Re: O(N^3) planning time in choose_plan_name() since 8c49a484e8e

On Wed, Nov 4, 2026 at 4:55 PM Manu <manuelreyesbravo(at)gmail(dot)com> wrote:
> With the 4000-arm UNION, planning takes 16.6 s on master, 22 ms with
> v5 or v6, and 19 ms on 18.6. With 4000 CTEs with different names it
> takes 153 ms on master and v5, 126 ms with v6 and 128 ms on 18.6.
> Below 32 names v6 only adds a pointer test or two per call. Small
> statements plan 2-4% slower with default builds, but the same
> (0.0%, 95% CI -0.9..+1.2) when both builds use -falign-functions=64,
> so I take that to be code layout.

Huh, that seems surprising. I expected the case with 4000 CTEs with
different names to be much worse. Why is the UNION case such a
disaster compared to everything else? I must be missing something
here. Of course, strcmp() on every list item is more expensive when
there's a prefix match, but I wouldn't expect that to make so much
difference.

--
Robert Haas
Databricks