Up to this point, we
have been looking at SAS application and server performance from an
internal point of view. Now we turn to an external point of view.
By performance externals, we mean several things. First, at what rate
is a server consuming resources such as CPU, memory, and DASD I/O?
Second, with what other workloads is a server competing for these
resources? And third, what policy is being used to manage a server's
access to resources with respect to other work in the system?
There are several monitors
available for MVS and VM to help you analyze a server's resource utilization
and contention with other workloads. On MVS, most sites license the
IBM RMF product. RMF Monitor II and Monitor III support interactive
analysis of
SAS/SHARE performance.
Also available on MVS are Candle Corporation's Omegamon and Landmark
System's TMON for MVS. Prominent products on VM include Omegamon from
Candle Corporation and XAMAP and XAMON from Velocity Software.
These monitors can help
you answer the following questions:
-
Are my servers getting appropriate
access to resources?
-
Is another workload causing a severe
contention problem for one of my servers? For example, is my server
fighting with another application over access to the same disk drive?
-
What resource bottlenecks are most
critical to my applications? Where should I direct my tuning efforts?
Often, solutions to
resource utilization problems result in making trade-offs among resources.
For example, you might be able to reduce I/O by allocating additional
buffers. But the additional buffer allocation will take more memory.
Use of one of these monitors can help you evaluate the effectiveness
of the trade-off.
It is beyond the scope
of this paper to tell you exactly how to use specific operating environment
performance monitors. We are making the non-trivial assumption that
you or someone else on your staff have that knowledge. Basically,
every system has three principal resources: CPU, I/O, and memory.
We will look at examples of managing each of these for servers: