Vue · Advanced · The edge cases the vue-pro docs never spell out

32
VUr/vue-pro·posted by kernel_panic·32 minutes agoTranslation

The edge cases the vue-pro docs never spell out

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

# Load test: do not jump straight to the max concurrency.
# Ramp it up, otherwise you miss the knee.
for c in 50 100 200 400 800; do
  wrk -t8 -c$c -d60s --latency http://127.0.0.1:8080/api/feed
  sleep 20
done

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.

Worth noting: the official docs do cover this, just in a very inconspicuous spot. I only found it reading the source comments, where the author explains the reasoning — roughly "so that it degrades into predictable behaviour in extreme cases".

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.

On trade-offs, my view is this: if nobody on the team owns this area long-term, do not introduce a second mechanism. With two coexistence you first have to work out which one is even in play when things break, and that costs far more than the performance you saved.

17 comments

17 comments

M
Ddev_zhouOP·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.

460
Oops_wangOP·2 days ago

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

425
Wwinter·yesterday

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

205
Zzhu_zong·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.

127
Kkernel_panicOP·3 minutes 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.

282
Lli_ming·3 minutes ago

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

66
Zzhu_zong·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.

106
KkiteMod·2 hours ago

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

459
Oops_wang·yesterdayedited

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

447
Kkite·3 minutes ago

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

32
Kkite·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.

27
Wwinter·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
Cchen_dev·12 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.

1
WwinterOP·3 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.

30
Cchen_dev·28 minutes ago

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

6
Sswoole_lee·3 minutes ago

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

186
Bbob_chenMod·2 days 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.

6

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