Ninety Days with DOM

Last quarter marked a fairly significant change in my career at Mozilla. I spent most of the quarter adjusting to multiple re-orgs which left me as the sole QA engineer on the DOM team. Fortunately, as the quarter wraps up I feel like I’ve begun to adjust to my new role and started to make an impact.

Engineering Impact

My main objective this quarter was to improve the flow of DOM bugs in Bugzilla by developing and documenting some QA processes. A big part of that work was determining how I was going to measure impact, and so I decided the most simple way to do that was to take the queries I was going to be working with and plot the data into Google docs.

The solution was fairly primitive and lacked the ability to feed into a dashboard in any meaningful way, but as a proof of concept it was good enough. I established a baseline using the week-by-week numbers going back a couple of years. What follows is a crude representation of these figures and how the first quarter of 2015 compares to the now three years of history I’ve recorded.

Volume of unresolved Regressions & Crashes
dom.regressions-vs-crashes.unresolved.alltime.2015q1Regressions +55%, Crashes +188% since 2012

Year-over-Year trend in Regressions and Crashes
dom.regressions-vs-crashes.unresolved.annual.2015q1Regressions +9%, Crashes +68% compared to same time last year.

Regressions and Crashes in First Quarters
dom.regressions-vs-crashes.unresolved.quarterly.2015q1Regressions -0.6%, Crashes +19% compared to previous 1st Quarters

Resolution Rate of Regressions and Crashes
dom.regressions-vs-crashes.fixrate.2015q190% of Regressions resolved (+2.5%), 80% of Crashes resolved (-7.0%)

Change in Resolution Rate compared to total Volume
dom.regressions-vs-crashes.volume.2015q1Regression resolution +2.5%, Crash resolution -6.9%, Total volume +68%

I know that’s a lot of data to digest but I believe they show embedding QA with the DOM team is having some initial success.

It’s important to acknowledge the DOM team for maintaining a very high resolution rate (90% for regressions, 80% for crashes) in the face of aggressive gains in total bug volume (68% in three years). They have done this largely on their own with minimal assistance from QA over the years, giving us a solid foundation from which we could build.

For DOM regressions I focused on making existing bug reports actionable with less focus on filing new regression bugs; this has been a two part effort. The first being focused on finding regression windows for known regression bugs, the second being focused on converting unconfirmed bugs into actionable regression reports. I believe this is why we see a marginal increase in the regression resolution rate (+0.4% last quarter).

For DOM crashes I focused on filing previously unreported crashes (basically anything above a 1% report threshold). Naturally this has led to an increase in reports but has also led to some crashes being fixed that wouldn’t have been otherwise. Overall the crash resolution rate declined by 2.6% last quarter but I believe this should ultimately lead to a more stable product in the future.

The Older Gets Older

The final chart below plots the age of unresolved DOM bugs week over week which currently sits at 542 days; an increase of 4.8% this past quarter and 241% since January 1, 2012. I include it here not as a visualization of impact but as a general curiosity.

Median Age of Unresolved DOM Bugs
dom.regressions-vs-crashes.fixrate.2015q1Median age is 542 days, +4.8% last quarter, +241% since 2012

I have not yet figured out what this means in terms of overall quality or whether it’s something we need to address. I suspect recently reported bugs tend to get fixed sooner since they tend to be more immediately visible than older bugs. A fact that is likely common to most, if not all components in Bugzilla. It might be interesting to see how this breaks down in terms of the age of the bugs being fixed.

What’s Next

My plan for the second quarter is to identify a subset of these to take outside of Google Docs and convert into a proof of concept dashboard. I’m hoping my peers on the DOM team can help me identify at least a couple that would be both interesting and useful. If it works out, I’d like to aim for expanding this to more Bugzilla components later in the year so more people can benefit.

If you share my interest and have any insights please leave a comment below.

As always, thank you for reading.

[UPDATE: I decided to quickly mock up a chart showing the age breakdown of bugs fixed this past quarter. As you can see below, younger bugs account for a much greater proportion of the bugs being fixed, perhaps expectedly.]

Screen Shot 2015-04-06 at 3.56.33 PM

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