I'd vote for explicitly not supported. We should keep our primitives narrow.
On Wed, Nov 27, 2019, 1:17 PM David Li <li.david...@gmail.com> wrote: > Thanks for the feedback. > > I do think if we had explicitly embraced gRPC from the beginning, > there are a lot of places where things could be made more ergonomic, > including with the metadata fields. But it would also have locked out > us of potential future transports. > > On another note: I hesitate to put too much into this method, but we > are looking at use cases where potentially, a client may want to > upload multiple distinct datasets (with differing schemas). (This is a > little tentative, and I can get more details...) Right now, each > logical stream in Flight must have a single, consistent schema; would > it make sense to look at ways to relax this, or declare this > explicitly out of scope (and require multiple calls and coordination > with the deployment topology) in order to accomplish this? > > Best, > David > > On 11/27/19, Jacques Nadeau <jacq...@apache.org> wrote: > > Fair enough. I'm okay with the bytes approach and the proposal looks good > > to me. > > > > On Fri, Nov 8, 2019 at 11:37 AM David Li <li.david...@gmail.com> wrote: > > > >> I've updated the proposal. > >> > >> On the subject of Protobuf Any vs bytes, and how to handle > >> errors/metadata, I still think using bytes is preferable: > >> - It doesn't require (conditionally) exposing or wrapping Protobuf > types, > >> - We wouldn't be able to practically expose the Protobuf field to C++ > >> users without causing build pains, > >> - We can't let Python users take advantage of the Protobuf field > >> without somehow being compatible with the Protobuf wheels (by linking > >> to the same version, and doing magic to turn the C++ Protobufs into > >> the Python ones), > >> - All our other application-defined fields are already bytes. > >> > >> Applications that want structure can encode JSON or Protobuf Any into > >> the bytes field themselves, much as you can already do for Ticket, > >> commands in FlightDescriptors, and application metadata in > >> DoGet/DoPut. I don't think this is (much) less efficient than using > >> Any directly, since Any itself is a bytes field with a tag, and must > >> invoke the Protobuf deserializer again to read the actual message. > >> > >> If we decide on using bytes, then I don't think it makes sense to > >> define a new message with a oneof either, since it would be redundant. > >> > >> Thanks, > >> David > >> > >> On 11/7/19, David Li <li.david...@gmail.com> wrote: > >> > I've been extremely backlogged, I will update the proposal when I get > >> > a chance and reply here when done. > >> > > >> > Best, > >> > David > >> > > >> > On 11/7/19, Wes McKinney <wesmck...@gmail.com> wrote: > >> >> Bumping this discussion since a couple of weeks have passed. It seems > >> >> there are still some questions here, could we summarize what are the > >> >> alternatives along with any public API implications so we can try to > >> >> render a decision? > >> >> > >> >> On Sat, Oct 26, 2019 at 7:19 PM David Li <li.david...@gmail.com> > >> >> wrote: > >> >>> > >> >>> Hi Wes, > >> >>> > >> >>> Responses inline: > >> >>> > >> >>> On Sat, Oct 26, 2019, 13:46 Wes McKinney <wesmck...@gmail.com> > wrote: > >> >>> > >> >>> > On Mon, Oct 21, 2019 at 7:40 PM David Li <li.david...