*bq. I agree with your assessment of the CheckpointStorage interface but I
want to push back at including those changes as a part of this FLIP.*
Makes sense, will start a separate discussion around this topic when
prepared.
*bq. One option could be to rename "CheckpointStorage" to
"CheckpointStorageAccess" and then use the name "CheckpointStorage" instead
of "SnapshotStorage". *
+1
And thanks for updating the document, some comments for the new version:
Questions around migration:
1. With `FSStateBackend`, we used to decide where to store the checkpoint
by the `state.backend.fs.memory-threshold` configuration, and we need to
decide how to align with this behavior with the new implementation.
2. With the new implementation, since users could set checkpoint storage
through API, do we also support the combination of
`EmbeddedRocksDBStateBackend` with `JobManagerCheckpointStorage`?
One answer to the above questions is making
`JobManagerCheckpointStorage` internal implementation and use it as the
default checkpoint storage. And when user sets to
use `FileSystemCheckpointStorage`, we will still switch to
`JobManagerCheckpointStorage` when the task checkpoint size is smaller than
`state.backend.fs.memory-threshold`, even with RocksDB state backend. This
will align with most of the current behavior except for RocksDB backend
with really small checkpoint size.
Minor issues:
1. There are still some `SnapshotStorage` / `JobManagerSnapshot` left in
the code samples, please clean them up
2. Personally I'm in favor of `JobManagerCheckpointStorage` /
`FileSystemCheckpointStorage` than `JobManagerStorage` / `FileSystemStorage`
Thanks.
Best Regards,
Yu
On Fri, 18 Sep 2020 at 01:58, Seth Wiesman <sjwies...@gmail.com> wrote:
> That makes sense to me, I've updated the FLIP and also took this chance to
> make it clearer what the goals and non-goals of this proposal are.
>
> Seth
>
> On Thu, Sep 17, 2020 at 9:17 AM Stephan Ewen <se...@apache.org> wrote:
>
> > Just a quick note that it should be possible to rename
> "CheckpointStorage"
> > because it is a purely internal interface.
> >
> > Looks like the "SnapshotStorage" takes some limited amount of
> functionality
> > from the "CheckpointStorage", like location pointer resolution.
> > One option could be to rename "CheckpointStorage" to
> > "CheckpointStorageAccess" and then use the name "CheckpointStorage"
> instead
> > of "SnapshotStorage".
> >
> >
> >
> > On Thu, Sep 17, 2020 at 3:47 PM Seth Wiesman <sjwies...@gmail.com>
> wrote:
> >
> > > Hi Yu,
> > >
> > > I've updated the Deprecation / Compatibility / Migration section to
> more
> > > explicitly lay out the steps that we would take as part of this FLIP.
> It
> > > includes your above concerns.
> > >
> > > Regarding SnapshotStorage vs CheckpointStorage. I'm not sure users are
> > > going to have a problem with this. I doubt many people outside this
> > thread
> > > are familiar with the CheckpointStorage interface today. Even with
> these
> > > changes implemented, most users will not interact with the
> > SnapshotStorage
> > > interface. They will only ever see JobManagerStorage and
> > FileSystemStorage.
> > >
> > > I agree with your assessment of the CheckpointStorage interface but I
> > want
> > > to push back at including those changes as a part of this FLIP. The
> goal
> > is
> > > to simplify users' understanding of state backends and checkpointing. I
> > > would like to keep anything related to the runtime or internal as a
> > > non-goal.
> > >
> > > Seth
> > >
> > > On Thu, Sep 17, 2020 at 3:03 AM Yu Li <car...@gmail.com> wrote:
> > >
> > > > Thanks for the suggestion and discussion, and sorry for being late to
> > the
> > > > party.
> > > >
> > > > For me, +1 for the idea, but +0 for the current FLIP document.
> > > >
> > > > First of all, I suggest we explicitly mention the deprecation of
> > existing
> > > > backends in the document. From the description, we plan to mark all
> > > > existing backend implementations (i.e.
> > > > RocksDBStateBackend/MemoryStateBackend/FSStateBackend) as deprecated,
> > and
> > > > in their javadoc we should give the suggestion of migration to new
> > > > implementations (i.e.
