Thursday, November 29, 2012
Difference between Delta and Full Load
Explain about deltas load and where we use it exactly.
A data load into a BI ODS/master data/cube can be either FULL or DELTA.
Full load is when you load data into BI for the first time i.e. you are seeding the destination BI object with initial data. A delta data load means that you are either loading changes to already loaded data or add new transactions.
Usually delta loads are done when the process has to sync any new data/changed data from the OLTP system i.e. SAP ECC or R/3 to SAP BI (DSS/BI). DSS stands for Decision Support Systems or system that is used for deriving Business Intelligence.
Let's say you are trying to derive a report to empower the management to figure out who are the customers who have bought the most from your company.
On the BI side, you create the necessary master data elements. You use the master data elements to create an ODS and a cube. The ODS and the cube will house the daily transactions that get added to the OLTP systems via a variety of applications.
Now you identify the datasource in ECC that will bring the necessary transactions to BI. You replicate the datasource in BI and map the data source to the ODS and map the ODS to the cube. Hence you create the Transformation and DTP as a full load for the first time.
At this point of time, your ODS and cube has the data for the last last x number of years where x stands for the life of your company. You also need to capture the daily transactions from here onwards going forward. What you do now is change the DTP to allow only delta records.
Now you schedule the execution of the datasource and loading of the data in a process chain. At run time, the process chain will get the new records from OLTP (since the datasource is already replicated keeping in mind that the datasource structure has not changed) and import those changes to the ODS and hence to the cube.
Any such loads that brings in new transactions or changes to earlier transactions will be called delta records and hence the load is called delta load.