Re: crash-safe visibility map, take three

On 30.11.2010 18:10, Tom Lane wrote:
> Heikki Linnakangas<heikki.linnakangas@enterprisedb.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