From: Jim C. Nasby <jim@nasby.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Tobias Brox <tobias@nordicbet.com>
Cc: Chris Browne <cbbrowne@acm.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Simple join optimized badly?
Date: Tue, 10 Oct 2006 09:00:50 -0500
Message-ID: <20061010140050.GZ72517@nasby.net> (raw)
In-Reply-To: <9723.1160433916@sss.pgh.pa.us>
References: <20061009213303.GA19144@oppetid.no>
<20061009223030.GW72517@nasby.net>
<9723.1160433916@sss.pgh.pa.us>
On Mon, Oct 09, 2006 at 06:45:16PM -0400, Tom Lane wrote:
> "Jim C. Nasby" <jim@nasby.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@nasby.net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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To: pgsql-performance@postgresql.org
Cc: jim@nasby.net, tgl@sss.pgh.pa.us, tobias@nordicbet.com, cbbrowne@acm.org
Subject: Re: Simple join optimized badly?
In-Reply-To: <20061010140050.GZ72517@nasby.net>
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