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by judofyr 595 days ago
One thing which wasn’t obvious to me from the benchmark: What’s the key distribution? A sharded map will probably have great performance on uniform keys, but in my experience it’s far more common to have power law distribution in real life scenarios.

It would be good to see a benchmark where it only touches a _single_ key. If Whirlwind is still fast than the others I would be far more convinced to use it unconditionally.

EDIT: I also see that you're benchmarking on a M3 Max. Note that this has 6 performance cores and 6 efficiency cores. This means that if you're running at <6 cores it will most likely start out running it at the efficiency core. From my experience it's quite important to do warmup phases in order to get stable results at low thread count. And even then I find it hard to reason about the results since you're running in mixed set of cores…
1 comments
willothy 595 days ago
Definitely a good point. I used dashmap's benchmark suite because it was already setup to bench many popular libraries, but I definitely want to get this tested in more varied scenarios. I'll try to add a benchmark for a single key only this week.

Regarding your edit: damn I hadn't thought of that. I'll rerun the benchmarks on my Linux desktop with a Ryzen chip and update the readme.

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judofyr 595 days ago
Very fascinating results though! The sharding approach is quite a simple way of doing more fine-grained locking, making sure that writes don't block all the reads. Pretty cool to see that it actually pays off even with the overhead of Tokie scheduling everything!

There might be some fairness concerns here? Since we're polling the lock (instead of adding ourselves to a queue) it could be the case that some requests are constantly "too late" to acquire it? Could be interesting to see the min/max/median/P99 of the requests themselves. It seems that Bustle only reports the average latency[1] which honestly doesn't tell us much more than the throughputs.

[1]: https://docs.rs/bustle/latest/bustle/struct.Measurement.html

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willothy 595 days ago
This is a great point too - I definitely want to run some more varied benchmarks to get a better idea of how this performs in different settings. We'll also be using it in prod soon, so we'll see how it does in a real use setting too :)
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