Poor Performance of the query.

Question

Hi all,
i am using this query
select address1,address2,address3,city,place,pincode,siteid,bpcnum_0, contactname,fax,mobile,phone,website
from (select address1,address2,address3,city,place,pincode,siteid,bpcnum_0, contactname,fax,mobile,phone,website,
             row_number() over (partition by contactname, address1
                               order by contactname, address1) as rn
        from vw_sub_cl_add1 where siteid=10 and bpcnum_0 = '0063') emp where rn =1I used explain plan for the query the result is
Plan hash value: 3976107967
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Inst |IN-OUT|
| 0 | SELECT STATEMENT | | | | 0 (0)| | |
| 1 | REMOTE | | | | | INFO | R->S |
8 rows returned in 0.04 seconds      but, actually the query return 10 rows.
the view "vw_sub_cl_add1" is created using database links(remote database server).
this query i am using in for loop to retrieve the records and print it one by one.
The problem is : The perfomance of the query is so poor. it takes 1.08 sec to display all the records.
what are the steps i should do to minimize the retrival time.?
Thanks in advance
bye
Srikavi

Answer 1

Since this is query that is processed completely on the remote site, there are at least two potential issues that you should check if you don't want to use the "materialized view" approach:
1. The time it takes to transport the result set to your local database, i.e. potential network issues
2. The time it takes to process the query on the remote site
Since you're only fetching 10 rows - if I understand you correctly - the first point shouldn't be an issue in your case.
If you have suitable access to the remote site you would need to generate an execution plan of the "local" version of the query by logging directly into the remote size to find out why it takes longer than you expect. Probably it's missing some indexes if the number of rows to process should be only a few and you expect it to return more quickly.
Here are simple instructions how to generate a meaningful execution plan if you want to post it here:
Could you please post an properly formatted explain plan output using DBMS_XPLAN.DISPLAY including the "Predicate Information" section below the plan to provide more details regarding your statement. Please use the \[code\] and \[code\] tags to enhance readability of the output provided:
In SQL*Plus:
SET LINESIZE 130
EXPLAIN PLAN FOR <your statement>;
SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);Note that the package DBMS_XPLAN.DISPLAY is only available from 9i on.
In previous versions you could run the following in SQL*Plus (on the server) instead:
@?/rdbms/admin/utlxplsA different approach in SQL*Plus:
SET AUTOTRACE ON EXPLAIN
<run your statement>;will also show the execution plan.
In order to get a better understanding where your statement spends the time you might want to turn on SQL trace as described here:
[When your query takes too long|http://forums.oracle.com/forums/thread.jspa?threadID=501834]
and post the "tkprof" output here, too.
Regards,
Randolf
Oracle related stuff blog:
http://oracle-randolf.blogspot.com/
SQLTools++ for Oracle (Open source Oracle GUI for Windows):
http://www.sqltools-plusplus.org:7676/
http://sourceforge.net/projects/sqlt-pp/