What is GOMAXPROCS? What happens if a very large number is set?

GOMAXPROCS is an environment variable or setting in Go that determines the maximum number of operating system threads (OS threads) that the Go scheduler can use to run goroutines simultaneously. By default, it is set to the number of logical processors on the machine.

If a very large number is set for GOMAXPROCS, for example, significantly exceeding the number of available cores, it can lead to excessive context switching between threads, increased scheduling overhead, and consequently, reduced program performance. In the worst case, it can cause degradation due to excessive competition for CPU resources.

Example of setting GOMAXPROCS in code:

import (
    "runtime"
)

func main() {
    runtime.GOMAXPROCS(8) // allow using up to 8 threads
    // ...
}

It is recommended to set GOMAXPROCS equal to the number of logical cores or slightly more, but not too large a value.