Thanks a lot John for these suggestions. @Matthias can share your thoughts on
the last two comments made in this chain.
Thanks,Navinder
On Monday, 14 September, 2020, 09:03:32 pm IST, John Roesler
<vvcep...@apache.org> wrote:
Hi Navinder,
Thanks for the reply.
I wasn't thinking of an _exponential_ backoff, but
otherwise, yes, that was the basic idea. Note, the mechanism
would be similar (if not the same) to what Matthias is
implementing for KIP-572:
https://cwiki.apache.org/confluence/display/KAFKA/KIP-572%3A+Improve+timeouts+and+retries+in+Kafka+Streams
Regarding whether we'd stay in RUNNING during global
restoration or not, I can see your point. It seems like we
have three choices with how we set the state during global
restoration:
1. stay in RUNNING: Users might get confused, since
processing could get stopped for some tasks. On the other
hand, processing for tasks not blocked by the global
restoration could proceed (if we adopt the other idea), so
maybe it still makes sense.
2. transition to REBALANCING: Users might get confused,
since there is no actual rebalance. However, the current
state for Kafka Streams during state restoration is actually
REBALANCING, so it seems people already should understand
that REBALANCING really means REBALANCING|RESTORING. This
choice would preseve the existing state machine as well as
the existing meaning of all states
3. add RESTORING: This could clarify the state machine, at
the expense of breaking compatibility. We could implement a
migration path by adding a new "state listener" interface
for the new state machine.
It seems like option 3 results in the most sensible system,
but I'm not sure if it's worth the hassle. It certainly
seems orthogonal to the goal of this KIP. Option 2 is
probably the best practical choice.
Regarding _how_ the global state restoration could set a
flag preventing access to the store... This is indeed the
central challenge to this new idea. Just throwing out one
possibility: Once the global thread marks the store for
restoration, it would throw an exception, such as
"StoreIsRestoringException" on any access. The processor
would _not_ catch this exception. Instead, the StreamThread
would catch it, put this record/task on ice, and re-try it
later.
That last mechanism is actually pretty complicated. For
example, what if the record is already partially processed
in the topology? We'd have to remember which ProcessorNode
to resume from when we re-try later.
This is really where the spiritual overlap with KIP-572
comes in. Maybe Matthias can share some thoughts.
Thanks,
-John
On Sun, 2020-09-13 at 07:50 +0000, Navinder Brar wrote:
>
> Hi John,
>
>
>
>
>
>
>
> If I understand this correctly, you are proposing to use exponential backoff
>
> in globalStore.get() to keep polling the global thread (whether it has
> restored
>
> completely or not) while the processor pauses the processing of a particular
>
> message which required querying on global store. That is stream threads
>
> are still in RUNNING state but kind of paused till global thread restores and
>
> gives a go-ahead that complete state has been restored. I like the idea for
> the first two reasons that you have mentioned but thinking from
> semanticspoint of view stream threads will be in RUNNING but still not
> processing events,
> will it be misleading for the users? Or you think we are doing it at enough
>
> places already and an exception should suffice. As they will not understand
>
> why the stream thread is not processing and how much more time it will not
>
> process for. If the state explicitly stated RESTORING,
>
> users might have clearly understood that why it is happening.
>
>
>
>
>
>
>
> Also, to achieve what we are discussing above, the store.get() on which call
> is
>
> made has to understand whether it is a global store or not and if it is a
> global store
>
> check whether it is restoring or not because both might be happening
>
> simultaneously with the above approach. With KIP-535 we have started serving
>
> normal stores in restoring state but those are just interactive queries but
> here
>
> globalStore.get() might be called while processing which we don’t want. So,
>
> restore for global store and get() might have to be exclusive. Is there a way
> for a
>
> store to know if it global store or not because now internally global and
> normal
>
> stores will behave differently. Although if everyone is fine with the above
> approach
>
> we can discuss this in PR as well.
>
>
>
>
>
>
>
> Regards,
> Navinder
>
> On Saturday, 5 September, 2020, 02:09:07 am IST, John Roesler
><vvcep...@apache.org> wrote:
>
> Hi all,
>
> This conversation sounds good to me so far.
>
> Sophie raised a concern before that changing the state
> machine would break state restore listeners. This is true,
> and we actually have not changed the main state machine in a
> long time. The last change I remember was that we used to go
> "CREATED -> RUNNING -> REBALANCING -> RUNNING", and now we
> just go "CREATED -> REBALANCING -> RUNNING". This is
> actually the reason why many state listeners check for
> "REBALANCING -> RUNNING", to filter out the old "phantom
> running" transition from "CREATED -> RUNNING".
>
> Anyway, the observation is that dropping the "phantom
> running" state didn't break any real use case we were aware
> of. But adding RESTORING between REBALACING and RUNNING
> certainly would break the common pattern that we're aware
> of. This would indeed be the first time we introduce a
> practically breaking change to the state machine at least
> since 2.0, and maybe since 1.0 too. We should probably
> consider the impact.
>
> One alternative is to consider the state machine and the
> state listener to be coupled APIs. We can deprecate and
> replace the current state listener, and also introduce a new
> state machine enum with our desired new state and
> transitions, while leaving the existing one alone and
> deprecating it. Then, no existing code would break, only get
> deprecation warnings.
>
>
>
> Matthias gave me an idea a few messages back with his note
> about setting/checking "flags". What if we flip it around,
> and set the flags on the global stores themselves. Then, we
> throw an exception when a processor queries the store while
> it's restoring. When they get that exception, they just put
> that task on the back burner for a while and try again later
> (similar to Matthias's timeout handling KIP). The global
> thread sets the flag on a particular store when it realizes
> it needs to be re-created and unsets it when the restore
> completes.
>
> Then:
> 1. Only the global stores that actually need to be restored
> block anything
> 2. Only the tasks that access the stores get blocked
> 3. No new states need to be introduced
>
> WDYT?
> -John
>
> On Fri, 2020-09-04 at 13:18 +0000, Navinder Brar wrote:
> > Hi Sophie,
> >
> > Thanks for the detailed explanation. I agree from a user standpoint, I
> > don't think there is any use-case to take any separate action in case of
> > GLOBAL_RESTORING and RESTORING phase.
> >
> > So, internally in the code we can handle the cases as Matthiasexplained
> > above and we can discuss those in the PR. I will update the KIP based on
> > what all we have converged towards including having an uber
> > RESTORING(rather than GLOBAL_RESTORING)state which takes stream and global
> > threads into consideration.
> >
> > I will update the KIP soon and share it again as a lot has changed from
> > where we started this KIP from.
> >
> > Regards,Navinder
> >
> > On Friday, 4 September, 2020, 04:19:20 am IST, Sophie Blee-Goldman
> ><sop...@confluent.io> wrote:
> >
> > Thanks Matthias, that sounds like what I was thinking. I think we should
> > always be
> > able to figure out what to do in various scenarios as outlined in the
> > previous email.
