Subject: [WIP RFC 0/5] Design for offloading part of packfile response to CDN

From: Jonathan Tan <[email-masked]>
Date: Mon, 3 Dec 2018 15:37:33 -0800

Some of us have been working on a design to improve the scalability of
Git servers by allowing them to offload part of the packfile response to
CDNs in this way: returning HTTP(S) URIs in fetch responses in addition
to packfiles.

This can reduce the load on individual Git servers and improves
proximity (by having data served from closer to the user).

I have included here a design document (patch 2) and a rough
implementation of the server (patch 5). Currently, the implementation
only allows replacing single blobs with URIs, but the protocol
improvement is designed in such a way as to allow independent
improvement of Git server implementations.

There is a potential issue: a server which produces both the URIs and
the packfile at roughly the same time (like the implementation in this
patch set) will not have sideband access until it has concluded sending
the URIs. Among other things, this means that the server cannot send
keepalive packets until quite late in the response. One solution to this
might be to add a feature that allows the server to use a sideband
throughout the whole response - and this has other benefits too like
allowing servers to inform the client throughout the whole fetch, not
just at the end.

Jonathan Tan (5):
  Documentation: order protocol v2 sections
  Documentation: add Packfile URIs design doc
  upload-pack: refactor reading of pack-objects out
  upload-pack: refactor writing of "packfile" line
  upload-pack: send part of packfile response as uri

 Documentation/technical/packfile-uri.txt |  83 +++++++++++++
 Documentation/technical/protocol-v2.txt  |  22 ++--
 builtin/pack-objects.c                   |  48 ++++++++
 fetch-pack.c                             |   9 ++
 t/t5702-protocol-v2.sh                   |  25 ++++
 upload-pack.c                            | 150 ++++++++++++++++-------
 6 files changed, 285 insertions(+), 52 deletions(-)
 create mode 100644 Documentation/technical/packfile-uri.txt

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