Re: Ideas of "printing out" the alternative paths

Zhan Li <zhanli89@gmail.com> writes:
> When searching all the possible paths of executing a query, the optimizer
> finds and saves the cheapest paths for the top level rel. I'd like to check
> out all the paths the optimizer has ever considered, which I believe, are
> stored in the pathlist of the top level rel.

No, most of them have been thrown away long before that.  See add_path.
Also realize that in a large join problem, a lot of potential plans never
get explicitly considered, because the input paths get pruned before we
get to considering the join rel at all.  (If this were not so, planning
would take too long.)

People have experimented with having add_path print something about each
path that's fed to it, but the output tends to be voluminous and not all
that useful.

                        regards, tom lane