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Comment by lmm | Hacker News Reader

Is the JVM overhead really significant these days? You're talking about wasting what, maybe 32MB for each instance? (which can have multiple threads, you don't need one per core). Is your RAM really so limited that you'd run out of RAM before maxing out all your CPUs or I/O in a Scala version?

(I am kind of interested in Rust, but not going to touch it until it gets proper HKT support - you have to duplicate so much code otherwise)

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It is a lot, when we need to scale by adding more Mesos tasks. Every task launches a new JVM instance, which adds to the total memory usage. Also by using a GC and not wanting to collect all the time, you need to add more memory overhead, which is not required with Rust.

Comparison: I have one app written with Scala and consuming 350 megabytes per Mesos task. The similar-sized Rust app is using 8-10 megabytes of RAM. When you have 1000 instances running during a peak, this escalates fast.

So, for jvm you create less tasks but with more ram, e.g. 100 tasks 4G RAM each, and problem is solved?

Having more of the smaller tasks spreads out the load more evenly and when rust apps starts in less than a second, it's easy to fine tune and reason about having more tasks running. With JVM, we just waste memory because of the overhead from GC, and I don't feel comfortable with the idea.

A bit odd to be running a VM on a VM. Did you consider using a Java "application server" or similar that can keep a VM running and run tasks within that?

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