Re: Reuse child_relids in try_partitionwise_join was Re: Assert failure on bms_equal(child_joinrel->relids, child_joinrelids) - Mailing list pgsql-hackers

Hi David,

Thanks for looking into this.

On Fri, May 31, 2024 at 2:19 AM David Christensen <david+pg@pgguru.net> wrote:

Hello,

I am looking through some outstanding CommitFest entries; I wonder if
this particular patch is already effectively fixed by 5278d0a2, which
is both attributed to the original author as well as an extremely
similar approach.  Can this entry
(https://commitfest.postgresql.org/48/4553/) be closed?

This is different. But it needs a rebase. PFA rebased patch. The revised commit message explains the change better.

Here are numbers revised after 5278d0a2. Since the code changes only affect partitionwise join code path, I am reporting only partition wise join numbers. The first column reports the number of joining relations, each having 1000 partitions. Rest of the column names are self-explanatory.

Planning memory used:

 num_joins | master  | patched | memory saved | memory saved
-----------+---------+---------+--------------+----------------------------
         2 | 31 MB   | 30 MB   | 525 kB       |                       1.68%
         3 | 111 MB  | 107 MB  | 4588 kB      |                       4.03%
         4 | 339 MB  | 321 MB  | 17 MB        |                       5.13%
         5 | 1062 MB | 967 MB  | 95 MB        |                       8.96%

Here's planning time measurements.

 num_joins | master (ms) | patched (ms) | change in planning time (ms) | change in planning time
-----------+-------------+--------------+------------------------------+---------------------------------------
         2 |      187.86 |       177.27 |                        10.59 |                                  5.64%
         3 |      721.81 |       758.80 |                       -36.99 |                                 -5.12%
         4 |     2239.87 |      2236.19 |                         3.68 |                                  0.16%
         5 |     6830.86 |      7027.76 |                      -196.90 |                                 -2.88%