Does aptly mirror update -latest behave like a filter?

[Rascalov]

We've been using -latest recently to speed up mirror sync at certain events (usually CVE patching requiring quick sync of bunch of pockets).
We retroactively set it on mirrors that already had a full archive.

I then noticed published snapshots of mirrors with -latest only had the latest package in their pool, regardless of whether the others were still present on filesystem.

The mirror itself reflects that in its amount of packages.

[ACCEPTANCE] root@repo:~# aptly mirror show elastic-9.x-stable-main | grep 'Number of packages'
Number of packages: 809
[ACCEPTANCE] root@repo:~# aptly mirror update -latest elastic-9.x-stable-main > /dev/null
[ACCEPTANCE] root@repo:~# aptly mirror show elastic-9.x-stable-main | grep 'Number of packages'
Number of packages: 16

This is the intended behavior, correct? The relevant Pull request gave me the impression that it would merely add the latest version of the package to the mirror. In reality It acts more like a filter.

As a write this, I kind of understand it better why, it keeps the pool small regardless of the amount of updates over time, and saves disk space (which was primary goal I imagine).
On the other hand, downgrading/rollback to previous package versions is now more tedious. Maybe a retention policy (e.g. latest 5 packages) could help that use case.

[usmanmateen]

Yes, that's how it works. With -latest, mirror update filters the upstream package list down to the newest version of each name/architecture before downloading (FilterLatest in deb/list.go), and the mirror's package list is then replaced with that filtered list. So the mirror, and any snapshot you take from it afterwards, only has the latest versions. The older .deb files stay in the pool until aptly db cleanup removes the ones nothing references anymore.

To keep quick CVE syncs and still be able to roll back, snapshot the mirror before each -latest update. Older snapshots keep their versions, and snapshot merge -no-remove keeps every version instead of replacing older ones:

aptly snapshot create elastic-9-2026-10-21 from mirror elastic-9.x-stable-main
aptly snapshot merge -no-remove elastic-9-all elastic-9-2026-10-14 elastic-9-2026-10-21

There's no "keep the latest N" option today, so that part would be a feature request.