On 3/28/25 00:18, Alexander Korotkov wrote:
The attached patch changes the reordering algorithm of
group_similar_or_args() in the following way. We reorder each group
of similar clauses so that the first item of the group stays in place,
but all the other items are moved after it. So, if there are no
similar clauses, the order of clauses stays the same. When there are
some groups, only required reordering happens while the rest of the
clauses remain in their places.
The patch looks good to me from a technical perspective. But it seems
like an overkill, isn't it?
You introduce additional CPU-consuming operations in the planning OR
operations.
My point is: 1) as Pavel has mentioned, Postgres doesn't guarantee the
evaluation/output order of the clauses at all. 2) we need that to keep
regression tests stable (don't forget extensions' and forks' developers
too). But it should be done once if we have no fluidity in OR clauses
order in general.
The trade-off with tricky query writers and regression tests may be
preserving the order until OR->ANY has happened. If it has happened,
just ensure the order is determined somehow. Except that, any other
spending on CPU cycles seems too expensive.
--
regards, Andrei Lepikhov
