Relevant PG18 commit:
c2a4078eba
- Enable buffer-usage reporting by default in `EXPLAIN ANALYZE` on
PostgreSQL 18 and above.
Solution:
- Introduce the explicit `BUFFERS OFF` option in every existing
regression test to maintain pre-PG18 output consistency.
- This appends, `BUFFERS OFF` to all `EXPLAIN ANALYZE(...)` calls in
src/test/regress/sql and the corresponding .out files.
fixes#8093
This PR fixes diffs in `columnnar_chunk_filtering` and `columnar_paths`
tests.
In `columnnar_chunk_filtering` an expression `(NOT (SubPlan 1))` changed
to `(NOT (ANY (a = (SubPlan 1).col1)))`. This is due to [aPG17
commit](https://github.com/postgres/postgres/commit/fd0398fc) that
improved how scalar subqueries (InitPlans) and ANY subqueries (SubPlans)
are EXPLAINed in expressions. The fix uses a helper function which
converts the PG17 format to the pre-PG17 format. It is done this way
because pre-PG17 EXPLAIN does not provide enough context to convert to
the PG17 format. The helper function can (and should) be retired when 17
becomes the minimum supported PG.
In `columnar_paths`, a merge join changed to a hash join. This is due to
[this PG17
commit](f7816aec23),
which improved the PG optimizer's ability to estimate the size of a CTE
scan. The impacted query involves a CTE scan with a point predicate
`(a=123)` and before the change the CTE size was estimated to be 5000,
but with the change it is correctly (given the data in the table)
estimated to be 1, making hash join a more attractive join method. The
fix is to have an alternative goldfile for pre-PG17. I tried, but was
unable, to force a specific kind of join method using the GUCs
(`enable_nestloop`, `enable_hashjoin`, `enable_mergejoin`), but it was
not possible to obtain a consistent plan across all supported PG
versions (in some cases the join inputs switched sides).
Mehmet YILMAZ
Colm