Do people here use pypy in production? What are the benefits?
At the time (a year ago) there wasn't a way to precompile using pypy, which meant shipping pypy along with gcc and a bunch of development headers for JIT-ing. Additionally a one of the extensions we used for request validation wasn't supported so we'd be forced to rewrite it. I also found that the warmup time was too much for my liking, it was several times longer than CPython's and it became a nuisance for development. I guess I could've pre-warmed it up automatically, but at that point I had better things to worry about and abandoned trying to switch.
I'm sure, given enough resources, it would be a lot better. But it's not quite as simple as switching over and realizing the performance increases without some initial investment.
It doesn't (or didn't) work when you need to rely on an extension that uses Python's C API. I haven't followed the scene in awhile so maybe that's changed. pypy's pip has so many libraries that I hardly notice, so maybe they solved that.
Unfortunately python is fundamentally slower than lua or JS, possibly due to the object model. Python traps all method calls, but even integer addition, comparisons, and so on are treated as metamethods. That's the case for Lua too, but e.g. it's absurdly easy to make a Python object have a custom length, whereas Lua didn't have a __len__ metamethod until after 5.1. I'm not sure it even works on LuaJIT either. Probably in the newer versions.
(And yeah the CPython API is still a pain point if you've got a library that uses it, although some stuff will still work using PyPy's emulation layer. It'd be great if people stopped using it though.)
You can't always inline the arithmetic ops effectively. You can recompile the method each time it's called with different types, but that's why the warmup time is an issue. This wouldn't be a problem if Python didn't make it so trivial to overload arithmetic. JS doesn't.
I'd love a comment/post that highlights the differences between JS and Lua as the reason why LuaJIT was able be so effective. There must be differences that make Lua possible to speed up so much. There are easy ones to think of, but the details matter a lot.
EDIT: I found some discussion at https://news.ycombinator.com/item?id=1188246 but it left me wanting more.
Related:
https://stackoverflow.com/questions/4911762/why-is-luajit-so...
PS: I do realize "digital forensics" is probably not the kind of "production environment" you were thinking. Just a small datapoint about a particular branch of software that, while getting good speedups, may not benefit as much as the "X times faster" line would suggest.
You have to not have problematic libraries in your system, but honestly they're all either shitty on CPython too (literally every GUI toolkit that is not Tkinter!) or they're stuff like lxml, where the author/maintainer just has an anti-PyPy bias that they won't drop.
Initially memory tradeoff was definitely significant, somewhere around 40% or so -- it's going to vary across applications though certainly, and in a lot of cases I'm a bit happy our memory usage went up because it forces us more towards "nicer" architectures where data and logic are cleanly separated.
Not that I mean to apologize too much for it, it's something certainly to watch, but for us on our most widely deployed low-latency, high-throughput app, we traded about 40% speedup for 40% RAM on an app that does very little true CPU-bound tasks (it's an s2s webapp where per-request we essentially are doing some JSON parsing, pulling some fields out, building some data structures, maybe calling a database or two, and assembling a response to serialize ~500 times/sec/CPU core).
On more CPU-bound workflows, like one we have that essentially just computes set memberships at 100% resource usage all day long, we saw multiplicative increases, and I can't even mention how much exactly, because the speedup was so great that we couldn't run it in our data center because it started using up all our bandwidth, so I only have numbers for once it was moved into AWS and onto different machines :).
Happy to elaborate more, as you can tell, I think companies with performance-sensitive workloads need to be looking at PyPy, so always happy to talk about our experiences.
They do work these days in PyPy though, so I'd feel comfortable doing so if we did, although I'd probably feel just as comfortable writing whatever numerics in pure-Python too unless it was stuff that already existed easily elsewhere.
On a personal note I've played with OpenCV as well (and done so with PyPy to do some real-time facial analysis on a video stream), but yeah also not for $PRODUCTION_WORK.