> HashMapStateBackend/EmbeddedRocksDBStateBackend).
> > > >
> > > > Secondly, I suggest we explicitly mention the user-facing changes for
> > > > customized state backends.
> > > >
> > > > To be more specific, the above two should be included in the
> > > > "Compatibility, Deprecation, and Migration Plan" section. The
> existing
> > > > document already mentioned these two aspects, but IMO not explicit
> > > enough.
> > > >
> > > > Thirdly, we already have a `CheckpointStorage` interface and now
> > > > introducing a new `SnapshotStoage`, and I share the same concern with
> > > > Stephan that these two interfaces might cause confusion, and suggest
> we
> > > > discuss more about this part.
> > > >
> > > > This might sound to be a little bit off-track, but I think it's
> > necessary
> > > > to review the necessity of the existence of current
> > `CheckpointStorage`.
> > > It
> > > > seems to me that only JM-side logic will use interfaces in
> > > > `CheckpointStorageCoordinatorView` and only TM-side logic use
> > > > `CheckpointStorageWorkerView`, but we combine these two together.
> > What's
> > > > more, if we check it carefully, we could find the signature of
> > > > `resolveCheckpoint` interface in current `StateBackend` and
> > > > `CheckpointStorageCoordinatorView` are exactly the same (even the
> > > javadoc),
> > > > which means if we simply extract `resolveCheckpoint` out into
> > > > `SnapshotStorage`, there will be two interfaces with the same
> signature
> > > in
> > > > `SnapshotStorage` and `CheckpointStorage`, which will be really
> > > confusing.
> > > > Sorry but I don't have a proposal of solution yet, but I suggest we
> > > figure
> > > > this out clearly.
> > > >
> > > > Thanks.
> > > >
> > > > Best Regards,
> > > > Yu
> > > >
> > > >
> > > > On Thu, 17 Sep 2020 at 13:19, Congxian Qiu <qcx978132...@gmail.com>
> > > wrote:
> > > >
> > > > > Thanks for the detailed replay, +1 from my side.
> > > > > Best,
> > > > > Congxian
> > > > >
> > > > >
> > > > > Seth Wiesman <sjwies...@gmail.com> 于2020年9月17日周四 上午1:33写道：
> > > > >
> > > > > > Hi Stephan,
> > > > > >
> > > > > > Regarding backward compatibility, I agree and the intention is
> that
> > > all
> > > > > > existing code will continue to function with the same semantics.
> My
> > > > > working
> > > > > > idea is to remove the two checkpoint-storage related methods from
> > > > > > StateBackend into a new SnapshotStorage interface but then have
> > > > > > AbstractFileStateBackend and RocksDBStateBackend implement
> snapshot
> > > > > > storage. If a state backend implements SnapshotStorage it will be
> > > used
> > > > > > unconditionally, even if a different snapshot storage
> > implementation
> > > is
> > > > > > configured. This way we don't change any of the concrete classes
> > that
> > > > > users
> > > > > > interact with. The only people who would see breaking changes are
> > > state
> > > > > > backend implementors and they only need to add `implements
> > > > > SnapshotStorage`
> > > > > > to their class.
> > > > > >
> > > > > > The reason I went with SnapshotStorage is there is already an
> > > interface
> > > > > > `org.apache.flink.runtime.state.CheckpointStorage` in
> > flink-runtime.
> > > If
> > > > > we
> > > > > > can rename this interface to something else I'm happy to take the
> > > name,
> > > > > but
> > > > > > if not I think it will lead to import confusion.
> > > > > >
> > > > > > Seth
> > > > > >
> > > > > > On Wed, Sep 16, 2020 at 11:54 AM Stephan Ewen <se...@apache.org>
> > > > wrote:
> > > > > >
> > > > > > > @Yun and @Congxian:
> > > > > > >
> > > > > > > I think "async", "incremental", and similar flags belong very
> > much
> > > > with
> > > > > > the
> > > > > > > state backend (the index structure).
> > > > > > > They define how the snapshotting procedure behaves.
> > > > > > >
> > > > > > > The SnapshotStorage is really just about storage of checkpoint
> > > > streams
> > > > > > > (bytes) and handles and pointers.
