Hello, Here below is a possible proposal for a more difficult Google Summer of Code 2020 project. A few questions: - is it too late to propose a new project idea for GSoC 2020? - is it too difficult of a project for GSoC? Best, Jakub Narębski -------------------------------------------------- ### Graph labelling for speeding up git commands - Language: C - Difficulty: hard / difficult - Possible mentors: Jakub Narębski Git uses various clever methods for making operations on very large repositories faster, from bitmap indices for git-fetch[1], to generation numbers (also known as topological levels) in the commit-graph file for commit graph traversal operations like `git log --graph`[2]. One possible improvement that can make Git even faster is using min-post intervals labelling. The basis of this labelling is post-visit order of a depth-first search traversal tree of a commit graph, let's call it 'post(v)'. If for each commit 'v' we would compute and store in the commit-graph file two numbers: 'post(v)' and the minimum of 'post(u)' for all commits reachable from 'v', let's call the latter 'min_graph(v)', then the following condition is true: if 'v' can reach 'u', then min_graph(v) <= post(u) <= post(v) If for each commit 'v' we would compute and store in the commit-graph file two numbers: 'post(v)' and the minimum of 'post(u)' for commits that were visited during the part of depth-first search that started from 'v' (which is the minimum of post-order number for subtree of a spanning tree that starts at 'v'). Let's call the later 'min_tree(v)'. Then the following condition is true: if min_tree(v) <= post(u) <= post(v), then 'v' can reach 'u' The task would be to implement computing such labelling (or a more involved variant of it[3][4]), storing it in commit-graph file, and using it for speeding up git commands (starting from a single chosen command) such as: - git merge-base --is-ancestor A B - git branch --contains A - git tag --contains A - git branch --merged A - git tag --merged A - git merge-base --all A B - git log --topo-sort References: 1. <http://githubengineering.com/counting-objects/> 2. <https://devblogs.microsoft.com/devops/supercharging-the-git-commit-graph-iii-generations/> 3. <https://arxiv.org/abs/1404.4465> 4. <https://github.com/steps/Ferrari> See also discussion in: <https://public-inbox.org/git/86tvl0zhos.fsf@xxxxxxxxx/t/>
