hesela.devRsync quick check
Rsync quick check is the regular-file selection heuristic that normally treats matching file size and modification time as sufficient to skip transferring file data.
The default timestamp comparison uses integer seconds; --modify-window=-1 also compares nanoseconds when the receiver supports it (3.1.3 or later). Finer precision cannot detect changed bytes whose timestamp is exactly preserved. --checksum selects using file contents instead of mtime for equal-size files, adding read work. [1]
Selection precedes delta transfer. In rsync v3.2.7, the regular-file quick_check_ok path tests size mismatch, checksum, size-only, ignore-times and mtime in that order. Combining --size-only with --ignore-times does not force equal-size files into transfer; combining --checksum with --ignore-times can still skip identical content. [2]
Hesela checked these boundaries with 42 constructed native runs, exact-byte comparisons and preserved timestamp controls. Every run returned zero, including metadata-selected skips that retained different destination bytes. This is a scoped software observation, not a rate of backup failures. Transfer verification does not validate the contents of metadata-skipped files. [3]
Relations
Advantages
- Avoids reading every matching-size file solely to decide whether it needs transfer.
Limitations
- Matching metadata is not a content-integrity proof.
- Different selection flags can have precedence rather than last-option-wins behavior.