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Re: A thought on Index Organized Tables

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Gokulakannan Somasundaram <gokul007(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Karl Schnaitter <karlsch(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, heikki(dot)linnakangas(at)enterprisedb(dot)com, pgsql-hackers list <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: A thought on Index Organized Tables
Date: 2010-02-25 21:08:26
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Lists: pgsql-hackers
On Thu, Feb 25, 2010 at 8:09 PM, Gokulakannan Somasundaram
<gokul007(at)gmail(dot)com> wrote:
>           I think, somewhere things have been misunderstood. we only need 8
> bytes more per index entry. I thought Postgres has a 8 byte transaction id,
> but it is only 4 bytes, so we only need to save the insertion and deletion
> xids. So 8 bytes more per tuple.

Well in the heap we need

4 bytes: xmin
4 bytes: xmax
4 bytes: cid
6 bytes: ctid
6 bytes: various info bits including natts

In indexes we currently get away with a reduced header which has few
of the 6 bytes of info bits. However the only reason we can do is
because we impose arbitrary limitations that work for indexes but
wouldn't be reasonable for tables. Such as a lower maximum number of
columns, inability to add new columns or drop columns later, etc.


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