OLAP Cache

Question

how does OLAP Cache work?

Answer 1

Logical File Names
Use
To save data in a file in the cache modes Main Memory Cache with Swapping, Flat File Cache per Application Server, or Cross-Application Server (see Cache Mode), the following specifications must first be set:
●      Definition of the logical file path and assignment to a platform-specific physical path
●      Definition of the logical file name
From the Cache Monitor screen, using  Logical File Names, you can access the complex table maintenance for logical file paths and names. The table maintenance consists of several subdialogs (views). SAP has delivered a proportion of the required settings.
You need to check these settings and make any necessary adjustments for your file system before you can use the persistent OLAP cache with a flat file as a background store.
Note that these assignments are subject to settings made for the transport connection (You need a request that can be transported).
Features
The following section gives an overview of the subdialog in the table maintenance using an example configuration. For more information about the procedure, see Defining Logical Path and File Names.
You can choose the following subdialogs using the dialog structure:
Logical File Path Definition
The (platform-independent) logical file path is evaluated at runtime to generate the (platform-dependent) physical path (see Assignment of Physical Paths to Logical Path).
Two examples of this are:
●        Logical file path: BW_OLAP_CACHE
Name: BI OLAP Cache
●        Logical file path: BW_OLAP_CACHE_SPAN
Name: BI OLAP Cache Cross-Application Server
Assignment of Physical Paths to Logical Path
At runtime, the physical path assigned to the corresponding operating system is generated from the logical file path. 
Since the physical path is platform-dependent, the customer has to specify it. The closer the file is to the application server or, with the cross-application server cache mode, to the application server, the faster it can be found and read. 
Log(ical) path: BW_OLAP_CACHE
Name: BI OLAP Cache
Syntax group: UNIX (all Unix platforms)
Phys(ical) path: /usr//global/ (You can choose the path up to <FILENAME> according to your own configuration.)
If you cannot find the relevant syntax group for file names and paths for your operating system, you can define your own (see Syntax Group Definition and Assignment of Operating System to Syntax Group).
The <FILENAME> parameter must always be set for the physical file name (see Logical File Name Definition, Cross-Client). At runtime, the complete platform-specific file name is automatically formed from the physical path and the physical file name.
Logical File Name Definition, Cross-Client
At runtime, a complete platform-specific file name including the path is generated for a (platform-independent) logical file name.
In the following example, cache data is stored on an application server:
Logical file: BW_OLAP_CACHE (we recommend you use the delivered attributes for the logical file).
Name: BI OLAP Cache Files 
Phys(ical) file: CACHE___
Data format: BIN (binary)
Application area: BW (Business Information Warehouse)
Logical path: BW_OLAP_CACHE (see Logical File Path Definition). Input help is available.
In the following example, cache data is stored cross-application server:
Log(ical) file: BW_OLAP_CACHE_SPAN
Name: BI OLAP Cache Cross-Application Server
Phys(ical) file: CACHE__
Data format: BIN
Application area: BW
Log(ical) path: BW_OLAP_CACHE_SPAN
Note that a particular schema is prescribed for the physical file name:
&#9679;      For application server storage (see Global Cache Parameters and Cache Mode Main Memory Cache with Swapping and Cluster / Flat File Cache per Application Server):
CACHE___
&#9679;      For cross application server storage (see Global Cache Parameters and Cache Mode Cluster / Flat file Cache Cross-application Server):
CACHE__
The following table offers an overview of the variables that are only replaced with actual values during runtime:
Variables in Physical File Names
Variable
Meaning
<HOST>
Computer/server name (for SY-HOST). 
If the data is stored cross-application server, this variable is not required. 
<SYSID>
System ID
For example, if two different BI systems are running on one application server, this variable serves to differentiate the systems so that they do not overwrite each other.
<PARAM_1>
External parameter 1 (sequential number in HEX)
Definition of Variables
If you want to use variables in physical file names and paths, you can define these by choosing New Entries.
Syntax Group Definition
You can define a new syntax group for operating systems with the same syntax for file names and paths by choosing New Entries.
Syntax grp: UNIX
Name: All Unix platforms
Length (of file name)
Extension: Choose this option if the data format for the logical data name is allowed as the file name extension for this syntax group.
Active: Choose this option if the operative system for this syntax group is used in the available system configuration.
Assignment of Operating System to Syntax Group
You can assign your operating system to a syntax group by choosing New Entries if necessary.
OP system: SunOS
Name: SUN Unix
Regards,
SUBHA