# Memcached Alternative for C#/.NET

I'm currently developing a software package that has to retrieve large amounts of data from a server. This data is needed frequently throughout the application and doesn't change much in a given day. This sounds like a perfect use case for Memcached, or so I thought. After I installed the .NET Memcached adapters, I was in for a big surprise. Memcached has a 1 MB value limit!

So, like any good developer I wrote my own tool. First, two caveats, as I don't want to waste your time. 1) I wouldn't use this in a production environment. It just hasn't had enough rigorous testing. YMMV. 2) It only works on the same machine that the app resides on. Yes, I realize that this is a huge caveat.

### Why?

So, what was my use case? I follow a loose Agile process of delivering every week. Well, as the production went on, more data would accumulate on the server. I needed a quick way to cache this data locally without rewriting my algorithms in the short term. Thus, MemMapCache was born.

### How Does It Work?

It uses memory mapped files that are new in .NET 4.0 (they just wrap the Win32 API). The client creates a key and persists the object value to a memory mapped file using the said key. It then passes the key onto the server so that the server can keep the reference. This prevents the .NET garbage collector from cleaning up the memory mapped file so that upon a new instance of the client, it can still retrieve the data.

### How do you use it?

Go clone this project: https://github.com/jprichardson/MemMapCache and then add MemMapCacheLib to your project. You'll need to make sure that MemMapCache.exe is running on your system.

var cache = new MemMapCache();
cache.Connect();

var col = new Dictionary<string, int>();

cache.Set("myKey", col);

var newCol = cache.Get<Dictionary<string,int>>("myKey");

//you can pass in an expiration time as DateTime or TimeSpan

//hypothetical large data repository that returns IEnumerable<double>
var dataRepo = new DataRepository();

//you can even call one function to retrieve the last value for a key, if it doesn't exist set a new value
IEnumerable<double> largeDataSet = cache.TryGetThenSet("dataSetKey", () => dataRepo.LoadLargeDataSet());

//you can also specify for the cache to always miss, in case you have it deeply embedded in your code and you want to run unit tests that aren't cache dependent
cache.CacheHitAlwaysMiss = true