This step applies to coupling facility log streams only. DASD-only
log streams can omit this step.
Do the following:
- Determine the attributes needed to define coupling
facility structures used by system logger applications.
See Planning a coupling facility policy to plan updates to the CFRM policy for system logger
applications. When planning preference and exclusion list specifications,
keep in mind that system logger requires a minimum CFLEVEL. See Understand the requirements for system logger for specific requirements.
The ALLOWAUTOALT(NO|YES) parameter
on a structure definition in the CFRM policy may affect structures
used by system logger. Since logger connects to a coupling facility
list structure using ALLOWALTER(YES), if you specify ALLOWAUTOALT(YES)
on the list structure definition in the CFRM policy, Cross System
Extended Services (XES) may automatically alter the size and ratio
attributes of the structure as needed. If your coupling facility is
size constrained and you must free up some space, you should probably
consider other structures for automatic altering first. If you must
allow automatic altering of the logger list structure, IBM® suggests that you also specify
a minimum size for the logger list structure with the MINSIZE parameter,
to ensure that logger always has enough space to do its work.
The
effects associated with the automatic altering of a list structure
in use by logger can vary depending on the number of log streams connected
to the structure. Consider the following cases:
- Case 1: A single log stream is connected to the list structure.
Depending
on how your applications use the log stream, you can find that there
are long periods when the log stream is relatively empty, followed
by peaks of system activity when the log stream quickly approaches
its high threshold. If you have specified ALLOWAUTOALT(YES), XES may
decide to alter your structure size to a smaller size during a low
usage period. When a period of peak usage occurs, write requests to
this now smaller structure area for this log stream could result in
a structure full condition, meaning there is no more space available
in the structure for this log stream. You can avoid this by specifying
a sufficient MINSIZE for the list structure.
- Case 2: Multiple log streams are connected to the list structure.
In
this case, since there is more than one log stream mapped and connected
to the list structure, the overall use of the structure space may
not be indicative of how any one log stream is performing. For example,
assume one log stream in the structure is using most, but not all,
of its share of the list structure space, and a second log stream
in the same structure is using very little of its share of the list
structure space. If automatic monitoring and altering processing is
allowed it could reduce this structure's size because the overall
use of the list structure space is relatively low. This size reduction
could cause the log stream that was using a large portion of its available
space to now exceed its available space. Subsequent write requests
to this log stream would result in a structure full condition, meaning
there is no more space available in the structure for this log stream.
The “structure full monitoring”
function become available in OS/390® V2R9.
See Monitoring structure utilization.
To allow installations to control
the monitor level, a new parameter was added to the CFRM policy, FULLTHRESHOLD.
Use this parameter to set the utilization value to which XCF is to
monitor the structure, with the default value being 80%. Setting FULLTHRESHOLD(0)
disables the monitor for that structure. For system logger structures,
it is advisable to set FULLTHRESHOLD to some value higher than the
HIGHOFFLOAD log stream parameter. XCF, when monitoring the number
of ENTRIES and ELEMENTS, will issue a warning message (IXC585E) when
the value reaches the FULLTHRESHOLD value. System logger will not
perform offload processing until the ELEMENTS value is at the HIGHOFFLOAD
value. Note that the HIGHOFFLOAD parameter is on a per log stream
basis, while the FULLTHRESHOLD parameter is on a structure basis.
For this reason, try to group log streams together that have similar
HIGHOFFLOAD values.
- Add information to the CFRM function
couple data set about the desired attributes of the coupling
facility list structures for system logger applications. To use
the IXCMIAPU utility to update the CFRM policy for logger information,
see CFRM parameters for administrative data utility.
Note that each coupling facility structure
that you define in the LOGR policy must match those defined in the
CFRM policy. See CFRM parameters for administrative data utility for using IXCMIAPU to update
the CFRM policy.
- Ensure adequate dump space is specified in a
CF definition in the CFRM policy that could contain list structures
that will be used by the system logger.
See Determining the amount of coupling facility dump space for
setting the DUMPSPACE parameter.
- Activate the CFRM function
couple data set using the SETXCF command.
See z/OS MVS System Commands for
the SETXCF command.