This parameter controls the total memory limit for the cluster caching facility,
also designated as the CF,
for this database.
- Configuration type
- Database
- 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.
Restrictions
- 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.
DB2 10.5 for Linux, UNIX, and Windows