On 11/12/2014 05:20 PM, Tom Lane wrote:
Heikki Linnakangas <[email protected]> writes:
On 11/12/2014 04:56 PM, Tom Lane wrote:
Not great either. What about an RBM_NOERROR mode that is like RBM_ZERO
in terms of handling error conditions, but does not forcibly zero the page
if it's already valid?
Anyway, you don't want to read the page from disk, just to check if it's
already valid.
Oh, good point.
(Note that when the page is already in the buffer-cache, RBM_ZERO
already doesn't zero the page. So this race condition only happens when
the page isn't in the buffer cache yet).
Right.
On reconsideration I think the "RBM_ZERO returns page already locked"
alternative may be the less ugly. That has the advantage that any code
that doesn't get updated will fail clearly and reliably.
Yeah, I'm leaning to that approach as well. It's made more ugly by the
fact that you sometimes need a cleanup lock on the buffer, so the caller
will somehow need to specify whether to get a cleanup lock or a normal
exclusive lock. Maybe add yet another mode, RBM_ZERO_WITH_CLEANUP_LOCK.
Could also rename RBM_ZERO to e.g. RBM_ZERO_AND_LOCK, to make any code
that's not updated to break even more obviously, at compile-time.
- Heikki
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