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Wednesday, December 30, 2009

EventMachine Client for CouchDB (em-couchdb)

I have been crazy about NoSql databases for sometime. CouchDB is one of my favorite apart from redis :). I was looking for clients for CouchDB in Ruby and found most to be using Net/Http and blocking in nature. So I began my quest of writing an asynchronous non blocking awesome EventMachine based CouchDB client inspired by EventMachine::Redis client.

Here is a sample code to enjoy... It creates a database, saves a document inside it, reads the doc, deletes it and then deletes the database.

The current version supports database manipulation like creation and deletion and document manipulation.

Looks cool for the code I wrote in a day but still there are things to improve (a lot). One thing is the CPS style. Because the code is asynchronous and the EventMachine reactor loop will take control once the code starts to run we need to explicitly pass callbacks to actions. This can be fixed as it was done in EM::Redis using callcc to make the passing implicit.

Please feel free to fork and contribute and happy hacking :).

The code is available at

Thursday, December 10, 2009

Simple (Or not so simple) Node.js Redis Client

I love node.js. For some reason I am fascinated by V8 javascript engine and its performance. I am also a big fan of Event driven I/O frameworks like twisted or EventMachine, Javascript and nosql databases of which redis is one of the stars. For those who are not familiar with terminology Google them :).

Here is a small redis client I wrote in node.js. All it can do is to see if a key can exist or not :).

Wednesday, December 9, 2009

What good is the feedback for?

What good is the feedback for if I am not going to use it to correct things? What good is a QA for sitting across my desk providing feedback if I am going to ignore it and continue what I am doing? What good is a showcase for if I am going to ignore my client's suggestions? What good is TDD for if I am not going to use it to evolve the design? I have heard a lot of people say the Agile is about short continuous feedback but the question comes back to why? Why we need feedback? Is feedback alone enough? Getting feedback is a way, part of the activity we are doing, not the end.

All these questions made me think about what it means to Agile? I always consider software development to be more of an exploration activity. We explore ways to do things better and along the way we learn new ways and also make a few mistakes. Working over the years my definition of Agile has evolved and my current one seems to be "Agile is a method which helps to reduce the assumptions we hold as fast as possible and make things concrete". When we work on a project we have base our work on a few assumptions or understanding of what needs to be done. They may be assumptions of what client is expecting, or assumptions about a design being evolutionary... But holding on to those assumptions and thinking that we are going down the right path is a way to disaster.

So how is Agile special in reducing the assumptions when compared to waterfall? Both help in that aspect of getting feedback except for Agile gives quick ways to correct our actions or find the right way. Waterfall delays it to the point where sometimes the cost of correction is too high.

Working closely with the client helps in making our understanding better or reducing the assumptions we make, TDD does the same for design, Continuous Integration and deployment helps us to reduce the assumptions we have on production environment. The examples are numerous but I hope you get the point.

So for me Agile is about reducing the assumptions and making things concrete so that we can continue working with confidence.

Let me know your thoughts.

Thursday, December 3, 2009

Curious case of object initialization in python

While working on writing some Async code for CouchDb connector using Tornado webclient I used the code of AyncHTTPClient as a doc. Reading the code I found an interesting piece of initialization method. This may not be anything new for a lot of python people but for me I found this pattern interesting. I had used python long time back while it was in 2.5.x time and I came back to it recently to work on UNICEF project. So my knowledge of python may not be as sharp as knife :)

So lets jump into the code directly. The initialization method as I remember in python is __init__. For those unfamiliar with python __init__ is the first method called when an object is initialized. Or in other words a constructor. Similar to ruby's init method. Pretty simple right?

But checkout the __new__ method. A simple example of usage of __new__ method for singleton pattern in python.

So how is __new__ method different from __init__? As seen from example __new__ gives a complete control of the object I construct. So when initializing the object the order of calling is
1. You try to create an object --> 2. __new__ called if available to create an instance --> 3. object initialized using __init__. Also __new__ can return an instance of the class you are creating. __init__ only does the job of initializing it and does not return anything.

I know a lot of you may know about this already. But I wanted to share what I understood. Let me know if you think there is a better explanation or I have goofed up something.

Eventlet based CouchDB connector

This is an attempt to write a nonblocking CouchDB API based on Eventlet. Eventlet is a wonderful python library written by Second Life people based on coroutine based nonblocking I/O. I also tried using AsyncHTTPClient provided by Tornado framework released by FriendFeed people but liked the eventlet version more. So here goes... This API may grow to be a full fledged one in future.

Also look out a Ruby non blocking one based on NeverBlock :)