Solved

Optimizing a DELETE statement for large number of records

Posted on 2008-10-16
12
2,937 Views
Last Modified: 2013-12-07
The column OPERAZIONE in the NEREPSTA_STORICO table can assume 2 values: 'IMPORT' or 'EXPORT'.

The column CENTRALE in the NEREPSTA_STORICO table can assume 10500 different values.

The DELETE statement you can see attached, keeps in the NEREPSTA_STORICO table keeps max 50 records for every different CENTRALE with OPERAZIONE = 'IMPORT', and max 50 records for every different CENTRALE with OPERAZIONE = 'EXPORT'.

So we can have maximum 50 * 2 * 10500  = 1050000 records on the NEREPSTA_STORICO table.

Explaination:

50 => max 50 record for every distinct couple (CENTRALE, OPERAZIONE)
2 => two types of OPERAZIONE ('IMPORT' or 'EXPORT')
10500 => the number of different CENTRALE values

How can I optimize the DELETE statement?  At the end of the transitory period, I'll have always 1050000 records, and I'm afraid of going deadlock to delete the records.

DELETE FROM nerepsta_storico@linkmaster

            WHERE ROWID IN (

                     SELECT rid

                       FROM (SELECT ROWID rid,

                                    ROW_NUMBER () OVER (PARTITION BY centrale, operazione ORDER BY data_inizio DESC)

                                                                           rn

                               FROM nerepsta_storico@linkmaster)

                      WHERE rn > 50);

Open in new window

0
Comment
Question by:CRISTIANO_CORRADI
  • 6
  • 6
12 Comments
 
LVL 27

Expert Comment

by:sujith80
ID: 22729131
What is the expected number of records that get deleted?

If this number is large, and If you dont have dependent objects on nerepsta_storico, then can you try to create a table with only the required records using CTAS, rename the original table to backup and rename the temp table to nerepsta_storico?

0
 

Author Comment

by:CRISTIANO_CORRADI
ID: 22729317
The expected number of deleted records for every delete statement is:

one for every couple (CENTRALE, OPERAZIONE), where CENTRALE can assume 10550 different values, and OPERAZIONE can assume two values: 'IMPORT' or 'EXPORT'.

The objective is to keep only 50 more recent records for every CENTRALE with OPERAZIONE = 'IMPORT', and only 50 more recent records for every CENTRALE with operazione = 'EXPORT'.
0
 
LVL 27

Expert Comment

by:sujith80
ID: 22729441
10550 * 2;
is it slow?
0
 

Author Comment

by:CRISTIANO_CORRADI
ID: 22730037
In a few months, the system will delete about 20000 records selected between over 1000000 records: is it not possible to optimize the query?  The clause "WHERE ROWID IN" is too heavy?  Have I to substitute it with "EXISTS" clause?
0
 
LVL 27

Accepted Solution

by:
sujith80 earned 500 total points
ID: 22737245
IN and EXISTS may not make a difference, as EXISTS is used in most of the cases to push the usage of an INDEX.
In my opinion, you have to think of a way to avoid the delete, say
- partition the table effectively and truncate the partition
- or create a new table with required data.(This approach is worth only if the required number of records are much lesser than the number of records to be deleted.)
0
 

Author Comment

by:CRISTIANO_CORRADI
ID: 22738522
OK.  Any other clues?
0
PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

 
LVL 27

Expert Comment

by:sujith80
ID: 22738868
Can you do this delete in the remote database directly, instead of going through the db-link?
0
 
LVL 27

Expert Comment

by:sujith80
ID: 22738875
If it is possible you may try to use parallelism in the delete, by altering the table to give a degree of parallelism.
0
 

Author Comment

by:CRISTIANO_CORRADI
ID: 22738915
@sujith80: No, I can't do this delete in the remote database :-(   What do you mean by using parallelism in the delete?
0
 
LVL 27

Expert Comment

by:sujith80
ID: 22738993
Read this link for details on parallel DML in oracle.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14223/usingpe.htm#sthref2120

But, i am not quite sure whether it will work for you, as you are doing the delete over a db-link(never tried it).
0
 

Author Comment

by:CRISTIANO_CORRADI
ID: 22739399
I was trying to use the WITH clase, but with the DELETE statement it doen't work, why??
WITH s AS

     (SELECT rid

        FROM (SELECT ROWID rid,

                     ROW_NUMBER () OVER (PARTITION BY centrale, operazione ORDER BY data_inizio DESC)

                                                                           rn

                FROM nerepsta_storico@linkmaster)

       WHERE rn > 5)

SELECT RID FROM S

Open in new window

0
 

Author Closing Comment

by:CRISTIANO_CORRADI
ID: 31506644
Thanks for your explaination!
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Pfile and SPfile - Oracle 2 57
PL/SQL LOOP CURSOR 3 59
C# Connection String for Oracle database is not working 22 93
Oracle Pivot Question 8 45
Background In several of the companies I have worked for, I noticed that corporate reporting is off loaded from the production database and done mainly on a clone database which needs to be kept up to date daily by various means, be it a logical…
Using SQL Scripts we can save all the SQL queries as files that we use very frequently on our database later point of time. This is one of the feature present under SQL Workshop in Oracle Application Express.
This video explains at a high level with the mandatory Oracle Memory processes are as well as touching on some of the more common optional ones.
This video shows how to set up a shell script to accept a positional parameter when called, pass that to a SQL script, accept the output from the statement back and then manipulate it in the Shell.

863 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

28 Experts available now in Live!

Get 1:1 Help Now