memory_map_file

🧠 Use Memory-Mapped Files for Zero-Copy Access

Memory‑mapping a file lets you treat file contents as if they were in-memory arrays, avoiding extra buffer copies and leveraging the OS page cache. For large datasets or performance‑critical workloads (e.g., binary parsing, image processing), use the mmap gem for direct and efficient access.

require 'mmap'

# Memory-map a 1GB file read-only
mm = Mmap.new('large_data.bin', Mmap::MAP_SHARED, Mmap::PROT_READ)

# Access bytes directly
puts mm[0, 16].unpack('H*')

# Modify in place if writable
# mm.protect = Mmap::PROT_READ | Mmap::PROT_WRITE
# mm[0] = 0xFF

mm.unmap

This approach bypasses Ruby’s IO buffers and uses the OS’s virtual memory mechanisms, providing near-native performance when iterating or slicing huge files.