> > > > > > >
> > > > > > > Best,
> > > > > > > Stephan
> > > > > > >
> > > > > > >
> > > > > > > On Wed, Sep 16, 2020 at 6:48 PM Stephan Ewen <se...@apache.org
> >
> > > > wrote:
> > > > > > >
> > > > > > > > Thanks for the great suggestion and the great discussion.
> > > Generally
> > > > > big
> > > > > > > +1
> > > > > > > > to this effort.
> > > > > > > > Some thoughts from my side:
> > > > > > > >
> > > > > > > > *## Backwards Compatibility*
> > > > > > > >
> > > > > > > > I think we should really strive to make this non breaking.
> > Maybe
> > > we
> > > > > > have
> > > > > > > > new classes / interfaces for StateBackends and
> > CheckpointStorage
> > > > and
> > > > > > let
> > > > > > > > the existing State Backend classes implement both (and
> > deprecate
> > > > > them)?
> > > > > > > >
> > > > > > > > In the past, I have gotten some harsh comments from users
> about
> > > > > > breaking
> > > > > > > > long-time effectively stable APIs, so let's try hard to avoid
> > > this
> > > > > > > (unless
> > > > > > > > it makes things impossible).
> > > > > > > >
> > > > > > > > *## Naming*
> > > > > > > >
> > > > > > > > HashMapStateBackend sounds good to me
> > > > > > > >
> > > > > > > > Could we rename the SnapshotStorage to CheckpointStorage? Or
> > > > converge
> > > > > > all
> > > > > > > > methods around "Snapshot"?
> > > > > > > > I think we already have some confusion from mixing the terms
> > > > > checkpoint
> > > > > > > > and snapshot and should converge in either direction.
> > > > > > > > I am slightly leaning towards converging around checkpoints,
> > > > because
> > > > > > > > that's the most commonly known term among users as far as I
> can
> > > > tell.
> > > > > > > > Checkpoints are Snapshots. But one could also just call them
> > > > > > Checkpoints
> > > > > > > > and let Savepoints be special Checkpoints.
> > > > > > > >
> > > > > > > > *## Integrated State / Storage Backends*
> > > > > > > >
> > > > > > > > There is an idea floating around now and then about a
> Cassandra
> > > > > backend
> > > > > > > > (or other K/V store) where the state index and durable
> location
> > > are
> > > > > > > tightly
> > > > > > > > intertwined.
> > > > > > > > However, I think this would not contradict, because it might
> > just
> > > > > mean
> > > > > > > > that the checkpoint storage is used less (maybe only for
> > > > savepoints,
> > > > > or
> > > > > > > for
> > > > > > > > WALs).
> > > > > > > >
> > > > > > > > *## Future Fault Tolerance Ideas*
> > > > > > > >
> > > > > > > > I think this conflicts with none of the future fault
> tolerance
> > > > ideas
> > > > > I
> > > > > > am
> > > > > > > > involved with.
> > > > > > > > Similar to the above, there is always some checkpoint storage
> > > > > involved,
> > > > > > > > for example for savepoints or for backup/consolidation, so no
> > > > > problem.
> > > > > > > >
> > > > > > > >
> > > > > > > > Best,
> > > > > > > > Stephan
> > > > > > > >
> > > > > > > > On Wed, Sep 16, 2020 at 5:11 PM Aljoscha Krettek <
> > > > > aljos...@apache.org>
> > > > > > > > wrote:
> > > > > > > >
> > > > > > > >> I think the mentioned settings should be in the state
> backend.
> > > > They
> > > > > > > >> configure how a certain backend writes to a snapshot
> storage,
> > > but
> > > > > it’s
> > > > > > > >> still the backend that has the logic and decides.
> > > > > > > >>
> > > > > > > >> I think it's a good point, though, to be conscious about
> those
> > > > > > settings.
> > > > > > > >> I'm sure we can figure out the details during
> implementation,
> > > > > though.
> > > > > > > >>
> > > > > > > >> Best,
> > > > > > > >> Aljoscha
> > > > > > > >>
> > > > > > > >> On 16.09.20 16:54, Seth Wiesman wrote:
> > > > > > > >> > Hi Congxian,
> > > > > > > >> >
> > > > > > > >> > There is an allusion to those configs in the wiki but let
> me
> > > > > better
> > > > > > > >> spell
> > > > > > > >> > out my thinking. The flink-conf configurations will not
> > change
> > > > > and I
> > > > > > > >> > believe the java code switches should remain on the state
> > > > backend
> > > > > > > >> objects.