@gmail.com> > >> >>> > wrote: > >> >>> > > > >> >>> > > The question is whether to repurpose the existing FlightData > >> >>> > > structure, and allow for the metadata field to be filled in and > >> data > >> >>> > > fields to be blank (as a control message), or to wrap the > >> FlightData > >> >>> > > structure in another structure that explicitly distinguishes > >> between > >> >>> > > control and data messages. > >> >>> > > >> >>> > I'm not super against having metadata-only FlightData with empty > >> body. > >> >>> > One question to consider is what changes (if any) would need to be > >> >>> > made to public APIs in either scenario. > >> >>> > > >> >>> > >> >>> We could leave DoGet/DoPut as-is for now, and allow empty data > >> >>> messages > >> >>> in > >> >>> the future. This would be a breaking change, but wouldn't change the > >> >>> wire > >> >>> format. I think the APIs could be changed backwards compatibly, > >> >>> though. > >> >>> > >> >>> > >> >>> > >> >>> > > The other question is how to handle the metadata fields. So far, > >> >>> > > we've > >> >>> > > used bytestring fields for application-defined data. This is > >> >>> > > workable > >> >>> > > if you want to use Protobuf to define the contents of those > >> >>> > > fields, > >> >>> > > but requires you to pack/unpack your Protobuf into/from the > >> >>> > > bytestring > >> >>> > > field. If we instead used the Protobuf Any field, a dynamically > >> >>> > > typed > >> >>> > > field, this would be more convenient, but then we'd be exposing > >> >>> > > Protobuf types. We could alternatively use a combination of a > >> >>> > > type > >> >>> > > field and a bytestring field, mimicking what the Protobuf Any > >> >>> > > type > >> >>> > > looks like on the wire. I'm not sure this is actually cleaner in > >> any > >> >>> > > of the language APIs, though. > >> >>> > > >> >>> > Leaving the deserialization of the app metadata to the particular > >> >>> > Flight implementation seems on first principles like the most > >> flexible > >> >>> > thing, if Any is used, does that mean the metadata _must_ be a > >> >>> > protobuf? > >> >>> > > >> >>> > >> >>> > >> >>> If Any is used, we could still expose a bytes-based API, but it > would > >> >>> have > >> >>> some more wrapping. (We could put a ByteString in Any.) Then the > >> >>> question > >> >>> would just be how to expose this (would be easier in Java, harder in > >> >>> C++). > >> >>> > >> >>> > >> >>> > >> >>> > > David > >> >>> > > > >> >>> > > On 10/21/19, Antoine Pitrou <anto...@python.org> wrote: > >> >>> > > > > >> >>> > > > Can one of you explain what is being proposed in non-protobuf > >> >>> > > > terms? > >> >>> > > > Knowledge of protobuf shouldn't be required to use Flight. > >> >>> > > > > >> >>> > > > Regards > >> >>> > > > > >> >>> > > > Antoine. > >> >>> > > > > >> >>> > > > > >> >>> > > > Le 21/10/2019 à 15:46, David Li a écrit : > >> >>> > > >> Oneof doesn't actually change the wire encoding; it would > just > >> be > >> >>> > > >> application-level logic. (The official guide doesn't even > >> mention > >> >>> > > >> it > >> >>> > > >> in the encoding docs; I found > >> >>> > > >> > >> >>> > > >> > https://stackoverflow.com/questions/52226409/how-protobuf-encodes-oneof-message-construct > >> >>> > > >> as well.) > >> >>> > > >> > >> >>> > > >> If I follow you, Jacques, then you are proposing essentially > >> >>> > > >> inlining > >> >>> > > >> the definition of