multi vs single instance business application

(This topic is so general there has to be an existing thread somewhere, but darned if I can find it. I did find several debates on the best way to enforce single instance apps.)

I've got an inhouse business app coded in .Net 3.5. I use ClickOnce to publish and the back end is SQL Server 2008. The app has always been set to single instance just to be on the safe side, but my users are starting to express interest in having multiple instances, mainly so they can view and compare different sets of data simultaneously.

I'm trying to think of possible dangers of a multi instance app, but so far nothing critical comes to mind. Obviously the instances will be 开发者_高级运维sharing some resources. Can anyone provide me with specific problems of having a multi instance app?

One thing I thought of was that ClickOnce checks for updates upon app startup. Suppose a user opens an instance, then a new version is published, then the user opens a second instance. Does ClickOnce handle the update elegantly? I suppose it would need to close all running instances, then update the version.

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If all your app does is communicate using ADO.NET to a SQL Server, there's not likely to be too many issues as multiple processes on one machine is going to look identical to multiple processes on separate machines as far as SQL Server is concerned. However, if your app uses local files or other shared resources you will have to co-ordinate sensibly between the running instances of your app.