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 >
