non deterministic bug or ndb?

17th March 2014

We recently made a bunch of perf fixes to reduce homepage load times (by 30% in some cases!).

Sounds too simple to be true, but we reduced time on both server and client by doing less stuff:

1) Remove unnecessary RPCs

2) Load less css / js

After these fixes were deployed, we noticed a small trickle of errors on homepage load:

TypeError: '_BaseValue' object is not subscriptable

The errors seemed non deterministic, and they seemed to happen more often when hitting non default versions of our app. After some sleuthing, we figured out what was going on, and this inspired the following quiz.

non-deterministic-bug-or-ndb

Enjoy!

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