Re: foreign table batch inserts

On 2016/05/30 22:59, Craig Ringer wrote:
> On 30 May 2016 at 16:17, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>
>> That's a good point, but the basic idea is to send the local query
>> almost-as-is to the remote server if possible. For example, if the local
>> query is "INSERT INTO foreign_table(a,b,c) VALUES (1, 2, 3), (4, 5, 6)",
>> send the remote query "INSERT INTO remote_table(a,b,c) VALUES (1, 2, 3),
>> (4, 5, 6)" to the remote server where remote_table is the table name for
>> the foreign table on the remote server. So, wouldn't the query string
>> length be a problem in many cases? Maybe I'm missing something, though.
>> <http://www.postgresql.org/mailpref/pgsql-hackers>
>
> FDWs don't operate at that level. They don't see the original query string.
> They're plan nodes that operate with a row-by-row push/pull model. The
> foreign table node in question has no idea you're doing a multivalued
> insert and doesn't care if it's INSERT INTO ... SELECT, INSERT INTO ...
> VALUES, or COPY.

IIUC, what Fujita-san seems to be referring to here is safe push-down of a
insert's query or values expression (and hence the whole insert itself)
considered during the *planning* step. Although that sounds like a
different optimization from what's being discussed on this thread. The
latter certainly seems to have its benefits in case of push-down failure
and might as well be the majority of cases.

Thanks,
Amit