My inclination is either #2 or #3. #4 is an option of course, but I like the more structured solution of explicitly requesting the schema given a descriptor.
In both cases, it's possible that schemas are sent twice, e.g. if you call GetSchema and then later call GetFlightInfo and so you receive the schema again. The schema is optional, so if it became a performance problem then a particular server might return the schema as null from GetFlightInfo. I think it's valid to want to make a single GetFlightInfo RPC request that returns _both_ the schema and the query plan. Thoughts from others? On Fri, Jun 28, 2019 at 8:52 PM Jacques Nadeau <jacq...@apache.org> wrote: > > My initial inclination is towards #3 but I'd be curious what others think. > In the case of #3, I wonder if it makes sense to then pull the Schema off > the GetFlightInfo response... > > On Fri, Jun 28, 2019 at 10:57 AM Ryan Murray <rym...@dremio.com> wrote: > > > Hi All, > > > > I have been working on building an arrow flight source for spark. The goal > > here is for Spark to be able to use a group of arrow flight endpoints to > > get a dataset pulled over to spark in parallel. > > > > I am unsure of the best model for the spark <-> flight conversation and > > wanted to get your opinion on the best way to go. > > > > I am breaking up the query to flight from spark into 3 parts: > > 1) get the schema using GetFlightInfo. This is needed to do further lazy > > operations in Spark > > 2) get the endpoints by calling GetFlightInfo a 2nd time with a different > > argument. This returns the list endpoints on the parallel flight server. > > The endpoints are not available till data is ready to be fetched, which is > > done after the schema but is needed before DoGet is called. > > 3) call get stream on all endpoints from 2 > > > > I think I have to do each step however I don't like having to call getInfo > > twice, it doesn't seem very elegant. I see a few options: > > 1) live with calling GetFlightInfo twice and with a custom bytes cmd to > > differentiate the purpose of each call > > 2) add an argument to GetFlightInfo to tell it its being called only for > > the schema > > 3) add another rpc endpoint: ie GetSchema(FlightDescriptor) to return just > > the Schema in question > > 4) use DoAction and wrap the expected FlightInfo in a Result > > > > I am aware that 4 is probably the least disruptive but I'm also not a fan > > as (to me) it implies performing an action on the server side. Suggestions > > 2 & 3 are larger changes and I am reluctant to do that unless there is a > > consensus here. None of them are great options and I am wondering what > > everyone thinks the best approach might be? Particularly as I think this is > > likely to come up in more applications than just spark. > > > > Best, > > Ryan > >
