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Memory profiling

Learn memory profile and the alloc distinction.

Memory profiling

The heap profile has two views: inuse (memory held right now; for hunting leaks) and alloc (total allocated since start; for reducing GC pressure).

go tool pprof -sample_index=inuse_space http://localhost:6060/debug/pprof/heap
go tool pprof -sample_index=alloc_space http://localhost:6060/debug/pprof/heap

To write to a file use pprof.WriteHeapProfile(f).

runtime.MemStats

For a quick measurement runtime.ReadMemStats is enough instead of a profile:

var m runtime.MemStats
runtime.ReadMemStats(&m)
fmt.Println("heap:", m.HeapAlloc/1024, "KB", "GC:", m.NumGC)

HeapAlloc gives the heap held, TotalAlloc the total allocated and NumGC the number of collections. The call needs a brief stop-the-world; don't call it often.

Practice Measure allocation

Read TotalAlloc with runtime.ReadMemStats, then allocate 1 MB with make([]byte, 1<<20) and measure again. Print whether the difference is at least 1 MB (diff >= 1<<20).

Starter code

main.go
package main

import (
    "fmt"
    "runtime"
)

func main() {
    // buraya yaz
}

Sample solution

main.go
package main

import (
    "fmt"
    "runtime"
)

var sink []byte

func main() {
    var a, b runtime.MemStats
    runtime.ReadMemStats(&a)
    sink = make([]byte, 1<<20)
    runtime.ReadMemStats(&b)
    fark := b.TotalAlloc - a.TotalAlloc
    fmt.Println(fark >= 1<<20)
}

Expected output

true

Questions and answers

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

1 If memory keeps growing, which view do you check first?

  • inuse_space Correct answer
  • alloc_objects
  • The CPU profile
  • trace

Explanation: inuse shows memory still reachable; a leak is found among the growing entries there.

2 Read the stats

Question 
var m runtime.MemStats
runtime.____(&m)
Answer 
var m runtime.MemStats
runtime.ReadMemStats(&m)

Explanation: ReadMemStats fills the given struct with memory statistics.

3 Memory metrics

Term Meaning
inuse_space Held now
alloc_space Total allocated
HeapAlloc Live heap bytes
NumGC GC count

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