| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, Merlin Moncure <mmoncure(at)gmail(dot)com> |
| Subject: | Re: Do we need so many hint bits? |
| Date: | 2012-11-17 21:30:07 |
| Message-ID: | 1353187807.10198.28.camel@jdavis-laptop |
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| Lists: | pgsql-hackers |
On Sat, 2012-11-17 at 14:24 +0100, Andres Freund wrote:
> I think the point is that to check whether the visibilitymap bit needs
> to be unset
What's the problem with that? If you already have the VM buffer pinned
(which should be possible if we keep the VM buffer in a longer-lived
structure), then doing the test is almost as cheap as checking
PD_ALL_VISIBLE, because you don't need any locks.
So, the proposal is:
1. Keep the VM buffer around in a longer-lived structure for scans and
nodeModifyTable.
2. Replace all tests of PD_ALL_VISIBLE with tests directly against the
VM, hopefully using a buffer that we already have a pin on.
I haven't really dug into this yet, but I don't see any obvious problem.
Regards,
Jeff Davis
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