From: | "Jim C(dot) Nasby" <jim(at)nasby(dot)net> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Tobias Brox <tobias(at)nordicbet(dot)com>, Chris Browne <cbbrowne(at)acm(dot)org>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Simple join optimized badly? |
Date: | 2006-10-10 14:00:50 |
Message-ID: | 20061010140050.GZ72517@nasby.net |
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Lists: | pgsql-performance |
On Mon, Oct 09, 2006 at 06:45:16PM -0400, Tom Lane wrote:
> "Jim C. Nasby" <jim(at)nasby(dot)net> writes:
> > One of the big problems with doing set enable_...=off is that there's no
> > way to embed that into something like a view, so you're almost forced
> > into putting into the application code itself, which makes matters even
> > worse. If you could hint this within a query (maybe even on a per-table
> > level), you could at least encapsulate that into a view.
>
> You've almost reinvented one of the points that was made in the last
> go-round on the subject of hints, which is that keeping them out of the
> application code is an important factor in making them manageable by a
> DBA. Hints stored in a system catalog (and probably having the form of
> "make this statistical assumption" rather than specifically "use that
> plan") would avoid many of the negatives.
Sure, but IIRC no one's figured out what that would actually look like,
while it's not hard to come up with a syntax that allows you to tell the
optimizer "scan index XYZ to access this table". (And if there's real
interest in adding that I'll come up with a proposal.)
I'd rather have the ugly solution sooner rather than the elegant one
later (if ever).
--
Jim Nasby jim(at)nasby(dot)net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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