> >
> > > For the same reason, I wouldn't want to combine global restoring and
> > normal restoring
> > > because then it would make all the restorings independent but we don't
> > want that. We
> > > want global stores to be available before any processing starts on the
> > active tasks.
> >
> > I'm not sure I follow this specific point, but I don't think I did a good
> > job of explaining my
> > proposal so it's probably my own fault. When I say that we should merge
> > RESTORING
> > and GLOBAL_RESTORING, I just mean that we should provide a single
> > user-facing
> > state to encompass any ongoing restoration. The point of the KafkaStreams
> > RESTORING
> > state is to alert users that their state may be unavailable for IQ, and
> > active tasks may be
> > idle. This is true for both global and non-global restoration. I think the
> > ultimate question
> > is whether as a user, I would react any differently to a GLOBAL_RESTORING
> > state vs
> > the regular RESTORING. My take is "no", in which case we should just
> > provide a single
> > unified state for the minimal public API. But if anyone can think of a
> > reason for the user
> > to need to distinguish between different types of restoration, that would
> > be a good
> > argument to keep them separate.
> >
> > Internally, we do need to keep track of a "global restore" flag to
> > determine the course
> > of action -- for example if a StreamThread transitions to RUNNING but sees
> > that the
> > KafkaStreams state is RESTORING, should it start processing or not? The
> > answer
> > depends on whether the state is RESTORING due to any global stores. But the
> > KafkaStreams state is a public interface, not an internal bookkeeper, so we
> > shouldn't
> > try to push our internal logic into the user-facing API.
> >
> >
> > On Thu, Sep 3, 2020 at 7:36 AM Matthias J. Sax <mj...@apache.org> wrote:
> >
> > > I think this issue can actually be resolved.
> > >
> > > - We need a flag on the stream-threads if global-restore is in
> > > progress; for this case, the stream-thread may go into RUNNING state,
> > > but it's not allowed to actually process data -- it will be allowed to
> > > update standby-task though.
> > >
> > > - If a stream-thread restores, its own state is RESTORING and it does
> > > not need to care about the "global restore flag".
> > >
> > > - The global-thread just does was we discussed, including using state
> > > RESTORING.
> > >
> > > - The KafkaStreams client state is in RESTORING, if at least one thread
> > > (stream-thread or global-thread) is in state RESTORING.
> > >
> > > - On startup, if there is a global-thread, the just set the
> > > global-restore flag upfront before we start the stream-threads (we can
> > > actually still do the rebalance and potential restore in stream-thread
> > > in parallel to global restore) and rely on the global-thread to unset
> > > the flag.
> > >
> > > - The tricky thing is, to "stop" processing in stream-threads if we
> > > need to wipe the global-store and rebuilt it. For this, we should set
> > > the "global restore flag" on the stream-threads, but we also need to
> > > "lock down" the global store in question and throw an exception if the
> > > stream-thread tries to access it; if the stream-thread get this
> > > exception, it need to cleanup itself, and wait until the "global restore
> > > flag" is unset before it can continue.
> > >
> > >
> > > Do we think this would work? -- Of course, the devil is in the details
> > > but it seems to become a PR discussion, and there is no reason to make
> > > it part of the KIP.
> > >
> > >
> > > -Matthias
> > >
> > > On 9/3/20 3:41 AM, Navinder Brar wrote:
> > > > Hi,
> > > >
> > > > Thanks, John, Matthias and Sophie for great feedback.
> > > >
> > > > On the point raised by Sophie that maybe we should allow normal
> > > restoring during GLOBAL_RESTORING, I think it makes sense but the
> > > challenge
> > > would be what happens when normal restoring(on actives) has finished but
> > > GLOBAL_RESTORINGis still going on. Currently, all restorings are
> > > independent of each other i.e. restoring happening on one task/thread
> > > doesn't affect another. But if we do go ahead with allowing normal
> > > restoring during GLOBAL_RESTORING then we willstill have to pause the
> > > active tasks from going to RUNNING if GLOBAL_RESTORING has not finished
> > > and
> > > normal restorings have finished. For the same reason, I wouldn't want to
> > > combine global restoring and normal restoring because then it would make
> > > all the restorings independent but we don't want that. We want global
> > > stores to be available before any processing starts on the active tasks.
> > > > Although I think restoring of replicas can still take place while global
> > > stores arerestoring because in replicas there is no danger of them
> > > starting
> > > processing.
> > > > Also, one point to bring up is that currently during application startup
> > > global stores restore first and then normal stream threads start.
> > > > Regards,Navinder
> > > >
> > > > On Thursday, 3 September, 2020, 06:58:40 am IST, Matthias J. Sax <
> > > mj...@apache.org> wrote:
> > > > Thanks for the input Sophie. Those are all good points and I fully
> > > >agree
> > > > with them.
> > > >
> > > > When saying "pausing the processing threads" I only considered them in
> > > > `RUNNING` and thought we figure out the detail on the PR... Excellent
> > > catch!
> > > > Changing state transitions is to some extend backward incompatible, but
> > > > I think (IIRC) we did it in the past and I personally tend to find it
> > > > ok. That's why we cover those changes in a KIP.
> > > >
> > > > -Matthias
> > > >
> > > > On 9/2/20 6:18 PM, Sophie Blee-Goldman wrote:
> > > > > If we're going to add a new GLOBAL_RESTORING state to the KafkaStreams
> > > FSM,
> > > > > maybe it would make sense to add a new plain RESTORING state that we
> > > > > transition
> > > > > to when restoring non-global state stores following a rebalance. Right
> > > now
> > > > > all restoration
> > > > > occurs within the REBALANCING state, which is pretty misleading.
> > > > > Applications that
> > > > > have large amounts of state to restore will appear to be stuck
> > > rebalancing
> > > > > according to
> > > > > the state listener, when in fact the rebalance has completed long ago.
> > > > > Given that there
> > > > > are very much real scenarios where you actually *are *stuck
> > > rebalancing, it
> > > > > seems useful to
> > > > > distinguish plain restoration from more insidious cases that may
> > > > > require
> > > > > investigation and/or
> > > > > intervention.
> > > > >
> > > > > I don't mean to hijack this KIP, I just think it would be odd to
> > > introduce
> > > > > GLOBAL_RESTORING
> > > > > when there is no other kind of RESTORING state. One question this
> > > > > brings
> > > > > up, and I
> > > > > apologize if this has already been addressed, is what to do when we
> > > > > are
> > > > > restoring
> > > > > both normal and global state stores? It sounds like we plan to pause
> > > > > the
> > > > > StreamThreads
> > > > > entirely, but there doesn't seem to be any reason not to allow regular
> > > > > state restoration -- or
> > > > > even standby processing -- while the global state is restoring.Given
> > > > > the
> > > > > current effort to move
> > > > > restoration & standbys to a separate thread, allowing them to continue
> > > > > while pausing
> > > > > only the StreamThread seems quite natural.
