Friday, January 18, 2019

Declustering / decoupling of SAP’s DB tables

Cluster and pooled tables are present in SAP NetWeaver ABAP stack based system for ages. They addressed requirements of SAP functional applications to present data from several database tables together. SAP introduced following table types in ABAP Dictionary to support that:

Cluster table - data logically belonging together of several cluster tables is stored together in a table cluster in the database. It represents a diagram type in the ABAP Dictionary. Such ABAP dictionary tables allow efficient access to a whole application object without using extensive join operations in database. Cluster tables are used very much in SAP’s HR module.

Pooled table - data of several pooled tables is stored together as a table pool in the database. Such ABAP dictionary tables are trying to solve a problem with large numbers of individual database objects (e.g. large number of small customizing tables).

However, these concepts are obsolete when it comes to modern databases. Organizing data in such a way in ABAP application server is no needed anymore. SAP is trying to remove these concepts by declustering / decoupling of such an objects. This means that all tables are converted to transparent tables. For any SAP NetWeaver system running on HANA DB such a tables are declustered and depooled per default. Also starting with SAP NetWeaver 7.5 on any DB the declustering / decoupling is mandatory by default. Operation of converting tables is doen during installation of NetWeaver 7.5 based systems. Manual conversion can be done in t-code SE11 together with SE14 and/or in ICNV.

One more thing worth mentioning is performance of declustering / decoupling operation. During SAP system installation it is usually very time consuming task. Therefore, it must be considered while preparing plans for installing of new systems.

More information:
1892354 - SAP Strategy for Cluster and Pool Tables
2227432 - How to: Declustering and depooling with NW 7.4 SP03 and higher on databases other than SAP HANA
1784377 - Checking pool tables and cluster tables

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