Differences between the number of concurrent connections of an SLB instance and the virtual users of PTS, Differences between the number of concurrent connections of an SLB instance and the virtual users of PTS - Performance Testing

This topic describes the differences between the number of concurrent connections of a Server Load Balancer (SLB) instance and the virtual users of Performance Testing Service (PTS).

Terms

Number of concurrent connections of an SLB instance: the total number of Transmission Control Protocol (TCP) connections that are established.
Virtual users of PTS: the users who operate the business at the same time in the real system. The concept is common in performance testing tools. The concept is typically based on the customer-side evaluation. However, it is not convenient for the server-side capacity evaluation and the high availability evaluation.

Description

For ease of understanding, assume that the stress testing scenario in PTS is session A, which contains stress testing API 1.

An SLB instance may still have the normal business traffic. Therefore, the number of virtual users of API 1 in PTS is basically close to or less than the number of concurrent connections of the SLB instance during the stress testing. However, because the monitoring data of the stress side in PTS is collected within seconds, while the monitoring data of the SLB instance is collected within 15 seconds or minutes, the number of virtual users of API 1 in PTS and the number of concurrent connections of the SLB instance have a specific error. In addition, note that if the tested server supports Keep-Alive and you set a think time that is longer than Keep-Alive for the session, the number of concurrent connections of the SLB instance, especially the number of active connections, may reduce.

Note

The number of concurrent connections of the SLB instance is the sum of the number of active connections and the number of inactive connections.

Number of active connections: the total number of TCP connections in the ESTABLISHED state. If persistent connections are used, a connection can transfer multiple files at the same time.
Number of inactive connections: the total number of TCP connections in all states except the ESTABLISHED state. You can run the netstat -an command to view the connections for both Windows and Linux instances.