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IS&T Staff Fixing Recent Problems With Primary Web and Mailing Servers

CORRECTION TO THIS ARTICLE: An April 25 article “IS&T Staff Fixing Recent Problems With Primary Web and Mailing Servers” gave an incorrect date for the start of problems with outgoing.mit.edu, the mail server which handles outgoing mail. The problems began on Friday, April 14, not Friday, March 14. The article should also have given a class year for Mark V. Silis ’99.

By John A. Hawkinson
STAFF REPORTER

Over the past week, Information Services & Technology has seen a variety of problems with web.mit.edu, MIT’s primary Web server, and also with the mail server outgoing.mit.edu, which is responsible for accepting outgoing e-mail from campus users and routing it to the correct destination.

Large files slow web server

Jeffrey I. Schiller ’79, MIT Network manager, said web.mit.edu’s slow performance and unavailability on Monday was caused by attempts to access several very large files. In attempting to serve those files, the web server encountered a performance bottleneck and became non-responsive.

To combat the problem, Schiller said, IS&T has limited the maximum size of files on web.mit.edu to 250 megabytes. Yesterday’s problems were caused by files as large as 2,000 megabytes.

Web server delays updates

Because of a change made last Thursday to web.mit.edu, users may see a delay of up to five minutes between changing a Web page and seeing that change on web.mit.edu. To mitigate this, users can use the “shift-Reload” feature of most browsers to force an update.

The delays are caused by the addition of a “Web cache” (using open-source software called “Squid”), Schiller said. The Web cache allows the Web servers to reduce their dependency on the AFS file system, which has been a source of recent sluggish performance. AFS is the mechanism used to access the data that the Web servers provide to browsers.

Indexing also causes web slowness

Separately, web.mit.edu continues to experience occasional slowdowns caused by automated search engine indexing. Search engines, like Google, build their databases by periodically retrieving all content on the Web. While Google’s indexing is not the cause of recent problems for web.mit.edu, other search engine indexers have been problematic.

According to Schiller, the indexing operations can interact poorly with the AFS file system used by the Web servers.

Because web.mit.edu is actually multiple machines with web traffic divided between them by a load balancer, IS&T has responded to these incidents by re-configuring the balancer to “funnel” the indexing traffic “to a dedicated set of web servers to reduce the impact on the web-viewing public,” Schiller said. There are three servers for general use, and two that handle this search engine traffic.

Every time a new search engine begins indexing, similar problems may arise, Schiller said. The most recent incident was Thursday, when an indexer identifying itself as “Scooter/3.3” began indexing web.mit.edu and caused major slowdowns.

Outgoing mail sees problems, too

According to Mark V. Silis, who manages the network services within IS&T, problems with outgoing.mit.edu have occurred sporadically since Friday, March 14. Only users who authenticate with passwords are affected; those who use Kerberos authentication are not affected. When the problem occurs, users get an error message when attempting to send outgoing mail.

IS&T has “not been able to catch” the failure while it is occurring or determined its exact cause, but will “continue to monitor the situation,” Silis said on Thursday.

Users can report problems to the Computing Helpdesk by called 617-253-1101 or emailing computing-help@mit.edu.