Custom transformations in SAP BW (as of SAP BW 7.
4) are implemented using
ABAP routines – Start, End or Expert – which are executed on the ABAP
Application server. During execution of ABAP based transformation, data is
retrieved from database to the application server for processing and transformed
data is written back into the database. Data transfer thus happens twice
during ABAP runtime, once from database to application server and again back to
the database. This, coupled with row-by-row processing of field-based calculations
add huge performance overheads to the data load process.
Transformation Execution on HANA
BW4HANA has the option to push down data transformation logic to HANA
database to improve data acquisition performance. The calculation execut ion and
parallelization while retrieving the data from the database significantly reduces
transformation runtime.
In a BW4HANA system, transformations will support both – ABAP and HANA
runtime. Once the transformation has been activated, system checks whet her the
transformation logic can be pushed down to the SAP HANA DB. There is an option
in BW4HANA to check whether execution can run in HANA runtime.
For custom transformations to be pushed down to SAP HANA database, start, end
and expert routine type need to be created as AMDP script (ABAP Managed
Database Procedure script).
In this blog, I will provide an overview on: Creating AMDP based transformations,
how to benchmark it against traditional ABAP routines and discuss its limitations.
How to create an AMDP script based transformation?
Step 1: Create an aDSO (Advanced Data Store Object) with activate data and write
change log as shown below in SAP BW Modeling tool (BWMT) in Eclipse.
Step 2: Create transformation between aDSO and data source.
Step 3: Create expert routine from Edit Menu -> Routine -> Expert Routine
Step 4: Pop-up will ask for confirmation to replace standard transformation with
expert routine. Click on the “Yes” button
Step 5: An AMDP Class will be generated with default method – PROCEDURE and
with default interface – IF_AMDP_MARKER_HDB
Step 6: Open ABAP development tools in Eclipse with BW4HANA system in ABAP
perspective to change the HANA SQL script
Features – AMDP Script vs ABAP Routine
Following are list of features available in AMDP script (ABAP Managed Database
Procedure script) compared to ABAP based transformation.
AMDP
Features ABAP routine
script
No (runs in ABAP Application
Execution push down to HANA database Yes
Server)
Supported Data Targets are Info Object
and advanced Data Store Object(aDSO) Yes Yes
(in BW/4HANA)
Supports SAP HANA SQL Script Yes No
Enable Error Handling for Expert Script
Yes No
in Transformation
Package based data processing Yes No
Row-by-row data processing No Yes
Objects like function module and class
No Yes
are supported
Supports AMDP objects like AMDP Class
Yes No
and AMDP Method
Calculation Engine functions can be
Yes No
leveraged
Listed below are some of points that need to be taken into consideration during
AMDP script based transformation:
Null values are allowed, so default initial values must be filled depend upon the
data type in script
Allow all special characters will cause failure of data load and activation
Derivation of time characteristics with time distribution is not supported by system
default, need to handle them in script
Fields must be filled using internal value representation
Data type of source and target should match, if not casting or conversion should be
carried out
Limitations:
All the BW transformations cannot be pushed down to SAP HANA using this
approach. Certain situations prevent transformation logic execution pushdown to
SAP HANA database. For example:
Queries as InfoProviders are not supported as the source
Rule groups are not supported
Customer-Defined Functions in the Formula Editor
To read data from Data Store objects, the entire key must be provided
Near-line connections are not supported
Note:
This Blog was written based on features in SAP BW4HANA support package level
01. It may change in upcoming releases and support packages of SAP BW4HANA.
