Welcome to the 103rd edition of Git Rev News, a digest of all things Git. For our goals, the archives, the way we work, and how to contribute or to subscribe, see the Git Rev News page on git.github.io.
This edition covers what happened during the months of August 2023 and September 2023.
Git participated in GSoC (Google Summer of Code) 2023
The following contributors have successfully passed their final evaluation and published a final report:
Shuqi Liang worked on the More Sparse Index Integrations project. She was mentored by Victoria Dye. The final report can be found on her website.
Kousik Sanagavarapu worked on the Unify ref-filter formats with other –pretty formats project. He was co-mentored by Christian Couder and Hariom Verma. The final report can be found on his website.
Congratulations to these contributors and their mentors!
Ronan Pigott noticed that when he fetched from some repos, for example from the “Linux Stable” repo on kernel.org, most of the time seemed to be spent transferring tags from the remote to the client.
When his local repo was up-to-date and git fetch was used with
--no-tags (or its -n shortcut), it took less than 0.4 seconds
versus more than 1.7 seconds without it.
He asked if there was a reason for this seemingly useless transfer of tags even when the remote didn’t have to send any commit.
Peff, alias Jeff King, replied that “this is how the Git protocol works”. He explained that the server only lists all the refs it knows about, and expects the client to select the refs it wants among them. “Only the client knows what it already has.” For example, there could be new tags on the server pointing to commits that the client already has.
Peff also mentioned that in recent Git versions an extension of the Git protocol allows clients to list only the refs they are interested in, so that the server can send “a much smaller ref advertisement”.
Ronan asked if Peff was talking about the --negotiation-tip
option, as some tests using this option didn’t result in better
performance.
Peff replied that --negotiation-tip was only useful when there are
commits that should be transferred. When histories on the client and
the server have diverged, this option helps them find a common
commit that can be the base for the commits that will be
transferred.
Peff said the extension of the Git protocol he was talking about are “ref-prefix” lines in Git’s “v2” protocol, which is the default protocol since Git v2.29. This protocol allows the client to speak first and specify which ref prefixes it’s interested in with these “ref-prefix” lines.
Setting the GIT_TRACE_PACKET to 1 allows one to see the packets
exchanged between the client and the server, especially the
“ref-prefix” lines when for example git fetch --no-tags origin
master is launched using a recent Git, or the “have” and “want”
lines when client and server have to negotiate a common commit.
Ronan tested Peff’s suggestions and thanked him as he then understood why the tag advertisement was useful.
Various
Light reading
.gitkeep files, use .gitignore instead by Adam Johnson.git fetch followed
by git rebase is a safer alternative (with a feature branch workflow).git bisect, reflog, git blame,
and various Git collaboration workflows.Easy watching
Git tools and sites
c0ffee. Written in Rust. Other similar tools:
git-remote-gitopia helper.
This edition of Git Rev News was curated by Christian Couder <christian.couder@gmail.com>, Jakub Narębski <jnareb@gmail.com>, Markus Jansen <mja@jansen-preisler.de> and Kaartic Sivaraam <kaartic.sivaraam@gmail.com> with help from Adam Johnson, Bruno Brito, Mirth Hickford and Štěpán Němec.