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Re: Full text search with ORDER BY performance issue

From: Matthew Wakeling <matthew(at)flymine(dot)org>
To: valgog <valgog(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Full text search with ORDER BY performance issue
Date: 2009-07-21 14:01:43
Message-ID: alpine.DEB.2.00.0907211454180.19493@aragorn.flymine.org (view raw or flat)
Thread:
Lists: pgsql-performance
On Tue, 21 Jul 2009, valgog wrote:
> There is a problem with GIN and GIST indexes, that they cannot be used
> by the ORDER BY. Maybe it will be a nice idea to ask Oleg to make it
> possible to use the b-tree columns in GIST or GIN to make the sort
> easier, but I have no idea how difficult it will be to implement it in
> current GIN or GIST structures. I think Oleg or even Tom will be the
> right people to ask it :)

I can answer that one for GiST, having had a good look at GiST recently. 
There is simply no useful information about order in a GiST index for it 
to be used by an ORDER BY. The index structure is just too general, 
because it needs to cope with the situation where a particular object type 
does not have a well defined order, or where the "order" is unuseful for 
indexing.

Matthew

-- 
 A good programmer is one who looks both ways before crossing a one-way street.
 Considering the quality and quantity of one-way streets in Cambridge, it
 should be no surprise that there are so many good programmers there.

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