Just guessing: the benchmark tells you the time complexity. It doesn't tell you the space complexity. The author is optimizing between the time- and space-complexity of the solutions, with the time-complexity benchmarks as an input. (Also, at a scale the benchmark doesn't reach, space-complexity starts to affect time-complexity, as large datasets become less able to be hot in disk cache.)
> Even though the data says hstore, knowing that posts will be seen by more and more people over time, I might choose the HLL solution for an actual implementation. It's far less likely to pose a bloated row problem, [...]
Hstore might have been the fastest but the way I am using it or the scales the use case could scale to might not work out.
Bigger benchmarks could have been done! Maybe a multi part post would have been better so I could split apart methodology and results/blabbering about approach!
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Has gitlab always enforced that, even for public repos? Or is the linked repo not public?
It spends a lot time building a benchmark framework and measuring things. At the end, hstore is the choice supported by the data. But instead the author writes:
> If we go strictly with the data, the best way looks to be the hstore-powered solution, but I think the HLL is probably the right choice.
?!? Why bother defining a framework for measurement if you're just going to substitute your own judgment? Perhaps the framework didn't capture something important -- like the absolute number of people looking at any given post, concurrent updates, etc.
I'm also confused by the benchmark. The autocannon script has:
Does this imply there's a path it can hit to get the list of users who saw a post? HLL is a probabilistic data structure, so it doesn't support that with 100% accuracy. You could reverse engineer it from the list of users, but the performance will vary with the number of users, which didn't seem to be captured by the benchmark. I tried to look at the source code, but the GitLab URL was 404ing for me.