| From: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> |
|---|---|
| To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>, "Bruce Momjian" <bruce(at)momjian(dot)us>, "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 07:47:41 |
| Message-ID: | 46E6481D.20407@enterprisedb.com |
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| Thread: | |
| Lists: | pgsql-patches |
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're only changing the offsetnumber part of it, which is 2 bytes. That
shouldn't cross a hardware sector boundary on any reasonable hardware.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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