Jeff Davis <[EMAIL PROTECTED]> writes: > On Wed, 2007-05-30 at 15:56 -0400, Tom Lane wrote: >> In the sync-scan case the idea seems pretty bogus anyway, because the >> actual working set will be N backends' rings not just one.
> I don't follow. Ideally, in the sync-scan case, the sets of buffers in > the ring of different scans on the same relation will overlap > completely, right? > We might not be at the ideal, but the sets of buffers in the rings > shouldn't be disjoint, should they? 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. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
