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Re: index item size 4496 exceeds maximum 2713

From: ghaverla(at)freenet(dot)edmonton(dot)ab(dot)ca
To: Andrew McMillan <andrew(at)catalyst(dot)net(dot)nz>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: index item size 4496 exceeds maximum 2713
Date: 2002-03-06 10:13:19
Message-ID: Pine.A41.3.95.1020306030937.69500D-100000@fn2.freenet.edmonton.ab.ca (view raw or flat)
Thread:
Lists: pgsql-novice
On 6 Mar 2002, Andrew McMillan wrote:
> On Tue, 2002-03-05 at 13:27, Jon Hassen wrote:

> > "ERROR:  btree: index item size 4496 exceeds maximum 2713"
> > 
> >   On another PGSQL database I only got that message when the size was above
> > 8192. How can I change my database to use the full 8192 size? Or how can I
> > get around this problem at all?
> 
> The maximum _indexable_ field size is 1/3 of the blocksize.  In most
> cases this will be 2713 which is 8192/3.
> 
> In reality there is usually very little value in indexing fields larger
> than a few hundred bytes, unless you are doing keyword or full-text
> indexing.
[ ... ]

Interesting note, not that I have the problem right now, but in
another (nameless) dbase, I will also have long fields I want
to index (GIS metadata).  Where does this number of 3 come from?
Just some small random integer?  Is there some fraction/performance
curve somewhere, which shows 3 is in some sense optimal?

Gord

Matter Realisations     http://www.materialisations.com/
Gordon Haverland, B.Sc. M.Eng. President
101  9504 182 St. NW    Edmonton, AB, CA  T5T 3A7
780/481-8019            ghaverla @ freenet.edmonton.ab.ca
780/993-1274 (cell)



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Subject: Re: index item size 4496 exceeds maximum 2713
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