MACROMEDIA COLDFUSION MX-CLUSTERCATS Manuel d'utilisateur télécharger pdf (Page 149)

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.

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MACROMEDIA COLDFUSION MX-CLUSTERCATS Manuel d'utilisateur Page 149

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