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ESP32 · Code review · Interview notes: how I answered a question about the esp32-review concurrency model

13
ESr/esp32-review·posted by bob_chen·3 hours agoReview

Interview notes: how I answered a question about the esp32-review concurrency model

It took me two weeks of on-and-off digging and plenty of wrong turns. Writing the process down as it happened so the next person spends less time.

What genuinely surprised me was the tail. The average looked great while P99 jumped by an order of magnitude past some threshold. The cause was not esp32-review itself but our upstream connection reuse — the load test traffic was too clean and hid the long-tail requests.

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9 comments

9 comments

M
Ddev_zhou·3 minutes ago

I see point 3 differently. The trade-off depends on your read/write ratio: read-heavy with little writing means caching actually widens the inconsistency window.

411
Rrase·2 hours ago

There is actually a simpler fix that needs no architecture change: move this check up to the gateway and the problem disappears. The cost is one extra lookup at the gateway.

232
Oops_wang·yesterday

Worth learning from this debugging approach. We went straight at the logs and took a much longer route.

23
Zzhou_yi·28 minutes ago

We have run this in production for two years without hitting it. That said, we never reached this scale, so our experience is not really evidence here.

18
Lli_ming·12 minutes ago

Agreeing with the above. One addition: with this option enabled the GC count in your metrics doubles, so adjust the alert threshold at the same time or it will keep firing.

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Bbob_chenOP·just now

This matches what we see in production. We only hit it past 3k QPS; the earlier load tests showed nothing — the test traffic was too clean, with no long-tail requests.

312
Hhuang_ke·just nowedited

Has anyone run a controlled experiment? I did, reducing it to a single variable, and the difference was 4% — within noise. So I suspect the main cause is something else.

507
Zzhu_zongOP·1 hour ago

A question: what changes in a container with a 512Mi memory limit? That is how we run it in production.

87
Zzhu_zong·1 hour ago

Can you give a minimal reproduction? I ran it locally for ten minutes and could not reproduce on macOS with the latest version.

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