Re: benchmarking the query planner

On Fri, 2008-12-12 at 11:16 -0500, Tom Lane wrote:

> If you want ANALYZE to be cheap then you simply don't get to have 
> a trustworthy value of ndistinct.

Understood, but a cheap ANALYZE isn't always a higher priority than all
other considerations.

Solutions can also include

* allowing user to note that we would actually like to scan the whole
table (stats_target = -2?)

* manual mechanism for setting ndistinct that doesn't keep getting
overwritten by subsequent ANALYZEs

* have the executor do non-transactional update of the value of
ndistinct if it ever builds a hash table that is larger than expected
(simple learning optimizer action)

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support