Re: Really dumb planner decision

On Thu, Apr 16, 2009 at 9:49 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Merlin Moncure <mmoncure(at)gmail(dot)com> writes:
>> On Thu, Apr 16, 2009 at 8:05 AM, Matthew Wakeling <matthew(at)flymine(dot)org> wrote:
>>> That solves the problem. So, a view is treated as a subquery then?
>
>> no...the view is simply inlined into the query (think C macro) using
>> the rules.  You just bumped into an arbitrary (and probably too low)
>> limit into the number of tables the planner can look at in terms of
>> optimizing certain types of plans.
>
> Bear in mind that those limits exist to keep you from running into
> exponentially increasing planning time when the size of a planning
> problem gets big.  "Raise 'em to the moon" isn't really a sane strategy.
> It might be that we could get away with raising them by one or two given
> the general improvement in hardware since the values were last looked
> at; but I'd be hesitant to push the defaults further than that.

I hasten to point out that I only suggested raising them to the moon
as a DEBUGGING strategy, not a production configuration.

I do however suspect that raising the defaults would be a good idea.
It seems that the limit has been 8 since those parameters were added
back in January of 2003, and yes, hardware is a lot better now. We
should probably raise geqo_threshold at the same time, since that's
supposed to be larger than these parameters and the default is only
12.

...Robert