Re: Seq scans status update

On Wed, 2007-05-30 at 17:45 -0400, Tom Lane wrote:
> According to Heikki's explanation here
> http://archives.postgresql.org/pgsql-patches/2007-05/msg00498.php
> each backend doing a heapscan would collect its own ring of buffers.
> You might have a few backends that are always followers, never leaders,
> and so never actually fetch any pages --- but for each backend that
> actually did any I/O there would be a separate ring.  In practice I'd
> expect the lead would "change hands" pretty often and so you'd see all
> the backends accumulating their own rings.
>

Oh, I see what you mean. The rings will actually become sparsely
populated with many concurrent scans, and therefore, extend outside of
L2 cache.

Regards,
    Jeff Davis