Zero-Copy Memory in Rust: How We Streamed 2GB Files Without Crashing the OS

When building high-speed data parsing utilities at Ryla Labs, our initial prototype worked fine on 10MB test payloads. But when a customer fed a 2.4GB JSON export into the parser, the server process consumed 8GB of virtual memory, triggered the Linux OOM-killer, and crashed hard.

The problem was defensive cloning: every parser stage was allocating new heap strings and copying bytes across struct boundaries.

Rewriting the pipeline using Rust’s zero-copy slice references solved the problem completely.

The Power of the Byte Slice &[u8]

Instead of converting raw file buffers into heap-allocated String objects, you can parse data by returning borrowed references directly into the original memory buffer:

// Zero-copy token structure referencing source memory buffer
pub struct Token<'a> {
    pub key: &'a [u8],
    pub value: &'a [u8],
}

impl<'a> Token<'a> {
    #[inline(always)]
    pub fn parse(buffer: &'a [u8], split_pos: usize) -> Self {
        Token {
            key: &buffer[..split_pos],
            value: &buffer[split_pos + 1..],
        }
    }
}

By pairing borrowed slices with mmap (memory-mapped file system calls), the operating system only pages in the exact 4KB disk blocks being read at that instant. Peak resident memory dropped from 8GB to 14MB, while parsing throughput doubled.

Never copy bytes in software if you can simply point to where they already live in RAM.