Re: ALTER TABLE lock strength reduction patch is unsafe - Mailing list pgsql-hackers

From Noah Misch
Subject Re: ALTER TABLE lock strength reduction patch is unsafe
Date
Msg-id 20120103044038.GA4070@tornado.leadboat.com
Whole thread Raw
In response to Re: ALTER TABLE lock strength reduction patch is unsafe  (Simon Riggs <simon@2ndQuadrant.com>)
Responses Re: ALTER TABLE lock strength reduction patch is unsafe
List pgsql-hackers
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


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