Multidimensional clustering (MDC) allows you to save the sorted data records in the active table of a DataStore object. Data records with the same key field values are saved in the same extents (related database storage unit). This prevents data records with the same key values from being spread over a large memory area and thereby reduces the number of extents to be read upon accessing tables. Multidimensional clustering greatly improves active table queries.
Currently, the function is only supported by the database platform IBM DB2 Universal Database for UNIX and Windows.
Multidimensional clustering organizes the data records of the active table of a DataStore object according to one or more fields of your choice. The selected fields are also marked as MDC dimensions. Only data records that have the same values in the MDC dimensions are saved in an extent. In the context of MDC, an extent is called a block.
The system creates block indexes from within the database for the selected fields. Block indexes link to extents instead of data record numbers and are therefore much smaller than row-based secondary indexes. They save memory space and the system can search through them more quickly. This accelerates table requests that are restricted to these fields.
You can select the key fields of an active table of a DataStore object as an MDC dimension.
Multidimensional clustering was introduced in Release SAP NetWeaver 7.0 and can be set up separately for each DataStore object.
For procedures, see Definition of Clustering.