From: Ben Peart <peartben@gmail.com>
To: Duy Nguyen <pclouds@gmail.com>, Ben Peart <Ben.Peart@microsoft.com>
Cc: Git Mailing List <git@vger.kernel.org>,
Junio C Hamano <gitster@pobox.com>,
Eric Sunshine <sunshine@sunshineco.com>
Subject: Re: [PATCH v3] checkout: optimize "git checkout -b <new_branch>"
Date: Fri, 17 Aug 2018 08:37:03 -0400 [thread overview]
Message-ID: <448bd740-73fb-aa3a-ded0-e4012cf6ec21@gmail.com> (raw)
In-Reply-To: <CACsJy8B84T9HSJKAErNAyoMwbBpu6Gwgyz3RsvmqD0+o=bg3Ng@mail.gmail.com>
On 8/16/2018 2:37 PM, Duy Nguyen wrote:
> On Thu, Aug 16, 2018 at 8:27 PM Ben Peart <Ben.Peart@microsoft.com> wrote:
>>
>> 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.
>
We have investigated some of these already - split index ended up
slowing things down more than it sped them up do to the higher compute
costs. Sparse checkout we've already optimized significantly - limiting
the patterns we accept so that we can do the lookup via a hashmap
instead of the robust pattern matching. We will continue to look for
other optimizations and appreciate any and all ideas!
In the end, this optimization makes a huge performance improvement by
avoiding doing a lot of work that isn't necessary. Taking a command
from 14+ seconds to sub-second is just too much of a win for us to ignore.
> But anyway, it's not my call. I'll stop here.
>
next prev parent reply other threads:[~2018-08-17 12:37 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-24 18:01 [PATCH v1] checkout: optionally speed up "git checkout -b foo" Ben Peart
2018-07-24 18:42 ` Eric Sunshine
2018-07-24 19:45 ` Ben Peart
2018-07-26 15:04 ` Junio C Hamano
2018-07-26 18:59 ` Eric Sunshine
2018-07-26 19:08 ` Eric Sunshine
2018-07-24 19:21 ` Junio C Hamano
2018-07-24 20:47 ` Ben Peart
2018-07-31 16:39 ` [PATCH v2] checkout: optimize "git checkout -b <new_branch>" Ben Peart
2018-07-31 20:01 ` Junio C Hamano
2018-08-01 15:10 ` Duy Nguyen
2018-08-02 18:02 ` Ben Peart
2018-08-03 15:58 ` Duy Nguyen
2018-08-06 14:25 ` Ben Peart
2018-08-15 21:05 ` Ben Peart
2018-08-05 8:57 ` Duy Nguyen
2018-08-16 18:27 ` [PATCH v3] " Ben Peart
2018-08-16 18:37 ` Duy Nguyen
2018-08-17 12:37 ` Ben Peart [this message]
2018-08-19 1:44 ` Elijah Newren
2018-08-20 13:40 ` Ben Peart
2018-08-20 18:16 ` Elijah Newren
2018-08-21 14:51 ` Duy Nguyen
2018-08-30 17:22 ` Elijah Newren
2018-09-04 16:46 ` Duy Nguyen
2018-08-20 18:31 ` Junio C Hamano
2018-09-18 5:34 ` [PATCH] config doc: add missing list separator for checkout.optimizeNewBranch Ævar Arnfjörð Bjarmason
2018-09-18 16:57 ` Taylor Blau
2018-09-18 17:16 ` Jeff King
2018-09-18 17:20 ` Taylor Blau
2018-09-18 17:13 ` Jeff King
2018-09-19 4:41 ` Ævar Arnfjörð Bjarmason
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