> > > > > > > >> >
> > > > > > > >> > We are of course not fully disentangling state backends
> from
> > > > > > snapshots
> > > > > > > >> and
> > > > > > > >> > these configurations affect how your state backend runs in
> > > > > > > production. I
> > > > > > > >> > believe users would find it strange to have configurations
> > > like
> > > > > > > >> > `state.backend.rocksdb.checkpoint.transfer.thred.num` not
> be
> > > > part
> > > > > of
> > > > > > > the
> > > > > > > >> > EmbeddedRocksdbStateBackend but somewhere else. This then
> > > leads
> > > > to
> > > > > > the
> > > > > > > >> > question, is it better to split configurations between
> > > multiple
> > > > > > places
> > > > > > > >> or
> > > > > > > >> > not. Users appreciate consistency, and so having all the
> > > > > > > configurations
> > > > > > > >> on
> > > > > > > >> > the state backend objects makes them more discoverable and
> > > your
> > > > > > > >> application
> > > > > > > >> > easier to reason about.
> > > > > > > >> >
> > > > > > > >> > Additionally, I view these as advanced configurations. My
> > hope
> > > > is
> > > > > > most
> > > > > > > >> > users can simply use the no-arg constructor for a state
> > > backend
> > > > in
> > > > > > > >> > production. If a user is changing the number of rocksdb
> > > transfer
> > > > > > > >> threads or
> > > > > > > >> > disabling async checkpoints, they likely know what they
> are
> > > > doing.
> > > > > > > >> >
> > > > > > > >> > Please let me know if you have any concerns or would like
> to
> > > > > cancel
> > > > > > > the
> > > > > > > >> > vote.
> > > > > > > >> >
> > > > > > > >> > Seth
> > > > > > > >> >
> > > > > > > >> > On Wed, Sep 16, 2020 at 12:37 AM Congxian Qiu <
> > > > > > qcx978132...@gmail.com
> > > > > > > >
> > > > > > > >> > wrote:
> > > > > > > >> >
> > > > > > > >> >> Sorry for jump late in.
> > > > > > > >> >>
> > > > > > > >> >> I like the separation here, this separation makes more
> user
> > > > > > friendly
> > > > > > > >> now.
> > > > > > > >> >>
> > > > > > > >> >> I just wonder how the configuration such as
> > > > > > > >> 'state.backend.incremental',
> > > > > > > >> >> 'state.backend.async' and
> > > > > > > >> >> `state.backend.rocksdb.checkpoint.transfer.thred.num`
> will
> > be
> > > > > > > >> configured
> > > > > > > >> >> after the separation, I think these configurations are
> more
> > > > > related
> > > > > > > to
> > > > > > > >> >> snapshots (maybe a little strange to configure these on
> > > > > > statebackend
> > > > > > > >> side).
> > > > > > > >> >> did not see this on the FLIP wiki currently.
> > > > > > > >> >>
> > > > > > > >> >> Best,
> > > > > > > >> >> Congxian
> > > > > > > >> >>
> > > > > > > >> >>
> > > > > > > >> >> Seth Wiesman <sjwies...@gmail.com> 于2020年9月15日周二
> 下午9:51写道：
> > > > > > > >> >>
> > > > > > > >> >>> Sounds good to me. I'll update the FLIP.
> > > > > > > >> >>>
> > > > > > > >> >>> On Tue, Sep 15, 2020 at 8:35 AM Dawid Wysakowicz <
> > > > > > > >> dwysakow...@apache.org
> > > > > > > >> >>>
> > > > > > > >> >>> wrote:
> > > > > > > >> >>>
> > > > > > > >> >>>> There is a good number of precedents that introduced
> > > > backwards
> > > > > > > >> >>>> incompatible changes to that interface (which is
> > > > PublicEvolving
> > > > > > > btw).
