TL;DR: run `git config protocol.version 2` in your local clones of the core and online repositories. That should reduce downstream traffic by over 50x (from 9MiB to 150kiB) in no-op `git fetch` commands. Client-side this only applies to git ≥2.18.0. Dear developers, We just upgraded https://gerrit.libreoffice.org to Gerrit v3.1. Thanks to upstream work by David Ostrovsky and others this version adds support for version 2 of the git wire protocol [0], which significantly improves performance of `git fetch` commands on repositories with many references such as ours. That's something we had our eyes on for a while [1]. core currently has over 300k references, the overwhelming majority of which from changesets (each changeset creates n+1 refs, where n is the number of its revisions). In version 1 of the git wire protocol the entire reference list, along with the commit IDs they point to, is sent to client in the initial server advertisement (as can be seen by adding ‘GIT_TRACE_PACKET=1’ to the environment of a git-fetch(1) command). This causes significant downstream traffic, especially because the commit IDs makes compression moot. On our large repositories this is even a noticeable bottleneck. In contrast, with version 2 only requested refs are being sent, thereby significantly reducing downstream traffic when the repository is already up to date. Here are some metrics for a fresh core clone: * `git fetch` yields an advertisement of size 8666kiB, and takes over 3s to complete (in the same datacenter); while * `git -c protocol.version=2 fetch` yields a response of size 150k and takes under 0.5s to complete. That's over 50× smaller! Of course on an “active” clone the initial advertisement won't be empty as it'll likely contain refs for the recent changesets you're working on, but certainly not the 300k (and counting) references. So most likely a two digit factor improvement :-) The performance gain is visible for other transports as well, so this applies to ssh://gerrit.libreoffice.org:9418 too (and even to the now deprecated git://git.libreoffice.org). Please run git config protocol.version 2 in your local clones to force the client to use version 2 of the wire protocol. Or even globally (it will fallback to the original wire protocol if the server doesn't support it) with git config --global protocol.version 2 To check if that worked, `GIT_TRACE_PACKET=1 git fetch 2>&1 | head` should produce the following output pkt-line.c:80 packet: git< version 2 pkt-line.c:80 packet: git< ls-refs […] pkt-line.c:80 packet: git< 0000 pkt-line.c:80 packet: fetch< version 2 pkt-line.c:80 packet: fetch< ls-refs […] This is a wire protocol, so the change is only relevant for transport. No need to re-create existing clones. I suppose git upstream will change the default protocol.version at some point, but given the above I see no reason to wait. Thanks! Cheers. -- Guilhem, for The Document Foundation's infrastructure team. PS: Please preserve the recipient list in replying. [0] https://git-scm.com/docs/protocol-v2 [1] https://lists.freedesktop.org/archives/libreoffice/2018-October/081249.html
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