Cache Structure 

When you call up a buffer object in the OLAP cache monitor the system displays information on the structure elements of the cross-transaction OLAP cache in the right-hand screen area.

Logically, the cross-transactional cache is structured as a hierarchy. This corresponds to  Hierarchical Display. For every query request a directory is displayed in an extensive query directory that maps the structure elements of the cache on a total of three levels.

Physically, all the elements are stored flat in the cache. Their sequence reflects the order in which they were created. This corresponds to  List Display.

The following table offers an overview of the logical structuring of information in the OLAP cache monitor according to the memory ID in the hierarchical display, and the corresponding structure element:

Mapping between memory IDs and structure elements of the cache

Memory ID	Structure element	Meaning
Query name (technical name)	QUERY	Table with queries in the cache (directory)
Hierarchies / variables	VAR/SH	Complex structure for variables in fixed filters and presentation hierarchies that have been requested for the query
Selection / data	FF	Complex structure for the entire selection for the query
	SP	Storage table: data package, a sequence of bytes

If you double-click on Query Name or Hierarchy / Variables the Detailed Display dialog box appears.  You get the following information on a query: query Name, Cache Created on, Cache Created By, Cache Last Accessed, Last Accessed By.

These details belong, like the query name itself, to the key for the cache.

If no data is loaded from the cache this is often due to the variable assignment.  You can use the Detailed Display for Hierarchies / Variables to check this:

If variables are part of a fixed filter and therefore cannot be changed for query navigation, and are filled differently in each case (by manual input or user-defined variables), the cache for the query has to regenerated every time.

We therefore recommend that you make variables for query navigation changeable. In this way you can achieve the highest possible level of reusability for the cache.

The following graphic shows the relationship between the different OLAP cache structure elements.

OLAP Cache Monitor Display

Column	Meaning
Columns in the  List Display and in the  Hierarchical Display:
Memory ID	Cache structure element ID
Swapped	Indicator is set when data from the cache is stored in the background store
Read flag	Indicator is set when data is read from the cache
Write flag	Indicator is set when data was written to the cache and the cache mode is actively persistent
Dirty flag	Indicator is set when data had to be written to the background store before data removal (cache mode = persistently active)
Directory	Query directory
Bytes	Cache structure element size in bytes
Buffer ID	Cache structure element number sequence in the memory (also part of flat file name, <PARAM_1>, see Logical File Names
Logical ID	Internal logical ID of the Cache structure element
Columns that are only shown in the  List Display:
Parent memory ID	Cache structure element ID that, logically, lies on the next highest hierarchy level
Parent logical ID	Internal logical ID of parent element

You can find additional information about the meaning of the individual flags under Cache Data Removal and Swapping.