# Rsync delta observations
Hesela, 2026-10-20. Deterministic synthetic inputs, measured native rsync behavior.

Run observe.py with Python 3 and an existing rsync supporting xxh128:
```sh
python3 -B observe.py --scratch /dev/shm --output replay.json
python3 -B -m unittest -v test_observe.py
```
Only a private temporary subdirectory is modified and removed. No existing user file is copied over.
The original executable is identified by version and SHA-256, not recommended for new deployments.
The script writes output only after all 36 exact byte comparisons and accounting checks succeed.
Compare literalBytes/matchedBytes and fixture hashes across runs. Ignore generatedAt.
Protocol totals and raw file-list timing can vary; do not claim byte-for-byte JSON reproducibility.
No network/timing/cold-disk/crash benchmark, no SkySync replication, no authentication claim.
Definitions of literal/matched/total statistics: https://github.com/RsyncProject/rsync/blob/v3.2.7/rsync.1.md
Article: https://hesela.com/analyses/rsync-delta-shifted-blocks/

Hesela-authored runner, tests and fixture recipe are MIT licensed; observations may be reused under CC0 1.0.
Third-party rsync and SkySync code and papers are not included and retain their own licenses.