Simon Riggs wrote:
On Wed, 2008-01-30 at 18:42 +0000, Heikki Linnakangas wrote:
It's even worse than that. Elsewhere in this thread Simon mentioned a
partitioned table, where each partition on its own is smaller than the
threshold, but you're seq scanning several partitions and the total size
of the seq scans is larger than memory size. In that scenario, you would
want BAS and synchronized scans, but even a per-table setting wouldn't
cut it.
For synchronized scans to help in the partitioned situation, I guess
you'd want to synchronize across partitions. If someone is already
scanning partition 5, you'd want to start from that partition and join
the pack, instead of starting from partition 1.
You're right, but in practice its not quite that bad with the
multi-table route. When you have partitions you generally exclude most
of them, with typically 1-2 per query, usually different ones.
Yep. And in that case, you *don't'* want BAS or sync scans to kick in,
because you're only accessing a relatively small chunk of data, and it's
worthwhile to cache it.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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