Added async query capability. Original patch by

Kai Londenberg, modified by Joe Conway

contrib/dblink/doc/query

@@ -118,3 +118,125 @@ Then you can simply write:
 
    select * from myremote_pg_proc where proname like 'bytea%';
 
+
+==================================================================
+Name
+
+dblink_send_query -- Sends an async query to a remote database
+
+Synopsis
+
+dblink_send_query(text connname, text sql)
+
+Inputs
+
+  connname
+    The specific connection name to use.
+
+  sql
+
+    sql statement that you wish to execute on the remote host
+    e.g. "select * from pg_class"
+
+Outputs
+
+  Returns int. A return value of 1 if the query was successfully dispatched,
+  0 otherwise. If 1, results must be fetched by dblink_get_result(connname).
+  A running query may be cancelled by dblink_cancel_query(connname).
+
+Example usage
+
+  SELECT dblink_connect('dtest1', 'dbname=contrib_regression');
+  SELECT * from 
+   dblink_send_query('dtest1', 'select * from foo where f1 < 3') as t1;
+
+==================================================================
+Name
+
+dblink_get_result -- Gets an async query result
+
+Synopsis
+
+dblink_get_result(text connname [, bool fail_on_error])
+
+Inputs
+
+  connname
+    The specific connection name to use. An asynchronous query must
+    have already been sent using dblink_send_query()
+
+  fail_on_error
+
+    If true (default when not present) then an ERROR thrown on the remote side
+    of the connection causes an ERROR to also be thrown locally. If false, the
+    remote ERROR is locally treated as a NOTICE, and no rows are returned.
+
+Outputs
+
+  Returns setof record
+
+Notes
+  Blocks until a result gets available.
+
+  This function *must* be called if dblink_send_query returned
+  a 1, even on cancelled queries - otherwise the connection
+  can't be used anymore. It must be called once for each query
+  sent, and one additional time to obtain an empty set result,
+  prior to using the connection again.
+
+Example usage
+
+contrib_regression=#   SELECT dblink_connect('dtest1', 'dbname=contrib_regression');
+ dblink_connect
+----------------
+ OK
+(1 row)
+
+contrib_regression=#   SELECT * from
+contrib_regression-#    dblink_send_query('dtest1', 'select * from foo where f1 < 3') as t1;
+ t1
+----
+  1
+(1 row)
+
+contrib_regression=#   SELECT * from dblink_get_result('dtest1') as t1(f1 int, f2 text, f3 text[]);
+ f1 | f2 |     f3
+----+----+------------
+  0 | a  | {a0,b0,c0}
+  1 | b  | {a1,b1,c1}
+  2 | c  | {a2,b2,c2}
+(3 rows)
+
+contrib_regression=#   SELECT * from dblink_get_result('dtest1') as t1(f1 int, f2 text, f3 text[]);
+ f1 | f2 | f3
+----+----+----
+(0 rows)
+
+contrib_regression=#   SELECT * from
+   dblink_send_query('dtest1', 'select * from foo where f1 < 3; select * from foo where f1 > 6') as t1;
+ t1
+----
+  1
+(1 row)
+
+contrib_regression=#   SELECT * from dblink_get_result('dtest1') as t1(f1 int, f2 text, f3 text[]);
+ f1 | f2 |     f3
+----+----+------------
+  0 | a  | {a0,b0,c0}
+  1 | b  | {a1,b1,c1}
+  2 | c  | {a2,b2,c2}
+(3 rows)
+
+contrib_regression=#   SELECT * from dblink_get_result('dtest1') as t1(f1 int, f2 text, f3 text[]);
+ f1 | f2 |      f3
+----+----+---------------
+  7 | h  | {a7,b7,c7}
+  8 | i  | {a8,b8,c8}
+  9 | j  | {a9,b9,c9}
+ 10 | k  | {a10,b10,c10}
+(4 rows)
+
+contrib_regression=#   SELECT * from dblink_get_result('dtest1') as t1(f1 int, f2 text, f3 text[]);
+ f1 | f2 | f3
+----+----+----
+(0 rows)