Re: [PATCH v3 0/4] connected: add incremental connectivity check

[Junio C Hamano <gitster@pobox.com>]

"Kristofer Karlsson via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> I'll just mention a short summary here, to avoid repeating what's already in
> the commit message. The incremental mode is faster than the full mode when
> there are few commits to verify and when the active object tree is large. In
> the happy case, the work tracks the changed paths and their comparison trees
> rather than the full reachable object closure, which substantially reduces
> the dependence on total repository size.

This is exciting.

> There are also regression cases in the synthetic fixtures. With long
> incoming histories, the extra parent-tree scans accumulate; in the synthetic
> fixture incremental is about 1.5x slower at 10000 commits. Per-commit
> ...
> A safety net for this regression could be to dynamically disable the
> incremental mode if the number of incoming commits is too large, but this is
> left out of the initial version to avoid overly speculative code.

Hmm, ... OK.

> Deepening fetches currently fall back to the full check because the full
> check omits --not --all for deepening -- there is no existing-reference
> boundary at which the walk can stop. An incremental approach is possible
> here too -- using the old shallow roots as the trusted boundary and walking
> the deepened ancestry forward -- but that is a separate change and left for
> future work. Deepening is also less common than regular fetch and
> receive-pack, where the speedup matters most.

OK.