| From: | "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)lab(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Remove xmin and cmin from frozen tuples |
| Date: | 2005-09-07 17:44:02 |
| Message-ID: | 20050907174402.GH60481@pervasive.com |
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| Lists: | pgsql-hackers |
On Wed, Sep 07, 2005 at 01:05:52PM -0400, Alvaro Herrera wrote:
> Anyway you are just moving the storage somewhere else -- instead of
> having 4 fields in the tuple itself, you have one field which points
> the same 4 fields elsewhere. I don't see how is that a win; it's
> actually worse because you have to do two lookups. (And actually you
> have just enlarged the storage requirements because you need to store
> the "vis_id" twice.)
It would only be of use if the table had few transactions in it; in
other words, if it was mostly read-only. For a true read-only table
there are other options people have suggested that are probably better.
BTW, this becomes even more attractive if vis_id is int2; in that case
you can keep the entire mapping in memory in ~1MB.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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