Go Garbage Collection — Tasks¶

Task 1 — GC Trace¶

Difficulty: Beginner

GODEBUG=gctrace=1 go run main.go 2>gc.log

Run a small program and inspect each line. Decode each field.

Task 2 — Tune GOGC¶

Difficulty: Beginner

Run a benchmark with different GOGC values:

GOGC=50  go test -bench=. -benchmem
GOGC=100 go test -bench=.
GOGC=200 go test -bench=.

Compare allocation rate and CPU time.

Task 3 — Memory Limit¶

Difficulty: Intermediate

import "runtime/debug"

func main() {
    debug.SetMemoryLimit(int64(50 * 1024 * 1024)) // 50 MB

    // Allocate progressively
    var alloc [][]byte
    for i := 0; i < 100; i++ {
        alloc = append(alloc, make([]byte, 1<<20)) // 1 MB
        time.Sleep(100 * time.Millisecond)
    }
}

Observe how GC adapts as you approach the limit.

Task 4 — Force GC and Measure Pause¶

Difficulty: Intermediate

import "runtime"

func measurePause() {
    var ms runtime.MemStats
    runtime.GC()
    runtime.ReadMemStats(&ms)
    pause := ms.PauseNs[(ms.NumGC+255)%256]
    fmt.Printf("Last GC pause: %d ns\n", pause)
}

Task 5 — Heap Profile¶

Difficulty: Intermediate

go test -bench=. -memprofile=mem.out
go tool pprof mem.out
top

Identify top allocators.

Task 6 — sync.Pool to Reduce GC¶

Difficulty: Advanced

Convert a hot allocation site to use sync.Pool. Compare GC frequency before/after with gctrace.

var pool = sync.Pool{New: func() any { return new(Buffer) }}

func use() {
    b := pool.Get().(*Buffer)
    defer func() { b.Reset(); pool.Put(b) }()
    // use b
}

Task 7 — Reduce Pointer Density¶

Difficulty: Advanced

Convert []*Item to []Item where ownership is exclusive. Measure GC pause time with both variants.

Task 8 — Live Profile Heap¶

Difficulty: Advanced

import _ "net/http/pprof"

go http.ListenAndServe("localhost:6060", nil)

Then:

go tool pprof http://localhost:6060/debug/pprof/heap

Inspect live heap of a running service.

Task 9 — debug.FreeOSMemory¶

Difficulty: Advanced

runtime.GC()
debug.FreeOSMemory()

Run after a known-large data structure is dropped. Observe RSS reduction (via ps or /proc/PID/status).

Task 10 — Detect Goroutine Leak¶

Difficulty: Advanced

import "runtime"

n := runtime.NumGoroutine()
// run suspect code
runtime.GC()
n2 := runtime.NumGoroutine()
if n2 > n { fmt.Println("leak detected") }

For deeper analysis: pprof goroutine.