Merging PRs takes very long time for large repository

[typeless]

• Gitea version (or commit ref):

Gitea Version: 1.0.0+76-geb9ce39

• Git version:

$ git --version
git version 2.7.4

• Operating system:

$ cat /etc/os-release
NAME="Ubuntu"
VERSION="16.04.1 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04.1 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"

• Database (use [x]):
  • PostgreSQL
  • MySQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No, https://try.gitea.io will report out-of-memory error when pushing a large repository.
  • Not relevant

Description

When merging a PR, Gitea will clone the whole repository, which is unacceptably time-consuming when the repository is large.

See https://github.com/go-gitea/gitea/blob/master/models/pull.go#L285

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[bkcsoft]

just changing the clone-path to owner/repo.{{.Time}}.git instead would speed it up considerably as git clone on the same mount-point is just a hardlink, also slaping on --local could speed it up in some cases.

Further improvements include --single-branch or --depth 1 to only fetch the branch you're merging into

--local, -l
When the repository to clone from is on a local machine, this flag bypasses the normal "Git aware" transport mechanism and clones the repository by making a copy of HEAD and everything under objects and refs directories. The files under .git/objects/
directory are hardlinked to save space when possible.

--no-hardlinks
Force the cloning process from a repository on a local filesystem to copy the files under the .git/objects directory instead of using hardlinks. This may be desirable if you are trying to make a back-up of your repository.

[typeless]

http://stackoverflow.com/questions/10637584/how-to-do-a-non-fast-forward-git-merge-to-a-branch-that-isnt-checked-out might be useful as well.

Edit: I have a patch experimenting with that, will submit it later.

[bkcsoft]

@typeless not sure if it works for bare repos though 🙁

[typeless]

For reference: https://gist.github.com/cool-RR/6575042