Re: Where can I get the number of plans that considered by Planner? - Mailing list pgsql-general

From Martijn van Oosterhout
Subject Re: Where can I get the number of plans that considered by Planner?
Date
Msg-id 20091004113554.GA10726@svana.org
Whole thread Raw
In response to Re: Where can I get the number of plans that considered by Planner?  (纪晓曦 <sheepjxx@gmail.com>)
Responses Re: Where can I get the number of plans that considered by Planner?
List pgsql-general
On Sat, Oct 03, 2009 at 04:20:59PM +1000, ????????? wrote:
> Since I also need to consider gego, is this the best way to do it?

I think you need to be clearer about what you're trying to count.
Consider a nestjoin plan where:

- For the inner side it considers 7 paths and throws away 4.
- For the outer side it considers 6 paths and throws away 2.

Do you want the number 3*4=12 or 7*6=42? Or something in between (what
if in addition to a nestjoin plan otther possibilities are possible).

As you can see, you can't talk about complete plans because they don't
exist until right at the end, until then it's just considering how to
combine different paths in sensible ways.

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Please line up in a tree and maintain the heap invariant while
> boarding. Thank you for flying nlogn airlines.

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