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Thursday, July 26, 2012

How can data caching have a negative effect on load testing results?

It is quite a heavy task to retrieve data from a certain repository if we see it through a performance point of view. It becomes much more difficult when the data repository lies too far from the application server.Retrieving data becomes difficult also when a specific type of data is accessed over and over again. 
Caching is a technique that has been developed as a measure for reducing the work load and the time consumed for retrieval of the data. 
In this article, we have discussed about the negative effects that simple data caching can have up on the load testing. 

Rules for Caching Concepts

Some rules have been laid down for the caching concepts which have been mentioned below:

1. The data caching is useful if used only for a short period of time and does not works when used through the life cycle of the software system or application.
2. Only that data which is not likely to be changed quite often should be cached.
3. There are certain data repositories that have the capability of supporting the notification events in case if the modification of the data takes place outside the application.

If these above stated rules are not followed properly, the data caching is sure to have a negative impact up on the load testing. 

How data caching produces a negative impact on load testing?

- This is so because the data caching has got some pitfalls which come in our observation only when there are potential situations when there is a possibility of data expiry and software system or application using inconsistent data. 
- Using caching technique is quite simple but any fault can cause an impact on load testing.
- Load testing involves putting demands on the software system or application in order measure its response. 
- The outcomes of the load testing helps in measuring the difference between the responses of the software system or application under normal as well as peak load conditions. 
- Load testing is usually used as a means to have a measure of the maximum capacity at which the software system or application can operate easily. 
- Data caching initiates quick response from the software system or application for obtaining cookies etc. 
- Though data caching responds faster than the usual memory transactions, it has a negative impact on the result of the load testing i.e. you will not get the original results rather the results you will get will be the altered ones. 

What you will get to see is the wrong performance of the software system or application. 

What is the purpose of caching?

- Caching is done with the purpose of storing certain data so that that data in the subsequent stages can be served faster. 
- Data caching affects load testing results in a way until and unless the cache is cleared up by the testing tool after every iteration of the virtual user, an artificial faster page load time is started to be given by the caching mechanism. 
- Such artificial timings will alter your load testing results and invalidate them. - In caching, all the recently visited web pages are stored. 
- When we carry out load testing, our aim is always to check the software system or application under load. 
- So if by chance the caching option is left enabled, what will happen is that the software system or application will try retrieving the data from the data that is locally saved giving false measure of the performance determination. 
- So, the caching option should always be disabled while you carry out load testing. 

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