From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Shigeru HANADA <hanada(at)metrosystems(dot)co(dot)jp>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, SAKAMOTO Masahiko <sakamoto(dot)masahiko(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: patch: SQL/MED(FDW) DDL |
Date: | 2010-10-05 15:06:47 |
Message-ID: | 24425.1286291207@sss.pgh.pa.us |
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, Oct 5, 2010 at 10:41 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> (I'd also say that your performance estimate is miles in advance of any
>> facts; but even if it's true, the caching ought to be inside the FDW,
>> because we have no clear idea of what it will need to cache.)
> I can't imagine how an FDW could possibly be expected to perform well
> without some persistent local data storage. Even assume the remote
> end is PG. To return a cost, it's going to need the contents of
> pg_statistic cached locally, for each remote table.
Or it could ask the remote side.
> Do you really
> think it's going to work to incur that overhead once per table per
> backend startup?
If you have a cache, how are you going to manage updates of it?
IMO this is a *clear* case of premature optimization being the root of
all evil. We should get it working first and then see what needs to be
optimized by measuring, rather than guessing in a vacuum.
(BTW, if the remote end is PG I would hardly think that we'd send SQL
queries at all. If we're interested in micro-optimization, we'd devise
some lower-level protocol.)
regards, tom lane
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