Keeping persistent data in memory

Question

I am about to develop a Windows service in C#. This service needs to keep track of events in the system, and write some data to files from time to time. These ongoing events form a certain state, so I'll keep the state in memory and update it as events will arrive. I don't want to over-complicate things so I don't want the state to be persistent on disk, but I'm wondering if I could somehow make it persistent in memory, so that if the service crashes (and auto restarts by Windows) it could pick up from where it left and go on (possibly losing some events, not a big deal).

I was thinking along the line of creating a "shared" memory area, thus letting Windows manage it, and using it only in the service - but I'm not sure that object will persist after the service dies.

Any ideas?

EDIT: I'm not looking for an overkill solution. The data is somewhat important so I'd like to keep it waiting in memory until the service is restarted, but the data is not too important. It's more of a nice-to-have feature if I can persist the data easily, without working with files, external 3rd party processes and so on. My ideal solution would be a simple built-in feature (in .NET or in Windows) that will provide me with some in-memoory persistence, just to recover from a crash event.

Answer 1

How about using isolated storage and persisting the object into memory that way?

Answer 2

You could use Memcached, or Redis (which also persists it's data on disk, but handles it automatically).

http://code.google.com/p/redis/

You could also take a look at this question:

http://stackoverflow.com/questions/351635/memcached-with-windows-and-net

Answer 3

Even if, for instance, you keep the data on a shared-memory of some other networked pc, how would you "guarantee" that the networked pc wont hang/restart/halt/etc? In that case your service will lose the persisted data anyway.

I would suggest, and chances are you'd likely to end up, storing the data on the same disk.

Note that, because of the volatile nature of memory(RAM) you cannot reload data that was previously there, before the system restart; not unless you use some mechanism to store/reload on disk.

--EDIT--

In that case, how about using MSMQ? So you can push everything over the queue, and even if your service gets a restart, it would look for the items in the queue and continue onwards.

Answer 4

I don't see why it'd be harder to persist to disk.

using db4o you can persist the instances you are already working with.

Answer 5

You can use a Persitent Caching Block from the Microsoft Enterprise Library.

It is configurable and you can use many backing stores like database and isolated storage.

Answer 6

I know you said that you don't want to over-complicate things by persisting it to disk, but it's definitely going to much more complicate to persist stuff into shared memory or any of the solutions listed here. The reason why so many applications use databases or file storage is because it's the simplest solution.

I would recommend you keep all the state in a single object or object hierarchy, serialize this object to XML and write it to a file. It really doesn't get much simpler than that.