Tom Lane wrote:
Heikki Linnakangas <[EMAIL PROTECTED]> writes:
A lot of people have suggested raising our default_statistics target,
and it has been rejected because there's some O(n^2) behavior in the
planner, and it makes ANALYZE slower, but it's not that crazy.
I think everyone agrees it ought to be raised. Where the rubber meets
the road is deciding just *what* to raise it to. We've got no
convincing evidence in favor of any particular value.
If someone actually wanted to put some effort into this, I'd suggest
taking some reasonably complex benchmark (maybe TPCH or one of the DBT
series) and plotting planner runtime for each query as a function of
statistics_target, taking care to mark the breakpoints where it shifted
to a better (or worse?) plan due to having better stats.
Yeah, that would be a good starting point. After we have some data to
work with, we could also look into making the planner faster with large
samples.
Another idea would be to take a large sample in ANALYZE, but if the
distribution looks "regular enough", store less samples in the
Most-Common-Values list and fewer histograms, to make the planning faster.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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