> > > > >
> > > > > Assuming that we actually do allow both types of restoration to occur
> > > > > at
> > > > > the same time,
> > > > > and if we did add a plain RESTORING state as well, which state should
> > > > > we
> > > > > end up in?
> > > > > AFAICT the main reason for having a distinct {GLOBAL_}RESTORING state
> > > is to
> > > > > alert
> > > > > users of the non-progress of their active tasks. In both cases, the
> > > active
> > > > > task is unable
> > > > > to continue until restoration has complete, so why distinguish between
> > > the
> > > > > two at all?
> > > > > Would it make sense to avoid a special GLOBAL_RESTORING state and just
> > > > > introduce
> > > > > a single unified RESTORING state to cover both the regular and global
> > > case?
> > > > > Just a thought
> > > > >
> > > > > My only concern is that this might be considered a breaking change:
> > > users
> > > > > might be
> > > > > looking for the REBALANCING -> RUNNING transition specifically in
> > > > > order
> > > to
> > > > > alert when
> > > > > the application has started up, and we would no long go directly from
> > > > > REBALANCING to
> > > > > RUNNING. I think we actually did/do this ourselves in a number of
> > > > > integration tests and
> > > > > possibly in some examples. That said, it seems more appropriate to
> > > > > just
> > > > > listen for
> > > > > the RUNNING state rather than for a specific transition, and we should
> > > > > encourage users
> > > > > to do so rather than go out of our way to support transition-type
> > > > > state
> > > > > listeners.
> > > > >
> > > > > Cheers,
> > > > > Sophie
> > > > >
> > > > > On Wed, Sep 2, 2020 at 5:53 PM Matthias J. Sax <mj...@apache.org>
> > > wrote:
> > > > > > I think this makes sense.
> > > > > >
> > > > > > When we introduce this new state, we might also tackle the jira a
> > > > > > mentioned. If there is a global thread, on startup of a
> > > > > > `KafakStreams`
> > > > > > client we should not transit to `REBALANCING` but to the new state,
> > > > > > and
> > > > > > maybe also make the "bootstrapping" non-blocking.
> > > > > >
> > > > > > I guess it's worth to mention this in the KIP.
> > > > > >
> > > > > > Btw: The new state for KafkaStreams should also be part of the KIP
> > > > > > as
> > > it
> > > > > > is a public API change, too.
> > > > > >
> > > > > >
> > > > > > -Matthias
> > > > > >
> > > > > > On 8/29/20 9:37 AM, John Roesler wrote:
> > > > > > > Hi Navinder,
> > > > > > >
> > > > > > > Thanks for the ping. Yes, that all sounds right to me. The name
> > > > > > “RESTORING_GLOBAL” sounds fine, too.
> > > > > > > I think as far as warnings go, we’d just propose to mention it in
> > > > > > > the
> > > > > > javadoc of the relevant methods that the given topics should be
> > > compacted.
> > > > > > > Thanks!
> > > > > > > -John
> > > > > > >
> > > > > > > On Fri, Aug 28, 2020, at 12:42, Navinder Brar wrote:
> > > > > > > > Gentle ping.
> > > > > > > >
> > > > > > > > ~ Navinder
> > > > > > > > On Wednesday, 19 August, 2020, 06:59:58 pm IST, Navinder Brar
> > > > > > > > <navinder_b...@yahoo.com.invalid> wrote:
> > > > > > > >
> > > > > > > >
> > > > > > > > Thanks Matthias & John,
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > I am glad we are converging towards an understanding. So, to
> > > summarize,
> > > > > > > > we will still keep treating this change in KIP and instead of
> > > providing
> > > > > > a reset
> > > > > > > > strategy, we will cleanup, and reset to earliest and build the
> > > > > > > > state.
> > > > > > > >
> > > > > > > > When we hit the exception and we are building the state, we
> > > > > > > > will stop
> > > > > > all
> > > > > > > > processing and change the state of KafkaStreams to something
> > > > > > > > like
> > > > > > > >
> > > > > > > > “RESTORING_GLOBAL” or the like.
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > How do we plan to educate users on the non desired effects of
> > > > > > > > using
> > > > > > > >
> > > > > > > > non-compacted global topics? (via the KIP itself?)
> > > > > > > >
> > > > > > > >
> > > > > > > > +1 on changing the KTable behavior, reset policy for global,
> > > connecting
> > > > > > > > processors to global for a later stage when demanded.
> > > > > > > >
> > > > > > > > Regards,
> > > > > > > > Navinder
> > > > > > > > On Wednesday, 19 August, 2020, 01:00:58 pm IST, Matthias J.
> > > > > > > >Sax
> > > > > > > > <mj...@apache.org> wrote:
> > > > > > > >
> > > > > > > > Your observation is correct. Connecting (regular) stores to
> > > processors
> > > > > > > > is necessary to "merge" sub-topologies into single ones if a
> > > > > > > > store is
> > > > > > > > shared. -- For global stores, the structure of the program does
> > > > > > > > not
> > > > > > > > change and thus connecting srocessors to global stores is not
> > > required.
> > > > > > > > Also given our experience with restoring regular state stores
> > > > > > > > (ie,
> > > > > > > > partial processing of task that don't need restore), it seems
> > > > > > > > better
> > > to
> > > > > > > > pause processing and move all CPU and network resources to the
> > > > > > > > global
> > > > > > > > thread to rebuild the global store as soon as possible instead
> > > > > > > > of
> > > > > > > > potentially slowing down the restore in order to make progress
> > > > > > > > on
> > > some
> > > > > > > > tasks.
> > > > > > > >
> > > > > > > > Of course, if we collect real world experience and it becomes an
> > > issue,
> > > > > > > > we could still try to change it?
> > > > > > > >
> > > > > > > >
> > > > > > > > -Matthias
> > > > > > > >
> > > > > > > >
> > > > > > > > On 8/18/20 3:31 PM, John Roesler wrote:
> > > > > > > > > Thanks Matthias,
> > > > > > > > >
> > > > > > > > > Sounds good. I'm on board with no public API change and just
> > > > > > > > > recovering instead of crashing.
> > > > > > > > >
> > > > > > > > > Also, to be clear, I wouldn't drag KTables into it; I was
> > > > > > > > > just trying to wrap my head around the congruity of our
> > > > > > > > > choice for GlobalKTable with respect to KTable.
> > > > > > > > >
> > > > > > > > > I agree that whatever we decide to do would probably also
> > > > > > > > > resolve KAFKA-7380.