Any, e.g. > >> >>> > > >> > >> >>> > > >> message FlightMessage { > >> >>> > > >> oneof message { > >> >>> > > >> FlightData data = 1; > >> >>> > > >> FlightAny metadata = 2; > >> >>> > > >> } > >> >>> > > >> } > >> >>> > > >> > >> >>> > > >> message FlightAny { > >> >>> > > >> string type = 1; > >> >>> > > >> bytes data = 2; > >> >>> > > >> } > >> >>> > > >> > >> >>> > > >> Is this correct? > >> >>> > > >> > >> >>> > > >> It might be nice to consider the wrapper message for > >> >>> > > >> DoGet/DoPut > >> >>> > > >> as > >> >>> > > >> well, but at that point, I'd rather we be consistent with all > >> >>> > > >> of > >> >>> > > >> them, > >> >>> > > >> rather than have one of the three methods do its own thing. > >> >>> > > >> > >> >>> > > >> Thanks, > >> >>> > > >> David > >> >>> > > >> > >> >>> > > >> On 10/20/19, Jacques Nadeau <jacq...@apache.org> wrote: > >> >>> > > >>> I think we could probably expose the oneof behavior without > >> >>> > > >>> exposing > >> >>> > the > >> >>> > > >>> protobuf functions. On the any... hmm. I guess we could > >> >>> > > >>> expose > >> >>> > > >>> as > >> >>> > > >>> two > >> >>> > > >>> fields: type and data. Then users could use it for whatever > >> >>> > > >>> but > >> >>> > > >>> if > >> >>> > > >>> people > >> >>> > > >>> wanted to treat it as any, it would work. (Basically a user > >> >>> > > >>> could > >> >>> > > >>> use > >> >>> > > >>> any > >> >>> > > >>> with it easily but they could also use any other mechanism). > >> >>> > > >>> At > >> >>> > least in > >> >>> > > >>> java, the any concepts are pretty simple/diy. Are other > >> language > >> >>> > > >>> bindings > >> >>> > > >>> less diy? > >> >>> > > >>> > >> >>> > > >>> I'm *not* hardcore against the empty FlightData + metadata > >> >>> > > >>> but > >> >>> > > >>> it > >> >>> > just > >> >>> > > >>> seemed a bit janky. > >> >>> > > >>> > >> >>> > > >>> Thinking about the control message/wrapper object thing, I > >> >>> > > >>> wonder > >> >>> > > >>> if > >> >>> > we > >> >>> > > >>> should redefine DoPut and DoGet to have the same property if > >> >>> > > >>> we > >> >>> > think it > >> >>> > > >>> is > >> >>> > > >>> a good idea... > >> >>> > > >>> > >> >>> > > >>> On Wed, Oct 16, 2019 at 5:13 PM David Li < > >> li.david...@gmail.com> > >> >>> > wrote: > >> >>> > > >>> > >> >>> > > >>>> I was definitely considering having control messages > without > >> >>> > > >>>> data, > >> >>> > and > >> >>> > > >>>> I thought that could be encoded by a FlightData with only > >> >>> > app_metadata > >> >>> > > >>>> set. I think I understand your position now: FlightData > >> >>> > > >>>> should > >> >>> > always > >> >>> > > >>>> carry (some) data (with optional metadata)? > >> >>> > > >>>> > >> >>> > > >>>> That makes sense to me, and is consistent with the > >> >>> > > >>>> documentation > >> >>> > > >>>> on > >> >>> > > >>>> FlightData in the Protobuf file. I was worried about having > >> >>> > > >>>> a > >> >>> > > >>>> redundant metadata field, but oneof prevents that from > >> >>> > > >>>> happening, > >> >>> > and > >> >>> > > >>>> overall having a clear separation between data and control > >> >>> > > >>>> messages > >> >>> > is > >> >>> > > >>>> cleaner. > >> >>> > > >>>> > >> >>> > > >>>> As for using Protobuf's Any: so far, we've refrained from > >> >>> > > >>>> exposing > >> >>> > > >>>> Protobuf by using bytes, would we want to change that now? > >> >>> > > >>>> > >> >>> > > >>>> Best, > >> >>> > > >>>> David > >> >>> > > >>>> > >> >>> > > >>>> On 10/16/19, Jacques Nadeau <jacq...