Re: One-Shot Plans

Simon Riggs <simon@2ndQuadrant.com> writes:
> One of the things I was looking at doing was allowing the operator
> estimation functions mark the plan as "one-shot" if they used
> non-uniform data to predict the estimate. That would require most
> functions to observe the rule that if a plan is marked unsafe then
> nobody marks it safe again later. More of a guideline, really.

> For example, if we a doing a PK retrieval it will have a uniform
> distribution and so we can always use the final plan, whereas a plan
> that relates to a highly skewed distribution would be dangerous and so
> would be marked one-shot.

I fail to detect the sanity in that.  You seem to be confusing "skewed"
with "changing rapidly".  There's no reason to assume that a nonuniform
distribution is less stable than one that is uniform, and in any case we
already invalidate all plans related to a table after any update of the
statistics by ANALYZE.
        regards, tom lane