Re: Query optimizer 8.0.1 (and 8.0)

Mark, Stephen, etc:

> > I can see your point, however I wonder if the issue is that the default
> > stats settings of '10' (3000 rows, 10 histogram buckets) is too low, and
> > maybe we should consider making a higher value (say '100') the default.
>
> Personally, I think that'd be reasonable.

I don't really think that we want to increase sampling for *all* columns.
Each column that doesn't get queried but has increased stats adds the size of
the pg_stats table and the amount of vacuuming it needs, decreasing
performance of stats lookups. Especially when very large text and BYTEA
columns are involved.

Neil and I talked about setting a seperate GUC, default_index_stats_target,
for 8.0 that would dramatically increase the stats sampling for indexed
columns only (say, to 250). Unfortunately, I was unable to come up with a
good test case for setting this value.

Perhaps the Tiger database would allow us to set up a good test case. Does
anyone have a well-indexed PG Tiger I could play with?

--
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco