From: Bill Moran <wmoran@collaborativefusion.com>
To: Csaba Nagy <nagy@ecircle-ag.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: TB-sized databases
Date: Wed, 28 Nov 2007 08:54:41 -0500
Message-ID: <20071128085441.51705627.wmoran@collaborativefusion.com> (raw)
In-Reply-To: <1196257702.31315.6.camel@PCD12478>
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<4544e0330711271218h56ce4cc3p280a9fefff24583d@mail.gmail.com>
<1196197045.4246.1154.camel@ebony.site>
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<Pine.LNX.4.58.0711281248290.3731@aragorn.flymine.org>
<20071128082716.91bbad9c.wmoran@collaborativefusion.com>
<1196257702.31315.6.camel@PCD12478>
In response to Csaba Nagy <nagy@ecircle-ag.com>:
> On Wed, 2007-11-28 at 08:27 -0500, Bill Moran wrote:
> > Is there something wrong with:
> > set enable_seqscan = off
> > ?
>
> Nothing wrong with enable_seqscan = off except it is all or nothing type
> of thing...
If that's true, then I have a bug report to file:
test=# set enable_seqscan=off;
SET
test=# show enable_seqscan;
enable_seqscan
----------------
off
(1 row)
test=# set enable_seqscan=on;
SET
test=# show enable_seqscan;
enable_seqscan
----------------
on
(1 row)
It looks to me to be session-alterable.
> if you want the big table to never use seqscan, but a medium
> table which is joined in should use it, then what you do ? And setting
> enable_seqscan = off will actually not mean the planner can't use a
> sequential scan for the query if no other alternative exist. In any case
> it doesn't mean "please throw an error if you can't do this without a
> sequential scan".
True. It would still choose some other plan.
> In fact an even more useful option would be to ask the planner to throw
> error if the expected cost exceeds a certain threshold...
Interesting concept.
--
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/
wmoran@collaborativefusion.com
Phone: 412-422-3463x4023
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To: pgsql-performance@postgresql.org
Cc: wmoran@collaborativefusion.com, nagy@ecircle-ag.com
Subject: Re: TB-sized databases
In-Reply-To: <20071128085441.51705627.wmoran@collaborativefusion.com>
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