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Re: Do we need so many hint bits?

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 (view raw, whole thread or download thread mbox)
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
  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.

	Jeff Davis

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