Re: [HACKERS] Add support for tuple routing to foreign partitions

On 2017/08/18 22:41, David Fetter wrote:
> On Fri, Aug 18, 2017 at 05:10:29PM +0900, Etsuro Fujita wrote:
>> 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.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?
>>
>> 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.
> 
> The naming seems reasonable.
> 
> I was trying to figure out whether this fits well enough with the bulk
> load APIs for databases other than PostgreSQL.  I'm guessing it's
> "well enough" based on checking MySQL, Oracle, and MS SQL Server.

Good to know.

Best regards,
Etsuro Fujita