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Use a coordinated transactor

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Chapter 10 - Designing Performance Testing Suites

Use a coordinated transactor when you are emulating the total transaction rate
applied to a server, rather than the rate of specific times a virtual tester runs a task.
For example, to emulate the number of hits per minute that a Web server can
handle, use a coordinated transactor.

An Independent transactor lets each virtual tester operate independently. It does not
coordinate the virtual testers under it with a built-in synchronization point. For
example, if you run a suite with 10 virtual testers and then run the same suite with
20 virtual testers, the total transaction rate doubles--because the number of virtual
testers has doubled.

Use an independent transactor if different user groups run the transaction at
different times or if you are emulating individual behavior rather than a group
behavior. For example, to emulate an Accounting user group that performs 10
calculations per hour but not all at the same time, use an independent transactor.

Once you have defined the transactor type, you must then specify the transactor rate:

Total rate

For a coordinated transactor, you generally select Total rate. This is

because whether 100 virtual testers or 50 virtual testers are participating, it has no
effect on the rate that TestManager submits transactions.

User rate

For an independent transactor, you must select User rate.

However, select User rate for a coordinated transactor if you expect to change the
rate frequently and want the convenience of not having to edit the suite. For
example, suppose you have inserted a coordinated transactor and you want to
compare a workload at 100 hits per minute, 200 hits per minute, and 300 hits per
minute--increasing the workload with each suite run. If you select User rate, you
do not have to change the rate in the transactor's properties. Instead, when you
run the suite at 100 virtual testers, 200 virtual testers, and 300 virtual testers, the
rate scales proportionally.

Next, specify the distribution of the transactor:

A Constant distribution means that each transaction occurs exactly at the rate you
specify. For example, if the transaction rate is 4 per minute, a transaction starts at
15 seconds, 30 seconds, 45 seconds, and 60 seconds--exactly four per minute,
evenly spaced, with a 15-second interval. Although this distribution is simple
conceptually, it does not accurately emulate the randomness of user behavior.

A Constant distribution is useful for emulating an automated process. For
example, you might want to emulate an environment where virtual testers are
uploading data to a database every half hour.