Hi, Thanks for the proposal Dawid, I have some questions and remarks:
1. How will stop-with-savepoint be handled? Shouldn't side effects be enforced in this case? (i.e. send notifyCheckpointComplete) 2. Instead of forcing re-upload, can we "inverse control" in no-claim mode? Anyways, any external tool will have to poll Flink API waiting for the next (full) checkpoint, before deleting the retained checkpoint, right? Instead, we can provide an API which tells whether the 1st checkpoint is still in use (and not force re-upload it). Under the hood, it can work like this: - for the checkpoint Flink recovers from, remember all shared state handles it is adding - when unregistering shared state handles, remove them from the set above - when the set becomes empty the 1st checkpoint can be deleted externally Besides not requiring re-upload, it seems much simpler and less invasive. On the downside, state deletion can be delayed; but I think this is a reasonable trade-off. 3. Alternatively, re-upload not necessarily on 1st checkpoint, but after a configured number of checkpoints? There is a high chance that after some more checkpoints, initial state will not be used (because of compaction), so backends won't have to re-upload anything (or small part). 4. Re-uploaded artifacts must not be deleted on checkpoin abortion This should be addressed in https://issues.apache.org/jira/browse/FLINK-24611. If not, I think the FLIP should consider this case. 5. Enforcing re-upload by a single task and Changelog state backend With Changelog state backend, a file can be shared by multiple operators. Therefore, getIntersection() is irrelevant here, because operators might not be sharing any key groups. (so we'll have to analyze "raw" file usage I think). 6. Enforcing re-upload by a single task and skew If we use some greedy logic like subtask 0 always re-uploads then it might be overloaded. So we'll have to obtain a full list of subtasks first (then probably choose randomly or round-robin). However, that requires rebuilding Task snapshot, which is doable but not trivial (which I think supports "reverse API option"). 7. I think it would be helpful to list file systems / object stores that support "fast" copy (ideally with latency numbers). Regards, Roman On Mon, Nov 22, 2021 at 9:24 AM Yun Gao <yungao...@aliyun.com.invalid> wrote: > > Hi, > > Very thanks Dawid for proposing the FLIP to clarify the ownership for the > states. +1 for the overall changes since it makes the behavior clear and > provide users a determined method to finally cleanup savepoints / retained > checkpoints. > > Regarding the changes to the public interface, it seems currently the changes > are all bound > to the savepoint, but from the FLIP it seems perhaps we might also need to > support the claim declaration > for retained checkpoints like in the cli side[1] ? If so, then might it be > better to change the option name > from `execution.savepoint.restore-mode` to something like > `execution.restore-mode`? > > Best, > Yun > > > [1] > https://nightlies.apache.org/flink/flink-docs-master/docs/ops/state/checkpoints/#resuming-from-a-retained-checkpoint > > > ------------------------------------------------------------------ > From:Konstantin Knauf <kna...@apache.org> > Send Time:2021 Nov. 19 (Fri.) 16:00 > To:dev <dev@flink.apache.org> > Subject:Re: [DISCUSS] FLIP-193: Snapshots ownership > > Hi Dawid, > > Thanks for working on this FLIP. Clarifying the differences and > guarantees around savepoints and checkpoints will make it easier and safer > for users and downstream projects and platforms to work with them. > > +1 to the changing the current (undefined) behavior when recovering from > retained checkpoints. Users can now choose between claiming and not > claiming, which I think will make the current mixed behavior obsolete. > > Cheers, > > Konstantin > > On Fri, Nov 19, 2021 at 8:19 AM Dawid Wysakowicz <dwysakow...@apache.org> > wrote: > > > Hi devs, > > > > I'd like to bring up for a discussion a proposal to clean up ownership > > of snapshots, both checkpoints and savepoints. > > > > The goal here is to make it clear who is responsible for deleting > > checkpoints/savepoints files and when can that be done in a safe manner. > > > > Looking forward for your feedback! > > > > Best, > > > > Dawid > > > > [1] https://cwiki.apache.org/confluence/x/bIyqCw > > > > > > > > -- > > Konstantin Knauf > > https://twitter.com/snntrable > > https://github.com/knaufk >