> > > > > > > > >
> > > > > > > > > Moving on to discuss the behavior change, I'm wondering if
> > > > > > > > > we really need to block all the StreamThreads. It seems like
> > > > > > > > > we only need to prevent processing on any task that's
> > > > > > > > > connected to the GlobalStore.
> > > > > > > > >
> > > > > > > > > I just took a look at the topology building code, and it
> > > > > > > > > actually seems that connections to global stores don't need
> > > > > > > > > to be declared. That's a bummer, since it means that we
> > > > > > > > > really do have to stop all processing while the global
> > > > > > > > > thread catches up.
> > > > > > > > >
> > > > > > > > > Changing this seems like it'd be out of scope right now, but
> > > > > > > > > I bring it up in case I'm wrong and it actually is possible
> > > > > > > > > to know which specific tasks need to be synchronized with
> > > > > > > > > which global state stores. If we could know that, then we'd
> > > > > > > > > only have to block some of the tasks, not all of the
> > > > > > > > > threads.
> > > > > > > > >
> > > > > > > > > Thanks,
> > > > > > > > > -John
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > On Tue, 2020-08-18 at 14:10 -0700, Matthias J. Sax wrote:
> > > > > > > > > > Thanks for the discussion.
> > > > > > > > > >
> > > > > > > > > > I agree that this KIP is justified in any case -- even if
> > > > > > > > > > we don't
> > > > > > > > > > change public API, as the change in behavior is significant.
> > > > > > > > > >
> > > > > > > > > > A better documentation for cleanup policy is always good
> > > > > > > > > > (even if
> > > I am
> > > > > > > > > > not aware of any concrete complaints atm that users were
> > > > > > > > > > not aware
> > > of
> > > > > > > > > > the implications). Of course, for a regular KTable, one can
> > > > > > > > > > enable/disable the source-topic-changelog optimization and
> > > > > > > > > > thus can
> > > > > > use
> > > > > > > > > > a non-compacted topic for this case, what is quite a
> > > > > > > > > > difference to
> > > > > > > > > > global stores/tables; so maybe it's worth to point out this
> > > difference
> > > > > > > > > > explicitly.
> > > > > > > > > >
> > > > > > > > > > As mentioned before, the main purpose of the original Jira
> > > > > > > > > > was to
> > > > > > avoid
> > > > > > > > > > the crash situation but to allow for auto-recovering while
> > > > > > > > > > it was
> > > an
> > > > > > > > > > open question if it makes sense / would be useful to allow
> > > > > > > > > > users to
> > > > > > > > > > specify a custom reset policy instead of using a hard-coded
> > > "earliest"
> > > > > > > > > > strategy. -- It seem it's still unclear if it would be
> > > > > > > > > > useful and
> > > thus
> > > > > > > > > > it might be best to not add it for now -- we can still add
> > > > > > > > > > it
> > > later if
> > > > > > > > > > there are concrete use-cases that need this feature.
> > > > > > > > > >
> > > > > > > > > > @John: I actually agree that it's also questionable to
> > > > > > > > > > allow a
> > > custom
> > > > > > > > > > reset policy for KTables... Not sure if we want to drag this
> > > question
> > > > > > > > > > into this KIP though?
> > > > > > > > > >
> > > > > > > > > > So it seem, we all agree that we actually don't need any
> > > > > > > > > > public API
> > > > > > > > > > changes, but we only want to avoid crashing?
> > > > > > > > > >
> > > > > > > > > > For this case, to preserve the current behavior that
> > > > > > > > > > guarantees
> > > that
> > > > > > the
> > > > > > > > > > global store/table is always loaded first, it seems we need
> > > > > > > > > > to
> > > have a
> > > > > > > > > > stop-the-world mechanism for the main `StreamThreads` for
> > > > > > > > > > this
> > > case --
> > > > > > > > > > do we need to add a new state to KafkaStreams client for
> > > > > > > > > > this case?
> > > > > > > > > >
> > > > > > > > > > Having a new state might also be helpful for
> > > > > > > > > > https://issues.apache.org/jira/browse/KAFKA-7380 ?
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > -Matthias
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > On 8/17/20 7:34 AM, John Roesler wrote:
> > > > > > > > > > > Hi Navinder,
> > > > > > > > > > >
> > > > > > > > > > > I see what you mean about the global consumer being
> > > > > > > > > > > similar
> > > > > > > > > > > to the restore consumer.
> > > > > > > > > > >
> > > > > > > > > > > I also agree that automatically performing the recovery
> > > > > > > > > > > steps should be strictly an improvement over the current
> > > > > > > > > > > situation.
> > > > > > > > > > >
> > > > > > > > > > > Also, yes, it would be a good idea to make it clear that
> > > > > > > > > > > the
> > > > > > > > > > > global topic should be compacted in order to ensure
> > > > > > > > > > > correct
> > > > > > > > > > > semantics. It's the same way with input topics for
> > > > > > > > > > > KTables;
> > > > > > > > > > > we rely on users to ensure the topics are compacted, and
> > > > > > > > > > > if
> > > > > > > > > > > they aren't, then the execution semantics will be broken.
> > > > > > > > > > >
> > > > > > > > > > > Thanks,
> > > > > > > > > > > -John
> > > > > > > > > > >
> > > > > > > > > > > On Sun, 2020-08-16 at 11:44 +0000, Navinder Brar wrote:
> > > > > > > > > > > > Hi John,
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > Thanks for your inputs. Since, global topics are in a
> > > > > > > > > > > > way their
> > > own
> > > > > > changelog, wouldn’t the global consumers be more akin to restore
> > > consumers
> > > > > > than the main consumer?
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > I am also +1 on catching the exception and setting it
> > > > > > > > > > > > to the
> > > > > > earliest for now. Whenever an instance starts, currently global
> > > > > > stream
> > > > > > thread(if available) goes to RUNNING before stream threads are
> > > > > > started
> > > so
> > > > > > that means the global state is available when the processing by
> > > > > > stream
> > > > > > threads start. So, with the new change of catching the exception,
> > > cleaning
> > > > > > store and resetting to earlier would probably be “stop the world” as
> > > you
> > > > > > said John, as I think we will have to pause the stream threads till
> > > > > > the
> > > > > > whole global state is recovered. I assume it is "stop the world"
> > > > > > right
> > > now
> > > > > > as well, since now also if an InvalidOffsetException comes, we throw
> > > > > > streams exception and the user has to clean up and handle all this
> > > manually
> > > > > > and when that instance will start, it will restore global state
> > > > > > first.
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > I had an additional thought to this whole problem,
> > > > > > > > > > > > would it be
> > > > > > helpful to educate the users that global topics should have cleanup
> > > policy
> > > > > > as compact, so that this invalid offset exception never arises for
> > > them.
