How to Calculate Concurrency (Vu) and TPS for Linux Systems

Concurrency and TPS

Term definitions

Concurrent users (Vu) refer to the users actively generating load on a system; in testing they are usually virtual users. Unlike registered or online users, concurrent users create pressure on the server.

TPS (Transaction Per Second) measures the number of transactions processed each second and is a key performance indicator.

How to obtain Vu and TPS

Obtaining concurrent users (Vu)

New system: without historical data, estimate through the business department.

Existing system: during a peak period, count the number of users in a given time window and take roughly 10% of that count as the concurrent user number. For example, if 10,000 users use the system within half an hour, use 1,000 as the concurrent user count.

Obtaining TPS

New system: estimate through the business department.

Existing system: during a peak period, record the total number of transactions over 5 or 10 minutes, then calculate TPS as transactions divided by the total seconds (5 × 60 or 10 × 60).

Resource consumption

1. Calculation of concurrent connections

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If a forum has 3,000 total users and 300 online users, each user makes 30 requests per hour, each request lasting 2 seconds, then:

Total requests = 300 * 30 = 9,000
Total time = 9,000 * 2 = 18,000 seconds
1 hour = 3,600 seconds
Average requests per second = 9,000 / 3,600 < 3
Because user activity is not uniform, the peak will be higher than 3 requests/second.

2. Memory consumption of concurrent links

Creating a linked list for each connection consumes memory; the exact amount depends on the implementation.

3. File descriptor consumption of concurrent connections

A simple web page may involve many elements (CSS, images, etc.), each requiring a file descriptor.