pkgdelta

pkgdelta [options] <old_package_or_file> <new_package_or_file> [<output_delta_file>]

<old_package_or_file>: Can be an installed package name or the path to an old .deb file.
<new_package_or_file>: Can be an installed package name or the path to a new .deb file.
<output_delta_file>: Optional. The path to save the generated delta. If omitted, the delta is usually written to standard output.

-o, --output-file
    Specifies the path for the output delta file.

-v, --verbose
    Enables verbose output, showing more details during delta generation.

-q, --quiet
    Suppresses most output, showing only critical errors or warnings.

-f, --force
    Forces delta generation even if conditions are not optimal (e.g., packages are identical).

--strict
    Exits with an error if the generated delta is not smaller than the new package.

--diff-cmd
    Specifies an alternative binary diff utility to use (e.g., bsdiff, xdelta).

pkgdelta is a command-line utility used to generate a binary delta between two versions of a software package, typically in the .deb format. It creates a small difference file (the delta) that, when applied to the older package, reconstructs the newer package. This mechanism significantly reduces the amount of data that needs to be transferred during package updates, making it highly beneficial for users with limited bandwidth or slow internet connections. pkgdelta can operate on installed packages by name or on specified .deb package files. It leverages sophisticated binary diffing algorithms to achieve high compression ratios for the difference.

Requires both versions: To generate a delta, pkgdelta needs access to both the exact old and new versions of the package.
Resource intensive: Delta generation can be CPU and I/O intensive, especially for large packages, which might impact system performance during the process.
Delta size variability: While generally small, the delta file can be substantial if the old and new packages differ drastically (e.g., a major version upgrade with extensive changes).
Debian/Ubuntu specific: pkgdelta is primarily part of the debdelta suite and is most commonly used within Debian-based Linux distributions.

At its core, pkgdelta uses advanced binary diffing algorithms (like bsdiff or xdelta) to compare the raw binary content of the old and new package files. It identifies common blocks and generates instructions to transform the old file into the new one, resulting in a delta file much smaller than the new package itself. This delta is then used by tools like applydelta to reconstruct the updated package.

The primary use case for pkgdelta (or the debdelta system it's part of) is for efficient package updates. Instead of downloading a 50MB new package, a user might only download a 500KB delta file. This is especially valuable in environments with slow internet connections, metered bandwidth, or frequent updates to large packages.

pkgdelta is an integral component of the debdelta project, which was initiated to revolutionize how Debian package updates are distributed. Its development aimed at drastically reducing bandwidth consumption for users by replacing full package downloads with small, efficient delta updates. The project has been a significant contributor to network efficiency in Debian-based ecosystems since its inception.

debdelta(1), applydelta(1), dpkg(1), apt(8), bsdiff(1)