From: Jim C. Nasby <jim@nasby.net>
To: Tobias Brox <tobias@nordicbet.com>
Cc: Chris Browne <cbbrowne@acm.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Simple join optimized badly?
Date: Mon, 9 Oct 2006 17:30:31 -0500
Message-ID: <20061009223030.GW72517@nasby.net> (raw)
In-Reply-To: <20061009213303.GA19144@oppetid.no>
References: <20061009213303.GA19144@oppetid.no>
On Mon, Oct 09, 2006 at 11:33:03PM +0200, Tobias Brox wrote:
> [Jim C. Nasby - Mon at 04:18:27PM -0500]
> > I can agree to that, but we'll never get any progress so long as every
> > time hints are brought up the response is that they're evil and should
> > never be in the database. I'll also say that a very simple hinting
> > language (ie: allowing you to specify access method for a table, and
> > join methods) would go a huge way towards enabling app developers to get
> > stuff done now while waiting for all these magical optimizer
> > improvements that have been talked about for years.
>
> Just a comment from the side line; can't the rough "set
> enable_seqscan=off" be considered as sort of a hint anyway? There have
> been situations where we've actually had to resort to such crud.
>
> Beeing able to i.e. force a particular index is something I really
> wouldn't put into the application except for as a very last resort,
> _but_ beeing able to force i.e. the use of a particular index in an
> interactive 'explain analyze'-query would often be ... if not outright
> useful, then at least very interessting.
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.
--
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, tobias@nordicbet.com, cbbrowne@acm.org
Subject: Re: Simple join optimized badly?
In-Reply-To: <20061009223030.GW72517@nasby.net>
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