> > > > > > > >> >> We
> > > > > > > >> >>>> introduced a couple of additional arguments to the
> > > > > > > >> >>>> createKeyedStateBackend method and later on removed the
> > > > methods
> > > > > > > with
> > > > > > > >> >>>> default implementation for backwards compatibility. I
> > want
> > > to
> > > > > > > >> introduce
> > > > > > > >> >>>> a backward incompatible change in FLIP-140 (replace the
> > > > > > > >> >>>> AbstractKeyedStateBackend with an interface). From my
> > > > > perspective
> > > > > > > we
> > > > > > > >> >>>> should just do these changes. The impact should be
> > minimal.
> > > > > > > >> >>>>
> > > > > > > >> >>>> Best,
> > > > > > > >> >>>>
> > > > > > > >> >>>> Dawid
> > > > > > > >> >>>>
> > > > > > > >> >>>>
> > > > > > > >> >>>> On 15/09/2020 15:20, Seth Wiesman wrote:
> > > > > > > >> >>>>> Hey Dawid,
> > > > > > > >> >>>>>
> > > > > > > >> >>>>> I didn't want to break compatibility but if there is
> > > > precedent
> > > > > > and
> > > > > > > >> >>>> everyone
> > > > > > > >> >>>>> is ok with it then I'm +1.
> > > > > > > >> >>>>>
> > > > > > > >> >>>>> Seth
> > > > > > > >> >>>>>
> > > > > > > >> >>>>> On Tue, Sep 15, 2020 at 2:22 AM Dawid Wysakowicz <
> > > > > > > >> >>> dwysakow...@apache.org
> > > > > > > >> >>>>>
> > > > > > > >> >>>>> wrote:
> > > > > > > >> >>>>>
> > > > > > > >> >>>>>> Sorry for joining so late.
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> Generally speaking I like this idea very much!
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> I have one idea about the StateBackend interface.
> Could
> > > we
> > > > > > > instead
> > > > > > > >> >> of
> > > > > > > >> >>>>>> adding a flag method boolean isLegacyStateBackend
> > remove
> > > > the
> > > > > > > >> >>>>>> checkpointstorage related methods from StateBackend
> > right
> > > > > away?
> > > > > > > The
> > > > > > > >> >>>>>> old/legacy implementations could then implement both
> > > > > > StateBackend
> > > > > > > >> >> and
> > > > > > > >> >>>>>> SnapshotStorage. In turn in the method
> > > env.setStateBackend
> > > > we
> > > > > > > could
> > > > > > > >> >>> do:
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> setStateBackend(StateBackend backend) {
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> this.stateBackend = backend;
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> if (backend instanceof SnapshotStorage) {
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> this.setSnapshotStorage(backend);
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> }
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> }
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> This has the benefit that we could already get rid
> off
> > > the
> > > > > > > methods
> > > > > > > >> >>> from
> > > > > > > >> >>>>>> StateBackend which would be problematic in the new
> > > > > > > implementations
> > > > > > > >> >>> (such
> > > > > > > >> >>>>>> as e.g. HashMapStateBackend - what would you return
> > > there?
> > > > > > > null?).
> > > > > > > >> I
> > > > > > > >> >>>>>> know this would break the interface, but StateBackend
> > is
> > > > > > actually
> > > > > > > >> >>> quite
> > > > > > > >> >>>>>> internal, we did it quite freely in the past, and I
> > don't
> > > > > think
> > > > > > > >> >> there
> > > > > > > >> >>>>>> are many custom state implementation in the wild. And
> > > even
> > > > if
> > > > > > > there
> > > > > > > >> >>> are
> > > > > > > >> >>>>>> some the workaround is as easy as simply adding
> > > implements
> > > > > > > >> >>>> SnapshotStorage.
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> Best,
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> Dawid
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>>> On 11/09/2020 16:48, Aljoscha Krettek wrote:
> > > > > > > >> >>>>>>> I could try and come up with a longer name if you
> need
> > > it
> > > > > ...
> > > > > > > ;-)
> > > > > > > >> >>>>>>>
> > > > > > > >> >>>>>>> Aljoscha
> > > > > > > >> >>>>>>>
> > > > > > > >> >>>>>>> On 11.09.20 16:25, Seth Wiesman wrote:
> > > > > > > >> >>>>>>>> Having thought about it more, HashMapStateBackend
> has
> > > won
> > > > > me
> > > > > > > >> over.
