Go Readdir vs ReadDir Micro Benchmark

Repository Raison d'Être

Go 1.16 introduced a new API function in the os package called ReadDir. ReadDir has the same functionality as the previously-existing Readdir, (both return a slice of the contents of a given directory). The intent is that ReadDir is much faster than Readdir, as ReadDir does not stat each file in the directory.

In order to test these claims (and measure the coolness of this new feature), this repo contains two Go benchmark tests: one for ReadDir and one for Readdir.

The benchmarked loop for each test consists of:

• Call to os.Open("/proc") to get a file handle to read ( + error check)
  • I chose to read /proc because it was part of the inspiration for this repo
• Call to the "readdir" function under test ( + error check)

How to Run the Benchmarks

Install the Go toolchain, navigate into the repo, and run

go test -bench=.

Results

From a run on my machine:

❯ go test -bench=.
goos: linux
goarch: amd64
pkg: github.com/nschmeller/go-readdir-benchmark
cpu: Intel(R) Xeon(R) Platinum 8375C CPU @ 2.90GHz
BenchmarkReaddir-32         1242            948619 ns/op
BenchmarkReadDir-32         3039            380531 ns/op
PASS
ok      github.com/nschmeller/go-readdir-benchmark      2.477s

ReadDir is 2.5x faster than Readdir here!

This result run can also be viewed in the GitHub Actions for this repo. From an example run:

Run go test -bench=.
goos: linux
goarch: amd64
pkg: github.com/nschmeller/go-readdir-benchmark
cpu: Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz
BenchmarkReaddir-2   	    8221	    148709 ns/op
BenchmarkReadDir-2   	   46755	     23487 ns/op
PASS
ok  	github.com/nschmeller/go-readdir-benchmark	3.179s

In this case, ReadDir is 6.3x faster than Readdir! 🔥