> > > > > > Assume for example, that the cleanup policy in global topic is
> > > "delete" and
> > > > > > it has deleted k1, k2 keys(via retention.ms) although all the
> > > instances
> > > > > > had already consumed them so they are in all global stores and all
> > > other
> > > > > > instances are up to date on the global data(so no
> > > InvalidOffsetException).
> > > > > > Now, a new instance is added to the cluster, and we have already
> > > > > > lost
> > > k1,
> > > > > > k2 from the global topic so it will start consuming from the
> > > > > > earliest
> > > point
> > > > > > in the global topic. So, wouldn’t this global store on the new
> > > instance has
> > > > > > 2 keys less than all the other global stores already available in
> > > > > > the
> > > > > > cluster? Please let me know if I am missing something. Thanks.
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > Regards,
> > > > > > > > > > > >
> > > > > > > > > > > > Navinder
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > On Friday, 14 August, 2020, 10:03:42 am IST, John
> > > > > > > > > > > >Roesler <
> > > > > > vvcep...@apache.org> wrote:
> > > > > > > > > > > > Hi all,
> > > > > > > > > > > >
> > > > > > > > > > > > It seems like the main motivation for this proposal is
> > > > > > > > > > > > satisfied
> > > if
> > > > > > we just implement some recovery mechanism instead of crashing. If
> > > > > > the
> > > > > > mechanism is going to be pausing all the threads until the state is
> > > > > > recovered, then it still seems like a big enough behavior change to
> > > warrant
> > > > > > a KIP still.
> > > > > > > > > > > > I have to confess I’m a little unclear on why a custom
> > > > > > > > > > > > reset
> > > policy
> > > > > > for a global store, table, or even consumer might be considered
> > > > > > wrong.
> > > It’s
> > > > > > clearly wrong for the restore consumer, but the global consumer
> > > > > > seems
> > > more
> > > > > > semantically akin to the main consumer than the restore consumer.
> > > > > > > > > > > > In other words, if it’s wrong to reset a GlobalKTable
> > > > > > > > > > > > from
> > > latest,
> > > > > > shouldn’t it also be wrong for a KTable, for exactly the same
> > > > > > reason?
> > > It
> > > > > > certainly seems like it would be an odd choice, but I’ve seen many
> > > choices
> > > > > > I thought were odd turn out to have perfectly reasonable use cases.
> > > > > > > > > > > > As far as the PAPI global store goes, I could see
> > > > > > > > > > > > adding the
> > > option
> > > > > > to configure it, since as Matthias pointed out, there’s really no
> > > specific
> > > > > > semantics for the PAPI. But if automatic recovery is really all
> > > Navinder
> > > > > > wanted, the I could also see deferring this until someone
> > > > > > specifically
> > > > > > wants it.
> > > > > > > > > > > > So the tl;dr is, if we just want to catch the exception
> > > > > > > > > > > > and
> > > rebuild
> > > > > > the store by seeking to earliest with no config or API changes, then
> > > I’m +1.
> > > > > > > > > > > > I’m wondering if we can improve on the “stop the world”
> > > > > > > > > > > > effect of
> > > > > > rebuilding the global store, though. It seems like we could put our
> > > heads
> > > > > > together and come up with a more fine-grained approach to
> > > > > > maintaining
> > > the
> > > > > > right semantics during recovery while still making some progress.
> > > > > > > > > > > > Thanks,
> > > > > > > > > > > > John
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > On Sun, Aug 9, 2020, at 02:04, Navinder Brar wrote:
> > > > > > > > > > > > > Hi Matthias,
> > > > > > > > > > > > >
> > > > > > > > > > > > > IMHO, now as you explained using
> > > > > > ‘global.consumer.auto.offset.reset’ is
> > > > > > > > > > > > > not as straightforward
> > > > > > > > > > > > > as it seems and it might change the existing behavior
> > > > > > > > > > > > > for users
> > > > > > without
> > > > > > > > > > > > > they releasing it, I also
> > > > > > > > > > > > >
> > > > > > > > > > > > > think that we should change the behavior inside
> > > > > > > > > > > > > global stream
> > > > > > thread to
> > > > > > > > > > > > > not die on
> > > > > > > > > > > > >
> > > > > > > > > > > > > InvalidOffsetException and instead clean and rebuild
> > > > > > > > > > > > > the state
> > > > > > from the
> > > > > > > > > > > > > earliest. On this, as you
> > > > > > > > > > > > >
> > > > > > > > > > > > > mentioned that we would need to pause the stream
> > > > > > > > > > > > > threads till
> > > the
> > > > > > > > > > > > > global store is completely restored.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Without it, there will be incorrect processing
> > > > > > > > > > > > > results if they
> > > are
> > > > > > > > > > > > > utilizing a global store during processing.
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > So, basically we can divide the use-cases into 4
> > > > > > > > > > > > > parts.
> > > > > > > > > > > > >
> > > > > > > > > > > > > - PAPI based global stores (will have the earliest
> > > hardcoded)
> > > > > > > > > > > > > - PAPI based state stores (already has
> > > > > > > > > > > > >auto.reset.config)
> > > > > > > > > > > > > - DSL based GlobalKTables (will have earliest
> > > > > > > > > > > > >hardcoded)
> > > > > > > > > > > > > - DSL based KTables (will continue with
> > > > > > > > > > > > >auto.reset.config)
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > So, this would mean that we are not changing any
> > > > > > > > > > > > > existing
> > > > > > behaviors
> > > > > > > > > > > > > with this if I am right.
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > I guess we could improve the code to actually log a
> > > > > > > > > > > > > warning for
> > > > > > this
> > > > > > > > > > > > > case, similar to what we do for some configs already
> > > > > > > > > > > > > (cf
> > > > > > > > > > > > >
> > > > > > > > > > > > > StreamsConfig#NON_CONFIGURABLE_CONSUMER_DEFAULT_CONFIGS).
> > > > > > > > > > > > >
> > > > > > > > > > > > > > > I like this idea. In case we go ahead with the
> > > > > > > > > > > > > > > above approach
> > > > > > and if we can’t
> > > > > > > > > > > > > deprecate it, we should educate users that this
> > > > > > > > > > > > > config doesn’t
> > > > > > work.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Looking forward to hearing thoughts from others as
> > > > > > > > > > > > > well.
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > - Navinder On Tuesday, 4 August, 2020, 05:07:59 am
> > > > > > > > > > > > > IST,
> > > > > > Matthias J.
