GLASS 101: Ready…

Before we point jcrawler at a Seaside application I would like to talk about what you should expect.

To start with, jcrawler is like a bull in a china shop. The algorithm jcrawler uses is not very deterministic nor is it discriminating, but it is thorough, relentless and highly parallel. Given an an initial set of URLs, jcrawler traverses each page and adds the links it finds to its list. Every so often, jcrawler creates a new thread to process another URL from the list. We can depend upon jcrawler to rattle every piece of china in an application and it will rattle more than one piece at a time, so we’d better be ready to deal with wreckage.

Jcrawler will help make your application bullet proof, but at potentially 15 errors/second spread across several vms, there can be a lot of wreckage to sift through.

I added an object log to GLASS a couple of weeks ago and over the last couple of days, I’ve added a Seaside application for viewing and manipulating the object log. Take look at a sample log (my blog is wide-image challenged). It’s not the purtiest page this side of the Mississippi (I am web-design challenged:), but it does the job.

In the object log, the entries labeled ‘– continuation –, represent object log entries that can be debugged via the ‘Debug’ button in the GemStone/S Transcript Window. If you take a peek at the pid column, you will notice that the log entries were generated by two different gems. There are three gems serving HTTP requests in the appliance.

The upshot is that after letting jcrawler hammer on your application, not only do you get an overview of the problems uncovered during the run, but you can open a debugger and investigate the issues that resulted in walkbacks.

I generated the sample object log by manually playing with the randomError application (http://localhost/seaside/examples/GemStone/randomError in the appliance) found in the GemStone Examples project. This little gem generates a simple log entry (‘random error’) or walkback (‘– continuation –‘) 12% of the time. You can also generate different kinds of errors by poking the links in the Error tab of the alltests application (http://localhost/seaside/tests/alltests in the appliance).

If you want to play with the object log, load up the latest version of the GLASS package (GLASS-dkh.103 in the GLASS project – it will also load the GemStone Examples). Poke around in the randErrror application until you get an error then head on over to the object log (http://localhost/seaside/tools/objectLog in the appliance). You can also try the remote debugger from your development image.

Next up we’ll talk a little bit about configuring jcrawler.