[DOC] Add Akka.Analyzers AK1006 documentation

[Arkatufus]

---

uid: AK1006
title: Akka.Analyzers Rule AK1006 - "Should not call Persist() or PersistAsync() inside a loop"

AK1006 - Warning

Calling Persist() or PersistAsync() inside a loop is an anti-pattern and is non-performant. Consider collecting all events in a collection and then call PersistAll() or PersistAllAsync() after the loop instead.

Cause

Akka.NET persistence tries its best to batch consecutive calls to Persist() or PersistAsync() methods, but there is no guarantee that all of them will be batched properly.

For example, lets assume that for each command, you generate 10 Persist() operations. This can potentially create 10 asynchronous database connection to complete:

using Akka.Persistence;

public class MyActor: ReceivePersistentActor
{
    public override string PersistenceId { get; }
    public MyActor(string persistenceId)
    {
        PersistenceId = persistenceId;
        CommandAny(obj =>
        {
            for (var i=0; i<10; i++)
            {
                Persist(i, o => {});
            }
        });
    }
}

Resolution

If you know that a group of events need to be batched, it is a lot more performant to batch all Persist() operations into a single PersistAll() operation after the loop

using Akka.Persistence;

public class MyActor: ReceivePersistentActor
{
    public override string PersistenceId { get; }
    public MyActor(string persistenceId)
    {
        PersistenceId = persistenceId;
        CommandAny(obj =>
        {
            var events = new List<int>();
            for (var i=0; i<10; i++)
            {
                events.Add(i);
            }
            PersistAll(events, o => {});
        });
    }
}

The persist success callback will be called for each event that are successfully persisted, so you do not need to change your logic inside the callback.

[Aaronontheweb]

LGTM