Configuring cluster caching facility (CF) memory for a database

Use the Db2® command line processor (CLP) or the Db2 configuration APIs to display and update cluster caching facility (CF) memory configuration parameters for the database.

About this task

The cluster caching facility (CF) structure memory configuration information is maintained as part of the Db2 database configuration information.

The cluster caching facility structure memory used for Group Buffer Pool (GBP), lock usage, and Shared Communication Area (SCA) is allocated for the cluster caching facility during the first database activation on any member and remains allocated until deactivation on the last member. These parameters have a default value set to AUTOMATIC. When set to AUTOMATIC, Db2 computes appropriate sizes for these parameters during database activation. Because these values are closely related and dependent on one another, manually setting at least one of the parameters causes none of the parameters to be calculated during activation even if some parameters remain set to AUTOMATIC. Their values are what the most recent automatically calculated value was and can be viewed with the GET DB CFG SHOW DETAIL command.

The ONLINE option is also supported for structure parameters. Any updates to CF memory parameters are applied immediately. Update requests are synchronous and are not returned until the new value is set by the CF server.

There are two ways to configure the cluster caching facility memory for a database:

Updating configuration parameters using the CLP
Updating configuration parameters using APIs

Procedure

To view the values of the CF structure configuration parameters in the CLP, issue the GET DATABASE CONFIGURATION command.
For example, this CF structure configuration information is displayed when this command is issued in a Db2 pureScale® instance:
```
CF Resource Configuration:

     CF self-tuning memory   = ON
     CF database memory size (4KB)           
              (CF_DB_MEM_SZ) = AUTOMATIC
     Group buffer pool size (4KB)            
              (CF_GBP_SZ)    = AUTOMATIC
     Global lock memory size (4KB)           
              (CF_LOCK_SZ)   = AUTOMATIC
     Shared communication area size (4KB)    
              (CF_SCA_SZ)    = AUTOMATIC
```
See the GET DATABASE CONFIGURATION command for more detailed output.

Note: The group buffer pool (GBP) parameter requires a sufficient amount of directory entries in the CACHE structure to handle read-and-register (RAR) requests. Db2 monitors free directory entries and data element counts on every RAR request and automatically adjusts these values as needed. This adjustment is done dynamically or by online updates, regardless of whether the cf_gbp_sz parameter is configured as AUTOMATIC or not. For more information about CF structure configuration parameters, see the topic "Configuration parameters summary for the Db2 pureScale Feature".
When you use the SHOW DETAIL option to view the current values for structure configuration parameters, this information is displayed:
```
CF Resource Configuration:

  CF self-tuning memory    = ON
  Group buffer pool size (4KB)          
              (CF_GBP_SZ)  = AUTOMATIC(32768)  AUTOMATIC(32768)
  Global lock memory size (4KB)         
              (CF_LOCK_SZ) = AUTOMATIC(17000)  AUTOMATIC(17000)
  Shared communication area size (4KB)  
              (CF_SCA_SZ)  = AUTOMATIC(1500)   AUTOMATIC(1500)
```
See the GET DATABASE CONFIGURATION command for more detailed output.

The result shown for each structure parameter has two corresponding values. If the values in parentheses are different there is a pending update to the value of the structure parameter. The value enclosed in the first set of parentheses is the current value for the structure parameter. The value enclosed in the second set of parentheses is the pending value for the structure parameter.

When there is both a primary CF server and a secondary CF server, only the configuration information for the primary CF server is displayed. The same value applies to both CF servers.
To update the values of CF structure configuration parameters in the CLP, issue the UPDATE DATABASE CONFIGURATION (or UPDATE DB CFG) command. Updating structure parameters to any value other than the default setting (AUTOMATIC) results in theCF structure memory size being fixed.
For example, this command is issued to set the size of the Global Lock Manager memory to 20,000 pages:
```
UPDATE DATABASE CONFIGURATION FOR WSDB USING CF_LOCK_SZ 20000
```
Note: An update to decrease the amount of memory for structure parameters does not take immediate effect if there is not enough unused memory to accommodate the request. To see if an update is pending for structure parameters issue the GET DB CFG command from the CLP.
To reset the values of CF structure configuration parameters in the CLP, issue the RESET DATABASE CONFIGURATION (or RESET DB CFG) command. The CF structure configuration parameters are reset to their default value of AUTOMATIC.

To update the values of CF structure configuration parameters using application programming interfaces (APIs), call the db2CfgSet API. To view the values, issue the db2CfgGet API.

The getting and setting of CF structure configuration parameters is supported by entries for the token element in the db2Cfg data structures used when calling the db2CfgGet or db2CfgSet APIs.

Table 1. Supported db2Cfg tokens in getting and setting of CF structure configuration parameters
Token	Data type
SQLF_DBTN_CF_GBP_SZ	Uint32
SQLF_DBTN_CF_SCA_SZ	Uint32
SQLF_DBTN_CF_LOCK_SZ	Uint32
SQLF_DBTN_CF_DB_MEM_SZ	Uint32