Go Performance

Go Performance Patterns

Performance-specific guidelines apply only to the hot path. Don't prematurely optimize—focus these patterns where they matter most.

Available Scripts

• scripts/bench-compare.sh — Runs Go benchmarks N times with optional baseline comparison via benchstat. Supports saving results for future comparison. Run bash scripts/bench-compare.sh --help for options.

Prefer strconv over fmt

When converting primitives to/from strings, strconv is faster than fmt:

s := strconv.Itoa(rand.Int()) // ~2x faster than fmt.Sprint()

Read references/STRING-OPTIMIZATION.md when choosing between strconv and fmt for type conversions, or for the full conversion table.

Avoid Repeated String-to-Byte Conversions

Convert a fixed string to []byte once outside the loop:

data := []byte("Hello world")
for i := 0; i < b.N; i++ {
    w.Write(data) // ~7x faster than []byte("...") each iteration
}

Prefer Specifying Container Capacity

Specify container capacity where possible to allocate memory up front.

Map Capacity Hints

m := make(map[string]os.DirEntry, len(files))

Slice Capacity

data := make([]int, 0, size)

The capacity version is ~12x faster due to zero reallocations during append.

Pass Values

Don't pass pointers as function arguments just to save a few bytes. If a function refers to its argument x only as *x throughout, then the argument shouldn't be a pointer.

func process(s string) { // not *string — strings are small fixed-size headers
    fmt.Println(s)
}

Common pass-by-value types: string, io.Reader, small structs.

Exceptions: Large structs where copying is expensive, or small structs that might grow in the future.

String Concatenation

Choose the right strategy based on complexity:

Read references/STRING-OPTIMIZATION.md when choosing a string concatenation strategy, using strings.Builder in loops, or deciding between fmt.Sprintf and manual concatenation.

Benchmarking and Profiling

Always measure before and after optimizing. Use Go's built-in benchmark framework and profiling tools.

go test -bench=. -benchmem -count=10 ./...

Read references/BENCHMARKS.md when writing benchmarks, comparing results with benchstat, profiling with pprof, or interpreting benchmark output.

Validation: After applying optimizations, run bash scripts/bench-compare.sh to measure the actual impact. Only keep optimizations with measurable improvement.

Quick Reference