Saturday, March 27, 2010

AS400 journalling

AS400 journalling

How many sites use as400 journalling in their applications. Seems to be that a lot of as400 developers dont actually understand journalling and the data integrity and audit capabilities it can add to an enterprise level system.

The DB2 UDB for AS400 journalling support supplies an audit trail and forward and backward recovery. Forward recovery can be used to take an older version of a table and apply the changes logged on the journal to the table. Backward recovery can be used to remove changes logged on the journal from the table.

When an SQL collection is created, a journal and journal receiver are created in the collection. When SQL creates the journal and journal receiver, they are only created on a user auxiliary storage pool (ASP) if the ASP clause is specified on the CREATE COLLECTION or the CREATE SCHEMA statement. However, because placing journal receivers on their own ASPs can improve performance, the person managing the journal might want to create all future journal receivers on a separate ASP.

When a table is created into the collection, it is automatically journaled to the journal DB2 UDB for AS/400 created in the collection (QSQJRN). A table created in a non-collection will also have journaling started if a journal named QSQJRN exists in that library. After this point, it is your responsibility to use the journal functions to manage the journal, the journal receivers, and the journaling of tables to the journal. For example, if a table is moved into a collection, no automatic change to the journaling status occurs. If a table is restored, the normal journal rules apply. That is, if the table was journaled at the time of the save, it is journaled to the same journal at restore time. If the table was not journaled at the time of the save, it is not journaled at restore time.

The journal created in the SQL collection is normally the journal used for logging all changes to SQL tables. You can, however, use the system journal functions to journal SQL tables to a different journal. This may be necessary if a table in one collection is a parent to a table in another collection. This is because DB2 UDB for AS/400 requires that the parent and dependent file in a referential constraint be journaled to the same journal when updates or deletes are performed to the parent table.

A user can stop journaling on any table using the journal functions, but doing so prevents an application from running under commitment control. If journaling is stopped on a parent table of a referential constraint with a delete rule of NO ACTION, CASCADE, SET NULL, or SET DEFAULT, all update and delete operations will be prevented. Otherwise, an application is still able to function if you have specified COMMIT(*NONE); however, this does not provide the same level of integrity that as400 journalling and commitment control provide

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