Re: [PATCH v3] checkout: optimize "git checkout -b <new_branch>"

From: Duy Nguyen <pclouds@gmail.com>
Date: Aug 16, 2018, 18:37 UTC
Message-ID: <CACsJy8B84T9HSJKAErNAyoMwbBpu6Gwgyz3RsvmqD0+o=bg3Ng@mail.gmail.com>
In-Reply-To: <20180816182653.15580-1-benpeart@microsoft.com>

On Thu, Aug 16, 2018 at 8:27 PM Ben Peart <Ben.Peart@microsoft.com> wrote:

Show 17 quoted lines

>
> From: Ben Peart <Ben.Peart@microsoft.com>
>
> Skip merging the commit, updating the index and working directory if and
> only if we are creating a new branch via "git checkout -b <new_branch>."
> Any other checkout options will still go through the former code path.
>
> If sparse_checkout is on, require the user to manually opt in to this
> optimzed behavior by setting the config setting checkout.optimizeNewBranch
> to true as we will no longer update the skip-worktree bit in the index, nor
> add/remove files in the working directory to reflect the current sparse
> checkout settings.
>
> For comparison, running "git checkout -b <new_branch>" on a large repo takes:
>
> 14.6 seconds - without this patch
> 0.3 seconds - with this patch

I still don't think we should do this. If you want lightning fast branch creation, just use 'git branch'. From the timing breakdown you shown in the other thread it looks like sparse checkout still takes seconds, which could be optimized (or even excluded, I mentioned this too). And split index (or something similar if you can't use it) would give you saving across the board. There is still one idea Elijah gave me that should further lower traverse_trees() cost.

But anyway, it's not my call. I'll stop here.

-- 
Duy