Select and Insert across dblink

Question

I am having a bit of trouble with a select into insert across a dblink in oracle 10. I am using the following statement:

INSERT INTO LOCAL.TABLE_1 ( COL1, COL2) 
SELECT  COL1, COL2
FROM REMOTE.TABLE1@dblink s
WHERE COL1 IN ( SELECT COL1 FROM WORKING_TABLE)

When I run the statement the following is what gets run against the remote server on the DB Link:

SELECT /*+ OPAQUE_TRANSFORM */ "COL1", "COL2"
FROM "REMOTE"."TABLE1" "S"

If I run the select only and do not do the insert into the following is run:

SELECT /*+ */ "A1"."COL1"
     , "A1"."COL2"
  FROM "REMOTE"."TABLE1" "A1"
 WHERE "A1"."COL1" =
   ANY ( SELECT "A2"."COL1"
       FROM "LOCAL"."TABLE1"@! "A2")

The issue is in the insert case the enitre table is being pulled across the dblink and then limited localy which takes a fair bit of time given the table size. Is there any reason adding the insert would change the behavior in this manner?

Answer 1

You may want to use the driving_site hint. There is a good explanation here: http://www.dba-oracle.com/t_sql_dblink_performance.htm

Answer 2

Leveraging the WITH clause could optimize your retrieval of your working set:

WITH remote_rows AS
     (SELECT /*+DRIVING_SITE(s)*/COL1, COL2
      FROM REMOTE.TABLE1@dblink s
      WHERE COL1 IN ( SELECT COL1 FROM WORKING_TABLE)) 
INSERT INTO LOCAL.TABLE_1 ( COL1, COL2)
SELECT  COL1, COL2
FROM remote_rows

Answer 3

When it comes to DML, oracle chooses to ignore any driving_site hint and executes the statement at the target site. So I doubt if you would be able to change that (even using WITH approach described above). A possible workaround is you can create a synonym for LOCAL.TABLE1 on the remote database and use the same in your INSERT statement.

Answer 4

How big is WORKING_TABLE ? If it is small enough, you could try selecting from work_table into a collection, and then passing the elements of that collect as elements in an IN list.

declare
  TYPE t_type IS TABLE OF VARCHAR2(60);
  v_coll t_type;
begin
  dbms_application_info.set_module('TEST','TEST');
  --
  select distinct object_type 
  bulk collect into v_coll
  from user_objects;
  --
  IF v_coll.count > 20 THEN
    raise_application_error(-20001,'You need '||v_coll.count||' elements in the IN list');
  ELSE
    v_coll.extend(20);
  END IF;
  insert into abc (object_type, object_name)
  select object_type, object_name
  from user_objects@tmfprd
  where object_type in 
            (v_coll(1), v_coll(2), v_coll(3), v_coll(4), v_coll(5), 
            v_coll(6), v_coll(7), v_coll(8), v_coll(9), v_coll(10),
            v_coll(11), v_coll(12), v_coll(13), v_coll(14), v_coll(15), 
            v_coll(16), v_coll(17), v_coll(18), v_coll(19), v_coll(20)
             );
  --
  dbms_output.put_line(sql%rowcount);
end;
/