I think it will, because Append itself has been made async-capable by one of the patches and UNION ALL uses Append. But as mentioned above, only the postgres_fdw foreign tables will be able to utilize this for now.
Ok, I'll re-run my test from a few weeks back and see if anything has changed.
I'm not able to discern any difference in plan between a 9.6 instance and this patch.
The basic outline of my test is:
EXPLAIN ANALYZE
SELECT c1, c2, ..., cN FROM tab1 WHERE date = '1 day ago'
UNION ALL
SELECT c1, c2, ..., cN FROM tab2 WHERE date = '2 days ago'
UNION ALL
SELECT c1, c2, ..., cN FROM tab3 WHERE date = '3 days ago'
UNION ALL
SELECT c1, c2, ..., cN FROM tab4 WHERE date = '4 days ago'
I've tried this test where tab1 through tab4 all are the same postgres_fdw foreign table.
I've tried this test where tab1 through tab4 all are different foreign tables pointing to the same remote table sharing a the same server definition.
I've tried this test where tab1 through tab4 all are different foreign tables pointing each with it's own foreign server definition, all of which happen to point to the same remote cluster.
Are there some postgresql.conf settings I should set to get a decent test?