> > > > > > > >> >>>> I'll
> > > > > > > >> >>>>>>>> update the FLIP. If there aren't any more comments
> > I'll
> > > > > open
> > > > > > it
> > > > > > > >> up
> > > > > > > >> >>> for
> > > > > > > >> >>>>>>>> voting on monday.
> > > > > > > >> >>>>>>>>
> > > > > > > >> >>>>>>>> Seth
> > > > > > > >> >>>>>>>>
> > > > > > > >> >>>>>>>> On Wed, Sep 9, 2020 at 9:09 AM Seth Wiesman <
> > > > > > > sjwies...@gmail.com
> > > > > > > >> >
> > > > > > > >> >>>>>> wrote:
> > > > > > > >> >>>>>>>>> @Yun yes, this is really about making
> > > CheckpointStorage
> > > > an
> > > > > > > >> >>> orthogonal
> > > > > > > >> >>>>>>>>> concept. I think we can remain pragmatic and keep
> > > > > > > state-backend
> > > > > > > >> >>>>>>>>> specific
> > > > > > > >> >>>>>>>>> configurations (async, incremental, etc) in the
> > state
> > > > > > backend
> > > > > > > >> >>>>>>>>> themselves. I
> > > > > > > >> >>>>>>>>> view these as more advanced configurations and by
> > the
> > > > time
> > > > > > > >> >> someone
> > > > > > > >> >>> is
> > > > > > > >> >>>>>>>>> changing the defaults they likely understand what
> is
> > > > going
> > > > > > on.
> > > > > > > >> My
> > > > > > > >> >>>>>>>>> goal is
> > > > > > > >> >>>>>>>>> to help on-board users and so long as each state
> > > backend
> > > > > > has a
> > > > > > > >> >>> no-arg
> > > > > > > >> >>>>>>>>> default constructor that works for many users I
> > think
> > > > > we've
> > > > > > > >> >>> achieved
> > > > > > > >> >>>>>>>>> that
> > > > > > > >> >>>>>>>>> goal.
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>> Regarding the checkpoint coordinator, that makes
> > sense
> > > > > but I
> > > > > > > >> will
> > > > > > > >> >>>>>>>>> consider
> > > > > > > >> >>>>>>>>> out of the scope of this FLIP. I want to focus on
> > > > > > simplifying
> > > > > > > >> >> APIs.
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>> @Aljoscha Krettek <aljos...@apache.org>
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>> My feeling is that state backends and
> checkpointing
> > > are
> > > > > > going
> > > > > > > to
> > > > > > > >> >> be
> > > > > > > >> >>>>>>>>> integral to Flink for many years, regardless or
> > other
> > > > > > > >> >> enhancements
> > > > > > > >> >>>>>>>>> so this
> > > > > > > >> >>>>>>>>> change is still valuable.
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>> Since this is a FLIP about improving the user api
> > I'm
> > > > > happy
> > > > > > to
> > > > > > > >> >>>> bikeshed
> > > > > > > >> >>>>>>>>> the names a little more than normal. HashMap makes
> > > > sense,
> > > > > my
> > > > > > > >> >> other
> > > > > > > >> >>>>>>>>> thought
> > > > > > > >> >>>>>>>>> was InMemory.
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>> Seth
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>> On Wed, Sep 9, 2020 at 8:04 AM Aljoscha Krettek <
> > > > > > > >> >>> aljos...@apache.org
> > > > > > > >> >>>>>
> > > > > > > >> >>>>>>>>> wrote:
> > > > > > > >> >>>>>>>>>
> > > > > > > >> >>>>>>>>>> I like it a lot!
> > > > > > > >> >>>>>>>>>>
> > > > > > > >> >>>>>>>>>> I think it makes sense to clean this up despite
> the
> > > > > planned
> > > > > > > new
> > > > > > > >> >>>>>>>>>> fault-tolerance mechanisms. In the future, users
> > will
> > > > > > decide
> > > > > > > >> >> which
> > > > > > > >> >>>>>>>>>> mechanism to use and I can imagine that a lot of
> > them
> > > > > will
> > > > > > > keep
> > > > > > > >> >>>> using
> > > > > > > >> >>>>>>>>>> the current mechanism for quite a while to come.
