User Guide

342 Chapter 15 Optimizing ClusterCATS
Load types
The probed JSP page is located at <CC_install_directory>/btauxdir/
getsimpleload.jsp
. The probe agent responds to output generated by this page and
uses it to calculate the overall load based on the weighting of the two available
metrics set in the
LOADTYPE variable:
•
AVG_REQ_TIME
AVG_REQ_TIME
calculates load based on the average service request time. The
load is derived by dividing the request time by the maximum acceptable request
time. This is the default metric.
•
ROUND_TRIP_TIME
ROUND_TRIP_TIME
calculates load based on the round trip time for the request.
This metric leaves all load calculation in the hands of the probe agent.
For servers that process database-intensive requests, ROUND_TRIP_TIME is not a good
indication of load because ColdFusion processes the threads that calculate
ROUND_TRIP_TIME differently than queued database connection requests. With this
in mind, if you have a Web server that uses many concurrent connections to a
database, either use AVG_REQ_TIME rather than ROUND_TRIP_TIME as your load type,
or include a database call in
getsimpleload.jsp to make this load type’s results
more indicative of actual conditions.
Output variables
During processing, getsimpleload.jsp generates three significant output variables
that are sent in response to the probe agent's HTTP query. This section describes
these variables.
• CCLOADVALUE
CCLOADVALUE is the load calculated by getsimpleload.jsp using one of the
available load metrics. The load value identifies how busy the server is as a
percentage of its total capacity.
• CCLOADMAX
CCLOADMAX is the maximum acceptable time (in milliseconds) for a request to
complete and marks the "busy threshold" for this server. In other words, this is
the basis upon which a load percentage is calculated given the results of the
AVG_REQ_TIME metric. The default maximum is 8 seconds (8000 ms), but this
value is arbitrary and should be customized to fit the capacity and expectations
of a particular Web site.
CCLOADMAX is one of two variables that you would typically change in
getsimpleload.jsp to customize your server’s load metrics. If you increase the
value of
CCLOADMAX, then the server can take longer for each request (on average)
before the server is declared busy. If you decrease
CCLOADMAX, then the server's
average request must be shorter before the server is declared busy.