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Clojure · Job board · Ten clojure-jobs anti-patterns — how many are you guilty of?

87
CLr/clojure-jobs·posted by bob_chen·5 minutes agoHelp

Ten clojure-jobs anti-patterns — how many are you guilty of?

Some background first. Our setup is clojure-jobs plus three downstream services, seven figures of daily requests, peaking around nine in the evening.

Order of investigation, by return on effort: 1. Check downstream latency first — usually it is not your problem 2. Then pool hit rate and wait-queue length 3. Only then GC and allocation 4. Suspect the framework last

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.

27 comments

27 comments

M
Hhuang_ke·2 hours 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.

513
Zzhu_zongMod·2 days ago

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

17
Wwinter·2 hours ago

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

366
Zzhou_yi·just nowedited

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.

357
Hhuang_ke·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.

193
Nnikic·2 hours agoedited

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.

94
Oops_wang·3 minutes ago

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

120
Kkernel_panic·28 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.

38
Wwinter·2 days 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.

108
Cchen_dev·yesterday

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

12
Mmike_xu·2 days 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.

481
Rrase·2 days ago

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

175
Ttang_hao·2 days ago

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

178
Kkernel_panic·2 days ago

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

23
Nnikic·2 days agoedited

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

91
Hhuang_ke·3 minutes agoedited

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

90
Zzhou_yi·12 minutes 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.

40
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.

284
Ddev_zhou·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.

86
Kkernel_panic·2 days agoedited

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

30
Lli_ming·5 hours agoedited

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

19
Oops_wang·5 hours ago

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

12
Sslow_query·2 days 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.

187
Ttang_hao·2 days 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.

9
Mmike_xu·just now

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

1
Sslow_query·5 hours ago

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

1
Rrase·2 days 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.

21

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