| From: | Noah Misch <noah(at)leadboat(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ALTER TABLE lock strength reduction patch is unsafe |
| Date: | 2012-01-03 04:40:38 |
| Message-ID: | 20120103044038.GA4070@tornado.leadboat.com |
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| Thread: | |
| Lists: | 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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