Thread: pgsql: Doc: add commentary about cowboy assignment of maintenance_work_

Doc: add commentary about cowboy assignment of maintenance_work_mem.

Whilst working on commit 041e8b95b I happened to notice that
parallel_vacuum_main() assigns directly to the maintenance_work_mem
GUC.  This is definitely not per project conventions, so I tried to
fix it to use SetConfigOption().  But that fails with "parameter
cannot be set during a parallel operation".  It doesn't seem worth
working on a cleaner answer, at least not till we have a few more
instances of similar problems.  But add some commentary, just so
nobody gets the idea that this is an approved way to set a GUC.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/53a49365052026907afff7613929710d1e7f0da0

Modified Files
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src/backend/commands/vacuumparallel.c | 7 +++++++
1 file changed, 7 insertions(+)