While running a schedule you will notice an error Connection timed Out for a few virtual users.
Now, is this error related to Rational Performance Tester (RPT) or Application / Database?
RPT is a load generation performance testing tool and mimics most of the recorded behavior during playback of the scripts. So overall whatever the connection times, response times, think times and so on are captured during recording is being utilized during playback action.
Considering this fact, the reason for time out behaviors could be many, but mostly related to how the application is responding to the requests during playback as compared to recorded mode. On the other hand RPT does allow you to modify Time-Out behavior of a recorded test. To access this setting:
1) Open a recorded HTTP test in RPT
2) On the right hand side under the Test Elements Details heading, select the HTTP Options tab (as seen below)
3) There are two settings that effect the Time-out behavior, Timeout action and Timeout
Indicates what the test should do if the primary request for a page does not succeed within the Timeout interval. If log error and continue execution is selected, the test logs the error and proceeds to the next page. If Try to reload the page is selected, the test attempts to reload the page one more time; if that attempt fails, the test logs an error and proceeds to the next page.
Specifies the time threshold for initiating the action that is selected for Timeout action. The test will wait up to this amount of time for a response. If the response comes back before the timeout limit, the test will proceed to the next action immediately when the response is received
The Timeout action and Timeout value settings apply to every page in the test
That being said, there could be several application behaviors which can also impact the time-out properties of requests/response data. Sometimes the host application server locks out your IP address because the server notes that your IP address sends several virtual users
Error occurred during connection to server 'servername.oscar.local'. Explanation message: 'Connection timed out: no further information'. This secondary request will be skipped.
In its literal sense RPT tried to open a connection while trying to execute a request to the server for a secondary request (ie. not the primary but something like a .gif) and RPT was unable to open the connection to the server.
It's probably worth looking at all the previous requests and responses. Use the Protocol viewer where you can see the browser view or the actual response from the server. If there are no errors, then the symptoms indicate a problem with the application or server under test.
In addition to this, if the network connectivity and bandwidth between the host controller and its agents are not uniform, then this might cause communication errors. Below are few such articles which probably can help you with the sort of configurations to be optimized from RPT perspective.