p_order := DESC causes partition_data_proc to fail

[mattklein]

I set up a parent table with monthly partitions:

SELECT partman.create_parent(
 p_parent_table => 'my_table',
 p_control      => 'start_timestamp',
 p_type         => 'range',
 p_interval     => '1 month',
 p_premake      => 3);

That creates partitions as expected (today is 2025-11-05):

Partitions: my_table_p20250801 FOR VALUES FROM ('2025-08-01 00:00:00+00') TO ('2025-09-01 00:00:00+00'),
            my_table_p20250901 FOR VALUES FROM ('2025-09-01 00:00:00+00') TO ('2025-10-01 00:00:00+00'),
            my_table_p20251001 FOR VALUES FROM ('2025-10-01 00:00:00+00') TO ('2025-11-01 00:00:00+00'),
            my_table_p20251101 FOR VALUES FROM ('2025-11-01 00:00:00+00') TO ('2025-12-01 00:00:00+00'),
            my_table_p20251201 FOR VALUES FROM ('2025-12-01 00:00:00+00') TO ('2026-01-01 00:00:00+00'),
            my_table_p20260101 FOR VALUES FROM ('2026-01-01 00:00:00+00') TO ('2026-02-01 00:00:00+00'),
            my_table_p20260201 FOR VALUES FROM ('2026-02-01 00:00:00+00') TO ('2026-03-01 00:00:00+00'),
            my_table_default DEFAULT

Then I can successfully call partition_data_proc with a p_interval less than the partition size:

CALL partman.partition_data_proc(
 p_parent_table := 'my_table',
 p_source_table := 'my_table_nonpartitioned',
 p_interval     := '1 hour');

But if I instead try the same call using p_order := DESC, this call fails:

CALL partman.partition_data_proc(
 p_parent_table := 'my_table',
 p_source_table := 'my_table_nonpartitioned',
 p_interval     := '1 hour',
 p_order        := 'DESC');

With this error:

ERROR:  relation "my_table_p20251105" does not exist

Note that it's attempting to insert data into a partition (20251105) that doesn't exist. It seems to be basing that on the current date / the "beginning" of the DESCENDING ordering -- instead of basing it on the MONTH START of that date.