Re: [GENERAL] how to get accurate values in pg_statistic (continued)

Mary Edie Meredith <maryedie@osdl.org> writes:
> For our testing purposes, however, consistent results are extremely
> important. We have observed that small difference in one plan for one of
> 22 queries can cause a difference in the DBT-3 results.  If this
> happens, a small change in performance runs between two Linux kernels
> may appear to be due to the kernels, when in fact it is due to the plan
> change.

Fair enough.  If you are trying to force exactly repeatable results,
why don't you just "set seed = 0" before you ANALYZE?  There's only
one random-number generator, so that should force ANALYZE to make the
same random sampling every time.

Also, it'd be a good idea to ANALYZE the needed tables by name,
explicitly, to ensure that they are analyzed in a known order
rather than whatever order ANALYZE happens to find them in pg_class.

            regards, tom lane