2016-01-18 23:50 GMT+01:00 Thomas Kellerer <spam_ea...@gmx.net>:
> 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.
>
for statements like INSERT INTO tab VALUES(..), UPDATE tab SET x = WHERE id
= .. will be planner significant overhead. But these statements are
relative simply and probably some solution is exists.
Regards
Pavel
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