dblink_is_busy — checks if connection is busy with an async query
dblink_is_busy(text connname) returns int
dblink_is_busy tests whether an async query is in progress.
connnameName of the connection to check.
Returns 1 if connection is busy, 0 if it is not busy.
If this function returns 0, it is guaranteed that
dblink_get_result will not block.
SELECT dblink_is_busy('dtest1');