Design a mini git
PremiumMachine codingHard
- Content addressing
- SHA 1
- Commit DAG
Quick answer
This machine coding interview question asks you to design a mini git. Aim for a design that meets its requirements at the stated scale, then explain its main components, data flow and trade-offs. Interviewers want to see how you scope the problem, size it and defend each choice.
The problem
Build a mini Git, a small version-control engine like the one developers use every day, working on an in-memory file system. It saves snapshots as commits, supports branches and merges two lines of work. The hard parts are content-addressed storage, finding the common ancestor and a three-way merge that reports conflicts.
Files live in an in-memory map from path to text. The working tree, the staging area and the object store are all in memory; the engine never touches the disk.
What must a mini git do?
- Stage and commit: add(path) stages current content; commit(message) stores the staged snapshot and moves the current branch to it. A commit with no changes is rejected.
- Merge: merge(branch) fast-forwards when possible; otherwise it finds the merge base, merges file by file and creates a two-parent commit, or reports conflicts and stops.
How well must it do it?
- Immutable history: Objects never change once written; a branch is only a name that points to a commit.
- Deduplication: The same content is stored once, whatever its path or commit.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Content addressing
- SHA 1
- Commit DAG
- Three way merge
- Merge base
- Branches and refs
How you’ll practise
- Requirements
- Entities and interfaces
- Core implementation
- Edge cases and tests
- Extensions
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any machine coding design round.
- Clarifies the requirements before drawing anything
- Uses a few numbers that actually change the design
- Draws a clear path from the client to storage
- Picks storage and caching with reasons, not by habit
- Explains what breaks first under load and how to fix it
- States trade-offs openly instead of claiming a perfect design
Questions people ask about this interview question
- Which design type is this question?
- It is a machine coding question. You design a mini git and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Hard. It suits engineers preparing for senior interviews, where you are expected to drive the discussion and go deep on trade-offs.
- What should I cover first?
- Start with the requirements: what the system must do, how well it must do it and which numbers change the design. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team