Return-Path: Received: from newsfeed.cts.com (newsfeed.cts.com [209.68.248.164]) by naude.co.za (8.11.2/8.11.2) with SMTP id g571rvg04782 for ; Thu, 6 Jun 2002 21:53:57 -0400 Received: from fatcity.UUCP (uucp@localhost) by newsfeed.cts.com (8.9.3/8.9.3) with UUCP id KAA54991; Thu, 6 Jun 2002 10:41:14 -0700 (PDT) Received: by fatcity.com (26-Feb-2001/v1.0g-b71/bab) via UUCP id 004766E9; Thu, 06 Jun 2002 10:13:23 -0800 Message-ID: Date: Thu, 06 Jun 2002 10:13:23 -0800 To: Multiple recipients of list ORACLE-L X-Comment: Oracle RDBMS Community Forum X-Sender: "Mercadante, Thomas F" Sender: root@fatcity.com Reply-To: ORACLE-L@fatcity.com Errors-To: ML-ERRORS@fatcity.com From: "Mercadante, Thomas F" Subject: RE: Database link performance Organization: Fat City Network Services, San Diego, California X-ListServer: v1.0g, build 71; ListGuru (c) 1996-2001 Bruce A. Bergman Precedence: bulk Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C20D7C.9E9FD198" ------_=_NextPart_001_01C20D7C.9E9FD198 Content-Type: text/plain 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@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@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. ------_=_NextPart_001_01C20D7C.9E9FD198 Content-Type: text/html Message
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-----
From: Michael Rosenblum [mailto:mrosenblum@dulcian.com]
Sent: Thursday, June 06, 2002 12:03 PM
To: Multiple recipients of list ORACLE-L
Subject: Re: Database link performance

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@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@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.

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