pgsql: Copy the INSERT query in postgres_fdw

Copy the INSERT query in postgres_fdw

When executing the INSERT with batching, we may need to rebuild the
query when the batch size changes, in which case we pfree the current
string. We must not release the original string, stored in fdw_private,
because that may be needed in EXPLAIN ANALYZE. So make copy of the SQL,
but only for INSERT queries.

Reported-by: Pavel Stehule
Discussion: https://postgr.es/m/CAFj8pRCL_Rjw-MCR6J7VX9OF7MR6PA5K8qUbrMvprW_e-aHkfQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c6a01d924939306e95c8deafd09352be6a955648

Modified Files
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contrib/postgres_fdw/postgres_fdw.c | 3 +++
1 file changed, 3 insertions(+)