Date: Fri, 20 Dec 2013 17:07:18 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Heikki Linnakangas <hlinnakangas@vmware.com>, Tomas Vondra <tv@fuzzy.cz>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: GIN improvements part 1: additional information
Message-ID: <20131220200717.GF22570@eldon.alvh.no-ip.org>
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Alexander Korotkov escribió:
> On Fri, Dec 20, 2013 at 11:43 PM, Alvaro Herrera
> <alvherre@2ndquadrant.com>wrote:
> 
> > Heikki Linnakangas escribió:
> >
> > > I believe that eliminates all encodings in the Simple family, as
> > > well as PForDelta, and surprisingly also Rice encoding. For example,
> > > if you have three items in consecutive offsets, the differences
> > > between them are encoded as 11 in rice encoding. If you remove the
> > > middle item, the encoding for the next item becomes 010, which takes
> > > more space than the original.
> >
> > I don't understand this.  If you have three consecutive entries, and the
> > differences between them are 11, you need to store two 11s.  But if you
> > have two items, you only need to store 010 once.  So the difference is
> > larger, but since you need to store only one of them then overall it's
> > still shorter than the original.  No?
> 
> I believe Heikki mean both differences are encoded as 11, each one is 1.

Oh, that sucks (or it's great, depending on perspective).

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services


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