Modern browsers issue requests in parallel to download webpages faster. StresStimulus simulates concurrent requests by mimicking the browser’s behavior based on the following test factors:
It does not use the information about parallel connections collected during the recording because this information is not entirely relevant to the emulated test conditions. Emulated browser types can be different from the browser type used for recording. Also, the server load during the test run is typically higher than the one during the recording.
The following behavior is emulated for every page and every VU independently:
1. Issue an initial request and wait for the response. During this time, all dependent requests are blocked.
2. Receive the primary response and handle dependent requests, which can be issued in parallel or sequentially.
To avoid sending the request out of order and preserve application integrity, StresStimulus has to issue requests sequentially that have certain conditions such as receiving Set-Cookie response header, receiving redirect response (301 and 302), or having an extractor.
Info: By default, the Set-cookie response header is one of the qualifying factors to send requests sequentially. To suppress this factor and allow such requests to be sent in parallel, select Test Case, and in property grid set property, Set-cookie header enforces sequential requests to No (default is Yes). Requests still can be sent sequentially if other qualifying factors exist.
3. After the last dependent response was received, the current page is finished processing.
4. Optional think time delay is injected.
5. The VU is ready for processing the next page.
Info: Sent and received traffic cannot exceed emulated network type bandwidth limits. The traffic can be appropriately slowed down in order to achieve this.
You can change the default request concurrency by turning the page breakdown, as described in the next section.
The above concurrency was determined by a request's MIME type (Content-type). Starting in v5.2, request concurrency can also be determined by recorded times.
When using recorded time concurrency, a request's recorded time is used to determine whether it is a parallel or sequential request.
So two requests issued in parallel during recording will be issued in parallel during the load test and vice-versa.
To change the concurrency mode of a test case, select the test case node in the test case tree, and set the Concurrency determined by property.
To view a test case's recorded waterfall, in the test case tree click the View Options button and select the Waterfall option