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Recycling application pools and session engines in Dimensions™

This is a complimentary tip available to SPSS Direct subscribers.

Question

I’ve noticed that my DimensionNet software (either mrInterview™ or mrTables™) seems to run more slowly than it used to. I also see runtime errors when I am working. What can I do to prevent these errors and make DimensionNet run more smoothly?

Answer

If you are a server administrator, you can prevent these errors by making sure to regularly recycle application pools and session engines. For example, the SPSSDimensionNetPool should be recycled on a daily basis, especially since this application pool runs the .NET applications used to create surveys and analyze data. You can automate recycling of the SPSSDimensionNetPool within Internet Information Services (IIS). In addition, you may also want to set up your DimensionNet server to reboot on a regular basis.

Periodically, users may report seeing runtime errors or “Object reference not set to an instance of an object” messages while using DimensionNet. These errors are within IIS and are logged in the Event Viewer on the server. To find the Event Viewer, go to Start|Control Panel|Administrative Tools|Event Viewer. You can also find IIS under Administrative Tools.

To recycle DimensionNet, expand the Application Pools folder in IIS and right-click on the SPSSDimensionNetPool. There is an option to recycle the pool, but you want to automate the recycling process from the Application Pool Properties dialog box, as shown below:


Select “Recycle worker process at the following times.” Choose a time when there are the least amount of DimensionNet users logged in; once DimensionNet begins recycling, all users will need to log in again using a new browser session. In the example above, you’ve set the application pool to automatically recycle at 2:00 a.m. each morning. This will stop the runtime errors, clear out old memory, and boost the overall performance of DimensionNet.

The SPSSmrInterviewPool runs the session engines for live interviews; in other words, it collects the data once your survey is created. This pool should also be recycled regularly, but it doesn’t need daily recycling like the SPSSDimensionNetPool.

When you recycle an application pool that runs a session engine, live interviews won’t be interrupted because the entire recycling process usually takes less than one second. If the engine is actually in the process of recycling when a respondent clicks the “Next” button on a survey, the Web tier may recognize that the engine is unavailable for a split second and roll the interview over to another engine if there is one available. This action will not be noticed by the respondent. Due to the quick recycle time, however, it is more likely that the respondent’s session will continue running on the exact same engine.

To learn more about how you can recycle application pools and session engines, please refer to Resolution 67906 on our Technical Support site or watch this video demonstration.