[ORCA] Maintaining explain plans in MDPs

[David Kimura]

Hi all,

For reference, this thread came out of a conversation [1] with Nishant.

ORCA uses MDPs to quickly test the optimizer for plan changes. But the format
is rather verbose and hard to visually parse compared to EXPLAIN plans. So, we
used to have a habit of including the EXPLAIN plan via a comment. But the
problem became that those comments quickly went out of date and were difficult
to maintain especially if a patch causes many plan changes.

But what if we could automate that process? It seems quite doable to add logic
into fixup_mdps.py to do that without too much effort (e.g.quick hack branch
[2]).

Any thoughts/opinions/concerns?

Thanks,
David

[1] https://github.com/greenplum-db/gpdb/pull/16731#discussion_r1444397969
[2] https://github.com/dgkimura/gpdb/tree/automate-mdp-fixup-explain

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