@apache.org> wrote: > >> >>> > > >>>>> Hey David, > >> >>> > > >>>>> > >> >>> > > >>>>> RE: Async: I was trying to match the pattern we use for > >> >>> > > >>>>> doget/doput > >> >>> > > >>>>> for > >> >>> > > >>>>> async. Yes, more thinking java given java grpc's async > >> >>> > > >>>>> always > >> >>> > pattern. > >> >>> > > >>>>> > >> >>> > > >>>>> On the comment around the FlightData, I think it is > >> >>> > > >>>>> overloading > >> >>> > > >>>>> the > >> >>> > > >>>> message > >> >>> > > >>>>> to use metadata for this. If I want to send a control > >> >>> > > >>>>> message > >> >>> > > >>>> independently > >> >>> > > >>>>> of the data message, I would have to define something like > >> >>> > > >>>>> an > >> >>> > > >>>>> empty > >> >>> > > >>>> flight > >> >>> > > >>>>> data message that has custom metadata. Why not support a > >> >>> > > >>>>> container > >> >>> > > >>>>> object > >> >>> > > >>>>> with a oneof{FlightData, Any} in it instead so users can > >> >>> > > >>>>> add > >> >>> > > >>>>> more > >> >>> > data > >> >>> > > >>>>> as > >> >>> > > >>>>> desired. The default impl could be a noop for the Any > >> >>> > > >>>>> messages. > >> >>> > > >>>>> > >> >>> > > >>>>> On Tue, Oct 15, 2019 at 6:50 PM David Li > >> >>> > > >>>>> <li.david...@gmail.com> > >> >>> > > >>>>> wrote: > >> >>> > > >>>>> > >> >>> > > >>>>>> Hi Jacques, > >> >>> > > >>>>>> > >> >>> > > >>>>>> Thanks for the comments. > >> >>> > > >>>>>> > >> >>> > > >>>>>> - I do agree DoExchange is a better name! > >> >>> > > >>>>>> - FlightData already has metadata fields as a result of > >> prior > >> >>> > > >>>>>> proposals, so I don't think we need a new message to > carry > >> >>> > > >>>>>> that > >> >>> > kind > >> >>> > > >>>>>> of information. > >> >>> > > >>>>>> - I like the suggestion of an async handler to handle > >> >>> > > >>>>>> incoming > >> >>> > > >>>>>> messages as the fundamental API; it would actually be > >> >>> > > >>>>>> quite > >> >>> > natural > >> >>> > > >>>>>> to > >> >>> > > >>>>>> implement in Flight/Java. I will note that it's not > >> >>> > > >>>>>> possible > >> >>> > > >>>>>> in > >> >>> > > >>>>>> C++/Python without spawning a thread, though. (In > essence, > >> >>> > gRPC-Java > >> >>> > > >>>>>> is async-always and gRPC-C++ is sync-always.) There are > >> >>> > experimental > >> >>> > > >>>>>> C++ APIs that would let us do something similar to Java, > >> >>> > > >>>>>> but > >> >>> > > >>>>>> those > >> >>> > > >>>>>> are > >> >>> > > >>>>>> only in relatively recent gRPC versions and are still > >> >>> > > >>>>>> under > >> >>> > > >>>>>> development (contrary to the interceptor APIs which have > >> been > >> >>> > around > >> >>> > > >>>>>> for quite a while). > >> >>> > > >>>>>> > >> >>> > > >>>>>> Thanks, > >> >>> > > >>>>>> David > >> >>> > > >>>>>> > >> >>> > > >>>>>> On 10/15/19, Jacques Nadeau <jacq...@apache.org> wrote: > >> >>> > > >>>>>>> I like it. Added some comments to the doc. Might worth > >> >>> > > >>>>>>> discussion > >> >>> > > >>>>>>> here > >> >>> > > >>>>>>> depending on your thoughts. > >> >>> > > >>>>>>> > >> >>> > > >>>>>>> On Tue, Oct 15, 2019 at 7:11 AM David Li > >> >>> > > >>>>>>> <li.david...