Re: FDW for PostgreSQL

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Stephen Frost <sfrost(at)snowman(dot)net>
Cc: Shigeru Hanada <shigeru(dot)hanada(at)gmail(dot)com>, Kohei KaiGai <kaigai(at)kaigai(dot)gr(dot)jp>, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: FDW for PostgreSQL
Date: 2013-03-28 15:54:59
Message-ID: 29998.1364486099@sss.pgh.pa.us
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Stephen Frost <sfrost(at)snowman(dot)net> writes:
> * Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)us) wrote:
>> ... The only way to
>> make this sane at all would be to provide user control of which
>> operations go to which connections; which is inherent in dblink's API
>> but is simply not a concept in the FDW universe. And I don't want to
>> try to plaster it on, either.

> This concern would make a lot more sense to me if we were sharing a
> given FDW connection between multiple client backends/sessions; I admit
> that I've not looked through the code but the documentation seems to
> imply that we create one-or-more FDW connection per backend session and
> there's no sharing going on.

Well, ATM postgres_fdw shares connections across tables and queries;
but my point is that that's all supposed to be transparent and invisible
to the user. I don't want to have API features that make connections
explicit, because I don't think that can be shoehorned into the FDW
model without considerable strain and weird corner cases.

regards, tom lane

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