RE: Database link performance

Tom,  

I tried both ways:
- creating the view on db_B and query it from db_A

• creating view of db_A using link to db_B

No difference.  

Michael Rosenblum,
Dulcian Inc.

-----Original Message-----
Sent: Thursday, June 06, 2002 1:07 PM
To: 'ORACLE-L_at_fatcity.com'
Cc: 'mrosenblum_at_dulcian.com'

Mike,  

you created the view on the db_B machine and called it from db_A, right?    

"To Tom Mercadante: creating of a view, that does filtering, did not help. Absolutely the same results!"  

Tom Mercadante
Oracle Certified Professional

-----Original Message-----
Sent: Thursday, June 06, 2002 12:03 PM
To: Multiple recipients of list ORACLE-L

Hi, all!  

Thanks for your help and suggestions. Here is some feedback on what I have found on the performance problem of the querying data between two databases using DB links.  

To John Kanagaraj: filter by ROWNUM does not make any difference - I have absolutely the same speed, when querying table with 5000 rows and filtering 'where ROWNUM <5000'.  

To Tom Mercadante: creating of a view, that does filtering, did not help. Absolutely the same results!  

Just remind you the case:

declare

   v_record B%rowtype;  

   cursor cB

   is

   select *

   from B_at_db_B.mycomp.com

   where rownum < 5000;

begin

   for c in cB

   loop

     v_record :=c;

   end loop;

end;  

My next step has been to analyze session-level statistics.  

When using link we have physically two sessions - from a client to db_A (opened explicitly) and from db_A to db_B (opened by Oracle automatically). After execution of a script:
- in the session to db_A we have 10000 SQL*Net roundtrips to/from
db_link

• in the session to db_B we have 10000 SQL*Net roundtrips to/from client.

But when I am running the same script directly (from client to db_B) - there is only ONE SQL*Net roundtrip to/from the client.  

I asked Paul Dorsey to check it out with Tom Kyte at yesterday's NYOUG meeting.  

Tom told us that Oracle 8.* does single record fetches when using database links. In general, database links have been tuned to support database replication. It means, that 'create table new_A as select . from table_A_at_db_B' runs quickly but querying from new_A is quite slow.  

The remaining question: has anybody tried to use database links in Oracle9i? Does the same single fetch limitation apply?  

Thank you,

Michael Rosenblum

Dulcian Inc.

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Michael Rosenblum
  INET: mrosenblum_at_dulcian.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).