Average Response Time

Response time refers to the amount of time Enterprise Server takes to return the results of a request to the user. The response time is affected by factors such as network bandwidth, number of users, number and type of requests submitted, and average think time.

In this section, response time refers to the mean, or average, response time. Each type of request has its own minimal response time. However, when evaluating system performance, base the analysis on the average response time of all requests.

The faster the response time, the more requests per minute are being processed. However, as the number of users on the system increases, the response time starts to increase as well, even though the number of requests per minute declines.

A system performance graph similar to this figure indicates that after a certain point, requests per minute are inversely proportional to response time. The sharper the decline in requests per minute, the steeper the increase in response time (represented by the dotted line arrow).

In the figure, the point of the peak load is the point at which requests per minute start to decline. Prior to this point, response time calculations are not necessarily accurate because they do not use peak numbers in the formula. After this point, (because of the inversely proportional relationship between requests per minute and response time), the administrator can more accurately calculate response time using maximum number of users and requests per minute.

Use the following formula to determine T_response, the response time (in seconds) at peak load:

T_response = n/r - T_think

where

• n is the number of concurrent users

• r is the number requests per second the server receives

• T_think is the average think time (in seconds)

  To obtain an accurate response time result, always include think time in the equation.

Example 2–1 Calculation of Response Time

If the following conditions exist:

• Maximum number of concurrent users, n, that the system can support at peak load is 5,000.

• Maximum number of requests, r, the system can process at peak load is 1,000 per second.

Average think time, T_think, is three seconds per request.

Thus, the calculation of response time is:

T_response = n/r - T_think = (5000/ 1000) - 3 sec. = 5 - 3 sec.

Therefore, the response time is two seconds.

After the system’s response time has been calculated, particularly at peak load, compare it to the acceptable response time for the application. Response time, along with throughput, is one of the main factors critical to the Application Server performance.