On Tue, Jan 19, 2016 at 4:20 AM, Thomas Kellerer <spam_ea...@gmx.net> wrote:
> 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).

I have heard the same feedback as above some time back from some
of the research fellows doing research in query optimization area.  They
come-up with different concept called "Plan Bouquet" [1] where
in they try to execute multiple plans during execution and proceed with
the best-among those or something like that to address bad
plan-selection problems and their claim is that this technique proves to
be better on benchmarks than existing mechanisms used for query

I am not advocating any such mechanism, but rather sharing an
information, I came across.

[1] - http://dsl.serc.iisc.ernet.in/publications/conference/bouquet.pdf

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

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