AsyncParallelForEach.cs

using (var session = documentStore.OpenSession())
{
    session.Advanced.MaxNumberOfRequestsPerSession = int.MaxValue;

    SynchronizationContext.SetSynchronizationContext(new SynchronizationContext());

    await GetDocumentsFromDatabase(session).AsyncParallelForEach(async entry => { 
            Console.WriteLine($"Processing entry '{entry.Id}'");
        }, 20, TaskScheduler.FromCurrentSynchronizationContext()
    );
}