GC and memory
- Go course
- Expert
- Lesson 11/34
- 4 min
Learn the heap vs stack split and escape analysis.
Reducing allocations
GC cost is proportional to the allocation rate and the live heap size. The most effective GC tuning is allocating less:
- Give slices and maps capacity with
make. - Reuse temporary buffers with
sync.Pool. - Avoid needless
anyconversions (boxing) in hot loops. - Pass small structs by value instead of pointer.
Using sync.Pool
An object taken from the pool must be reset before use and put back when done:
var tampon = sync.Pool{New: func() any { return new(bytes.Buffer) }}
b := tampon.Get().(*bytes.Buffer)
b.Reset()
b.WriteString("yanıt")
// ... use it ...
tampon.Put(b)Not putting back very large buffers keeps a single big request from bloating the pool.
Practice Pooled buffer
Set up a *bytes.Buffer pool with sync.Pool (using the New field). Get one, Reset it, write "merhaba", print the contents and Put it back.
Starter code
package main
import (
"bytes"
"fmt"
"sync"
)
func main() {
// buraya yaz
}Sample solution
package main
import (
"bytes"
"fmt"
"sync"
)
var havuz = sync.Pool{New: func() any { return new(bytes.Buffer) }}
func main() {
b := havuz.Get().(*bytes.Buffer)
b.Reset()
b.WriteString("merhaba")
fmt.Println(b.String())
havuz.Put(b)
}Expected output
merhaba
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What can happen to objects in a <code>sync.Pool</code>?
- They are copied
- They can be dropped during GC; the pool isn't a permanent cache Correct answer
- They are kept forever
- They are written to disk
Explanation: A pool may empty itself across GC cycles; it suits only temporary objects that can be recreated.
2 Put it back
b := havuz.Get().(*bytes.Buffer)
b.Reset()
// ...
havuz.____(b)b := havuz.Get().(*bytes.Buffer)
b.Reset()
// ...
havuz.Put(b)Explanation: Put leaves the object in the pool; a later Get can reuse it.
3 Technique and gain
| Term | Meaning |
|---|---|
make(..., 0, n) |
No growth copies |
sync.Pool |
Buffer reuse |
Value struct |
No heap allocation |
strings.Builder |
Few intermediate strings |