Spotting planner errors (was Re: Query planner is using wrong index.)

Tom Lane wrote:
> Brian Herlihy <btherl(at)yahoo(dot)com(dot)au> writes:
>> Before I go, I have a question - From discussions on the Postgresql irc
>> channel, and from reading the TODO list on the website, I am under the
>> impression that there are no plans to allow optimizer hints, such as "use index
>> table_pkey". Is this really true?
>
> I personally don't think it's a good idea: the time spent in designing,
> implementing, and maintaining a usable hint system would be significant,
> and IMHO the effort is better spent on *fixing* the optimizer problems
> than working around them.

Tom - does the planner/executor know it's got row estimates wrong? That
is, if I'm not running an EXPLAIN ANALYSE is there a point at which we
could log "planner estimate for X out by factor of Y"?

--
Richard Huxton
Archonet Ltd