Re: Automatic function replanning

Jim C. Nasby wrote:
> On Wed, Dec 21, 2005 at 05:43:38PM -0500, Bruce Momjian wrote:
>
>>Rick Gigger wrote:
>>
>>>It seems to me like there are two classes of problems here:
>>>
>>>1) Simply invalidating plans made with out of date statistics.
>>>2) Using run-time collected data to update the plan to something more
>>>intelligent.
>>>
>>>It also seems like #1 would be fairly straightforward and simple
>>>whereas #2 would be much more complex. #1 would do me a world of
>>>good and probably other people as well. Postgres's query planning
>>>has always been fine for me, or at least I have always been able to
>>>optimize my queries when I've got a representative data set to work
>>>with. Query plan caching only gets me when the query plan is created
>>>before the statistics are present to create a good plan.
>>>
>>>Just one users 2 cents.
>>
>>Agreed. I just can't add #2 unless we get more agreement from the
>>group, because it has been a disputed issue in the past.
>
>
> Well, how about this, since it's a prerequisit for #2 and would be
> generally useful anyway:
>
> Track normal resource consumption (ie: tuples read) for planned queries
> and record parameter values that result in drastically different
> resource consumption.
>
> This would at least make it easy for admins to identify prepared queries
> that have a highly variable execution cost.

Yeah, it seems such a log would be very helpful in its own right for
DBA's and also as a feedback loop to find possibles issues in the query
planner. And maybe one day this feedback loop can be even directly used
by the server itself.

regards,
Lukas Smith