The read mode determines how the OLAP processor acquires data during navigation. You set the mode for InfoProviders in Customizing and for queries in the query monitor.
The following types are supported:
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 Query to Read Data during Navigation mode, 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.
The OLAP processor only requests data that is needed for each navigational status of the query in the front end. The data that is needed is read for each step in the navigation.
Unlike with the Query to be read when you navigate or expand hierarchies mode, presentation hierarchies are always imported completely at 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.
There is only one read process in this mode. When you execute the query in the Business Explorer on the front end, 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 Query to be read when you navigate or expand hierarchies read mode 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 mode, the Query to read data during navigation setting only effects performance for queries with presentation hierarchies.
Unlike the other two modes, the Query to Read All Data At Once setting also improves performance for queries with free characteristics. The OLAP processor aggregates on the corresponding query view. For this reason, the aggregation concept, working with pre-aggregated data, is least supported in the Query to Read All Data At Once mode.
We recommend using the Query to be read when you navigate or expand hierarchies mode.
Only choose a different read mode in exceptional circumstances. The Query to Read All Data At Once read mode might be of use in the following cases: