Another way to talk about CQRS/Event Sourcing

"A more promising model, used in some systems, is to think of a database as an always-growing collection of immutable facts. You can query it at some point in time — but that’s still old, imperative style thinking. A more fruitful approach is to take the streams of facts as they come in, and functionally process them in real-time."

Turning the database inside-out with Apache Samz
https://martin.kleppmann.com/2015/03/04/turning-the-database-inside-out.html

CQRS and Event Sourcing example : USING LOGS TO BUILD A SOLID DATA INFRASTRUCTURE

USING LOGS TO BUILD A SOLID DATA INFRASTRUCTURE
http://blog.confluent.io/2015/05/27/using-logs-to-build-a-solid-data-infrastructure-or-why-dual-writes-are-a-bad-idea/

Architectures Comparison Summary

For Event-Driven architecture. there are two problems:
Testability and Development

But with CQRS/Event Sourcing, it is very easy to create BDD unit test.

Source:
http://www.oreilly.com/programming/free/files/software-architecture-patterns.pdf

How to deal with communication between aggregate roots?

http://danielwhittaker.me/2014/11/22/4-secrets-inter-aggregate-communication-event-sourced-system/

What is Event-driven architecture?

Behind Event-driven architecture, system model is treated as a state machine. After a command changed the state, an event is generated to notify other components.
http://c2.com/cgi/wiki?EventDrivenArchitecture

What is category in Event Store?

 If put dash into stream name, the first part will be saved as category name

Source code from Event Store 

  _handler = new CategorizeEventsByStreamPath("-", Console.WriteLine);

        public override string GetCategoryByStreamId(string streamId)
        {
            string category = null;
            if (!streamId.StartsWith("$"))
            {
                var lastSeparatorPosition = streamId.IndexOf(_separator);
                if (lastSeparatorPosition > 0)
                    category = streamId.Substring(0, lastSeparatorPosition);
            }
            return category;

        }



http://codeofrob.com/entries/creating-a-projection-per-stream-in-the-eventstore.html

What is unit of work and relationship with CQRS/Event Sourcing?

See
http://martinfowler.com/eaaCatalog/unitOfWork.html

But I think this pattern is not applicable for CQRS/Event Sourcing, because SAGA is the way to deal with transaction in CQRS/Event Sourcing.
Reference:
https://msdn.microsoft.com/en-us/library/jj591569.aspx

How to solve problem: customized projection is not running in Event Store

The defualt setting is  --run-projections=SYSTEM
Need to change
--run-projections=ALL

Reference:
https://github.com/EventStore/EventStore/wiki/Command-Line-Arguments

How to solve problem "Read access denied for stream" while reading events from event store?

Get this error on following line:
var event = connection.ReadStreamEventsForwardAsync(streamid, 0, 1, false).Result;

Need to add credential for reading
var event = connection.ReadStreamEventsForwardAsync(streamid, 0, 1, false,  new UserCredentials("admin", "changeit")).Result;

How to solve problem "System.AggregateException: One or more errors occured ---> EventStore.ClientAPI.Exceptions.RetriesLimitReachedException" when try to connect to write event to Event Store?

This error happened  after downloaded Event Store 3.0.1 and tried following code for the testing

            string serverIpaddress = "127.0.0.1";
            var connection = EventStoreConnection.Create(new IPEndPoint(IPAddress.Parse(serverIpaddress), 2113));
            connection.ConnectAsync().Wait();
            var myEvent = new EventData(Guid.NewGuid(), "testEvent", false,
                                        Encoding.UTF8.GetBytes("some data1"),
                                        Encoding.UTF8.GetBytes("some metadata"));
            connection.AppendToStreamAsync("test-stream",
                               ExpectedVersion.Any, myEvent).Wait();

On line of AppendToStreamAsync, exception throws:
 "System.AggregateException: One or more errors occured ---> EventStore.ClientAPI.Exceptions.RetriesLimitReachedException"

Cause: .NET API of Event Store goes by TCP port, which default value is 1113, http port number is 2113 by default.

Just change to            
          var connection = EventStoreConnection.Create(new IPEndPoint(IPAddress.Parse(serverIpaddress), 1113));

Reference
https://groups.google.com/forum/#!topic/event-store/5uWEqybibw8

What is projection in event sourcing

Projection is about deriving current state from the stream of events
Reference:
http://abdullin.com/post/event-sourcing-projections/

Reading about CQRS and event souring

Exploring CQRS and Event Sourcing
https://msdn.microsoft.com/en-us/library/jj554200.aspx

Applying CQRS and Event Sourcing in Microsoft .NET Applications TechEd Europe 2014
https://www.youtube.com/watch?v=z5FPkCgcH4M