Robert Haas wrote:
> This isn't the first complaint about this mechanism that we've gotten,
> and it won't be the last. Way too many of our users are way more
> aware than they should be that the threshold here is five rather than
> any other number, which to me is a clear-cut sign that this needs to
> be improved. How to improve it is a harder question. We lack the
> ability to do any kind of sensitivity analysis on a plan, so we can't
> know whether there are other parameter values that would have resulted
> in a different plan, nor can we test whether a particular set of
> parameter values would have changed the outcome.
(I initially posted that question on the JDBC mailing list)
To be honest: looking at the efforts Oracle has done since 9 up until 12 I
am not sure this is a problem that can be solved by caching plans.
Even with the new "in-flight" re-planning in Oracle 12 ("cardinality
feedback") and all the effort that goes into caching plans we are still
seeing similar problems with (prepared) statements that are suddenly slow.
And as far as I can tell, the infrastructure around plan caching,
invalidation, bind variable peeking and all that seems to be a *lot* more
complex ("sophisticated") in Oracle compared to Postgres. And the results
don't seem to justify the effort (at least in my experience).
With all the problems I have seen (in Oracle and Postgres) I think that
maybe a better solution to this problem is to make the planner fast (and
reliable) enough so that plan caching isn't necessary in the first place.
However I have no idea how feasible that is.
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