Re: Using ZChunk for setup…

[Jon Turney <jon.turney@dronecode.org.uk>]

On 09/01/2022 11:05, Achim Gratz wrote:
> 
> I've been experimenting with ZChunk with the idea of eventually using it
> for setup:
> 
> https://www.jdieter.net/posts/2018/05/31/what-is-zchunk/
> https://github.com/zchunk/zchunk
> 
> The chunked ini file is ~10…15% larger than the original (after
> compression).  In order to minimize the overhead, I've re-arranged the
> package entries to have one chunk for every source package.  The actual
> benefit is that the typical download size reduces to less than 5% of the
> original.  Two examples of much longer timespans between updates are
> provided at the end, which would still download only around a third of
> the original:
> 
[...]
> 
> WDYT?

This seems like a nice thing to have.

How would the signature be checked?  Is it for the reconstructed full 
zchunk file?

One slightly related issue which it would be good to address if possible 
when adding this is that rsync is only file-atomic, not repo-atomic, so 
we may get a compressed ini file and signature which don't match as they 
are different moments in time during an update. I think currently no-one 
notices this if it happens, as setup silently falls back to an older 
compression type, but it would be nice to stop generating those eventually.