11
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
this post was submitted on 15 Jun 2023
11 points (92.3% liked)
Programming
17314 readers
185 users here now
Welcome to the main community in programming.dev! Feel free to post anything relating to programming here!
Cross posting is strongly encouraged in the instance. If you feel your post or another person's post makes sense in another community cross post into it.
Hope you enjoy the instance!
Rules
Rules
- Follow the programming.dev instance rules
- Keep content related to programming in some way
- If you're posting long videos try to add in some form of tldr for those who don't want to watch videos
Wormhole
Follow the wormhole through a path of communities !webdev@programming.dev
founded 1 year ago
MODERATORS
These are garbage collected languages and come with the overhead of such a process. Rust has no GC process and instead relies on reference counters to statically track live memory.
"GC overhead" only matter for extreme realtime applications, like emulators, games, drivers, simulators, etc. a 10msec (or even a 100msec) pause in a request processing isn't gonna even be noticed when your network, database and disk IO are literally orders of magnitude higher. Use Rust for web services if you like the language, comfortable with it, etc. Don't use it because you think it'll give you "more performance" or "reduce GC overhead".
Java, C#, Python, Node, or even PHP as languages will never be your web backend bottleneck. Large scale web services performance tuning is entirely architectural. What caches you keep, how you organize your data, how many network operation does 1 user interaction translate to, stateful vs stateless components etc.
+1, exactly this.
As an aside, "stop the world" GC pauses can affect web server performance in interesting ways. Some web application servers have a perf profile where throughput drops off a cliff as the server approaches max memory load. This is fine, so long as you know what's happening, and can tune your auto scaling to spin up new servers before you start to hit that threshold. This likely wouldn't be a reason to not use a particular lang / server, except at the most massive scales.
Meta: Hmmm... replying to kbin.social users appears to be bugged from my instance (lemmy.world).
I'm replying to you instead. It doesn't change the meaning of my post at least, but we're definitely experiencing some bugs / growing pains with regards to Lemmy (and particularly lemmy.world).
GC overhead is mostly memory-based too, not CPU-based.
Because modern C++ (and Rust) is almost entirely based around refcount++ and refcount-- (and if refcount==0 then call destructor), the CPU-usage of such calls is surprisingly high in a multithreaded environment. That refcount++ and refcount-- needs to be synchronized between threads (atomics + memory barriers, or lock/unlock), which is slower than people expect.
Even then, C malloc/free isn't really cheap either. Its just that in C we can do tricks like struct Foo{ char endOfStructTrick[0]; } and store malloc((sizeof(struct Foo)) + 255); or whatever the size of the end-of-struct string is, to collate malloc / frees together and otherwise abuse memory-layouts for faster code.
If you don't use such tricks, I don't think that C's malloc/free is much faster than GC.
Furthermore, Fragmentation is worse in C's malloc/free land (many GCs can compact and fix fragmentation issues). Once we take into account fragmentation issues, the memory advantage diminishes.
Still, C and C++ almost always seems to use less memory than Java and other GC languages. So the memory-savings are substantial. But CPU-power savings? I don't think that's a major concern. Maybe its just CPUs are so much faster today than before that its memory that we practically care about.
Only for things that you specifically want shared between threads – namely this (synchronized refcount) is an
std::sync::Arc. What you want to share really depends on the app; in database-backed web services it's quite common to have pretty much zero state shared across threads. Multithreaded environment doesn't imply sharing!The refcount absolutely is shared state across threads.
If Thread#1 thinks the refcount is 5, but Thread#2 thinks the refcount is 0, you've got problems.