Plugin proposal: Akka.Persistence.SqlServer

[Horusiath]

Add Journal and (optionally) SnapshotStore implementations using SqlServer database on the backend. Since SqlServer is considered an important part of a .NET dev culture, I think it should be placed in contrib lib with support from Akka.NET community.

• It also should provide some easy way to check and run necessary database schema update if required.
• I think that it should support SqlServer 2008 and above.

Minimal Journal configuration necessary to make plugin work with Akka.Persistence correctly:

akka.persistence.journal {
  plugin = "akka.persistence.journal.sql-server"
  sql-server {
      class = "Akka.Persistence.SqlServer.SqlServerJournal, Akka.Persistence.SqlServer"
      plugin-dispatcher = "akka.actor.default-dispatcher"

      # connection string to SqlServer database
      connection-string= "Server=myServerAddress;Database=myDataBase;User Id=myUsername;"
  }
}

In case if plugin will also implement SnapshotStore based on SqlServer, this is minimal configuration necessary to make plugin work with Akka.Persistence correctly:

akka.persistence.snapshot-store {
  plugin = "akka.persistence.snapshot-store.sql-server"
  sql-server {
    class = "Akka.Persistence.SqlServer.SqlServerSnapshotStore, Akka.Persistence.SqlServer"
    plugin-dispatcher = "akka.persistence.dispatchers.default-plugin-dispatcher"

     # connection string to SqlServer database
     connection-string= "Server=myServerAddress;Database=myDataBase;User Id=myUsername;"
  }
}

Integration tests can be done fairly simply using Akka.Persistence.TestKit library (see Akka.Persistence.TestKit.Tests for more details).

References:

• MemoryJournal implementation based on AsyncWriteProxy. For SQL databases more adviced is to use SyncWriteJournal instead (see canonical Akka's LevelDbJournal)

[Horusiath]

Completed by #842 and #901