git merge

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Purpose

git merge is used to combine changes from one branch into another branch.

It integrates the history of two branches.

Unlike rebase, merge does NOT rewrite history.

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Basic Syntax

git merge branch-name

Example:

git switch main

git merge feature-branch

This merges feature-branch into main.

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What Happens Internally

Git finds the common ancestor between branches and combines changes.

There are two main types of merge:

1. Fast-forward merge

2. Three-way merge (creates merge commit)

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1. Fast-Forward Merge

Before:

main: A — B

feature: A — B — C

If you merge feature into main:

git switch main

git merge feature

After:

main: A — B — C

• No merge commit created.
• History remains linear.

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2. Three-Way Merge (Non Fast-Forward)

Before:

main: A — B — C

feature: A — B — D — E

After:

git switch main

git merge feature

Result:

A — B — C ——– M \ / D — E

Git creates a merge commit (M).

This preserves branch history.

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Force Merge Commit (Even If Fast-Forward)

git merge –no-ff feature-branch

Creates a merge commit even when fast-forward is possible.

Used when:

• You want clear branch history
• You want feature tracking

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Handling Merge Conflicts

If conflict occurs:

1. Git marks conflict in files
2. Manually resolve conflicts

3. Stage resolved files:

   git add .

4. Complete merge:

   git commit

To abort merge:

git merge –abort

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Common Real-World Backend Use Cases

1. Merging feature branch into main
2. Integrating release branch
3. Combining hotfix branch into production
4. Team collaboration workflow

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Merge vs Rebase

Merge:

• Preserves complete history
• Safe for shared branches
• Creates merge commits
• No history rewriting

Rebase:

• Rewrites history
• Cleaner linear history
• Dangerous if used on public branches

Rule of thumb:

Use merge for shared branches. Use rebase for local feature cleanup.

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Common Mistakes

1. Merging without pulling latest main
2. Resolving conflicts incorrectly
3. Merging large outdated branches

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Best Practice in Enterprise Projects

Before merging:

git fetch

git switch feature-branch

git rebase origin/main

Then:

git switch main

git merge feature-branch

This reduces merge conflicts and keeps history clean.

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Summary

git merge combines branches.

Types:

• Fast-forward merge
• Three-way merge (merge commit)

Safe for team environments.
Does not rewrite history.