Optimizing Proposed Aggregates (SAP Library

Optimizing Proposed Aggregates

Use

If the query analysis or BW statistics has come up with several proposals for aggregates, it is not necessarily advisable to activate all of them.

This reduces the run-times for queries, and optimizes the roll-up of aggregates in a way that allows aggregates that are already rolled up and available to be used. But, as a rule, it takes up too much memory space, and it takes too long to fill the aggregates.

In addition to the runtime for the queries, complete optimization must also take into account the dependencies of the aggregates, their memory requirement and the time taken to roll up new data amongst other factors.

Activities

A simplified optimization is available over the pushbutton Proposal ® Optimize.

For this optimization it is usually assumed (heuristics), that the number of aggregates should be reduced first. In addition, those aggregates are selected that have been called up least often and together account for 20% of all calls. These aggregates are checked, one after the other, to see if there are aggregates with exactly one extra component.

If several aggregates with exactly one extra component are found, the one with the most number of calls is selected. These are taken into account with the aggregates that have been checked. The checked aggregate (from the 20% quantity) is then deleted from the proposal list.

Note

However, this only happens if the number of calls for the checked aggregate is not more than double the calls for the aggregate with the extra components. This prevents aggregates from being replaced by others that are used relatively rarely.

You can continue to optimize until the point where the aggregate is small enough, or until no more aggregates can be brought together.

Note

Because the optimizer has no information on the data structure, you should check the proposals again before filling with data. For example, a proposed aggregate can contain a characteristic that is almost the same size as the InfoCube. When the aggregate is filled, therefore, practically a copy of the InfoCube is created, which is not normally advisable or of any use.