Re: [HACKERS] Optimizer speed and GEQO (was: nested loops in joins)

> The main thing that jumps out from the profiles is that on these complex
> searches, the optimizer spends practically *all* of its time down inside
> better_path, scanning the list of already known access paths to see if a
> proposed new path is a duplicate of one already known.  (Most of the time
> it is not, as shown by the small number of times path_is_cheaper gets
> called from better_path.)  This scanning is O(N^2) in the number of paths
> considered, whereas it seems that all the other work is no worse than O(N)
> in the number of paths.  The bottom of the duplicate check is equal(),
> which as you can see is getting called a horrendous number of times.

The ironic thing about add_pathlist() is that the slowness is due to the
code using a nested loop to merge duplicate RelOptInfo paths, rather
than some sort of mergejoin.

I will keep studying it, but from your comments, I can see you
understood the code much better than I had.  I am just understanding
your conclusions.

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