| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: crash-safe visibility map, take three |
| Date: | 2010-11-30 16:30:53 |
| Message-ID: | 4CF526BD.7050203@enterprisedb.com |
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| Lists: | pgsql-hackers |
On 30.11.2010 18:10, Tom Lane wrote:
> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
>> Yeah, I'm not terribly excited about any of these schemes. The "intent"
>> record seems like the simplest one, but even that is quite different
>> from the traditional WAL-logging we do that it makes me slightly nervous.
>
> I'm not convinced it works at all. Consider write intent record,
> checkpoint, set bit, crash before completing vacuum. There will be
> no second intent record at which you could clean up if things are
> inconsistent.
That's why you need to check the RedoRecPtr when you set the bit. If it
has changed, ie. a checkpoint has happened, the set bit step will write
a new intent record.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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