Re: [Question] Can git cat-file have a type filtering option?

From: Taylor Blau <me@ttaylorr.com>
Date: Apr 9, 2023, 01:28 UTC
Message-ID: <ZDIUvK/bF7BFqX5q@nand.local>
In-Reply-To: <CAOLTT8SXXKG3uEd8Q=uh3zx7XeUDUWezGgNUSCd1Fpq-Kyy-2A@mail.gmail.com>

On Sat, Apr 08, 2023 at 02:27:53PM +0800, ZheNing Hu wrote:

> Okay, you're right. It's not "ungraceful" to have each task do its own thing.
> I should clarify that for a command like `git cat-file --batch-all-objects`,
> which traverses all objects, it would be better to have a filter. It might be
> more performant than using `git rev-list --filter | git cat-file --batch`?

Perhaps slightly so, since there is naturally going to be some duplicated effort spawning processes, loading any shared libraries, initializing the repository and reading its configuration, etc.

But I'd wager that these are all a negligible cost when compared to the time we'll have to spend reading, inflating, and printing out all of the objects in your repository.

Hopefully any task(s) where that cost *wouldn't* be negligible relative to the rest of the job would be small enough that they could fit into a single process.

> I don't think so. While `git rev-list` traverses objects and performs
> filtering within a revision, `git cat-file --batch-all-objects` traverses
> all loose and packed objects. It might be difficult to perfectly
> extract the filtering from `git rev-list` and apply it to `git cat-file`.

`rev-list`'s `--all` option does exactly the former: it looks at all loose and packed objects instead of doing a traditional object walk.

Thanks, Taylor