Using CouchDB to store state: My hack to manage multi-machine data processing

This article describes how I use CouchDB to manage multiple computing jobs. I make no claims that this is the best way to do things. Rather I want to show how using CouchDB in a small way gradually led to a solution that I could not have come up with using a traditional relational database.

The fundamental problem is that I don’t know what I am doing when it comes to managing a cluster of available computers. As a researcher I often run into big problems that require lots of data crunching. I have access to about 6 computers at any given time, two older, low-powered servers, two better servers, and two workstations, one at work and one at home. If one computer can’t handle a task, it usually means I have to spread the pain around on as many idle CPUs as I can. Of course I’ve heard of cloud computing solutions from Amazon, Joyent, and others, but quite frankly I’ve never had the time and the budget to try out these services for myself.

At the same time, although I can install and manage Gentoo on my machines, I’m not really a sysadmin, and I really can’t wire up a proper distributed heterogeneous computing environment using cool technologies like Ømq. What I’ve always done is human-in-the-loop parallel processing. My problems have some natural parallelism—for example, the data might be split across the 58 counties of California. This means that I can manually run one job per county on each available CPU core.

This human-in-the-loop distributed computer model has its limits however. Sometimes it is difficult to get every available machine to have the same computational environment. Other times it just gets to be a pain to have to manually check on all the jobs and keep track of which are done and which still need doing. And when a job crashes halfway through, then my manual method sucks pretty hard, as it usually means restarting that job from the beginning.

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