Re: GIN improvements part 1: additional information

From: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: GIN improvements part 1: additional information
Date: 2013-12-20 19:55:50
Message-ID: CAPpHfdts_8PAo_DjASEUJFznPGgauqjDo_nQW1BQAZR_u4bqmw@mail.gmail.com
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On Fri, Dec 20, 2013 at 11:43 PM, Alvaro Herrera
<alvherre(at)2ndquadrant(dot)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.

------
With best regards,
Alexander Korotkov.

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