects/flink/flink-docs-release-1.2/dev/state.html#checkpointing-instance-fields

On October 17, 2016 at 11:32:07 AM, Li Wang (wangli1426@gmail.com) wrote:

Hi Gordon,

Thanks for your prompt reply.
So do you mean when we are about to checkpoint the state of an operator, we first copy its
state and then checkpoint the copied state while the operator continues processing?

Thanks,
Li


On Oct 17, 2016, at 11:10 AM, Tzu-Li (Gordon) Tai <tzulitai@apache.org> wrote:

Hi!

No, the operator does not need to pause processing input records while the checkpointing of
its state is in progress.
The checkpointing of operator state is asynchronous. The operator state does not need to be
immutable, since its a copy of the snapshot state that’s checkpointed.

Regards,
Gordon


On October 17, 2016 at 10:28:34 AM, Li Wang (wangli1426@gmail.com) wrote:

Hi All, 

Any feedback is highly appreciated. 

Thanks. 
Li 

> On Oct 15, 2016, at 11:17 AM, Li Wang <wangli1426@gmail.com> wrote: 
>  
> Hi all, 
>  
> As far as I know, a stateful operator will checkpoint its current state to a persistent
storage when it receives all the barrier from all of its upstream operators. My question is
that does the operator doing the checkpoint need to pause processing the input tuples for
the next batch until the checkpoint is done? If yes, will it introduce significant processing
latency when the state is large. If no, does this need the operator state to be immutable? 
>  
> Thanks, 
> Li


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