On Sun, Jun 10, 2018 at 07:14:55PM +0200, Michael Stapelberg wrote: > The zchunk format, outlined in the post, is being introduced in Fedora for > efficient metadata transfer.
As I understand it, zchunk isn't competition for pdiff (per se), but competition for the compressed files xz/bz2/gz as files aren't only downloaded in zchunk format but also stored in that format. So what we (can) do at the moment with downloading the smallest files (like xz) and store it in a format for fastest access vs. space usage like uncompressed or lz4 compressed wouldn't be possible anymore. It therefore also pre-depends on people and programs stopping to access files in /var/lib/apt/lists directly, which we would like to reach some point, but aren't there yet. This format also depends on having random access to remote files aka HTTP range requests – suprising as it sounds, some users in the wild interact with servers who do not support this feature & support for having multiple ranges in the request is another beast to implement in both server and client. For those users the format would combine all disadvantages – and these users happen to be the ones where download metrics matter the most (at least in my experience). That is entirely ignoring if that has any actual benefits as I haven't tried it at all, which would probably be the very first step – to actually verify that there is a point in all this. Judging just by the text, it seems to combine all the worst aspects it can in the worst case and seems to have only marginal benefits above what we have¹ in the best case, but a reality check might provide another/better view (not volunteering myself). Best regards David Kalnischkies ¹ which is different from Fedora both in that they have no pdiff and that they don't keep indexes in a as central location as we do (from my limited understanding of never actually having used yum/dnf).
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