Date: Fri, 20 Dec 2013 16:43:59 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Heikki Linnakangas <hlinnakangas@vmware.com>
Cc: Alexander Korotkov <aekorotkov@gmail.com>, Tomas Vondra <tv@fuzzy.cz>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: GIN improvements part 1: additional information
Message-ID: <20131220194359.GE22570@eldon.alvh.no-ip.org>
References: 
 <CAPpHfdvP3G2k04tpCyEA0mAd2e8xOQyuj=2wwAj0UVhB1_oe+g@mail.gmail.com>
 <52A58AD5.6030808@vmware.com>
 <CAPpHfdvKC9HE_D+BYBUpxqyWSE4UD_=ykZgfSxkAv4P3LBFQjg@mail.gmail.com>
 <52A62771.3070800@vmware.com>
 <CAPpHfdu2nXxxNCmtMBBiS+3CRdgF8AHCLt2w9Z4s2kKisJSPuA@mail.gmail.com>
 <52AEE445.1060206@vmware.com>
 <CAPpHfdvK3eZr8iQJtp9ax9k80MKRKkPKgqcc0SB1bn+_KVq-Xg@mail.gmail.com>
 <52AF837C.3040201@vmware.com> <52B2F5B0.1030809@vmware.com>
 <52B49C34.8060300@vmware.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <52B49C34.8060300@vmware.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

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?

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


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers