Re: [RFC PATCH 00/12] Integrate commit-graph into 'fsck' and 'gc'

> The commit-graph feature is not useful to end users until the
> commit-graph file is maintained automatically by Git during normal
> upkeep operations. One natural place to trigger this write is during
> 'git gc'.
>
> Before automatically generating a commit-graph, we need to be able to
> verify the contents of a commit-graph file. Integrate commit-graph
> checks into 'fsck' that check the commit-graph contents against commits
> in the object database.
>
> Things to think about:
>
> * Are these the right integration points?
>
> * gc.commitGraph defaults to true right now for the purpose of testing,
>    but may not be required to start. The goal is to have this default to
>    true eventually, but we may want to delay that until the feature is
>    stable.
>
> * I implement a "--reachable" option to 'git commit-graph write' that
>    iterates over all refs. This does the same as
>
> 	git show-ref -s | git commit-graph write --stdin-commits
>
>    but I don't know how to pipe two child processes together inside of Git.
>    Perhaps this is a better solution, anyway.
>
> What other things should I be considering in this case? I'm unfamiliar
> with the inner-workings of 'fsck' and 'gc', so this is a new space for me.
>
> This RFC is based on v3 of ds/generation-numbers, and the first commit
> is a fixup! based on a bug in that version that I caught while prepping
> this series.
>
> Thanks,
> -Stolee
>
> Derrick Stolee (12):
>    fixup! commit-graph: always load commit-graph information
>    commit-graph: add 'check' subcommand
>    commit-graph: check file header information
>    commit-graph: parse commit from chosen graph
>    commit-graph: check fanout and lookup table
>    commit: force commit to parse from object database
>    commit-graph: load a root tree from specific graph
>    commit-graph: verify commit contents against odb
>    fsck: check commit-graph
>    commit-graph: add '--reachable' option
>    gc: automatically write commit-graph files
>    commit-graph: update design document
>
>   Documentation/git-commit-graph.txt       |  15 +-
>   Documentation/git-gc.txt                 |   4 +
>   Documentation/technical/commit-graph.txt |   9 --
>   builtin/commit-graph.c                   |  79 +++++++++-
>   builtin/fsck.c                           |  13 ++
>   builtin/gc.c                             |   8 +
>   commit-graph.c                           | 178 ++++++++++++++++++++++-
>   commit-graph.h                           |   2 +
>   commit.c                                 |  14 +-
>   commit.h                                 |   1 +
>   t/t5318-commit-graph.sh                  |  15 ++
>   11 files changed, 311 insertions(+), 27 deletions(-)