From: | Greg Stark <gsstark(at)mit(dot)edu> |
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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 |
Message-ID: | 407d949e1002251308n2fdf3e19j34b55d8d656add30@mail.gmail.com |
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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.
--
greg
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