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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