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Summary - pprof

Combine CPU and memory profiles to write an analysis.

Profiling summary

The order of performance work: measure → find the biggest cost → change → measure again. The tools:

  • net/http/pprof or runtime/pprof: CPU and heap profiles.
  • go test -bench -cpuprofile -memprofile: repeatable measurement.
  • go tool trace: timing and parallelism.
  • runtime.ReadMemStats: a quick memory reading.

PGO: profile-guided optimization

Since Go 1.21 a CPU profile taken from production can be given to the compiler. It inlines hot functions more aggressively; typical gains are 2–14%.

cp cpu.prof default.pgo   // into the main package folder
go build                   // default.pgo is used automatically

Practice Before/after measurement

Compare two ways of joining with testing.AllocsPerRun: one with s += "x" in a loop, the other with strings.Builder (with Grow(100)). Print both allocation counts for 100 items on one line.

Starter code

main.go
package main

import (
    "fmt"
    "strings"
    "testing"
)

func main() {
    // buraya yaz
}

Sample solution

main.go
package main

import (
    "fmt"
    "strings"
    "testing"
)

var sink string

func main() {
    a := testing.AllocsPerRun(10, func() {
        s := ""
        for i := 0; i < 100; i++ {
            s += "x"
        }
        sink = s
    })
    b := testing.AllocsPerRun(10, func() {
        var sb strings.Builder
        sb.Grow(100)
        for i := 0; i < 100; i++ {
            sb.WriteString("x")
        }
        sink = sb.String()
    })
    fmt.Println(a > b, b)
}

Expected output

true 1

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 If a function uses 2% of total CPU, what does making it 10× faster gain?

  • Nothing can be measured
  • At most about 2% Correct answer
  • 20%
  • The program becomes 10× faster

Explanation: The gain is limited by the function's share of the total (Amdahl's law); focus on the largest shares first.

2 PGO file

Question 
cp cpu.prof ____
go build
Answer 
cp cpu.prof default.pgo
go build

Explanation: default.pgo in the main package folder is read automatically by go build.

3 Group summary

Term Meaning
pprof Where is it spent?
trace When does it happen?
-benchmem Allocation count
default.pgo Profile-guided build

All lessons in Advanced

1 Reflection

  1. The reflect package
  2. reflect.Type
  3. reflect.Value
  4. Reflecting struct fields
  5. Dynamic call
  6. Summary - Reflection

2 unsafe

  1. The unsafe package
  2. unsafe.Pointer
  3. Sizeof and Alignof
  4. Offsetof
  5. unsafe and slice
  6. Summary - unsafe

3 cgo

  1. What is cgo?
  2. Calling C code
  3. C data types
  4. Go-C conversion
  5. cgo and memory
  6. Summary - cgo

4 plugin

  1. The plugin package
  2. Building a plugin
  3. Loading a plugin
  4. Plugin symbol
  5. Plugin and error
  6. Summary - plugin

5 database/sql

  1. The database/sql package
  2. sql.Open
  3. Query and Exec
  4. Prepared statement
  5. Transaction
  6. Summary - database/sql

6 Middleware

  1. The middleware concept
  2. HTTP middleware
  3. Middleware chain
  4. Logging middleware
  5. Auth middleware
  6. Summary - Middleware

7 gRPC

  1. What is gRPC?
  2. Protobuf definition
  3. Compiling with protoc
  4. gRPC server
  5. gRPC client
  6. Summary - gRPC

8 Project: Microservice

  1. Service skeleton
  2. Database layer
  3. HTTP API
  4. Docker and deployment

9 Docker

  1. Dockerfile
  2. Multi-stage build
  3. scratch image
  4. docker-compose
  5. Build args and labels
  6. Summary - Docker

10 pprof

  1. What is pprof?
  2. CPU profiling
  3. Memory profiling
  4. go test -cpuprofile
  5. The trace tool
  6. Summary - pprof

11 Observability

  1. log/slog
  2. Metrics
  3. Tracing
  4. OpenTelemetry
  5. Health check
  6. Summary - Observability

12 Advanced final

  1. Challenge 1 - Reflection
  2. Challenge 2 - Microservice
  3. Challenge 3 - Performance
  4. Challenge 4 - Database