pgsql: Allow parallelism in COPY (query) TO ...;

Allow parallelism in COPY (query) TO ...;

Previously this was not allowed, as copy.c didn't set the
CURSOR_OPT_PARALLEL_OK flag when planning the query. Set it.

While the lack of parallel query for COPY isn't strictly speaking a
bug, it does prevent parallelism from being used in a facility
commonly used to run long running queries. Thus backpatch to 9.6.

Author: Andres Freund
Discussion: https://postgr.es/m/20170531231958.ihanapplorptykzm@alap3.anarazel.de
Backpatch: 9.6, where parallelism was introduced.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/34aebcf42a70089b76ff8e9ccda331f111153eeb

Modified Files
--------------
src/backend/commands/copy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)