Concurrent pool size and browser emulation in JMeter

Since JMeter 2.5 there is a new option called “Concurrent pool size”.

Whats so important about this feature?

To answer this lets first understand how browser works and what an end user response time means.

Once the browser fetches a page, it subsequently fetches all the page’s resources like images, css, javascript etc. During the fetch time, the browser can open series of parallel connections to the remote server(s) hosting the embeded resources. Number of parallel connections vary from browser to browser. Chrome opens 6 parallel connections where as IE10 opens 8 connections.

For more information on parallel http connections in a browser go to following link.

http://stackoverflow.com/questions/985431/max-parallel-http-connections-in-a-browser

Fetching the content of a page using parallel connections dramatically reduces the render time.

Now, in JMeter,

Concurrent pool size is the number of parallel connection that JMeter will open while fetching the resources. if we set this as 4 connections, then it means 4 connections per threads (users). So if the load generator can support 200 user threads, using connection pool option you should reduce the user threads per machine accordingly.