Sunday, 26 May 2013

Model of distributed system

Post #2 of the distributed computing discussion series 

Previous post gave the high level introduction of the distributed system. In this post we will discuss about model of distributed system.

Once defined, model will help us understand many features and flavours of distributed computing challenges and put them in perspective and allow us to formulate workarounds or solutions to solve or overcome those challenges. These models will be used throughout in our next set of blogs related to the topic. Hence it is important to focus on the subject and understand clearly.

How do we visualize a distributed system?

Here is how I would describe a distributed system in simple terms. 
  • message passing system - nodes interact by sending/receiving messages
  • loosely coupled - no upper bound on message arrival time
  • no shared memory - all nodes have their own private memory
  • no global clock - clocks of different nodes can't be synchronized globally
  • a graph topology - consisting of processes as graph nodes and channels for message passing as edges (directional)
  • ordering of messages are not assumed in channels 
A simple figure to describe what I wrote above;

Monday, 6 May 2013

Distributed System - a high level introduction

Post #1 of the distributed computing discussion series

This is the beginning of the series of articles/blogs on the distributed computing. I will try to first put forward some of the basic concepts of the distributed computing and then take up some of the related problems and dig deeper. In the process I would also dedicate few blogs on existing products/systems which are relevant to the discussion and try to explain why few things are done in some manners or how someone has solved or overcome a problem.

This post is to quickly give you the introduction on the distributed computing from high level as it will be referred at many places in future blogs. Please note that this subject is too vast to cover in a single blog hence I will try to focus on stuff important from practical design and implementation perspective.

Distributed System

For simplicity and for the discussion sake lets define distributed system as a collection of multiple processors (programs, computers etc...) connected by a communication network. These connected processors try to achieve a common goal by communicating with each other using messages that are sent over the network.