Re: .deb format: let's use 0.939, zstd, drop bzip2
On Fri, May 10, 2019 at 09:15:49PM +0100, Ian Jackson wrote:
> dpkg-deb has a built-in decoder for the subset of ar that is used for
> deb(5). One reason I chose ar rather than tar is that handwriting a
> decoder for ar was much simpler than for tar.
I wonder then, why the speed loss? A good ar decoder should be able to peel
away that layer without any difference: you just tell the tar decoder that
it has a tarball X bytes long. (Ar members are always contiguous without
holes or sub-blocks, right?)
A stock library like libarchive has to be able to handle arbitrary filters,
the vast majority of which are not transparent zero-copy. Thus, I
understand why my experiments show the difference with a libarchive-based
backend[1]. But if dpkg is faster with 0.939, that's an obvious missed
optimization.
Meow!
[1}. libarchive claims to be zero-copy here but it splits the input into
tiny blocks.
--
⢀⣴⠾⠻⢶⣦⠀
⣾⠁⢰⠒⠀⣿⡁ Historic linguists analyze word roots, right? So 4294967296 is
⢿⡄⠘⠷⠚⠋⠀ a core constant for them?
⠈⠳⣄⠀⠀⠀⠀
Reply to:
- References:
- .deb format: let's use 0.939, zstd, drop bzip2
- From: Adam Borowski <kilobyte@angband.pl>
- Re: .deb format: let's use 0.939, zstd, drop bzip2
- From: Guillem Jover <guillem@debian.org>
- Re: .deb format: let's use 0.939, zstd, drop bzip2
- From: Michael Stone <mstone@debian.org>
- Re: .deb format: let's use 0.939, zstd, drop bzip2
- From: Sam Hartman <hartmans@debian.org>
- Re: .deb format: let's use 0.939, zstd, drop bzip2
- From: Ian Jackson <ijackson@chiark.greenend.org.uk>