This is allways tricky task. The size of transaction (e.g. for safe rollback) is limited by the size of transaction log. The transaction log is filled not only by yours sql commands but also by the commands of other users using db in the same moment.
I would suggest using one of/or combination of following methods
1. Commits
Do commmits often - in your case I would put one commit after each delete command
2. Increase the size of transaction log
As I recall default db2 transaction log is not very big. The size of transaction log should be calculated/tuned for each db individually. Reference here and with more details here
3. Stored procedure
Write and call stored procedure which does deletes in blocks, e.g.:
-- USAGE - create: db2 -td@ -vf del_blocks.sql -- USAGE - call: db2 "call DEL_BLOCKS(4, ?)" drop PROCEDURE DEL_BLOCKS@ CREATE PROCEDURE DEL_BLOCKS(IN PK_FROM INTEGER, IN PK_TO INTEGER) LANGUAGE SQL BEGIN declare v_CNT_BLOCK bigint; set v_CNT_BLOCK = 0; FOR r_cur as c_cur cursor with hold for select tableky from tablename where tableky between pk_from and pk_to for read only DO delete from tablename where tableky=r_cur.tableky; set v_CNT_BLOCK=v_CNT_BLOCK+1; if v_CNT_BLOCK >= 5000 then set v_CNT_BLOCK = 0; commit; end if; END FOR; commit; END@
4. Export + import with replace option
In some cases when I needed to purge very big tables or leave just small amount of records (and had no FK constraints), then I used export + import(replace). The replace import option is very destructive - it purges the whole table before import of new records starts (reference of db2 import command), so be sure what you're doing and make backup before. For such sensitive operations I create 3 scripts and run each separately: backup, export, import. Here is the script for export:
echo '===================== export started ';
values current time;
export to tablename.del of del
select * from tablename where (tableky between 1 and 1000
or tableky between 2000 and 3000
or tableky between 5000 and 7000
) ;
echo '===================== export finished ';
values current time;
Here is the import script:
echo '===================== import started ';
values current time;
import from tablename.del of del allow write access commitcount 2000
-- !!!! this is IMPORTANT and VERY VERY destructive option
replace
into tablename ;
echo '===================== import finished ';
5. Truncate command
Db2 in version 9.7 introduced TRUNCATE statement which:
deletes all of the rows from a table.
Basically:
TRUNCATE TABLE <tablename> IMMEDIATE
I had no experience with TRUNCATE in db2 but in some other engines, the command is very fast and does not use transaction log (at least not in usual manner). Please check all details here or in official documentation. As solution 4, this method too is very destructive - it purges the whole table so be very careful before issuing the command. Ensure previous state with table/db backup doing first.
Note about when to do this
When there are no other users on db, or ensure this by locking the table.
Note about rollback
In transaction db (like db2) rollback can restore db state to the state when transaction started. In methods 1,3 and 4 this can't be achieved, so if you need feature "restoring to the original state", the only option which ensures this is the method nr. 2 - increase transaction log.