Re: Avoiding bad prepared-statement plans.

On Sat, Feb 27, 2010 at 11:22 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Fri, Feb 26, 2010 at 7:03 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Wouldn't it be better if it just did the right thing automatically?
>>>
>>> The sort of heuristic I'm envisioning would essentially do "replan every
>>> time" for some number of executions, and give up only if it noticed that
>>> it wasn't getting anything better than the generic plan.  So you'd have
>>> a fixed maximum overhead per session when the custom plan was useless,
>>> and the Right Thing when it wasn't.
>
>> Which is likely useless for my use case.
>
> [ shrug... ]  You'd better explain exactly why, if you want me to take
> that objection seriously.

Hmm... on further thought, maybe it *would* work in that case.  I'm
still not convinced this is going to be generally satisfactory.  It
seems like it depends a great deal on how many times the function
figures to be called per session and in what percentage of those cases
a non-generic plan figures to be better.  The appeal of a
user-controllable knob is that I am pretty sure from experience that I
can set it correctly, but hey...

...Robert