Re: ALTER TABLE lock strength reduction patch is unsafe

On Tue, Jan 03, 2012 at 01:18:41AM +0000, Simon Riggs wrote:
> Just for the record, yes we do run multiple catalog scans in some
> parts of the code.
> 
> So I can see how we might trigger 4 nested scans, using cache
> replacement while scanning, so best assume more, with no guarantee of
> them being neatly stacked for pop/push type access.

Yeah, I wouldn't want to commit to a nesting limit.  However, I _would_ have
expected that a stack would suffice; PushActiveSnapshot()/PopActiveSnapshot()
is adequate for a great deal of the backend, after all.  In what sort of
situation do catalog scans not strictly nest?

Thanks,
nm