I've put up a candidate implementation sans integration test [1]. Some caveats: - java.net.URI doesn't accept 'scheme://', only 'scheme:/' or 'scheme://?' (yes, an empty query string pacifies it). I've chosen the latter since the former is technically a URI with a non-empty path but neither are ideal. - I've changed the scheme to 'arrow-flight-reuse-connection' to be more faithful to the intended use than 'fallback'.
[1]: https://github.com/apache/arrow/pull/40084 On Tue, Feb 13, 2024, at 13:01, Jean-Baptiste Onofré wrote: > Hi David, > > It's reasonable. I think we can start with your initial proposal (it > sounds fine to me) and we can always improve step by step. > > Thanks ! > Regards > JB > > On Tue, Feb 13, 2024 at 4:53 PM David Li <lidav...@apache.org> wrote: >> >> I'm going to keep the proposal as-is then. It can be extended if this use >> case comes up. >> >> I'll start work on candidate implementations now. >> >> On Tue, Feb 13, 2024, at 03:22, Antoine Pitrou wrote: >> > I think the original proposal is sufficient. >> > >> > Also, it is not obvious to me how one would switch from e.g. grpc+tls to >> > http without an explicit server location (unless both Flight servers are >> > hosted under the same port?). So the "+" proposal seems a bit weird. >> > >> > >> > Le 12/02/2024 à 23:39, David Li a écrit : >> >> The idea is that the client would reuse the existing connection, in which >> >> case the protocol and such are implicit. (If the client doesn't have a >> >> connection anymore, it can't use the fallback anyways.) >> >> >> >> I suppose this has the advantage that you could "fall back" to a known >> >> hostname with a different protocol, but I'm not sure that always applies >> >> anyways. (Correct me if I'm wrong Matt, but as I recall, UCX addresses >> >> aren't hostnames but rather opaque byte blobs, for instance.) >> >> >> >> If we do prefer this, to avoid overloading the hostname, there's also the >> >> informal convention of using + in the scheme, so it could be >> >> arrow-flight-fallback+grpc+tls://, arrow-flight-fallback+http://, etc. >> >> >> >> On Mon, Feb 12, 2024, at 17:03, Joel Lubinitsky wrote: >> >>> Thanks for clarifying. >> >>> >> >>> Given the relationship between these two proposals, would it also be >> >>> necessary to distinguish the scheme (or schemes) supported by the >> >>> originating Flight RPC service? >> >>> >> >>> If that is the case, it may be preferred to use the "host" portion of the >> >>> URI rather than the "scheme" to denote the location of the data. In this >> >>> scenario, the host "0.0.0.0" could be used. This IP address is defined in >> >>> IETF RFC1122 [1] as "This host on this network", which seems most >> >>> consistent with the intended use-case. There are some caveats to this >> >>> usage >> >>> but in my experience it's not uncommon for protocols to extend the >> >>> definition of this address in their own usage. >> >>> >> >>> A benefit of this convention is that the scheme remains available in the >> >>> URI to specify the transport available. For example, the following list >> >>> of >> >>> locations may be included in the response: >> >>> >> >>> ["grpc://0.0.0.0", "ucx://0.0.0.0", "grpc://1.2.3.4", >> >>> <other_locations>...] >> >>> >> >>> This would indicate that grpc and ucx transport is available from the >> >>> current service, grpc is available at 1.2.3.4, and possibly more >> >>> combinations of scheme/host. >> >>> >> >>> [1] https://datatracker.ietf.org/doc/html/rfc1122#section-3.2.1.3 >> >>> >> >>> On Mon, Feb 12, 2024 at 2:53 PM David Li <lidav...@apache.org> wrote: >> >>> >> >>>> Ah, while I was thinking of it as useful for a fallback, I'm not >> >>>> specifying it that way. Better ideas for names would be appreciated. >> >>>> >> >>>> The actual precedence has never been specified. All endpoints are >> >>>> equivalent, so clients may use what is "best". For instance, with Matt >> >>>> Topol's concurrent proposal, a GPU-enabled client may preferentially try >> >>>> UCX endpoints while other clients may choose to ignore them entirely >> >>>> (e.g. >> >>>> because they don't have UCX installed). >> >>>> >> >>>> In practice the ADBC/JDBC drivers just scan the list left to right and >> >>>> try >> >>>> each endpoint in turn for lack of a better heuristic. >> >>>> >> >>>> On Mon, Feb 12, 2024, at 14:28, Joel Lubinitsky wrote: >> >>>>> Thanks for proposing this David. >> >>>>> >> >>>>> I think the ability to include the Flight RPC service itself in the >> >>>>> list >> >>>> of >> >>>>> endpoints from which data can be fetched is a helpful addition. >> >>>>> >> >>>>> The current choice of name for the URI (arrow-flight-fallback://) seems >> >>>> to >> >>>>> imply that there is an order of precedence that should be considered in >> >>>> the >> >>>>> list of URI’s. Specifically, as a developer receiving the list of >> >>>> locations >> >>>>> I might assume that I should try fetching from other locations first. >> >>>>> If >> >>>>> those do not succeed, I may try the original service as a fallback. >> >>>>> >> >>>>> Are these the intended semantics? If so, is there a way to include the >> >>>>> original service in the list of locations without the implied >> >>>>> precedence? >> >>>>> >> >>>>> Thanks, >> >>>>> Joel >> >>>>> >> >>>>> On Mon, Feb 12, 2024 at 11:52 James Duong <james.du...@improving.com >> >>>> .invalid> >> >>>>> wrote: >> >>>>> >> >>>>>> This seems like a good idea, and also improves consistency with >> >>>>>> clients >> >>>>>> that erroneously assumed that the service endpoint was always in the >> >>>> list >> >>>>>> of endpoints. >> >>>>>> >> >>>>>> From: Antoine Pitrou <anto...@python.org> >> >>>>>> Date: Monday, February 12, 2024 at 6:05 AM >> >>>>>> To: dev@arrow.apache.org <dev@arrow.apache.org> >> >>>>>> Subject: Re: [DISCUSS] Flight RPC: add 'fallback' URI scheme >> >>>>>> >> >>>>>> Hello, >> >>>>>> >> >>>>>> This looks fine to me. >> >>>>>> >> >>>>>> Regards >> >>>>>> >> >>>>>> Antoine. >> >>>>>> >> >>>>>> >> >>>>>> Le 12/02/2024 à 14:46, David Li a écrit : >> >>>>>>> Hello, >> >>>>>>> >> >>>>>>> I'd like to propose a slight update to Flight RPC to make Flight SQL >> >>>>>> work better in different deployment scenarios. Comments on the doc >> >>>> would >> >>>>>> be appreciated: >> >>>>>>> >> >>>>>>> >> >>>>>> >> >>>> https://docs.google.com/document/d/1g9M9FmsZhkewlT1mLibuceQO8ugI0-fqumVAXKFjVGg/edit?usp=sharing >> >>>>>>> >> >>>>>>> The gist is that FlightEndpoint allows specifying either (1) a list >> >>>>>>> of >> >>>>>> concrete URIs to fetch data from or (2) no URIs, meaning to fetch from >> >>>> the >> >>>>>> Flight RPC service itself; but it would be useful to combine both >> >>>> behaviors >> >>>>>> (try these concrete URIs and fall back to the Flight RPC service >> >>>>>> itself) >> >>>>>> without requiring the service to know its own public address. >> >>>>>>> >> >>>>>>> Best, >> >>>>>>> David >> >>>>>> >> >>>>
