Monday, 15 April 2013

Welcome to Grid Quorum

A quorum is the minimum number of votes that a distributed transaction has to obtain in order to be allowed to perform an operation in a distributed scenario. A quorum-based technique is implemented to enforce consistent operation in a distributed system.

Typically mutual exclusion is sought to avoid conflict and in distributed system this becomes a rather complex job. Timestamps, Token-based algorithms are the other ways of doing the same, but they are vulnerable to failures, whereas quorum based algorithms don't have single point of failure. In the timestamps based algorithm, the process seeks permissions from all other participating processes to enter a critical section. In the token based algorithm the permission is required from one process. The quorum based algorithm, however, seeks permission from a subset of processes called request set.

There are three metrics to compare various quorum systems;

        a. Quorum Size - small size would mean less message overhead
        b. Availability - probability that at least one quorum is active in failing
             processes scenario to ensure alive processes can work properly
        c. Load - load on processes due to access by other processes for
            constructing quorums

Grid Quorum is one of the quorum based algorithms to resolve conflicts in distributed computing systems. Technically in a crumbling wall logical arrangement, a grid quorum system is a set of N (=d^2) processes arranged in a grid with d rows and d columns and  quorum is formed with all elements of a row and at least one from each rows below to ensure that the conflict is avoided.

Finally, a quorum is also the minimum number of members of a deliberative assembly necessary to conduct the business of that group. Quoted by Wikipedia, according to Robert's Rules of Order Newly Revised, the "requirement for a quorum is protection against totally unrepresentative action in the name of the body by an unduly small number of persons."

Hence appropriately for the blog as well, we will have quorum of selected technical bloggers who would blog about typically contemporary and relevant technological stuff related to software building. GridQuorum will primarily focus on areas like distributed computing, NoSql, application scalability, open source etc.

If you are interested in publishing an article, please contact me at sachin@iqlect.com, I would be happy to assist you there.

Thanks for reading through the post.

Best,
Sachin Sinha
GridQuorum