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PWA · Interviews · The pwa-interview execution flow in one diagram (with sequence chart)

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PWr/pwa-interview·posted by kernel_panic·2 hours agoPostmortem

The pwa-interview execution flow in one diagram (with sequence chart)

Most pwa-interview articles stop at "how to use it" and never cover "when not to use it". This is an attempt at the second half.

We also fixed monitoring along the way: replaced average-based alerts with percentiles and split them per endpoint. False alerts dropped by about seventy percent and the on-call rotation visibly cheered up.

One last trap: in container environments remember to adjust the memory-related parameters in step. Otherwise the host limit and the process expectation disagree, and the symptom is intermittent, unreproducible failure.

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10 comments

10 comments

M
Lli_ming·just now

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

209
Kkernel_panic·12 minutes ago

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

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Rrase·1 hour ago

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.

55
Bbob_chen·1 hour 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.

207
Bbob_chen·just now

Saved. I am reworking this area this week — this saves a lot of wrong turns.

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Oops_wangOP·3 minutes agoedited

Sharing our numbers, 8 cores 16GB, same scenario:

| Concurrency | P50 | P99 |
|---|---|---|
| 200 | 12ms | 88ms |
| 500 | 31ms | 340ms |

P99 clearly collapses at 500 concurrency, which lines up with your knee point.

38
Ddev_zhou·1 hour ago

Thanks for sharing real numbers — far more useful than the articles that only cover concepts.

445
Ttang_haoOP·3 minutes ago

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.

6
Zzhou_yiOP·3 minutes ago

I just read the pwa-interview source — the author actually explains the reasoning in a comment, roughly "so that it degrades into predictable behaviour in extreme cases".

4
Mmike_xu·3 minutes ago

This is not a pwa-interview problem, it is a usage problem. The docs say this API is not thread-safe and you must lock around it yourself.

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