deleting a large number of rows from a table

StackOverflow https://stackoverflow.com/questions/2579375

  •  24-09-2019
  •  | 
  •  

Question

We have a requirement to delete rows in the order of millions from multiple tables as a batch job (note that we are not deleting all the rows, we are deleting based on a timestamp stored in an indexed column). Obviously a normal DELETE takes forever (because of logging, referential constraint checking etc.). I know in the LUW world, we have ALTER TABLE NOT LOGGED INITIALLY but I can't seem to find the an equivalent SQL statement for DB2 v8 z/OS. Any one has any ideas on how to do this really fast? Also, any ideas on how to avoid the referential checks when deleting the rows? Please let me know.

Was it helpful?

Solution 3

We modified the tablespace so the lock would occur at the tablespace level instead of at the page level. Once we changed that DB2 only required one lock to do the DELETE and we didn't have any issues with locking. As for the logging, we just asked the customer to be aware of the amount of logging required (as there did not seem to be a solution to get around the logging issue). As for the constraints, we just dropped and recreated them after the delete.

Thanks all for your help.

OTHER TIPS

In the past I have solved this kind of problem by exporting the data and re-loading it with a replace style command. For example:

EXPORT to myfile.ixf OF ixf
SELECT * 
FROM my_table 
WHERE last_modified < CURRENT TIMESTAMP - 30 DAYS;

Then you can LOAD it back in, replacing the old stuff.

LOAD FROM myfile.ixf OF ixf
REPLACE INTO my_table
NONRECOVERABLE INDEXING MODE INCREMENTAL;

I'm not sure whether this will be faster or not for you (probably it depends on whether you're deleting more than you're keeping).

  1. Do the foreign keys already have indexes as well?

  2. How do you have your delete action set? CASCADE, NULL, NO ACTION

  3. Use SET INTEGRITY to temporarily disable constraints on the batch process. http://www.ibm.com/developerworks/data/library/techarticle/dm-0401melnyk/index.html

http://publib.boulder.ibm.com/infocenter/db2luw/v8/index.jsp?topic=/com.ibm.db2.udb.doc/admin/r

Licensed under: CC-BY-SA with attribution
Not affiliated with StackOverflow
scroll top