Re: Use merge-based matching for MCVs in eqjoinsel

David Geier <geidav.pg@gmail.com>

From: David Geier <geidav.pg@gmail.com>

To: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2025-09-08T07:11:24Z

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Speed up eqjoinsel() with lots of MCV entries.
- 057012b205a0 19 (unreleased) landed

Hi!

On 03.09.2025 18:53, Ilia Evdokimov wrote:
> Following up on my previous messages about optimizing eqjoinsel() and
> eqjoinsel_semi() for Var1 = Var2 clauses, I’d like to share detailed
> profiling results showing the effect of the patch on JOB for different
> values of default_statistics_target.
>
> The first table shows the total planner time (summed over all 113
> queries) before and after applying the patch, along with the speedup
> achieved:
>
> default_statistics_target | Planner Speedup (×) | Planner Before (ms) |
> Planner After (ms)
> --------------------------+---------------------+---------------------
> +--------------------
>                      100  | *1.00x*       | 1828.433     |        1820.556
>                     1000  | *1.12x*       | 2194.282     |        1963.110
>                     2500  | *2.15x*       | 4606.705     |        2140.126
>                     5000  | *6.37x*       | 16661.581     |
2616.109
>                     7500  | *11.76x*       | 35988.569     |
> 3061.161
>                    10000  | *19.01x*       | 66616.620     |
> 3504.144
>

It looks to me like these results are with optimizations disabled?

Can you share the SQL script you used for testing?

--
David Geier