git-2-49-features

# Git 2.49+ Features (2025)

## git-backfill Command (New in 2.49)

**What:** Efficiently download missing objects in partial clones using the path-walk API.

**Why:** Dramatically improves delta compression when fetching objects from partial clones, resulting in smaller downloads and better performance.

### Basic Usage

```bash
# Check if you have a partial clone
git config extensions.partialClone

# Download missing objects in background
git backfill

# Download with custom batch size
git backfill --batch-size=1000

# Respect sparse-checkout patterns (only fetch needed files)
git backfill --sparse

# Check progress
git backfill --verbose
```

### When to Use

**Scenario 1: After cloning with --filter=blob:none**
```bash
# Clone without blobs
git clone --filter=blob:none https://github.com/large/repo.git
cd repo

# Later, prefetch all missing objects efficiently
git backfill
```

**Scenario 2: Sparse-checkout + Partial clone**
```bash
# Clone with both optimizations
git clone --filter=blob:none --sparse https://github.com/monorepo.git
cd monorepo
git sparse-checkout set src/api

# Fetch only needed objects
git backfill --sparse
```

**Scenario 3: CI/CD Optimization**
```bash
# In CI pipeline - fetch only what's needed
git clone --filter=blob:none --depth=1 repo
git backfill --sparse
# Much faster than full clone
```

### Performance Comparison

**Traditional partial clone fetch:**
```bash
git fetch --unshallow
# Downloads 500MB in random order
# Poor delta compression
```

**With git-backfill:**
```bash
git backfill
# Downloads 150MB with optimized delta compression (70% reduction)
# Groups objects by path for better compression
```

## Path-Walk API (New in 2.49)

**What:** Internal API that groups together objects appearing at the same path, enabling much better delta compression.

**How it works:** Instead of processing objects in commit order, path-walk processes them by filesystem path, allowing Git to find better delta bases.

**Benefits:**
- 50-70% better c