v0 of recursive deltas

[cgwalters]

The deltas code/design supports recursion, but we didn't really follow through implementing this. There's both client side and compiler work for this.

The goal should be that we support upgrading from both N-2 and N-1 to N reasonably.

[gatispaeglis]

+1 This is a feature I would like to see in the upcoming ostree releases. I am wondering if this is something that could be available in a near future or is it low in the priority list?

[cgwalters]

We can also do client-side delta chaining; the main issue is it would make the already-past-its-complexity-budget pull code even more complex. But perhaps not unreasonably so, particularly if we started to spit ostree-repo-pull.c → ostree-repo-pull-loose.c and ostree-repo-pull-deltas.c or so.

In the short term, I'm thinking more ostreedev/ostree-releng-scripts#10

[sinnykumari]

Any plan to fully support applying recursive deltas on client side? This will be useful where we want to rely on deltas only repos (like FCOS mirroring fedora-infra/mirrormanager2#258 ).

I was trying locally to pull ostree content using delta-only repo.

1. Created static delta from scratch for commit C1
2. client side pull works fine with option --require-static-deltas and pulls in C1
3. Created static delta from commit C1 to C2
4. Client side pull to C2 works fine when client side repo is already on C1
5. Client side pull gives error if client wants to pull directly C2 from an empty repo . (error: Static deltas required, but none found for BRANCH to C2)
6. Similarly, consider more commits like C3 and C4 and we have created incremental delta from C2 to C3 and then C3 to C4. Client can't update from C2 to C4 because there is no direct static delta from C2 to C4

It will be nice if ostree can apply recursive delta on client side so that we don't have to really create static delta for all permutations (which will grow as the project grows).