What is GOMEMLIMIT and memory ballasting in Go?

Question

Accepted Answer

GOMEMLIMIT is a **memory limit** for the Go runtime (Go 1.19+), allowing more precise GC management.

```go
import "runtime/debug"

func main() {
    // Setting memory limit
    debug.SetMemoryLimit(1 << 30)  // 1GB

// Disabling automatic GC
    debug.SetGCPercent(-1)

// Monitoring
    var stats runtime.MemStats
    runtime.ReadMemStats(&stats)
    fmt.Printf("Alloc: %d MB
", stats.HeapAlloc/1024/1024)
    fmt.Printf("Sys: %d MB
", stats.Sys/1024/1024)
}

// Memory ballasting: allocating memory for predictable GC
func setupMemoryBallast(sizeMB int) {
    ballast := make([]byte, sizeMB*1024*1024)
    runtime.KeepAlive(ballast)  // Prevent GC from collecting
}

// Usage
func main() {
    // Allocate 500MB for ballast
    setupMemoryBallast(500)

// Now GC will run less frequently
    // Because it "thinks" there's already a lot of memory
}

// In Docker/Kubernetes
// Set GOMEMLIMIT = 80% of container limit
// GOMEMLIMIT=1717986918  # 80% of 2GB

// Configuration
func configureForDocker() {
    // Read limit from environment variable
    if memLimit := os.Getenv("GOMEMLIMIT"); memLimit != "" {
        limit, _ := strconv.ParseInt(memLimit, 10, 64)
        debug.SetMemoryLimit(limit)
    }
    debug.SetGCPercent(100)
}
```

**Advantages:**
- Predictable memory usage.
- Fewer GC pauses.
- Ideal for containers.

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