> > But
> > > > I'm
> > > > > > > happy
> > > > > > > >> >> to
> > > > > > > >> >>>>>>>>>> yield
> > > > > > > >> >>>>>>>>>> to Stephan's opinion here, he knows more about
> the
> > > > > progress
> > > > > > > of
> > > > > > > >> >>> that
> > > > > > > >> >>>>>>>>>> work.
> > > > > > > >> >>>>>>>>>>
> > > > > > > >> >>>>>>>>>> The one nitpick I have is about naming: will
> users
> > > > > > understand
> > > > > > > >> >>>>>>>>>> OnHeapStateBackend? I mean, do they know what
> > > > > > > on-heap/off-heap
> > > > > > > >> >>>>>>>>>> memory is
> > > > > > > >> >>>>>>>>>> and the tradeoffs? An alternative could be
> > > > > > > HashMapStateBackend,
> > > > > > > >> >>>>>>>>>> because
> > > > > > > >> >>>>>>>>>> that's essentially what it is. I wouldn't block
> > > > anything
> > > > > on
> > > > > > > >> >> this,
> > > > > > > >> >>>>>>>>>> though.
> > > > > > > >> >>>>>>>>>>
> > > > > > > >> >>>>>>>>>> Aljoscha
> > > > > > > >> >>>>>>>>>>
> > > > > > > >> >>>>>>>>>> On 09.09.20 10:05, Konstantin Knauf wrote:
> > > > > > > >> >>>>>>>>>>> Thanks for the initiative. Big +1. Would be
> > > interested
> > > > > to
> > > > > > > hear
> > > > > > > >> >> if
> > > > > > > >> >>>> the
> > > > > > > >> >>>>>>>>>>> proposed interfaces still make sense in the face
> > of
> > > > the
> > > > > > new
> > > > > > > >> >>>>>>>>>> fault-tolerance
> > > > > > > >> >>>>>>>>>>> work that is planned. Stephan/Piotr will know.
> > > > > > > >> >>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>> On Tue, Sep 8, 2020 at 7:05 PM Seth Wiesman <
> > > > > > > >> >> sjwies...@gmail.com
> > > > > > > >> >>>>
> > > > > > > >> >>>>>>>>>> wrote:
> > > > > > > >> >>>>>>>>>>>> Hi Devs,
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>> I'd like to propose an update to how state
> > backends
> > > > and
> > > > > > > >> >>> checkpoint
> > > > > > > >> >>>>>>>>>> storage
> > > > > > > >> >>>>>>>>>>>> are configured to help users better understand
> > > Flink.
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>> Apache Flink's durability story is a mystery to
> > > many
> > > > > > users.
> > > > > > > >> >> One
> > > > > > > >> >>>>>>>>>>>> of the
> > > > > > > >> >>>>>>>>>> most
> > > > > > > >> >>>>>>>>>>>> common recurring questions from users comes
> from
> > > not
> > > > > > > >> >>>>>>>>>>>> understanding the
> > > > > > > >> >>>>>>>>>>>> relationship between state, state backends, and
> > > > > > snapshots.
> > > > > > > >> >> Some
> > > > > > > >> >>>>>>>>>>>> of this
> > > > > > > >> >>>>>>>>>>>> confusion can be abated with learning material
> > but
> > > > the
> > > > > > > >> >> question
> > > > > > > >> >>>>>>>>>>>> is so
> > > > > > > >> >>>>>>>>>>>> pervasive that we believe Flink’s user APIs
> > should
> > > be
> > > > > > > better
> > > > > > > >> >>>>>>>>>> communicate
> > > > > > > >> >>>>>>>>>>>> what different components are responsible for.
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>
> > > > > > > >> >>>
> > > > > > > >> >>
> > > > > > > >>
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-142%3A+Disentangle+StateBackends+from+Checkpointing
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>> I look forward to a healthy discussion.
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>> Seth
> > > > > > > >> >>>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>>
> > > > > > > >> >>>>>>>>>>
> > > > > > > >> >>>>>>
> > > > > > > >> >>>>
> > > > > > > >> >>>>
> > > > > > > >> >>>
> > > > > > > >> >>
> > > > > > > >> >
> > > > > > > >>
> > > > > > > >>
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
