cf_db_mem_sz - Database memory configuration parameter

This parameter controls the total memory limit for the cluster caching facility, also designated as the CF, for this database.

Configuration type
Applies to
Applies to a Db2® pureScale® instance only.
  • Database server with local and remote clients
Parameter type
Configurable online
Default [range]
AUTOMATIC [32768 - 4 294 967 295]
Unit of measure
Pages (4 KB)

The sum of the cluster caching facility structure memory limits for the cf_gbp_sz, cf_lock_sz, and cf_sca_sz parameters must be less than the CF structure memory limit for the cf_db_mem_sz parameter. Automatic memory tuning between CF resources such as the group buffer pool (GBP), shared communication area (SCA), and lock structures from within the same database is bound by the cf_db_mem_sz parameter.

Usage notes

  • Set the value of the numdb configuration parameter higher than or equal to the total number of databases on the instance. Additionally, set the value of DB2_DATABASE_CF_MEMORY to a value that allows for every database on this instance, whether normally inactive or active, to be active at the same time.
  • When manually setting the value of cf_db_mem_sz, the value must be less than the total CF server memory. The total CF server memory is controlled by the cf_mem_sz database manager configuration parameter.
  • If the previous value of the cf_db_mem_sz parameter was set to AUTOMATIC, then the current value can be determined by using the SHOW DETAIL option of the GET DATABASE CONFIGURATION command.
  • Use of the cf_db_mem_sz configuration parameter must be coordinated with the DB2_DATABASE_CF_MEMORY registry variable and the numdb configuration parameter.


  • There is an additional 3840 4k pages taken from the cf_mem_sz parameter to be used internally by the CF. Additionally, there is an additional 256 4k pages reserved from cf_mem_sz for every active database in the instance. These additional pages only needs to be taken into consideration when setting cf_mem_sz manually.
  • If altering the fixed value for this parameter to a new value that is lower than the current value, the new value must be greater than the sum of the memory sizes for the cf_gbp_sz, cf_lock_sz, and cf_sca_sz structure parameters or the operation will fail. To avoid this problem, lower the individual structure memory sizes before attempting to lower this parameter.
  • If altering the fixed value for this parameter to a new value that is higher than the current value, there is an upper limit imposed, in addition to the total CF server memory defined by the cf_mem_sz parameter. Typically, this upper limit is defined by a memory buffer of between 3600 and 5000 pages that is required between the cf_db_mem_sz and cf_mem_sz parameter values. The value of the cf_db_mem_sz parameter should not exceed the difference of cf_mem_sz and this memory buffer.