| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Florian Pflug <fgp(dot)phlo(dot)org(at)gmail(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org> |
| Subject: | Re: HOT patch - version 15 |
| Date: | 2007-09-11 06:35:55 |
| Message-ID: | 1189492555.4281.341.camel@ebony.site |
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| Lists: | pgsql-patches |
On Mon, 2007-09-10 at 22:24 -0400, Tom Lane wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> > On Tue, 2007-09-11 at 01:22 +0530, Pavan Deolasee wrote:
> >> I think the only difference is that the quick pruning does not mark
> >> intermediate tuples ~LP_USED and hence we may avoid WAL logging.
>
> > Sounds great.
>
> What it sounds is utterly unsafe. You can get away with not WAL-logging
> individual bit flips (that is, hint-bit-setting) because either state of
> the page is valid. If I read this proposal correctly it is to change
> t_ctid without WAL-logging, which means that a partial page write (torn
> page syndrome) could leave the page undetectably corrupted --- t_ctid
> is 6 bytes and could easily cross a hardware sector boundary.
We can calculate where they are, if thats the objection.
--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.com
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