N-Tier Application Performance Issue

Hypothesis

Users are complaining about slow response time from an in-house web application. This application being an N-tier architecture, its performance as seen by a client is tied to several parameters:

• DNS latency to resolve web server name from the client host (see** DNS Response Time**)
• Connection time to server
• Data Transfer Time between these hosts
• DNS latency to resolve other server names accessed from the web server (database servers for instance, see DNS Response Time)
• Connection and data transfer times between these hosts
• Server response time of these servers

Identifying the culprit

First, we need to find out if the experienced slowdown is due to the web front-end itself. To this end, check every component of the EURT:

• If SRT is fast but RTT and/or DTT (see also Connection Time), then we are facing a network slowdown. Refer to previous sections of this guide to further track down the problem.
• If SRT is preponderant compared to DTT and RTT, then the application itself is to blame. Proceed to find out what is affecting performance.
• Then check the EURT between web server and each other involved servers (databases, etc.)

If some of these EURTs appear to be degraded then check recursively these other hosts. If not, then check the web server’s load average.