@gmail.com> > >> >>> > > >>>> wrote: > >> >>> > > >>>>>>> > >> >>> > > >>>>>>>> Hey Ryan, > >> >>> > > >>>>>>>> > >> >>> > > >>>>>>>> Thanks for the comments. > >> >>> > > >>>>>>>> > >> >>> > > >>>>>>>> Concrete example: I've edited the doc to provide a > >> >>> > > >>>>>>>> Python > >> >>> > strawman. > >> >>> > > >>>>>>>> > >> >>> > > >>>>>>>> Sync vs async: while I don't touch on it, you could > >> >>> > > >>>>>>>> interleave > >> >>> > > >>>> uploads > >> >>> > > >>>>>>>> and downloads if you were so inclined. Right now, > >> >>> > > >>>>>>>> synchronous > >> >>> > APIs > >> >>> > > >>>>>>>> make this error-prone, e.g. if both client and server > >> >>> > > >>>>>>>> wait > >> >>> > > >>>>>>>> for > >> >>> > each > >> >>> > > >>>>>>>> other due to an application logic bug. (gRPC doesn't > >> >>> > > >>>>>>>> give > >> >>> > > >>>>>>>> us > >> >>> > > >>>>>>>> the > >> >>> > > >>>>>>>> ability to have per-read timeouts, only an overall > >> >>> > > >>>>>>>> timeout.) > >> >>> > > >>>>>>>> As > >> >>> > an > >> >>> > > >>>>>>>> example of this happening with DoPut, see ARROW-6063: > >> >>> > > >>>>>>>> https://issues.apache.org/jira/browse/ARROW-6063 > >> >>> > > >>>>>>>> > >> >>> > > >>>>>>>> This is mostly tangential though, eventually we will > >> >>> > > >>>>>>>> want > >> >>> > > >>>>>>>> to > >> >>> > design > >> >>> > > >>>>>>>> asynchronous APIs for Flight as a whole. A > bidirectional > >> >>> > > >>>>>>>> stream > >> >>> > > >>>>>>>> like > >> >>> > > >>>>>>>> this (and like DoPut) just makes these pitfalls easier > >> >>> > > >>>>>>>> to > >> >>> > > >>>>>>>> run > >> >>> > into. > >> >>> > > >>>>>>>> > >> >>> > > >>>>>>>> Using DoPut+DoGet: I discussed this in the proposal, > but > >> >>> > > >>>>>>>> the > >> >>> > main > >> >>> > > >>>>>>>> concern is that depending on how you deploy, two > >> >>> > > >>>>>>>> separate > >> >>> > > >>>>>>>> calls > >> >>> > > >>>>>>>> could > >> >>> > > >>>>>>>> get routed to different instances. Additionally, gRPC > >> >>> > > >>>>>>>> has > >> >>> > > >>>>>>>> some > >> >>> > > >>>>>>>> reconnection behaviors; if the server goes away in > >> >>> > > >>>>>>>> between > >> >>> > > >>>>>>>> the > >> >>> > two > >> >>> > > >>>>>>>> calls, but it then restarts or there is another > instance > >> >>> > available, > >> >>> > > >>>>>>>> the client will happily reconnect to the new server > >> without > >> >>> > > >>>>>>>> warning. > >> >>> > > >>>>>>>> > >> >>> > > >>>>>>>> Thanks, > >> >>> > > >>>>>>>> David > >> >>> > > >>>>>>>> > >> >>> > > >>>>>>>> On 10/15/19, Ryan Murray <rym...@dremio.com> wrote: > >> >>> > > >>>>>>>>> Hey David, > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> I think this proposal makes a lot of sense. I like it > >> >>> > > >>>>>>>>> and > >> >>> > > >>>>>>>>> the > >> >>> > > >>>>>>>>> possibility > >> >>> > > >>>>>>>>> of remote compute via arrow buffers. One thing that > >> >>> > > >>>>>>>>> would > >> >>> > > >>>>>>>>> help > >> >>> > me > >> >>> > > >>>>>> would > >> >>> > > >>>>>>>> be > >> >>> > > >>>>>>>>> a concrete example of the API in a real life use case. > >> >>> > > >>>>>>>>> Also, > >> >>> > what > >> >>> > > >>>>>> would > >> >>> > > >>>>>>>> the > >> >>> > > >>>>>>>>> client experience be in terms of sync vs asyc? Would > >> >>> > > >>>>>>>>> the > >> >>> > > >>>>>>>>> client > >> >>> > > >>>>>>>>> block > >> >>> > > >>>>>>>> till > >> >>> > > >>>>>>>>> the bidirectional call return ie c = > >> flight.vector_mult(a, > >> >>> > > >>>>>>>>> b) > >> >>> > or > >> >>> > > >>>>>>>>> would > >> >>> > > >>>>>>>> the > >> >>> > > >>>>>>>>> client wait to be signaled that computation was done. > >> >>> > > >>>>>>>>> If > >> >>> > > >>>>>>>>> the > >> >>> > > >>>>>>>>> later > >> >>> > > >>>>>>>>> how > >> >>> > > >>>>>>>>> is > >> >>> > > >>>>>>>>> that different from a DoPut then DoGet? I suppose that > >> >>> > > >>>>>>>>> this > >> >>> > could > >> >>> > > >>>> be > >> >>> > > >>>>>>>>> implemented without extending the RPC interface but > >> rather > >> >>> > > >>>>>>>>> by a > >> >>> > > >>>>>>>>> function/util? > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> Best, > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> Ryan > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> On Sun, Oct 13, 2019 at 9:24 PM David Li < > >> >>> > li.david...@gmail.com> > >> >>> > > >>>>>> wrote: > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>>> Hi all, > >> >>> > > >>>>>>>>>> > >> >>> > > >>>>>>>>>> We've been using Flight quite successfully so far, > but > >> we > >> >>> > > >>>>>>>>>> have > >> >>> > > >>>>>>>>>> identified a new use case on the horizon: being able > >> >>> > > >>>>>>>>>> to > >> >>> > > >>>>>>>>>> both > >> >>> > > >>>>>>>>>> send > >> >>> > > >>>>>>>>>> and > >> >>> > > >>>>>>>>>> retrieve Arrow data within a single RPC call. To that > >> >>> > > >>>>>>>>>> end, > >> >>> > I've > >> >>> > > >>>>>>>>>> written up a proposal for a new RPC method: > >> >>> > > >>>>>>>>>> > >> >>> > > >>>>>>>>>> > >> >>> > > >>>>>>>> > >> >>> > > >>>>>> > >> >>> > > >>>> > >> >>> > > >> > https://docs.google.com/document/d/1Hh-3Z0hK5PxyEYFxwVxp77jens3yAgC_cpp0TGW-dcw/edit?usp=sharing > >> >>> > > >>>>>>>>>> > >> >>> > > >>>>>>>>>> Please let me know if you can't view or comment on > the > >> >>> > document. > >> >>> > > >>>>>>>>>> I'd > >> >>> > > >>>>>>>>>> appreciate any feedback; I think this is a relatively > >> >>> > > >>>>>>>>>> straightforward > >> >>> > > >>>>>>>>>> addition - it is essentially "DoPutThenGet". > >> >>> > > >>>>>>>>>> > >> >>> > > >>>>>>>>>> This is a format change and would require a vote. > I've > >> >>> > > >>>>>>>>>> decided > >> >>> > > >>>>>>>>>> to > >> >>> > > >>>>>>>>>> table the other format change I had proposed (on > >> >>> > > >>>>>>>>>> DoPut), > >> >>> > > >>>>>>>>>> as > >> >>> > > >>>>>>>>>> it > >> >>> > > >>>>>> doesn't > >> >>> > > >>>>>>>>>> functionally change Flight, just the interpretation > of > >> >>> > > >>>>>>>>>> the > >> >>> > > >>>>>>>>>> semantics. > >> >>> > > >>>>>>>>>> > >> >>> > > >>>>>>>>>> Thanks, > >> >>> > > >>>>>>>>>> David > >> >>> > > >>>>>>>>>> > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> -- > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> Ryan Murray | Principal Consulting Engineer > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> +447540852009 | rym...@dremio.com > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>>> <https://www.dremio.com/> > >> >>> > > >>>>>>>>> Check out our GitHub <https://www.github.com/dremio>, > >> join > >> >>> > > >>>>>>>>> our > >> >>> > > >>>>>>>>> community > >> >>> > > >>>>>>>>> site <https://community.dremio.com/> & Download > Dremio > >> >>> > > >>>>>>>>> <https://www.dremio.com/download> > >> >>> > > >>>>>>>>> > >> >>> > > >>>>>>>> > >> >>> > > >>>>>>> > >> >>> > > >>>>>> > >> >>> > > >>>>> > >> >>> > > >>>> > >> >>> > > >>> > >> >>> > > > > >> >>> > > >> >> > >> > > >> > > >
