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The trace tool

Learn the timeline with go tool trace.

The trace tool

pprof collects samples; go tool trace shows events on a timeline: when goroutines ran on which P, when they blocked, when GC kicked in.

f, _ := os.Create("trace.out")
trace.Start(f)
defer trace.Stop()

// code to inspect

Inspect with go tool trace trace.out, which opens a UI in the browser.

Tasks and regions

You can add your own markers to a trace, so you see units of work by name on the timeline:

ctx, task := trace.NewTask(ctx, "siparis")
defer task.End()
trace.WithRegion(ctx, "odeme", func() {
    odemeAl()
})

Trace files grow large; a few seconds of recording is usually enough.

Practice Trace recording

Start recording into a bytes.Buffer with runtime/trace, compute 10 squared inside trace.WithRegion(context.Background(), "hesap", ...) and stop recording. Print the result and buf.Len() > 0.

Starter code

main.go
package main

import (
    "bytes"
    "context"
    "fmt"
    "runtime/trace"
)

func main() {
    // buraya yaz
}

Sample solution

main.go
package main

import (
    "bytes"
    "context"
    "fmt"
    "runtime/trace"
)

func main() {
    var buf bytes.Buffer
    trace.Start(&buf)
    sonuc := 0
    trace.WithRegion(context.Background(), "hesap", func() {
        sonuc = 10 * 10
    })
    trace.Stop()
    fmt.Println(sonuc, buf.Len() > 0)
}

Expected output

100 true

Questions and answers

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

1 For which question is trace better than pprof?

  • Which line allocates the most memory?
  • How many tests passed?
  • Why aren't my goroutines running in parallel? Correct answer
  • Which function uses the most CPU?

Explanation: Parallelism, waiting and latency problems are about time; trace visualizes them. Total-cost questions belong to pprof.

2 Start recording

Question 
f, _ := os.Create("trace.out")
trace.____(f)
defer trace.Stop()
Answer 
f, _ := os.Create("trace.out")
trace.Start(f)
defer trace.Stop()

Explanation: trace.Start begins recording events; trace.Stop ends it.

3 Tool and focus

Term Meaning
pprof CPU Total CPU cost
pprof heap Memory
trace Timeline
trace.WithRegion Named region

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