Does JMeter pool HTTP connections?

Question

I know when using the built-in Java HTTP client in a JMeter HTTP Request sampler connections may or may not be pooled, depending on the JVM implementation and c

Answer 1

JMeter does some pooling of HTTP connections when using HttpClient3.1 or HttpClient4.

In both cases, connections are pooled per-thread. Connections are NOT shared across threads.

When using HttpClient3.1, JMeter uses an instance of SimpleHttpConnectionManager on each thread.

When using HttpClient4, JMeter uses an instance of a subclass of PoolingClientConnectionManager on each thread, and it uses PoolingClientConnectonManager's default settings (2 connections per route, and 20 maximum connections).

JMeter does not provide a mechanism for controlling the parameters of the connection pools.

I had to go to JMeter's source code to find this answer. See the following links for reference (the 2.13 tagged code):

• HTTPHC3Impl.java
• HTTPHC4Impl.java
• MeasuringConnectionManager.java

Note: this answer is accurate for JMeter 2.13. The answer may be different for other versions of JMeter.

Answer 2

Update for JMeter 3: in your HTTPSampler configuration you can use the entries

 <boolProp name="HTTPSampler.concurrentDwn">true</boolProp>
 <stringProp name="HTTPSampler.concurrentPool">10</stringProp>

to specify connection pool size according to this Code-Snippet (from http://svn.apache.org/viewvc/jmeter/tags/v3_0/src/protocol/http/org/apache/jmeter/protocol/http/sampler/HTTPHC4Impl.java?view=markup line 785ff)

      if(this.testElement.isConcurrentDwn()) {
            try {
                int maxConcurrentDownloads = Integer.parseInt(this.testElement.getConcurrentPool());
                    connManager.setDefaultMaxPerRoute(Math.max(maxConcurrentDownloads, connManager.getDefaultMaxPerRoute()));                
                } catch (NumberFormatException nfe) {
                   // no need to log -> will be done by the sampler
                }
            }
       }

The configuration via JMeter UI is a bit quirky:

switch the HTTP Sampler Configuration View to "Advanced", tick "Retrieve all embedded resources", then "Parallel Downloads" and enter a number. You may untick "Retrieve all embedded resources" after that if you don't want JMeter to parse your responses for images