pgsql: Fix performance issue in deadlock-parallel isolation test.

Fix performance issue in deadlock-parallel isolation test.

With debug_discard_caches = 1, the runtime of this test script
increased by about a factor of 10 after commit 0dca5d68d. That's
causing some of our buildfarm animals to fail with a timeout.

The reason for the increased time is that now we are re-planning
some intentionally-non-inlineable SQL functions on every execution,
where the previous coding held onto the original plans throughout
the outer query. The previous behavior was arguably quite buggy,
so I don't think 0dca5d68d deserves blame here. But we would
like this test script to not take so long.

To fix, instead of forcing a "parallel safe" label via a
non-inlineable SQL function, apply it directly to the advisory-lock
functions by making internal-language aliases for them. A small
problem is that the advisory-lock functions return void but this
test would really like them to return integer 1. I cheated here by
declaring the aliases as returning "int". That's perhaps undue
familiarity with the implementation of PG_RETURN_VOID(), but that
hasn't changed in twenty years and is unlikely to do so in the next
twenty. That gets us an integer 0 result, and then an inline-able
wrapper to convert that to an integer 1 allows the rest of the script
to remain unchanged.

For me, this reduces the runtime with debug_discard_caches = 1
by about 100x, making the test comfortably faster than before
instead of slower.

Discussion: https://postgr.es/m/136163.1744179562@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/837cc73af29cd9c63515a6f2a36f54dd703a3a3f

Modified Files
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src/test/isolation/specs/deadlock-parallel.spec | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)