Technical news reports - 2004

lcl121

May 5, 2004

Re: Chronic "500" errors when using our web site.

The SETI@home web site gets over two million hits a day. A large chunk of these hits are statistics queries which load down the server. At peak times (usually in the middle of the U.S. work day) the server can't gracefully handle the load and requests fail with an ugly "500" internal server error (which shows up in different ways depending on your browser).

To help alleviate this problem, we set up a second web server just to handle stats requests (called setiathome2). However, a lot of people (and pieces of software) have setiathome.ssl.berkeley.edu bookmarked as the site to look up statistics. These links still work, but still occasionally get overloaded.

So, if you are getting such errors, check your URL - make sure that the beginning is: http://setiathome2.ssl.berkeley.edu, and not http://setiathome.ssl.berkeley.edu.

Q: Why do you use two separate names (setiathome and setiathome2) as opposed to using some form of automatic load balancing?

A: Well, because in theory we want these web servers to do two entirely different things. The first (setiathome) would host the home page (and all the other static pages). The second (setiathome2) would host all the dynamically generated pages, handle forms, etc. When everything was on one server, heavy loads due to excess queries prevented other people from loading the home page and downloading the software, and this was quite embarrassing. This scheme would keep this activity localized to the second server, so the informational pages on the first would always load (and load quickly).

In practice, however, this proved difficult. As stated above, many people bookmarked (and pieces of software hardwired) the first server as the stats server, and we couldn't just break all those links. So to be nice we left those channels open on the first server, but enough activity (via links on the web page) was shoveled over to the second server to vastly reduce the load.

We are working on the next generation website (to be launched in tandem with the next generation of software) where most everything is dynamically generated. At this point we'll (hopefully) throw more web servers into the fold and use some automatic load balancing technique which won't require us to advertise different server names for different kinds of web activity.

May 4, 2004

It's been a while (over a year) since the last technical news update. This may make it seem that nothing much is happening here at the lab, but that's hardly the case. We've had (and continue to have) more than our fair share of random failures and outages. Most of these events are noted among the regular news items, but we have been failing to elaborate on them in this section of the web site. Disasters aren't that much fun to write about and probably not that much fun to read either.

Most of our technical effort over the past year has been focused on ramping up SETI@home II, which involves an entirely new client/server architecture we are developing called BOINC. BOINC has been in alpha/beta test for a while now, and we're hoping to release an early version soon. The bottom line is we are currently running two SETI@home-sized projects on the same amount of hardware that up until recently ran just one project. This is difficult to say the least, but BOINC's flexible server architecture and several recent hardware donations from our major sponsors are making for a smoother transition.