R7I333 - Mehrdimensionales Clustering für DataStore-Objekte

SAP Error Message - Details

• Message type: E = Error

• Message class: R7I - InfoProvider

• Message number: 333

• Message text: Mehrdimensionales Clustering für DataStore-Objekte

Was verursacht dieses Problem?

You want to select InfoObjects for multidimensional clustering (MDC) of
the DataStore object.

Systemantwort

Multidimensional clustering (MDC) physically organizes a table in
blocks. Each block only contains data records with the same values in
the MDC dimensions. The size of a block is fixed and corresponds to the
EXTENTSIZE of the tablespace. This is at least 2 pages. If a page is
16K, a block requires at least 32K of memory.
Multi-dimensional clustering can significantly improve the performance
of database queries. If the queries contain restrictions on MDC
dimensions, only the blocks of the table that contain the corresponding
dimension values must be read. For the data access block indexes are
used, which are considerably smaller than conventional row indexes and
can therefore be searched more quickly.
The deletion performance also benefits from the physical organization of
an MDC table and from the easier maintenance of smaller block indexes.

Wie behebe ich diesen Fehler?

Select one or more InfoObjects as MDC dimensions by assigning the
InfoObjects sequential status numbers beginning with 1.
Follow these steps when selecting InfoObjects:
Select InfoObjects that you frequently use as restrictions in your
queries. For example, a time characteristic that you often use as a
restriction in your queries is well-suited as an MDC dimension.
Select InfoObjects with a low cardinality. For example, the time
characteristic 0CALMONTH instead of 0CALDAY.
You cannot select more than three InfoObjects.
Assign the status numbers according to the following criteria:
Sort the InfoObjects according to how frequently they are used in BI
queries. That is, assign the lower status number to the InfoObject that
is used more frequently in BI queries.
Sort the InfoObjects according to their selectivity. That is, assign the
lower status number to the InfoObject with the higher selectivity.
Note that for every combination of values in the MDC dimensions at least
one block is created that has at least 32K of memory. This memory area
is allocated independent of the number of data records that have the
same combination of values in the MDC dimensions. If the number of data
records with the same combination of values is not sufficient to
completely fill the block, the free memory remains unused. This is
because data records with a different combination of values in the MDC
dimensions cannot be written to the block.
If in the selected InfoObjects there are only a few data records in the
DataStore object for each combination that arises in the DataStore
object, and most of the blocks therefore have unused, free memory, an
unnecessarily large amount of memory space is used for the table. The
performance of the database queries therefore decreases, because many,
only partially filled pages have to be read.
It is not necessary to create additional secondary indexes on the MDC
dimensions. The database uses the MDC block indexes for database
queries.

Vorgehensweise für Systemadministratoren

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