Change log data for DSO

Change Log Data : I think there is lot of confusion in forums on deleting changelog data. Some say we can delete the changelog data no problem, some say we will get incorrect data if there are any updates for deleted old data.

For the record, change log data can be deleted, there are no issues with it even when we get changes for the records we deleted. Here is how change log /delta from ODS to the cube works.

1.    Data is first loaded into new table (This is before ODS activation)

2.    ODS Activation : During activation SAP compares records in new table with records in active table and generates changelog records and puts them under a unique id which corresponds to request id in the active table. Records in new table are deleted at the end of activation.

3.    Now when you do a delta from the ODS to the cube it loads the records from changelog table based on request id, after the delta load is complete the records in change log table are never used for anything again unless you want to reconstruct/reload data requests by requests.

4.    Even if you need to reload you do it by either full or delta init loads or data will be loaded from active table.