Update:
I am going to try what David Li suggested here:
https://lists.apache.org/thread/8yfvvyyc79m11z9wql0gzdr25x4b3g7v
This seems to be the least amount of code. This does require calling
"DoGet" at Acero plan/node creation time rather than execution time but I
don't think it's a big deal for now.
The alternative path of subclassing SourceNode and having ExecNode::Init or
ExecNode::StartProducing seems quite a bit of change (also I don't think
SourceNode is exposed via public header). But let me know if you think I am
missing something.
Li
On Tue, Sep 6, 2022 at 4:57 AM Yaron Gvili <rt...@hotmail.com> wrote:
> Hi Li,
>
> Here's my 2 cents about the Ibis/Substrait part of this.
>
> An Ibis expression carries a schema. If you're planning to create an
> integrated Ibis/Substrait/Arrow solution, then you'll need the schema to be
> available to Ibis in Python. So, you'll need a Python wrapper for the C++
> implementation you have in mind for the GetSchema method. I think you
> should pass the schema obtained by (the wrapped) GetSchema to an Ibis node,
> rather than defining a new Ibis node that would have to access the network
> to get the schema on its own.
>
> Given the above, I agree with you that when the Acero node is created its
> schema would already be known.
>
>
> Yaron.
> ________________________________
> From: Li Jin <ice.xell...@gmail.com>
> Sent: Thursday, September 1, 2022 2:49 PM
> To: dev@arrow.apache.org <dev@arrow.apache.org>
> Subject: Re: Integration between Flight and Acero
>
> Thanks David. I think my original question might not have been accurate so
> I will try to rephrase my question:
>
> My ultimate goal is to add an ibis source node:
>
> class MyStorageTable(ibis.TableNode, sch.HasSchema):
> url = ... # e.g. "my_storage://my_path"
> begin = ... # e.g. "20220101"
> end = ... # e.g. "20220201"
>
> and pass it to Acero and have Acero create a source node that knows how to
> read from my_storage. Currently, I have a C++ class that looks like this
> that knows how to read/write data:
>
> class MyStorageClient {
>
> public:
>
> /// \brief Construct a client
>
> MyStorageClient(const std::string& service_location);
>
>
>
> /// \brief Read data from a table streamingly
>
> /// \param[in] table_uri
>
> /// \param[in] start_time The start time (inclusive), e.g.,
> '20100101'
>
> /// \param[in] end_time The end time (exclusive), e.g., '20100110'
>
> arrow::Result<std::unique_ptr<arrow::flight::FlightStreamReader>>
> ReadStream(const std::string& table_uri, const std::string& start_time,
> const std::string& end_time);
>
>
>
> /// \brief Write data to a table streamingly
>
> /// This method will return a FlightStreamWriter that can be used
> for streaming data into
>
> /// \param[in] table_uri
>
> /// \param[in] start_time The start time (inclusive), e.g.,
> '20100101'
>
> /// \param[in] end_time The end time (exclusive), e.g., '20100110'
>
> arrow::Result<DoPutResult> WriteStream(const std::string&
> table_uri, const std::shared_ptr<arrow::Schema> &schema, const std::string
> &start_time, const std::string &end_time);
>
>
>
> /// \brief Get schema of a table.
>
> /// \param[in] table The Smooth table name, e.g.,
> smooth:/research/user/ljin/test
>
> arrow::Result<std::shared_ptr<arrow::Schema>> GetSchema(const
> std::string& table_uri);
> };
>
> I think Acero node's schema must be known when the node is created, I'd
> imagine I would implement MyStorageExecNode that gets created by
> SubstraitConsumer (via some registration mechanism in SubstraitConsumer):
>
> (1) GetSchema is called in SubstraitConsumer when creating the node
> (network call to the storage backend to get schema)
> (2) ReadStream is called in either ExecNode::Init or
> ExecNode::StartProducing
> to create the FlightStreamReader (3) Some thread (either the Plan's
> execution thread or the thread owned by MyStorageExecNode) will read from
> FlightStreamReader and send data downstream.
>
> Does that sound like the right approach or is there some other way I should
> do this?
>
> On Wed, Aug 31, 2022 at 6:16 PM David Li <lidav...@apache.org> wrote:
>
> > Hi Li,
> >
> > It'd depend on how exactly you expect everything to fit together, and I
> > think the way you'd go about it would depend on what exactly the
> > application is. For instance, you could have the application code do
> > everything up through DoGet and get a reader, then create a SourceNode
> from
> > the reader and continue from there.
> >
> > Otherwise, I would think the way to go would be to be able to create a
> > node from a FlightDescriptor (which would contain the URL/parameters in
> > your example). In that case, I think it'd fit into Arrow Dataset, under
> > ARROW-10524 [1]. In that case, I'd equate GetFlightInfo to dataset
> > discovery, and each FlightEndpoint in the FlightInfo to a Fragment. As a
> > bonus, there's already good integration between Dataset and Acero and
> this
> > should naturally do things like read the FlightEndpoints in parallel with
> > readahead and so on.
> >
> > That means: you'd start with the FlightDescriptor, and create a Dataset
> > from it. This will call GetFlightInfo under the hood. (There's a minor
> > catch here: this assumes the service that returns the FlightInfo can
> embed
> > an accurate schema into it. If that's not true, there'll have to be some
> > finagling with various ways of getting the actual schema, depending on
> what
> > exactly your service supports.) Once you have a Dataset, you can create
> an
> > ExecPlan and proceed like normal.
> >
> > Of course, if you then want to get things into Python, R, Substrait,
> > etc... that requires some more work - especially for Substrait where I'm
> > not sure how best to encode a custom source like that.
> >
> > [1]: https://issues.apache.org/jira/browse/ARROW-10524
> >
> > -David
> >
> > On Wed, Aug 31, 2022, at 17:09, Li Jin wrote:
> > > Hello!
> > >
> > > I have recently started to look into integrating Flight RPC with Acero
> > > source/sink node.
> > >
> > > In Flight, the life cycle of a "read" request looks sth like:
> > >
> > > - User specifies a URL (e.g. my_storage://my_path) and parameter
> > (e.g.,
> > > begin = "20220101", end = "20220201")
> > > - Client issue GetFlightInfo and get FlightInfo from server
> > > - Client issue DoGet with the FlightInfo and get a stream reader
> > > - Client calls Nextuntil stream is exhausted
> > >
> > > My question is, how does the above life cycle fit in an Acero node? In
> > > other words, what are the proper places in Acero node lifecycle to
> issue
> > > the corresponding flight RPC?
> > >
> > > Appreciate any thoughts,
> > > Li
> >
>
