How do you profile a Go application using pprof?

Go ships net/http/pprof (for running services) and the runtime/pprof package for programmatic profiling. Profiles are the primary tool for diagnosing CPU hotspots, memory leaks, and goroutine leaks in production.

// ── HTTP endpoint (register once, profile on demand) ──
import _ "net/http/pprof" // blank import registers handlers
import "net/http"

go func() {
    log.Println(http.ListenAndServe("localhost:6060", nil))
}()

// Profile endpoints:
// http://localhost:6060/debug/pprof/goroutine?debug=1  — goroutines
// http://localhost:6060/debug/pprof/heap               — heap snapshot
// http://localhost:6060/debug/pprof/profile?seconds=30 — CPU profile

// ── CLI usage ──
// Download and view CPU profile:
// go tool pprof http://localhost:6060/debug/pprof/profile?seconds=30
// (pprof) top10    — top 10 functions by CPU
// (pprof) web      — opens flame graph in browser
// (pprof) list myFunc — annotated source for myFunc

// Heap profile:
// go tool pprof http://localhost:6060/debug/pprof/heap
// (pprof) top10 -cum   — cumulative allocation
// (pprof) alloc_space  — total bytes allocated (not just live)
// (pprof) inuse_space  — currently live bytes

// ── Benchmark profiling ──
// go test -bench=. -cpuprofile=cpu.out -memprofile=mem.out
// go tool pprof cpu.out

// ── Programmatic (for batch programs) ──
f, _ := os.Create("cpu.prof")
pprof.StartCPUProfile(f)
defer pprof.StopCPUProfile()
// ... run workload ...
// go tool pprof cpu.prof

The execution tracer (go tool trace) complements pprof: it shows fine-grained goroutine scheduling, syscall latency, and GC events on a timeline — useful when pprof shows low CPU usage but latency is still high (often caused by goroutine blocking or GC pauses).

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