dblink_send_query
sends a query to be executed
asynchronously, that is, without immediately waiting for the result.
There must not be an async query already in progress on the
connection.
After successfully dispatching an async query, completion status
can be checked with dblink_is_busy
, and the results
are ultimately collected with dblink_get_result
.
It is also possible to attempt to cancel an active async query
using dblink_cancel_query
.