> > > > > > > > > > > > > Sax <mj...@apache.org> wrote:
> > > > > > > > > > > > >
> > > > > > > > > > > > > Navinder,
> > > > > > > > > > > > >
> > > > > > > > > > > > > thanks for updating the KIP. I think the motivation
> > > > > > > > > > > > > section is
> > > not
> > > > > > > > > > > > > totally accurate (what is not your fault though, as
> > > > > > > > > > > > > the history
> > > of
> > > > > > how
> > > > > > > > > > > > > we handle this case is intertwined...) For example,
> > > > > > "auto.offset.reset"
> > > > > > > > > > > > > is hard-coded for the global consumer to "none" and
> > > > > > > > > > > > > using
> > > > > > > > > > > > > "global.consumer.auto.offset.reset" has no effect (cf
> > > > > > > > > > > > >
> > > https://kafka.apache.org/25/documentation/streams/developer-guide/config-streams.html#default-values
> > > > > > )
> > > > > > > > > > > > > Also, we could not even really deprecate the config as
> > > mentioned in
> > > > > > > > > > > > > rejected alternatives sections, because we need
> > > > > > `auto.offset.reset` for
> > > > > > > > > > > > > the main consumer -- and adding a prefix is
> > > > > > > > > > > > > independent of it.
> > > > > > Also,
> > > > > > > > > > > > > because we ignore the config, it's is also
> > > > > > > > > > > > > deprecated/removed if
> > > > > > you wish.
> > > > > > > > > > > > > I guess we could improve the code to actually log a
> > > > > > > > > > > > > warning for
> > > > > > this
> > > > > > > > > > > > > case, similar to what we do for some configs already
> > > > > > > > > > > > > (cf
> > > > > > > > > > > > > StreamsConfig#NON_CONFIGURABLE_CONSUMER_DEFAULT_CONFIGS).
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > The other question is about compatibility with regard
> > > > > > > > > > > > > to default
> > > > > > > > > > > > > behavior: if we want to reintroduce
> > > > > > `global.consumer.auto.offset.reset`
> > > > > > > > > > > > > this basically implies that we need to respect
> > > > > > `auto.offset.reset`, too.
> > > > > > > > > > > > > Remember, that any config without prefix is applied
> > > > > > > > > > > > > to all
> > > clients
> > > > > > that
> > > > > > > > > > > > > support this config. Thus, if a user does not limit
> > > > > > > > > > > > > the scope of
> > > > > > the
> > > > > > > > > > > > > config to the main consumer (via
> > > > > > `main.consumer.auto.offset.reset`) but
> > > > > > > > > > > > > uses the non-prefix versions and sets it to "latest"
> > > > > > > > > > > > > (and relies
> > > > > > on the
> > > > > > > > > > > > > current behavior that `auto.offset.reset` is "none",
> > > > > > > > > > > > > and
> > > > > > effectively
> > > > > > > > > > > > > "earliest" on the global consumer), the user might
> > > > > > > > > > > > > end up with a
> > > > > > > > > > > > > surprise as the global consumer behavior would switch
> > > > > > > > > > > > > from
> > > > > > "earliest" to
> > > > > > > > > > > > > "latest" (most likely unintentionally). Bottom line
> > > > > > > > > > > > > is, that
> > > users
> > > > > > might
> > > > > > > > > > > > > need to change configs to preserve the old behavior...
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > However, before we discuss those details, I think we
> > > > > > > > > > > > > should
> > > > > > discuss the
> > > > > > > > > > > > > topic in a broader context first:
> > > > > > > > > > > > >
> > > > > > > > > > > > > - for a GlobalKTable, does it even make sense from a
> > > correctness
> > > > > > point
> > > > > > > > > > > > > of view, to allow users to set a custom reset policy?
> > > > > > > > > > > > > It seems
> > > you
> > > > > > > > > > > > > currently don't propose this in the KIP, but as you
> > > > > > > > > > > > > don't
> > > mention
> > > > > > it
> > > > > > > > > > > > > explicitly it's unclear if that on purpose of an
> > > > > > > > > > > > > oversight?
> > > > > > > > > > > > >
> > > > > > > > > > > > > - Should we treat global stores differently to
> > > > > > > > > > > > >GlobalKTables
> > > and
> > > > > > allow
> > > > > > > > > > > > > for more flexibility (as the PAPI does not really
> > > > > > > > > > > > > provide any
> > > > > > semantic
> > > > > > > > > > > > > contract). It seems that is what you propose in the
> > > > > > > > > > > > > KIP. We
> > > should
> > > > > > > > > > > > > discuss if this flexibility does make sense or not
> > > > > > > > > > > > > for the PAPI,
> > > > > > or if
> > > > > > > > > > > > > we should apply the same reasoning about correctness
> > > > > > > > > > > > > we use for
> > > > > > KTables
> > > > > > > > > > > > > to global stores? To what extend are/should they be
> > > > > > > > > > > > > different?
> > > > > > > > > > > > >
> > > > > > > > > > > > > - If we support auto.offset.reset for global store,
> > > > > > > > > > > > >how
> > > should we
> > > > > > > > > > > > > handle the initial bootstrapping of the store/table
> > > > > > > > > > > > > (that is
> > > > > > hard-coded
> > > > > > > > > > > > > atm)? Should we skip it if the policy is "latest" and
> > > > > > > > > > > > > start
> > > with an
> > > > > > > > > > > > > empty state? Note that we did consider this behavior
> > > > > > > > > > > > > incorrect
> > > via
> > > > > > > > > > > > > https://issues.apache.org/jira/browse/KAFKA-6121 and
> > > > > > > > > > > > > thus I am
> > > > > > wondering
> > > > > > > > > > > > > why should we change it back again?
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > Finally, the main motivation for the Jira ticket was
> > > > > > > > > > > > > to let the
> > > > > > runtime
> > > > > > > > > > > > > auto-recover instead of dying as it does currently.
> > > > > > > > > > > > > If we decide
> > > > > > that a
> > > > > > > > > > > > > custom reset policy does actually not make sense, we
> > > > > > > > > > > > > can just
> > > > > > change the
> > > > > > > > > > > > > global-thread to not die any longer on an
> > > `InvalidOffsetException`
> > > > > > but
> > > > > > > > > > > > > rebuild the state automatically. This would be "only"
> > > > > > > > > > > > > a behavior
> > > > > > change
> > > > > > > > > > > > > but does not require any public API changes. -- For
> > > > > > > > > > > > > this case,
> > > we
> > > > > > should
> > > > > > > > > > > > > also think about the synchronization with the main
> > > > > > > > > > > > > processing
> > > > > > threads?
> > > > > > > > > > > > > On startup we bootstrap the global stores before
> > > > > > > > > > > > > processing
> > > > > > happens.
> > > > > > > > > > > > > Thus, if an `InvalidOffsetException` happen and the
> > > > > > > > > > > > > global
> > > thread
> > > > > > dies,
> > > > > > > > > > > > > the main threads cannot access the global stores any
> > > > > > > > > > > > > longer an
> > > > > > also die.
> > > > > > > > > > > > > If we re-build the state though, do we need to pause
> > > > > > > > > > > > > the main
> > > > > > thread
> > > > > > > > > > > > > during this phase?
