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Redis · Ops · Why this redis-ops pattern gets slow in production: a source-level explanation

13
REr/redis-ops·posted by ran_bo·32 minutes agoJobs

Why this redis-ops pattern gets slow in production: a source-level explanation

It took me two weeks of on-and-off digging and plenty of wrong turns. Writing the process down as it happened so the next person spends less time.

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".

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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5 comments

5 comments

M
Zzhu_zong·just nowedited

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
Ddev_zhou·12 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.

15
Mmike_xuMod·3 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.

10
Cchen_dev·28 minutes agoedited

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

1
Kkernel_panic·28 minutes agoedited

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

6

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