Comparing Heap Allocation in Go vs. Rust
In the world of high-performance systems, memory is the final frontier. While both Go and Rust are modern, powerful, and efficient, they handle the heap—the memory used for dynamic allocations—with fundamentally different philosophies.
If you are a developer moving between these two languages, understanding these differences is the key to preventing memory leaks in Rust and latency spikes in Go.
1. The Core Philosophy: GC vs. Ownership
The primary difference lies in who is responsible for cleaning up the heap.
Go: The Hands-Off Approach
Go uses a garbage collector (GC). When you create an object, the Go runtime decides whether to put it on the stack or the heap (via escape analysis). If it lands on the heap, the GC will eventually scan your memory and reclaim what you are not using.
Pros: High developer productivity; no need to worry about manual memory management.
Cons: Non-deterministic stop-the-world pauses (even if sub-millisecond).
Rust: The Pay-as-you-go Approach
Rust uses an ownership and borrowing model. Memory is tied to the scope of a variable. When a variable goes out of scope, its memory is freed immediately. No collector, no background scanning, just deterministic cleanup.
Pros: Zero-cost abstractions; predictable performance; no GC overhead.
Cons: The borrow checker can be difficult for beginners to navigate.
2. Visualizing Memory Lifecycle
In Go, memory stays alive as long as there is a pointer to it. In Rust, memory stays alive as long as the owner is alive.
3. Code Example: Allocating a Struct
Let us see how both languages handle a simple scenario: creating a user on the heap.
Go: Escape Analysis
In Go, you do not explicitly say put this on the heap. The compiler decides.
type User struct {
ID int
}
func CreateUser() *User {
u := User{ID: 1}
return &u // This escapes to the heap because it's returned as a pointer
}What happens: the compiler sees you are returning a pointer to a local variable. Since that variable needs to outlive the function call, Go moves it to the heap. The GC tracks this User and deletes it only when nobody holds a pointer to it anymore.
Rust: Explicit Box
In Rust, you are explicit about where data lives.
struct User {
id: i32,
}
fn create_user() -> Box {
let u = User { id: 1 };
Box::new(u) // Explicitly move the User to the heap
} // Memory is NOT freed here because the Box was returned to the caller What happens: using Box<T> explicitly puts the User on the heap. The caller now owns that box. As soon as the caller is finished and the variable goes out of scope, the memory is freed instantly—no waiting for a GC cycle.
4. Fragmentation and the Stutter
Because Go manages memory for you, it has to deal with fragmentation. Over time, the heap can become a Swiss cheese of used and unused blocks.
Go's strategy: Uses a TCMalloc-style allocator with size classes.
Rust's strategy: Typically uses jemalloc or the system allocator; stack usage keeps heap pressure lower.
5. Performance Implications
| Feature | Go | Rust |
|---|---|---|
| Allocation speed | Very fast (bumping a pointer) | Fast (system call or jemalloc) |
| Cleanup speed | Delayed (GC cycles) | Instant (deterministic) |
| CPU overhead | Higher (GC background work) | Negligible |
| Developer effort | Low | High (initial learning curve) |
Which one should you choose?
Choose Go if you need to build microservices quickly, value developer velocity, and can tolerate the small overhead of a garbage collector.
Choose Rust if you are building critical path infrastructure where every microsecond matters and you want absolute control over your hardware.