On 2017/08/17 23:48, David Fetter wrote:
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.ets...@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?
Maybe I'm missing something, but I think these would allow the FDW to do
the remote copy the way it would like; in ExecForeignCopyInOneRow, for
example, the FDW could buffer tuples in a buffer memory and transmit the
buffered data to the remote server if the data size exceeds a threshold.
The naming is not so good? Suggestions are welcome.
Best regards,
Etsuro Fujita
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