The following describes typical approaches to performance management and describes a general procedure for troubleshooting performance problems. References are made to various parameters. For the descriptions and values of these parameters, see UNRESOLVED XREF-0.
We'll first look at paging activity, because the paging in and paging out is costly in terms of both disk and CPU overhead. Run the sar -pgrwud report. With this information, you can determine whether more memory is needed.
vflt/s value shown by sar -p
is greater than 50, then look at sar -g.
High values for
pfree/s imply that the page-stealing daemon
is working overtime to find free pages because of a memory shortage.
A high attach rate and a high
indicate a memory shortage, also.
Other indicators of a memory shortage are the
value of sar -r and the
swpot/s value of sar -w.
A value of
swpot/s that is consistently greater than
``0'' is also an indicator of a memory shortage.
If memory shortages occur frequently, increase memory in one of two ways: Uninstalling optional kernel utilities that are not needed by your applications frees the memory used by the utilities so it can be used by user applications. If this is not possible, you probably need to add extra memory.
If the value of
%wio (from the sar -u report)
is greater than 10 percent, or if the
for a disk drive (obtained by sar -d ) is greater than 50 percent,
then the system has a disk slowdown.
Some ways to alleviate a disk slowdown are:
%wcache< 65) and high
%wcachevalues are low temporarily when you start up an application or bring in new data. However, if these values are always low, your system may be a heavier than average user of filesystem data.
Run sar -y and review the report describing activity on
If the number of modem interrupts per second,
mdmin/s, is much greater than 0,
your system may have faulty communications hardware.
Run the sar -vt report to check for potential table overflows. This report lets you know if overflows have occurred in the process or inode tables. Overflows can occur if a memory shortage occurs or if the maximum table size is reached. If memory is the problem, the table limits have not been reached. If the table limits are reached, the system tunable should be increased. To avoid overflows in these tables, increase the Process Limit Parameter NPROC and the Filesystem Parameters S5NINODE, SFSNINODE, VXFSNINODE depending on the filesystems you are using. Use the System Tuner or the idtune command. See ``Performing basic system monitoring and tuning'' for information about the System Tuner, or idtune(ADM).
You can obtain a system activity report for I/O resources by executing
You can obtain a system activity report for memory resource usage by executing
Identify jobs that can be shifted to off-hours.