Question: We are developing an RetailPOS .net (windows) application. 

One of the customer asks 'What will happen to current data being processed in the application when a power went off suddenly?', 'Will the application able to recover the unsaved data?'

I am wondering, how this feature can be included in the .net application? 

Can some help me, what needs to be done for this?

Answer: 
You can append the current information being received to the file system. It will be a performance hit, but will allow you to get back to the last item being captured. 

When the application starts detect if there is a pending file, and provide the option to recover. Load the data saved in the file appropriately.

Once you have all the information, when you are doing the process that happens when paying, make sure to record any significant changes in the process atomically. If you are hitting external systems, record when you are initiating the operation and when it comes back right away. In the above there is always a window of time when it can fail, but you want to keep it as short as possible and to have enough information for the recovery processes. Worst case if the system can't automatically recover, you want it to have enough information to determine where in the process it stopped.
You might want to consider having your application use [SQLite](http://www.sqlite.org).

They have some great info on their [when to use page](http://www.sqlite.org/whentouse.html).

Some points that stand out are:

> 
> * Updates happen atomically as application content is revised
> * Content is updated continuously and atomically so that there is no work lost in the event of a power failure or crash.
> 
> 
> 

I'm looking for a similar option for an application I am going to implement which will be used in a third world country where the power goes out frequently throughout the day....so far SQLite seems to stand out as a good possible choice.

But at the end of the day, your choice will depend on your individual circumstances and requirements.