Behavior of debug_parallel_query=regress

Hi,

For the context, debug_parallel_query has three states (according to the
documentation):
on: use parallel if safe
off: use parallel if improves performance
regress: use parallel if safe + suppress context line + hide
gather node in explain output

I am looking for a combination of the 'off' and 'regress' state, which is:
use parallel if improves performance + suppress context line (if
parallel is used)

Our project, Apache AGE, has a regression test for cypher MATCH queries. If
that test is run repeatedly, the optimizer chooses a parallel plan at a random
iteration (the issue is reported here:
https://github.com/apache/age/issues/1439)
In that case, the test fails due to the addition of 'CONTEXT: parallel worker'
line in the diff.

I have thought about using 'debug_parallel_query=regress' to suppress the line.
However, the 'regress' state also has the same behavior as 'on', whereas I would
prefer 'off'. I would still want the optimizer to choose a parallel
plan based on
the possibility of performance improvement, rather than forcing it.

Any suggestions on this issue are welcome. It does not have to be related to
debug_parallel_query.

Regards,
Rafsun Masud
Apache AGE Contributor: https://github.com/apache/age