| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Gokulakannan Somasundaram <gokul007(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: An idle thought |
| Date: | 2010-03-18 20:34:58 |
| Message-ID: | 1268944498.4053.514.camel@monkey-cat.sm.truviso.com |
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| Lists: | pgsql-hackers |
On Fri, 2010-03-19 at 01:59 +0530, Gokulakannan Somasundaram wrote:
>
> The visibility map itself is already an example of
> compression. If
> visibility information were randomly distributed among tuples,
> the
> visibility map would be nearly useless.
>
>
> I believe it is very difficult to make visibility map update friendly
> without compromising durability. But such a functionality is very
> much wanted in PG still.
Surely the VM is already update-friendly. If you update a tuple in a
page with the visibility bit set, the bit must be unset or you will get
wrong results.
Regards,
Jeff Davis
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