Hi again all, I've sent a PR including this new option, and while implementing it, I realized we also have to make a (source-compatible) addition to the QueryableStoreType interface, so that the IQ store wrapper can pass the flag down to the composite store provider.
See https://github.com/apache/kafka/pull/7962 In particular: https://github.com/apache/kafka/pull/7962/files#diff-d0242b7289f4e0886490351a5a803d41 If there are no objections to these additions, I'll update the KIP tomorrow. Thanks, -John On Tue, Jan 14, 2020, at 14:11, John Roesler wrote: > Thanks for calling this out, Matthias. You're correct that this looks like a > harmful behavioral change. I'm fine with adding the new overload you > mentioned, just a simple boolean flag to enable the new behavior. > > I'd actually propose that we call this flag "queryStaleData", with a default > of "false". The meaning of this would be to preserve exactly the existing > semantics. I.e., that the store must be both active and running to be > included. > > It seems less severe to just suddenly start returning queries from standbys, > but in the interest of safety, the easiest thing is just flag the whole > feature. > > If you, Navinder, and Vinoth agree, we can just update the KIP. It seems like > a pretty uncontroversial amendment to avoid breaking query consistency > semantics. > > Thanks, > -John > > > On Tue, Jan 14, 2020, at 13:21, Matthias J. Sax wrote: > > During the discussion of KIP-216 > > (https://cwiki.apache.org/confluence/display/KAFKA/KIP-216%3A+IQ+should+throw+different+exceptions+for+different+errors) > > we encountered that KIP-535 introduces a behavior change that is not > > backward compatible, hence, I would like to request a small change. > > > > KIP-535 suggests, that active tasks can be queried during recovery and > > no exception would be thrown and longer. This is a change in behavior > > and in fact introduces a race condition for users that only want to > > query consistent state. Querying inconsistent state should be an opt-in, > > and for StandbyTasks, user can opt-in by querying them or opt-out by not > > querying them. However, for active task, if we don't throw an exception > > during recovery, users cannot opt-out of querying potentially > > inconsistent state, because they would need to check the state (ie, == > > RUNNING) before they would query the active task -- however, the state > > might change at any point in between, and there is a race. > > > > Hence, I would suggest to actually not change the default behavior of > > existing methods and we should throw an exception during restore if an > > active task is queried. To allow user to opt-in to query an active task > > during restore, we would add an overload > > > > > KafkaStream#store(..., boolean allowQueryWhileStateIsRestoring) > > > > (with an hopefully better/short variable name). Developers would use > > this new method to opt-into querying active tasks during restore. > > > > Thoughts? > > > > > > -Matthias > > > > On 11/18/19 10:45 AM, Vinoth Chandar wrote: > > > Thanks, everyone involved! > > > > > > On Mon, Nov 18, 2019 at 7:51 AM John Roesler <j...@confluent.io> wrote: > > > > > >> Thanks to you, also, Navinder! > > >> > > >> Looking forward to getting this feature in. > > >> -John > > >> > > >> On Sun, Nov 17, 2019 at 11:34 PM Navinder Brar > > >> <navinder_b...@yahoo.com.invalid> wrote: > > >>> > > >>> Hello all, > > >>> > > >>> With 4 binding +1 votes from Guozhang Wang, Matthias J. Sax, Bill > > >>> Bejeck, > > >>> and John Roesler, the vote passes. > > >>> Thanks Guozhang, Matthias, Bill, John, Sophie for the healthy > > >> discussions and Vinoth for all the help on this KIP. > > >>> Best, > > >>> Navinder > > >>> > > >>> On Friday, 15 November, 2019, 11:32:31 pm IST, John Roesler < > > >> j...@confluent.io> wrote: > > >>> > > >>> I'm +1 (binding) as well. > > >>> > > >>> Thanks, > > >>> -John > > >>> > > >>> On Fri, Nov 15, 2019 at 6:20 AM Bill Bejeck <bbej...@gmail.com> wrote: > > >>>> > > >>>> +1 (binding) > > >>>> > > >>>> On Fri, Nov 15, 2019 at 1:11 AM Matthias J. Sax <matth...@confluent.io > > >>> > > >>>> wrote: > > >>>> > > >>>>> +1 (binding) > > >>>>> > > >>>>> > > >>>>> On 11/14/19 3:48 PM, Guozhang Wang wrote: > > >>>>>> +1 (binding), thanks for the KIP! > > >>>>>> > > >>>>>> Guozhang > > >>>>>> > > >>>>>> On Fri, Nov 15, 2019 at 4:38 AM Navinder Brar > > >>>>>> <navinder_b...@yahoo.com.invalid> wrote: > > >>>>>> > > >>>>>>> Hello all, > > >>>>>>> > > >>>>>>> I'd like to propose a vote for serving interactive queries during > > >>>>>>> Rebalancing, as it is a big deal for applications looking for high > > >>>>>>> availability. With this change, users will have control over the > > >>>>> tradeoff > > >>>>>>> between consistency and availability during serving. > > >>>>>>> The full KIP is provided here: > > >>>>>>> > > >>>>>>> > > >>>>> > > >> https://cwiki.apache.org/confluence/display/KAFKA/KIP-535%3A+Allow+state+stores+to+serve+stale+reads+during+rebalance > > >>>>>>> > > >>>>>>> > > >>>>>>> Thanks, > > >>>>>>> Navinder > > >>>>>> > > >>>>>> > > >>>>>> > > >>>>> > > >>>>> > > >>> > > >> > > > > > > > > > Attachments: > > * signature.asc >
