World’s Smallest No SQL database
time to read 18 min | 3457 words

I used the following in a lecture called “Why you should never write your own database”. It has never been run, tested, or anything, but it serves as a good way to discuss the challenges involved in building real world  databases.

Here is the server side code:

   1: public class NoSqlDbController : ApiController
   2: {
   3:     static readonly ConcurrentDictionary<string, byte[]> data = 
   4:         new ConcurrentDictionary<string, byte[]>(StringComparer.InvariantCultureIgnoreCase); 
   5:  
   6:     public HttpResponseMessage Get(string key)
   7:     {
   8:         byte[] value;
   9:         if(data.TryGetValue(key, out value) == false)
  10:             return new HttpResponseMessage(HttpStatusCode.NotFound);
  11:  
  12:         return new HttpResponseMessage
  13:             {
  14:                 Content = new ByteArrayContent(value)
  15:             };
  16:     }
  17:  
  18:     public void Put(string key, [FromBody]byte[] value)
  19:     {
  20:         data.AddOrUpdate(key, value, (_, __) => value);
  21:     }
  22:  
  23:     public void Delete(string key)
  24:     {
  25:         byte[] value;
  26:         data.TryRemove(key, out value);
  27:     }
  28: }

And the client side code:

   1: public class NoSqlDbClient
   2: {
   3:     private readonly HttpClient[] clients;
   4:  
   5:     public NoSqlDbClient(string[] urls)
   6:     {
   7:         clients = new HttpClient[urls.Length];
   8:         for (var i = 0; i < urls.Length; i++)
   9:         {
  10:             clients[i] = new HttpClient { BaseAddress = new Uri(urls[i]) };
  11:         }
  12:     }
  13:  
  14:     public Task PutAsync(string key, byte[] data)
  15:     {
  16:         var client = clients[key.GetHashCode()%clients.Length];
  17:         return client.PutAsync("?key=" + key, new ByteArrayContent(data));
  18:     }
  19:  
  20:     public Task DeleteAsync(string key, byte[] data)
  21:     {
  22:         var client = clients[key.GetHashCode() % clients.Length];
  23:         return client.DeleteAsync("?key=" + key);
  24:     }
  25:  
  26:     public async Task<byte[]> GetAsync(string key)
  27:     {
  28:         var client = clients[key.GetHashCode() % clients.Length];
  29:         var r = await client.GetAsync("?key=" + key);
  30:         return await r.Content.ReadAsByteArrayAsync();
  31:  
  32:     }
  33: }

And yes, that is a fully functional, scale out capable, sharding enabled No SQL Key/Value store in less than 60 lines of code.

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