Thanks for the confirmation. I guess listener would make sense if I did some caching of the store and needed to refresh it for every change in the underlying store.
On Tue, Aug 1, 2017 at 6:10 PM, Damian Guy <damian....@gmail.com> wrote: > No you don't need to set a listener. Was just mentioning as it an option > if you wan't to know that the metadata needs refreshing, > > On Tue, 1 Aug 2017 at 13:25 Debasish Ghosh <ghosh.debas...@gmail.com> > wrote: > >> Regarding the last point, do I need to set up the listener ? >> >> All I want is to do a query from the store. For that I need to invoke >> streams.store() >> first, which can potentially throw an InvalidStateStoreException during >> rebalancing / migration of stores. If I call streams.store() with >> retries till the rebalancing is done or I exceed some max retry count, then >> I think I should good. >> >> Or am I missing something ? >> >> regards. >> >> On Tue, Aug 1, 2017 at 1:10 PM, Damian Guy <damian....@gmail.com> wrote: >> >>> Hi, >>> >>> On Tue, 1 Aug 2017 at 08:34 Debasish Ghosh <ghosh.debas...@gmail.com> >>> wrote: >>> >>>> Hi - >>>> >>>> I have a Kafka Streams application that needs to run on multiple >>>> instances. >>>> It fetches metadata from all local stores and has an http query layer >>>> for >>>> interactive queries. In some cases when I have new instances deployed, >>>> store migration takes place making the current metadata invalid. Here >>>> are >>>> my questions regarding some of the best practices to be followed to >>>> handle >>>> this issue of store migration - >>>> >>>> - When the migration is in process, a query for the metadata may >>>> result >>>> in InvalidStateStoreException - is it a good practice to always have >>>> a >>>> retry semantics based query for the metadata ? >>>> >>> >>> Yes. Whenever the application is rebalancing the stores will be >>> unavailable, so retrying is the right thing to do. >>> >>> >>>> - Should I check KafkaStreams.state() and only assume that I have got >>>> the correct metadata when the state() call returns Running. If it >>>> returns Rebalancing, then I should re-query. Is this correct >>>> approach ? >>>> >>> >>> Correct again! If the state is rebalancing, then the metadata (for some >>> stores at least) is going to change, so you should get it again. You can >>> set a StateListener on the KafkaStreams instance to listen to these events. >>> >>> >>>> >>>> regards. >>>> >>>> -- >>>> Debasish Ghosh >>>> http://manning.com/ghosh2 >>>> http://manning.com/ghosh >>>> >>>> Twttr: @debasishg >>>> Blog: http://debasishg.blogspot.com >>>> Code: http://github.com/debasishg >>>> >>> >> >> >> -- >> Debasish Ghosh >> http://manning.com/ghosh2 >> http://manning.com/ghosh >> >> Twttr: @debasishg >> Blog: http://debasishg.blogspot.com >> Code: http://github.com/debasishg >> > -- Debasish Ghosh http://manning.com/ghosh2 http://manning.com/ghosh Twttr: @debasishg Blog: http://debasishg.blogspot.com Code: http://github.com/debasishg
