SID-00548: TagMePlugin takes CPU to 100%

Status:	Answered	TWiki version:	4.0.1	Perl version:	CPAN Perl 5.8.8
Category:	CategoryPlugins	Server OS:	Fedora Core 5	Last update:	16 years ago

On the surface it appears that I'm having trouble with the TagMePlugin and I posted a query on that plugin's dev page. Peter Theony replied that this doesn't seem like a plugin problem and suggested that I post this problem here.

We have a decent sized site with <10K pages and a handful of subwebs. We plan to upgrade to the latest TWiki release soon, but I wanted to get started with the TagMePlugin. The installation went without a hitch once I downloaded extender.pl. However immediately after enabling the TagMePlugin we started having severe performance problems.

Every page being viewed tries to use 100% of the CPU. When I restart Apache, the CPU will return to normal until somebody tries to view a page. The first page viewed causes the CPU to hit the ceiling again. When this happens, the CPU never returns to normal utilization. While the CPU is pegged, you can't bring up a single page, including the configure script. In top, each page requested appears as another 'view' that's taking it's share of the 100%, but at the browser the page never appears.

To recover my TWiki site I stopped Apache and restored everything from a nightly backup. If I reinstall the TagMePlugin, everything behaves OK. Nothing seems broken in the Twiki site until I turn on the TagMePlugin via the configure script and somebody tries to view a page. Then the CPU gets pegged at 100% again and the Twiki site is rendered unusable.

I originally thought there's something I'm not understanding about how the plugin works or should be configured. For example, I wondered if the TagMePlugin needs to do some long-running initial processing, like indexing all of the pages?

Peter's comment leaves me with doubts about the underlying cause of this misbehavior.

Any suggestions?

-- JeffChapman - 2009-10-05

Discussion and Answer

OK, so you verified that it is TagMePlugin related.

There is no indexing going on. TWiki.org has now 97k pages, with 3.8k tags applied to 2k pages. I don't think you hit a performance limit on this plugin, it looks more like a bug, such an infinite loop triggered by something.

Earlier plugin versions stored tag data in twiki/pub/TWiki/TagMePlugin. Tagging data now resides in twiki/working/work_areas/TagMePlugin. The plugin is designed to move data on first run. Possibly a bug in that part? I recommend to do this:

1. Create a twiki/working/work_areas/TagMePlugin directory if it does not already exist
2. Move all files starting with _* from twiki/pub/TWiki/TagMePlugin to twiki/working/work_areas/TagMePlugin
3. Recursively set ownership of all dirs and files below twiki/working to the webserver user (such as chown -R apache.apache =twiki/working)

-- PeterThoeny - 2009-10-05

Closing this question after more than 30 days of inactivity. Feel free to reopen if needed. Consider engaging one of the TWiki consultants if you need timely help. We invite you to get involved with the community, it is more likely you get community support if you support the open source project!

-- PeterThoeny - 2009-11-23

If you answer a question - or someone answered one of your questions - please remember to edit the page and set the status to answered. The status selector is below the edit box.