On 25.03.2011 16:52, Merlin Moncure wrote:
> Without this bit, the only way to set hint bits going during bufmgr
> eviction is to do a visibility check on every tuple, which would
> probably be prohibitively expensive.
I don't think the naive approach of scanning all tuples would be too
bad, actually. The hint bits only need to be set once, and it'd be
bgwriter shouldering the overhead.
The problem with setting hing bits when a buffer is evicted is that it
doesn't help with the bulk load case. The hint bits can't be set for a
bulk load until the load is finished and the transaction commits.
Maybe it would still be worthwhile to have bgwriter set hint bits, to
reduce I/O caused by hint bit updates in an OLTP workload, but that's
not what people usually complain about.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com