On Mon, Dec 21, 2020, at 1:07 PM, Neal Gompa wrote:
> 
> Sure, this makes some degree of sense, but it doesn't reduce the IOPS
> for actually *doing* the installation.

Yes it does.  It avoids writing the compressed data and then copying it back 
out uncompressed, which is the same amount of savings as the reflink approach.

(It's also equally incompatible with deltarpm)

> This is also a flaw with RPM-OSTree, since you have to fetch
> everything individually

No - static deltas exist, plus layered RPMs work on the wire the same.  But 
this isn't really relevant here.

> and construct the root by shifting hardlinks
> or reflinks around.

Adding a hardlink indeed requires updating inodes proportional to the number of 
files, but that's more an implementation of the transactional update approach, 
not of the "download and unpack in parallel" part which is more what we're 
discussing here.  (Though they are entangled a bit)

Anyways, I'd still stand by my summary that the much lower tech "files in 
temporary directory that get rename()d" approach would be all of *more* 
efficient on disk, simpler to implement and much less disruptive than an RPM 
format change.  (The main cost would be a new temporary directory path that 
would need cleanup as part of e.g. `yum clean` etc.)
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