Re: Add support for tuple routing to foreign partitions

On Thu, Aug 17, 2017 at 05:27:05PM +0900, Etsuro Fujita wrote:
> On 2017/07/11 6:56, Robert Haas wrote:
> >On Thu, Jun 29, 2017 at 6:20 AM, Etsuro Fujita
> ><fujita.etsuro@lab.ntt.co.jp> wrote:
> >>So, I dropped the COPY part.
> >
> >Ouch.  I think we should try to figure out how the COPY part will be
> >handled before we commit to a design.
> 
> I spent some time on this.  To handle that, I'd like to propose doing
> something similar to \copy (frontend copy): submit a COPY query "COPY ...
> FROM STDIN" to the remote server and route data from a file to the remote
> server.  For that, I'd like to add new FDW APIs called during CopyFrom that
> allow us to copy to foreign tables:
> 
> * BeginForeignCopyIn: this would be called after creating a ResultRelInfo
> for the target table (or each leaf partition of the target partitioned
> table) if it's a foreign table, and perform any initialization needed before
> the remote copy can start.  In the postgres_fdw case, I think this function
> would be a good place to send "COPY ... FROM STDIN" to the remote server.
> 
> * ExecForeignCopyInOneRow: this would be called instead of heap_insert if
> the target is a foreign table, and route the tuple read from the file by
> NextCopyFrom to the remote server.  In the postgres_fdw case, I think this
> function would convert the tuple to text format for portability, and then
> send the data to the remote server using PQputCopyData.
> 
> * EndForeignCopyIn: this would be called at the bottom of CopyFrom, and
> release resources such as connections to the remote server.  In the
> postgres_fdw case, this function would do PQputCopyEnd to terminate data
> transfer.

These primitives look good.  I know it seems unlikely at first blush,
but do we know of bulk load APIs for non-PostgreSQL data stores that
this would be unable to serve?

Best,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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