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > -Matthias
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > On 8/2/20 8:48 AM, Navinder Brar wrote:
> > > > > > > > > > > > > > Hi John,
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > I have updated the KIP to make the motivation more
> > > > > > > > > > > > > > clear. In a
> > > > > > nutshell, we will use the already existing config
> > > > > > "global.consumer.auto.offset.reset" for users to set a blanket reset
> > > policy
> > > > > > for all global topics and add a new interface to set per-topic reset
> > > policy
> > > > > > for each global topic(for which we specifically need this KIP).
> > > > > > There
> > > was a
> > > > > > point raised from Matthias above to always reset to earliest by
> > > cleaning
> > > > > > the stores and seekToBeginning in case of InvalidOffsetException. We
> > > can go
> > > > > > with that route as well and I don't think it would need a KIP as if
> > > > > > we
> > > are
> > > > > > not providing users an option to have blanket reset policy on global
> > > > > > topics, then a per-topic override would also not be required(the
> > > > > > KIP is
> > > > > > required basically for that). Although, I think if users have an
> > > option to
> > > > > > choose reset policy for StreamThread then the option should be
> > > provided for
> > > > > > GlobalStreamThread as well and if we don't want to use the
> > > > > > "global.consumer.auto.offset.reset" then we would need to deprecate
> > > > > > it
> > > > > > because currently it's not serving any purpose. For now, I have
> > > > > > added
> > > it in
> > > > > > rejected alternatives but we can discuss this.
> > > > > > > > > > > > > > On the query that I had for Guozhang, thanks to
> > > > > > > > > > > > > > Matthias we
> > > have
> > > > > > fixed it last week as part of KAFKA-10306.
> > > > > > > > > > > > > > ~Navinder
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > On Sunday, 26 July, 2020, 07:37:34 pm IST,
> > > > > > > > > > > > > >Navinder Brar <
> > > > > > navinder_b...@yahoo.com.invalid> wrote:
> > > > > > > > > > > > > > Hi,
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Sorry, it took some time to respond back.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > “but I thought we would pass the config through to
> > > > > > > > > > > > > > the client.”
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > @John, sure we can use the config in
> > > > > > > > > > > > > > > > GloablStreamThread, that
> > > > > > could be one of the way to solve it.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > @Matthias, sure cleaning the store and recreating
> > > > > > > > > > > > > > is one way
> > > but
> > > > > > since we are giving an option to reset in StreamThread why the
> > > > > > implementation should be different in GlobalStreamThread. I think we
> > > should
> > > > > > use the global.consumer.auto.offset.reset config to accept the reset
> > > > > > strategy opted by the user although I would be ok with just cleaning
> > > and
> > > > > > resetting to the latest as well for now. Currently, we throw a
> > > > > > StreamsException in case of InvalidOffsetException in
> > > GlobalStreamThread so
> > > > > > just resetting would still be better than what happens currently.
> > > > > > > > > > > > > > Matthias, I found this comment in StreamBuilder for
> > > GlobalKTable
> > > > > > ‘* Note that {@link GlobalKTable} always applies {@code
> > > > > > "auto.offset.reset"} strategy {@code "earliest"} regardless of the
> > > > > > specified value in {@link StreamsConfig} or {@link Consumed}.’
> > > > > > > > > > > > > > So, I guess we are already cleaning up and
> > > > > > > > > > > > > > recreating for
> > > > > > GlobalKTable from earliest offset.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > @Guozhan while looking at the code, I also noticed
> > > > > > > > > > > > > > a TODO:
> > > > > > pending in GlobalStateManagerImpl, when InvalidOffsetException is
> > > thrown.
> > > > > > Earlier, we were directly clearing the store here and recreating
> > > > > > from
> > > > > > scratch but that code piece is removed now. Are you working on a
> > > follow-up
> > > > > > PR for this or just handling the reset in GlobalStreamThread should
> > > > > > be
> > > > > > sufficient?
> > > > > > > > > > > > > > Regards,
> > > > > > > > > > > > > > Navinder
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > On Tuesday, 7 July, 2020, 12:53:36 am IST,
> > > > > > > > > > > > > >Matthias J. Sax
> > > <
> > > > > > mj...@apache.org> wrote:
> > > > > > > > > > > > > > Atm, the config should be ignored and the
> > > > > > > > > > > > > >global-consumer
> > > > > > should use
> > > > > > > > > > > > > > "none" in a hard-coded way.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > However, if am still wondering if we actually
> > > > > > > > > > > > > > want/need to
> > > allow
> > > > > > users
> > > > > > > > > > > > > > to specify the reset policy? It might be worth to
> > > > > > > > > > > > > > consider, to
> > > > > > just
> > > > > > > > > > > > > > change the behavior: catch the exception, log an
> > > > > > > > > > > > > > ERROR (for
> > > > > > information
> > > > > > > > > > > > > > purpose), wipe the store, seekToBeginning(), and
> > > > > > > > > > > > > > recreate the
> > > > > > store?
> > > > > > > > > > > > > > Btw: if we want to allow users to set the reset
> > > > > > > > > > > > > > policy, this
> > > > > > should be
> > > > > > > > > > > > > > possible via the config, or via overwriting the
> > > > > > > > > > > > > > config in the
> > > > > > method
> > > > > > > > > > > > > > itself. Thus, we would need to add the new
> > > > > > > > > > > > > > overloaded method to
> > > > > > > > > > > > > > `Topology` and `StreamsBuilder`.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Another question to ask: what about GlobalKTables?
> > > > > > > > > > > > > > Should they
> > > > > > behave
> > > > > > > > > > > > > > the same? An alternative design could be, to allow
> > > > > > > > > > > > > > users to
> > > > > > specify a
> > > > > > > > > > > > > > flexible reset policy for global-stores, but not for
> > > > > > GlobalKTables and
> > > > > > > > > > > > > > use the strategy suggested above for this case.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Thoughts?
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > -Matthias
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > On 7/2/20 2:14 PM, John Roesler wrote:
> > > > > > > > > > > > > > > Hi Navinder,
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Thanks for the response. I’m sorry if I’m being
> > > > > > > > > > > > > > > dense... You
> > > > > > said we are not currently using the config, but I thought we would
> > > pass the
> > > > > > config through to the client. Can you confirm whether or not the
> > > existing
> > > > > > config works for your use case?
> > > > > > > > > > > > > > > Thanks,
> > > > > > > > > > > > > > > John
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > On Sun, Jun 28, 2020, at 14:09, Navinder Brar
> > > > > > > > > > > > > > > wrote:
> > > > > > > > > > > > > > > > Sorry my bad. Found it.
