Zig Memory Management: Small Binaries, Big Impact

2025-02-18

Zig's memory management enables exceptionally small binaries while maintaining safety. Here's how its allocator system outperforms Rust in Docker and embedded contexts.

Core Allocators

GeneralPurposeAllocator (GPA)

var gpa = std.heap.GeneralPurposeAllocator(.{}){};
const allocator = gpa.allocator();
defer _ = gpa.deinit();

// 300KB static binary vs Rust's 2.8MB
const list = std.ArrayList(u8).init(allocator);

ArenaAllocator

var arena = std.heap.ArenaAllocator.init(allocator);
defer arena.deinit();

// Bulk allocations with zero tracking overhead
const json = try std.json.parseFromTokens(
    Value,
    &parser,
    arena.allocator()
);

FixedBufferAllocator

var buffer: [1024]u8 = undefined;
var fba = std.heap.FixedBufferAllocator.init(&buffer);

// Zero runtime, perfect for embedded
const small_str = try fba.allocator().alloc(u8, 5);

PageAllocator

const page = std.heap.page_allocator;
const big_buffer = try page.alloc(u8, 1024 * 1024);
defer page.free(big_buffer);

Docker Impact

Production Binary Sizes:

• Basic HTTP Server: 300KB (Zig) vs 2.8MB (Rust)
• JSON + SQLite: 850KB (Zig) vs 4.2MB (Rust)
• Full REST API: 1.2MB (Zig) vs 6.8MB (Rust)

Minimal Dockerfile

FROM alpine:3.18 as builder
COPY . /app
WORKDIR /app
RUN wget https://ziglang.org/download/0.11.0/zig-linux-x86_64-0.11.0.tar.xz && \
    tar -xf zig-linux-x86_64-0.11.0.tar.xz
RUN ./zig-linux-x86_64-0.11.0/zig build -Doptimize=ReleaseSmall

FROM scratch
COPY --from=builder /app/zig-out/bin/server /server
ENTRYPOINT ["/server"]

Key Benefits

• Zero Runtime: No mandatory safety checks
• Explicit Control: Choose exactly what overhead you need
• True Static Linking: Complete musl integration

Memory Usage Under Load

# Idle
zig-server   1.2MB
rust-server  8.4MB

# 1000 req/s
zig-server   2.8MB
rust-server  12.6MB

The difference comes from Zig's allocator philosophy: pay only for what you use. Each allocator serves a specific need, from GPA's safety to FixedBuffer's embedded efficiency, enabling precise optimization for your use case.

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