| From: | Gregory Stark <stark(at)enterprisedb(dot)com> |
|---|---|
| To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Mark Kirkwood" <markir(at)paradise(dot)net(dot)nz>, "Pavan Deolasee" <pavan(at)enterprisedb(dot)com>, "Gavin Sherry" <swm(at)alcove(dot)com(dot)au>, "Luke Lonergan" <llonergan(at)greenplum(dot)com>, "PGSQL Hackers" <pgsql-hackers(at)postgresql(dot)org>, "Doug Rady" <drady(at)greenplum(dot)com>, "Sherry Moore" <sherry(dot)moore(at)sun(dot)com> |
| Subject: | Re: Bug: Buffer cache is not scan resistant |
| Date: | 2007-03-06 01:31:46 |
| Message-ID: | 874pozcg3h.fsf@stark.xeocode.com |
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"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> I don't see any good reason why overwriting a whole cache line oughtn't be
> the same speed either way.
I can think of a couple theories, but I don't know if they're reasonable. The
one the comes to mind is the inter-processor cache coherency protocol. When
writing to a cache line the processor already owns maybe it can skip having to
check for other processors owning that cache line?
What happens if VACUUM comes across buffers that *are* already in the buffer
cache. Does it throw those on the freelist too? That seems like it would be
dangerous if they were in the buffer cache for a reason.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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