hi folks, I left some feedback on this PR. If others could take a look (particularly at the .proto service definition) that would be useful.
We should decide on an approach to getting multiple production-worthy Flight/RPC implementations ready to go. It would be a good goal to deliver (end-to-end send/receive data between Python and Java, or Python and other Python processes) in the next couple releases. - Wes On Wed, May 30, 2018 at 12:44 PM, Jacques Nadeau <jacq...@apache.org> wrote: > Correct, I'm maintaining standard protobuf encoding so a consumer that > doesn't go byte by byte can still consumer/produce the messages. > > More impls: for sure. > > On Wed, May 30, 2018 at 9:01 AM, Wes McKinney <wesmck...@gmail.com> wrote: > >> I see; looking more closely I see you've sidestepped the standard >> Protobuf serialization to write the stream as tagged components: >> >> https://github.com/apache/arrow/compare/master...jacques-n:flight#diff- >> 02cfc9235e22653fce8a7636c9f95507R241 >> >> and then reading the fields of the message tag by tag >> >> https://github.com/apache/arrow/compare/master...jacques-n:flight#diff- >> 02cfc9235e22653fce8a7636c9f95507R159 >> >> Would it be correct that if a GRPC implementation doesn't provide >> sufficient access to the byte stream (or if it doesn't care enough >> about zero copy) that you could allow GRPC to return an instance of >> the FlightData structure? >> >> I expect we'd want to see a few interoperable implementations (I >> suggest Java, C++, Go) to harden the fine details. >> >> - Wes >> >> On Mon, May 28, 2018 at 3:32 PM, Jacques Nadeau <jacq...@apache.org> >> wrote: >> > Cutting through the layers of GRPC will be a per language approach thing. >> > Assuming that each GRPC language implementation does a good job of >> > separating message encapsulation from the base library, this should be >> > straight-forward-ish. Hope improves around this as I see creation of >> > non-protobuf protocols built on top of the base GRPC [1]. How to do this >> in >> > each language will probably take time looking at the GRPC internals for >> > that language but can be a secondary step once you get the protocol >> working >> > (you can just pay for extra copies until then). >> > >> > In my Java approach I believe I do one read copy and zero write copies >> > (needs more testing) which was my target. (Getting to zero-copy on read >> > means a lot more complexity because your socket-reading has to be >> protocol >> > aware: even our bespoke layer in Dremio doesn't try to do that. I'd guess >> > KRPC does the same but haven't reviewed the code to confirm.) >> > >> > Will try to get some more slides/readme and a proper proposed patch up >> soon. >> > >> > [1] https://grpc.io/blog/flatbuffers >> > >> > >> > >> > On Mon, May 28, 2018 at 1:05 AM, Wes McKinney <wesmck...@gmail.com> >> wrote: >> > >> >> hey Jacques, >> >> >> >> This is great news, I look forward to digging into this. My biggest >> >> initial question is the Protobuf encapsulation, specifically: >> >> >> >> https://github.com/jacques-n/arrow/blob/flight/java/flight/ >> >> src/main/protobuf/flight.proto#L99 >> >> >> >> My understanding of Protocol Buffers is that on read, the "data_body" >> >> memory would be copied out of the serialized protobuf that came across >> >> the wire. Your comment in the .proto says this "comes last in the >> >> definition to help with sidecar patterns" -- my read is that it would >> >> be up to us to do our own sidecar implementation, similar to how >> >> Apache Kudu has zero-copy sidecars in their KRPC system [1] (the >> >> comment there describes pretty much exactly the problem we have). I >> >> saw that you also replied on a GRPC thread about this issue [2]. Could >> >> you summarize what (if anything) stands in the way to get zero-copy on >> >> write and read? >> >> >> >> - Wes >> >> >> >> [1]: https://github.com/apache/kudu/blob/master/src/kudu/rpc/ >> >> rpc_sidecar.h#L34 >> >> [2]: https://github.com/grpc/grpc-java/issues/1054#issuecomment- >> 391692087 >> >> >> >> On Thu, May 24, 2018 at 6:57 AM, Jacques Nadeau <jacq...@apache.org> >> >> wrote: >> >> > FYI, if you want to see an example server you can run with a GRPC >> >> generated >> >> > client, you can run the ExampleFlightServer located at [1]. Very basic >> >> > 'test' with that class and client is located at [2]. >> >> > >> >> > [1] >> >> > https://github.com/jacques-n/arrow/tree/flight/java/flight/ >> >> src/main/java/org/apache/arrow/flight/example >> >> > [2] >> >> > https://github.com/jacques-n/arrow/blob/flight/java/flight/ >> >> src/test/java/org/apache/arrow/flight/example/TestExampleServer.java >> >> > >> >> > >> >> > On Thu, May 24, 2018 at 11:51 AM, Jacques Nadeau <jacq...@apache.org> >> >> wrote: >> >> > >> >> >> Hey All, >> >> >> >> >> >> I used my Strata talk today as a forcing function to make additional >> >> >> progress on a GRPC-based Arrow RPC protocol [1]. I’m calling it >> “Apache >> >> >> Arrow Flight”. You can take a look at the work here [2]. I’ll work to >> >> clean >> >> >> up my work and explain my thoughts about the protocol in the coming >> >> days. >> >> >> High-level: use protobuf as a encapsulation format so that any client >> >> that >> >> >> is supported in GRPC will work. However, we can optimize the >> read/write >> >> >> path for targeted languages and hand control the >> >> >> serialization/deserialization and memory handling. (I did that in >> this >> >> Java >> >> >> patch [3][4][5].) I also looked at starting to use GRPC generated >> >> bindings >> >> >> within Python but it looks like some glue code may be needed in the >> C++ >> >> >> layer since Python delegates down frequently. I also am still trying >> to >> >> >> understand GRPC back-pressure patterns and whether the protocol >> >> >> realistically needs to change to cover real-world high performance >> use >> >> >> cases. >> >> >> >> >> >> I’ll send out some slides about the ideas and update README, etc. >> soon. >> >> >> >> >> >> Thanks, >> >> >> Jacques >> >> >> >> >> >> [1] https://github.com/jacques-n/arrow/blob/flight/java/flight/ >> >> >> src/main/protobuf/flight.proto >> >> >> [2] http://github.com/jacques-n/arrow/ >> >> >> [3] https://github.com/jacques-n/arrow/tree/flight/ >> >> >> java/flight/src/main/java/org/apache/arrow/flight/grpc >> >> >> [4] https://github.com/jacques-n/arrow/blob/flight/ >> >> >> java/flight/src/main/java/org/apache/arrow/flight/ >> >> ArrowMessage.java#L253 >> >> >> <https://github.com/jacques-n/arrow/blob/flight/java/flight/ >> >> src/main/java/org/apache/arrow/flight/ArrowMessage.java#L253> >> >> >> [5] https://github.com/jacques-n/arrow/blob/flight/ >> >> >> java/flight/src/main/java/org/apache/arrow/flight/ >> >> ArrowMessage.java#L185 >> >> >> >> >> >> >> >> >>
