Git Maintenance Optimization

Git Maintenance & Optimization

Trigger: Use when optimizing git performance, reducing disk usage, or running scheduled maintenance.

Key Commands

Git GC

# Standard garbage collection
git gc

# Aggressive (slower, better compression)
git gc --aggressive

# Prune old objects (default: 2 weeks)
git gc --prune=now                 # Immediate cleanup
git gc --prune=1.week.ago          # Keep objects < 1 week

# Auto mode (runs when needed)
git gc --auto

# Check what gc would do
git gc --dry-run

Manual Repacking

# Repack all objects into one pack (best compression)
git repack -a -d --depth=250 --window=250

# Repack with bitmap (faster clones/fetches)
git repack -a -d --write-bitmap-index

# Delta islands (monorepos — separate object sharing)
git repack -a -d --delta-islands

# Show pack info
git count-objects -vH

Git Maintenance (v2.30+)

# Start automatic background maintenance
git maintenance start

# View current tasks
git maintenance run

# Run specific task
git maintenance run --task=gc
git maintenance run --task=prefetch
git maintenance run --task=loose-objects
git maintenance run --task=incremental-repack
git maintenance run --task=pack-refs

# Stop maintenance
git maintenance stop

# Register repo for maintenance
git maintenance register

Maintenance Config

# Maintenance strategy
git config maintenance.strategy incremental
# Options: none, incremental, full

# Task schedule
git config maintenance.gc.auto 1
git config maintenance.commit-graph.auto 1

Integrity Checks

# Full filesystem check
git fsck

# Check only for corruption (not dangling objects)
git fsck --strict

# Check connectivity
git fsck --connectivity-only

# Check all objects
git fsck --full

# Check specific object
git fsck <object-sha>

# Auto-fix (only safe fixes)
git fsck --auto

Performance Tuning

# Optimize commit graph (faster git log)
git commit-graph write --reachable

# Enable commit-graph for all clones
git config --global fetch.writeCommitGraph true

# Increase pack window for better compression
git config pack.window 250
git config pack.depth 250

# Multi-pack index (faster object lookup with many packs)
git multi-pack-index write

# Enable feature.manyFiles (monorepo optimization)
git config feature.manyFiles true

Scheduled Maintenance Script

#!/bin/bash
# ~/.local/bin/git-maintenance.sh — run weekly via cron
for repo in ~/projects/*/; do
    cd "$repo"
    echo "=== $(basename "$repo") ==="
    git gc --auto --quiet
    git commit-graph write --reachable --changed-paths
done

Disk Usage Analysis

# Show object store size
git count-objects -vH

# Large objects
git rev-list --all --objects | \
  git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize) %(rest)' | \
  awk '/^blob/ {print $3, $4}' | sort -rn | head -10

# Top largest files (with names)
git rev-list --objects --all | \
  git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize) %(rest)' | \
  sed -n 's/^blob //p' | sort -rn -k1 | head -20

Pitfalls

• gc --aggressive: Very slow on large repos (hours) — only run when needed
• prune=now: Can lose objects currently referenced by reflog entries — expire reflog first
• Shared repos: Running git gc on a --shared clone can corrupt other clones
• Maintenance v2.30+: Older git versions don't have git maintenance — use cron scripts instead
• Network drives: git gc on network filesystems can be unreliable — run locally

Verification

git count-objects -vH                 # Disk usage
git fsck --connectivity-only          # Health check
git maintenance run --dry-run         # Maintenance preview
git commit-graph verify               # Commit graph integrity