Re: [PATCH 03/10] builtin/gc.c: ignore cruft packs with `--keep-largest-pack`

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 17, 2023, 22:54 UTC
Message-ID: <xmqqildui0gk.fsf@gitster.g>
In-Reply-To: <796df920ad6af0ee9101a0f3f80edbc793987336.1681764848.git.me@ttaylorr.com>

Taylor Blau <me@ttaylorr.com> writes:

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> When cruft packs were implemented, we never adjusted the code for `git
> gc`'s `--keep-largest-pack` and `gc.bigPackThreshold` to ignore cruft
> packs. This option and configuration option share a common
> implementation, but including cruft packs is wrong in both cases:
>
>   - Running `git gc --keep-largest-pack` in a repository where the
>     largest pack is the cruft pack itself will make it impossible for
>     `git gc` to prune objects, since the cruft pack itself is kept.

Makes sense. We want to keep the largest pack that is actually in use, and we want to consolidate other non-cruft packs into one.

>   - The same is true for `gc.bigPackThreshold`, if the size of the cruft
>     pack exceeds the limit set by the caller.

This is not as cut-and-dried clear as the previous one. "This pack is so large that it is not worth rewriting it only to expunge a handful of objects that are no longer reachable from it" is the main motivation to use this configuration, but doesn't some part of the same reasoning apply equally to a large cruft pack? But let's assume that the configuration is totally irrelevant to cruft packs and read on.

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>  --keep-largest-pack::
> -	All packs except the largest pack and those marked with a
> -	`.keep` files are consolidated into a single pack. When this
> -	option is used, `gc.bigPackThreshold` is ignored.
> +	All packs except the largest pack, any packs marked with a
> +	`.keep` file, and any cruft pack(s) are consolidated into a
> +	single pack. When this option is used, `gc.bigPackThreshold` is
> +	ignored.

"except the largest pack" -> "except the largest, non-cruft pack"