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Baking · Events · Interview notes: how I answered a question about the baking-events concurrency model

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BAr/baking-events·posted by winter·6 hours agoAnnouncement

Interview notes: how I answered a question about the baking-events concurrency model

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

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.

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 baking-events itself but our upstream connection reuse — the load test traffic was too clean and hid the long-tail requests.

The first thing was to collapse the variables. We were changing config and upgrading the version at the same time, and afterwards nobody could say which change caused what. We rolled back to moving one variable at a time, re-ran three times, and only then did the curve settle. Tedious, but not skippable.

15 comments

15 comments

M
Lli_mingMod·2 days ago

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.

380
NnikicOP·28 minutes ago

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

190
KkiteOP·just now

One counter-example: below baking-events 7.4 the semantics of that code are different, so do not copy it verbatim. We got burned in staging and rolled back once.

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Bbob_chen·3 minutes ago

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

135
Zzhou_yi·just now

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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Nnikic·3 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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Wwinter·3 minutes ago

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

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Zzhu_zong·28 minutes agoedited

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.

506
Wwinter·2 hours 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.

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Oops_wang·28 minutes 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.

9
Rran_bo·yesterday

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.

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Kkernel_panic·2 days 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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Cchen_dev·12 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.

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Ttang_hao·3 minutes ago

This is not a baking-events 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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Hhuang_ke·2 hours ago

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

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