"Ballista is an experimental distributed compute platform, powered by Apache Arrow, with support for Rust and JVM (Java, Kotlin, and Scala)."

Plus he's got Docker, the Rust library, musl, and jemalloc sometimes. There's no application. All this is just infrastructure.

Musl doesn't do much on its own. But it does do stdio buffering. Could it be that the buffering system is making too many I/O calls, like flushing on every write?