Read Mode 

Definition

The read mode determines how the OLAP processor gets data during navigation. You can set the mode in Customizing for an InfoProvider and in the Query Monitor for a query.

Use

The following types are supported:

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       1.      Query to be read when you navigate or expand hierarchies (H)

The amount of data transferred from the database to the OLAP processor is the smallest in this mode. However, it has the highest number of read processes.

In the following mode Query to read data during navigation, the data for the fully expanded hierarchy is requested for a hierarchy drilldown. In the Query to be read when you navigate or expand hierarchies mode, the data across the hierarchy is aggregated and transferred to the OLAP processor on the hierarchy level that is the lowest in the start list. When expanding a hierarchy node, the children of this node are then read.

You can improve the performance of queries with large presentation hierarchies by creating aggregates on a middle hierarchy level that is greater or the same as the hierarchy start level.

       2.      Query to read data during navigation (X)

The OLAP processor only requests data that is needed for each navigational status of the query in the Business Explorer. The data that is needed is read for each step in the navigation.

In contrast to the Query to be read when you navigate or expand hierarchies mode, presentation hierarchies are always imported completely on a leaf level here.

The OLAP processor can read data from the main memory when the nodes are expanded.

When accessing the database, the best aggregate table is used and, if possible, data is aggregated in the database.

       3.      Query to read all data at once (A)

There is only one read process in this mode. When you execute the query in the Business Explorer, all data in the main memory area of the OLAP processor that is needed for all possible navigational steps of this query is read. During navigation, all new navigational states are aggregated and calculated from the data from the main memory.

The read mode Query to be read when you navigate or expand hierarchies significantly improves performance in almost all cases compared to the other two modes. The reason for this is that only the data the user wants to see is requested in this mode.

Compared to the Query to be read when you navigate or expand hierarchies, the setting Query to read data during navigation only effects performance for queries with presentation hierarchies.

Unlike the other two modes, the setting Query to Read All Data At Once also has an effect on performance for queries with free characteristics. The OLAP processor aggregates on the corresponding query view. For this reason, the aggregation concept, that is, working with pre-aggregated data, is least supported in the Query to read all data at once mode.

We recommend you choose the mode Query to be read when you navigate or expand hierarchies.

Only choose a different read mode in exceptional circumstances. The read mode Query to read all data at once may be of use in the following cases:

§         The InfoProvider does not support selection. The OLAP processor reads significantly more data than the query needs anyway.

§         A user exit is active in a query. This prevents data from already being aggregated in the database.

Integration

You can find additional information under Query Properties.