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Redis · Ops · Those easily-missed type details in redis-ops

126
REr/redis-ops·posted by li_ming·2 hours agoHelp

Those easily-missed type details in redis-ops

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

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.

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22 comments

22 comments

M
Zzhou_yi·12 minutes agoedited

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

399
Sswoole_lee·28 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.

342
Bbob_chenOP·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.

259
Wwinter·just now

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.

341
Zzhu_zong·just now

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

32
Bbob_chen·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.

198
Ddev_zhou·2 days agoedited

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.

1
Ttang_haoOP·1 hour ago

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

216
Aalice_dev·yesterday

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

276
Cchen_dev·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.

202
Rran_bo·12 minutes ago

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

99
Rrase·just now

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.

87
Sswoole_lee·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.

75
Zzhou_yiOP·2 hours ago

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

11
Sslow_query·2 days ago

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

130
Zzhu_zong·2 days ago

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

3
Cchen_dev·5 hours 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.

1
Ttang_hao·1 hour ago

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

241
Cchen_dev·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.

37
Rran_bo·3 minutes ago

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

7
Ttang_hao·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.

276
Zzhou_yi·2 days ago

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

26

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