Monthly Archives: April 2015

Ranking CS Departments by Publication Productivity, Interactively

Anyone familiar with American academia will tell you that the US News rankings of academic programs play an outsized role in this world. Among other things, US News ranks graduate programs of computer science, by their strength in the field at large as well as certain specialties. One of these specialties is Programming Languages, the focus of this blog.

The US News rankings are based solely on surveys. Department heads and directors of graduate studies at a couple of hundred universities are asked to assign numerical scores to graduate programs. Departments are ranked by the average score that they receive.

It’s easy to see that much can go wrong with such a methodology. A reputation-based ranking system is an election, and elections are meaningful only when their voters are well-informed. The worry here is that respondents are not necessarily qualified to rank programs in research areas that are not their own. Also, it is plausible that respondents would give higher scores to departments that have high overall prestige or that they are personally familiar with.

In this post, I propose using publication metrics as an input to a well-informed ranking process. Rather than propose a one-size-fits-all ranking, I provide a web application to allow users to compute their own rankings. This approach has limitations, which I discuss in detail, but I believe it’s a reasonable start to a better system.

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Filed under Process, Rankings, Research, Science

Dynamic Software Updating: Linux 4.0 and Beyond

Last month,  of ZDNet alerted us that Linux 4.0 will provide support for “no-reboot patching.” The gist: When a security patch or other critical OS update comes out, you can apply it without rebooting.

While rebootless patching is convenient for everyone, it’s a game changer for some applications. For example, web and cloud hosting services normally require customers to experience some downtime while the OS infrastructure is upgraded; with rebootless patching, upgrades happen seamlessly. Or, imagine upgrades to systems hosting in-memory databases: Right now, you have to checkpoint the DB to stable storage, stop the system, upgrade it, restart it, read the data from stable storage, and restart service. Just the checkpointing and re-reading from disk could take tens of minutes. With rebootless patching, this disruption is avoided; cf. Facebook’s usage of a modified memcached that supports preserving state across updates.

I’m particularly excited by this announcement because I’ve been working on the general problem of updating running software, which I call dynamic software updating (DSU), for nearly 15 years. In this post, co-authored with my PhD student Luís Pina, I take a closer look at the challenge that DSU presents, showing that what Linux will support is still quite far from what we might hope for, but that ideas from the research community promise to get us closer to the ideal, both for operating systems and hopefully for many other applications as well.

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Filed under Research, Systems