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Re: Missing results from scroll cursor in PostgreSQL8.3.3?

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Mark Cave-Ayland <mark(dot)cave-ayland(at)siriusit(dot)co(dot)uk>, pgsql-hackers(at)postgresql(dot)org, Teodor Sigaev <teodor(at)sigaev(dot)ru>
Subject: Re: Missing results from scroll cursor in PostgreSQL8.3.3?
Date: 2008-09-25 17:56:54
Message-ID: 1222365414.4445.823.camel@ebony.2ndQuadrant (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, 2008-09-25 at 12:27 -0400, Tom Lane wrote:
> Mark Cave-Ayland <mark(dot)cave-ayland(at)siriusit(dot)co(dot)uk> writes:
> > Following up a report on the PostGIS bugtracker (also submitted to 
> > pgsql-bugs here: 
> > http://archives.postgresql.org/pgsql-bugs/2008-09/msg00086.php), I'm 
> > wondering if there is a bug in the way that GiST indexes interact with 
> > scroll cursors.
> 
> I remember Teodor remarking that there's some problem with fetching
> backwards in a GIST indexscan, but I don't know the details --- in
> particular, no idea whether it's fixable or we need to put in something
> to prevent trying it.  The latter would be a bit of a PITA since right
> now indexscans are assumed to support backwards scan regardless of
> index type.

Does ABSOLUTE 3 do a backward scan? Hope not. Just rewind and forward
scan. Presumably the bug is present when you don't do ABSOLUTE -1 first?

Seems like GIST should be able to fake a backwards scan if needed.

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support


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