Databases Reference
In-Depth Information
mine if any one application is using more than its fair share of CPU cycles. If
so, look more closely at how that application is designed and coded, as
described in “The Database Application,” page 269.
•
How many processes or threads are waiting to be serviced in the CPU's
run queue?
A single queue is used for CPU requests, even on computers with
multiple processors. If all processors are busy, threads must wait until CPU
cycles are free to perform work. Processes waiting in the queue for sustained
periods indicate a CPU bottleneck.
•
What is the rate that the operating system switches processes or threads to
perform work for other waiting threads?
A
context switch
is the process of
storing and restoring the state (context) of a CPU so that multiple processes
can share a single CPU resource. Every time the CPU stops running one
process and starts running another, a context switch occurs. For example, if
your application is waiting for a row lock to release so that it can update data,
the operating system may switch the context so that the CPU can perform
work on behalf of another application while your application is waiting for
the lock to release. Context switching requires significant processor time, so
excessive context switches and high CPU use tend to go hand in hand.
Network Adapter
Computers that are connected to a network have at least one network adapter
that is used to send and receive network packets across the network. See
“Network,” page 86, for more information.
This section provides several troubleshooting case studies to help you think
through some varied performance issues and how to resolve them. All the infor-
mation that you need to solve these issues has been presented in this topic.
The database application in this case study supports the FBI. The application is
GUI based and displays one record at a time. The application allows FBI agents
from around the country to retrieve information about at-large criminals by
state. Each record contains first name, last name, crimes, previous convictions,
last known address, and a photo of the person. Each query can return as many as
