MACROMEDIA COLDFUSION MX-CLUSTERCATS, Руководство пользователя

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Configuring load-balancing metrics 139
Load types
The page ClusterCATS probes for load-balancing options,
getsimpleload.jsp
for
JRun and
getsimpleload.cfm
for ColdFusion, is located in
<CC_install_directory>/btauxdir
. The probe agent responds to output generated by
this page and uses it to calculate the overall load, based on the weighting of the metrics
set in the
LOADTYPE
variable:
•
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
— calculates load based on the round-trip time for the request.
This metric leaves all load calculation to the probe agent.
•
PREV_REQ_TIME
(ColdFusion only) — calculates load based on the time to process
the last request to the server.
For servers that process database-intensive requests,
ROUND_TRIP_TIME
is not a good
indication of load, because JRun/ColdFusion processes the threads that calculate
ROUND_TRIP_TIME
differently than queued database connection requests. With this in
mind, if your web server uses many concurrent connections to a database, either use
AVG_REQ_TIME
as your load type, or include a database call in
getsimpleload.jsp/
getsimpleload.cfm
to make this load type’s results more indicative of actual conditions.
Output variables
During processing,
getsimpleload.jsp/getsimpleload.cfm
generates three
significant output variables that are sent in response to the probe agent's HTTP query:
•
CCLOADVALUE — the load calculated by
getsimpleload.jsp/
getsimpleload.cfm
using one of the available load metrics. The load value
identifies how busy the server is as a percentage of its total capacity.
•
CCLOADMAX — the maximum acceptable time (in milliseconds) for a request to
complete; marks the "busy threshold" for this server. The load percentage calculation
is based on it, given the results of the
AVG_REQ_TIME
metric. The default maximum is
8 seconds (8000 ms), but this value is arbitrary and you should customize it to fit the
capacity and expectations of your particular website.
If you increase the value of
CCLOADMAX
, the server can take longer (on average) for
each request before the server is declared busy. If you decrease
CCLOADMAX
, the server's
average request is shorter when the server is declared busy.
•
CCRTTPercent — the percentage of the calculated average
ROUND_TRIP_TIME
that
the probe agent applies to the load metric supplied by
CCLOADVALUE
.
CCRTTPercent
is the second variable that you might change to customize your
server’s load metrics. It lets you “tune” the amount of external influence on server
performance to calculate into the server's overall load value.
For example, increase
CCRTTPercent
to apply a greater weighting to the
ROUND_TRIP_TIME
metric in the overall load calculations. The default value of
CCRTTPercent
is 0 (disabled). If you change the load type to
ROUND_TRIP_TIME
, the
default value of
CCRTTPercent
is 100, which gives
ROUND_TRIP_TIME
the maximum
weighting.