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Prefix used to override {@link KafkaConsumer
> > > > > > > > > > > > > > > > consumer}
> > > configs
> > > > > > for the
> > > > > > > > > > > > > > > > global consumer client from
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > * the general consumer client configs. The
> > > > > > > > > > > > > > > > override
> > > precedence
> > > > > > is the
> > > > > > > > > > > > > > > > following (from highest to lowest precedence):
> > > > > > > > > > > > > > > > * 1. global.consumer.[config-name]..
> > > > > > > > > > > > > > > > public static final String
> > > > > > > > > > > > > > > > GLOBAL_CONSUMER_PREFIX =
> > > > > > "global.consumer.";
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > So, that's great. We already have a config
> > > > > > > > > > > > > > > > exposed to reset
> > > > > > offsets for
> > > > > > > > > > > > > > > > global topics via
> > > > > > > > > > > > > > > > global.consumer.auto.offset.reset just that
> > > > > > we are
> > > > > > > > > > > > > > > > not actually using it inside GlobalStreamThread
> > > > > > > > > > > > > > > > to reset.
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > -Navinder
> > > > > > > > > > > > > > > > On Monday, 29 June, 2020, 12:24:21 am IST,
> > > > > > > > > > > > > > > >Navinder Brar
> > > > > > > > > > > > > > > > <navinder_b...@yahoo.com.invalid> wrote:
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Hi John,
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Thanks for your feedback.
> > > > > > > > > > > > > > > > 1. I think there is some confusion on my first
> > > > > > > > > > > > > > > > point, the
> > > enum
> > > > > > I am
> > > > > > > > > > > > > > > > sure we can use the same one but the external
> > > > > > > > > > > > > > > > config which
> > > > > > controls the
> > > > > > > > > > > > > > > > resetting in global stream thread either we can
> > > > > > > > > > > > > > > > the same one
> > > > > > which
> > > > > > > > > > > > > > > > users use for source topics(StreamThread) or we
> > > > > > > > > > > > > > > > can provide a
> > > > > > new one
> > > > > > > > > > > > > > > > which specifically controls global topics. For
> > > > > > > > > > > > > > > > e.g. currently
> > > > > > if I get
> > > > > > > > > > > > > > > > an InvalidOffsetException in any of my source
> > > > > > > > > > > > > > > > topics, I can
> > > > > > choose
> > > > > > > > > > > > > > > > whether to reset from Earliest or Latest(with
> > > > > > auto.offset.reset). Now
> > > > > > > > > > > > > > > > either we can use the same option and say if I
> > > > > > > > > > > > > > > > get the same
> > > > > > exception
> > > > > > > > > > > > > > > > for global topics I will follow same resetting.
> > > > > > > > > > > > > > > > Or some users
> > > > > > might
> > > > > > > > > > > > > > > > want to have totally different setting for both
> > > > > > > > > > > > > > > > source and
> > > > > > global
> > > > > > > > > > > > > > > > topics, like for source topic I want resetting
> > > > > > > > > > > > > > > > from Latest
> > > but
> > > > > > for
> > > > > > > > > > > > > > > > global topics I want resetting from Earliest so
> > > > > > > > > > > > > > > > in that case
> > > > > > adding a
> > > > > > > > > > > > > > > > new config might be better.
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > 2. I couldn't find this config currently
> > > > > > > > > > > > > > > > "global.consumer.auto.offset.reset". Infact in
> > > > > > GlobalStreamThread.java
> > > > > > > > > > > > > > > > we are throwing a StreamsException for
> > > > > > > > > > > > > > > > InvalidOffsetException
> > > > > > and there
> > > > > > > > > > > > > > > > is a test as
> > > > > > > > > > > > > > > > well
> > > > > > GlobalStreamThreadTest#shouldDieOnInvalidOffsetException(), so I
> > > > > > > > > > > > > > > > think this is the config we are trying to
> > > > > > > > > > > > > > > > introduce with this
> > > > > > KIP.
> > > > > > > > > > > > > > > > -Navinder On Saturday, 27 June, 2020, 07:03:04
> > > > > > > > > > > > > > > > pm IST, John
> > > > > > Roesler
> > > > > > > > > > > > > > > > <j...@vvcephei.org> wrote:
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Hi Navinder,
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Thanks for this proposal!
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Regarding your question about whether to use
> > > > > > > > > > > > > > > > the same policy
> > > > > > > > > > > > > > > > enum or not, the underlying mechanism is the
> > > > > > > > > > > > > > > > same, so I think
> > > > > > > > > > > > > > > > we can just use the same AutoOffsetReset enum.
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Can you confirm whether setting the reset
> > > > > > > > > > > > > > > > policy config on
> > > the
> > > > > > > > > > > > > > > > global consumer currently works or not? Based
> > > > > > > > > > > > > > > > on my reading
> > > > > > > > > > > > > > > > of StreamsConfig, it looks like it would be:
> > > > > > > > > > > > > > > > "global.consumer.auto.offset.reset".
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > If that does work, would you still propose to
> > > > > > > > > > > > > > > > augment the
> > > > > > > > > > > > > > > > Java API?
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Thanks,
> > > > > > > > > > > > > > > > -John
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > On Fri, Jun 26, 2020, at 23:52, Navinder Brar
> > > > > > > > > > > > > > > > wrote:
> > > > > > > > > > > > > > > > > Hi,
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > KIP:
> > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-406%3A+GlobalStreamThread+should+honor+custom+reset+policy
> > > > > > > > > > > > > > > > > I have taken over this KIP since it has been
> > > > > > > > > > > > > > > > > dormant for a
> > > > > > long time
> > > > > > > > > > > > > > > > > and this looks important for use-cases that
> > > > > > > > > > > > > > > > > have large
> > > global
> > > > > > data, so
> > > > > > > > > > > > > > > > > rebuilding global stores from scratch might
> > > > > > > > > > > > > > > > > seem overkill in
> > > > > > case of
> > > > > > > > > > > > > > > > > InvalidOffsetExecption.
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > We want to give users the control to use
> > > > > > > > > > > > > > > > > reset policy(as we
> > > do
> > > > > > in
> > > > > > > > > > > > > > > > > StreamThread) in case they hit invalid
> > > > > > > > > > > > > > > > > offsets. I have still
> > > > > > not
> > > > > > > > > > > > > > > > > decided whether to restrict this option to
> > > > > > > > > > > > > > > > > the same reset
> > > > > > policy being
> > > > > > > > > > > > > > > > > used by StreamThread(using auto.offset.reset
> > > > > > > > > > > > > > > > > config) or add
> > > > > > another
> > > > > > > > > > > > > > > > > reset config specifically for global stores
> > > > > > > > > > > > > > > > > "global.auto.offset.reset" which gives users
> > > > > > > > > > > > > > > > > more control to
> > > > > > choose
> > > > > > > > > > > > > > > > > separate policies for global and stream
> > > > > > > > > > > > > > > > > threads.
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > I would like to hear your opinions on the KIP.
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > -Navinder
> > >
> > >
>
>
