atomicfile

func WriteIfChanged ¶

func WriteIfChanged(path string, data []byte, perm os.FileMode) (bool, error)

WriteIfChanged writes data to path via a unique temp file, an fsync and a rename, so a reader never sees a half-written file and a crash never loses a published one, and skips the write entirely when path already holds exactly these bytes.

The skip is the point. A daemon that re-persists a snapshot on a fixed tick spends a write, a rename and a dirtied page every tick even when nothing happened, which on a laptop keeps the disk and the writeback path from ever settling. Comparing against what is already there costs one read of a small, page-cached file. Reports whether it wrote.