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How to avoid heap allocations in a performance-critical golang function
How to avoid heap allocations in a performance-critical golang function
To reduce the heap allocation of critical path functions in Go, four methods can be taken: 1. Use stack variables to avoid escape; 2. Pre-allocate and reuse objects; 3. Avoid implicit escape writing; 4. Use tools to verify escape. Specifically, it includes avoiding returning local variable pointers, using value types to reduce escape, pre-allocate slice capacity, using sync.Pool to cache objects, avoiding closures to capture large structures, not assign interface types, and checking escape points through -gcflags=-m, thereby reducing GC pressure and improving performance.
In languages like Go, performance-sensitive functions often need to avoid heap allocation as much as possible, because frequent garbage collection (GC) will affect the overall performance of the program. If you want to reduce or even avoid heap memory allocation in a function on a critical path, you can start with the following aspects.
1. Use stack variables instead of dynamic structures
The Go compiler will perform escape analysis during the compilation period to determine which variables can be allocated on the stack and which must be allocated on the heap. To ensure that variables do not escape, avoid operations that will cause escape by returning them, passing them to other goroutines, or assigning values to interfaces.
suggestion:
- Avoid passing local variables out after addressing, such as as return values or incoming closures.
- Try to use value types instead of pointer types unless shared state is indeed required.
- Do not assign variables to
interface{}, this will trigger escape.
For example:
func badFunc() *int {
x := 10
return &x // Here x must be allocated on the heap}Change it to this way and you won't escape:
func goodFunc() int {
x := 10
return x // x allocated on stack}2. Preallocate objects and reuse them
For some temporary objects, such as slice, map, or structure, repeatedly creating in loops or high-frequency calls will cause unnecessary heap allocation. Overhead can be reduced through preallocated and object pooling.
suggestion:
- Use
make([]T, 0, cap)to specify the capacity in advance to avoid multiple expansions. - Object pools can use
sync.Poolto cache temporary objects, but pay attention to their life cycle and concurrency security.
Example:
// Pre-allocated slice
s := make([]int, 0, 10)
for i := 0; i < 10; i {
s = append(s, i) // No additional allocation is triggered}
// Use sync.Pool to cache buffers
var bufPool = sync.Pool{
New: func() any {
b := make([]byte, 1024)
return &b
},
}
func getBuffer() []byte {
return *bufPool.Get().(*[]byte)
}
func putBuffer(b []byte) {
bufPool.Put(&b)
}3. Common writing methods to avoid implicit escape
Some of the writing seems simple, but it will cause the variable to "secretly" escape. Common ones are:
- Reference external variables in closure.
- Pass the variable to
fmt.Println,log.Printfand other printing functions. - Assign to interface types, such as
anyanderror.
These will cause variables to be allocated to the heap.
suggestion:
- If it is only used for log output, you can consider extracting the basic type first and then passing it into the print function.
- Try to avoid capturing large structures in closures and use parameter passing instead.
- Check if you really need to assign variables to the interface.
4. Use tools to verify escape situations
Go provides -gcflags=-m parameter to view the compiler's escape analysis results, which is the most direct way to confirm whether there is unexpected heap allocation.
Operation steps:
Execute the command:
go build -gcflags="-m" main.go
Check the word
escapes to heapin the output and locate the escape point.Pay attention to repeated prompts, which may mean repeated allocation problems.
If you find that a variable should not escape but escape, you can adjust the code structure according to the prompts, such as avoiding address fetching, splitting logic, etc.
Basically that's it. Avoiding heap allocation is not just about pursuing zero GC pressure, but optimizing performance bottlenecks on critical paths. In many cases, rational use of stack variables and object reuse can significantly reduce the pressure while keeping the code clear and easy to read.
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How to avoid heap allocations in a performance-critical golang function
Jul 13, 2025 am 03:06 AM
To reduce the heap allocation of critical path functions in Go, four methods can be taken: 1. Use stack variables to avoid escape; 2. Pre-allocate and reuse objects; 3. Avoid implicit escape writing; 4. Use tools to verify escape. Specifically, it includes avoiding returning local variable pointers, using value types to reduce escape, pre-allocate slice capacity, using sync.Pool to cache objects, avoiding closures to capture large structures, not assign interface types, and checking escape points through -gcflags=-m, thereby reducing GC pressure and improving performance.
