The Bug Was in My Benchmark: Attaching a Debugger to Chromium Throttles fetch() Uploads 20x

We chased an upload running 8x below what the link could do, shipped three fixes that turned out to fix nothing, and found a real one that turned out to be far smaller than it looked — because the thing measuring the bug was also causing it.

The crime

I work on — though, as the numbers above say, it is worth about 30% in one engine rather than the 5x we thought we'd found.