SubsystemsBranchModel

Subsystem branch models

0. Current model

master -------------------------------------------------------
                 \            \           \
                  \            \           \
mp                 ----         ----        ------------

Use milestone-proposed to control merge windows.

Drawbacks:

• no subsystems with area experts
• no staging ground for features that are not release-ready
• feature freeze between last milestone and RC1
• painful cherry-picks while MP exists

1. Just add subsystem branches

subsystem --------------------------------------------------
             \ /    \ /     \ /        \ /      \ /   \ /
master -------------------------------------------------------
                 \            \           \
                  \            \           \
mp                 ----         ----        ------------

• Add subsystem branch(es) where possible
• Features that do not belong to a subsystem land directly in master
• Use milestone-proposed to control merge windows.

Drawbacks:

• no staging ground for features that are not release-ready (for features not in subsystems)
• feature freeze between last milestone and RC1
• painful cherry-picks while MP exists

2. "Default" subsystem model

defaultsubsystem    --------------------------------------------------
                         \ /    \ /     \ /        \ /      \ /   \ /
release --------------------------------------------------------------
                / \   / \           / \       / \
subsystem2    --------------------------------------------------------

• Only features that are ready land in the release branch
• Default subsystem branch used when feature does not belong to specific

Drawbacks:

• No obvious "master" branch (release branch will be often frozen and therefore out of date)

3. The master subsystem model

subsystem    --------------------------------------------------
               \ /    \ /     \ /        \ /      \ /   \ /
master    -----------------------------------------------------
                         \  /                 \  /
release -------------------------------------------------------

• Subsystem branches get often proposed to master branch
• Other changes get directly to master branch
• Update release branch with master content at merge point, merge back RC bugfixes after release
• RC fixes land in release branch

Drawbacks:

• No release-readiness review (master needs to be release-ready all the time)
• No feature staging ground unless you use subsystems
• no staging ground for features that are not release-ready (for features not in subsystems)
• feature freeze between last milestone and RC1 (for features not in subsystems)

4. Combo subsystem model

defaultsubsystem    --------------------------------------------------
                         \ /    \ /     \ /        \ /      \ /   \ /
master  --------------------------------------------------------------
                 / \          \                        / \  \
mp              /   \          ------                 /   \  -------
subsystem2    --------------------------------------------------------

• Only features that are ready land in the master branch
• Default subsystem branch used when feature does not belong to specific
• Use milestone-proposed to control merge windows

Drawbacks:

• No feature staging ground unless you use subsystems
• painful cherry-picks when you're out of the merge window