How to Migrate a Large SVN Repo to Git

Seamlessly Transitioning Your Large SVN Repository

Migrating a massive SVN repository with over 155,000 revisions to Git is a challenging yet essential task for modernizing your version control system. Leveraging svn2git on a Linux Red Hat system, you can ensure the most efficient conversion process. However, it's important to implement a transition strategy to periodically sync the SVN repo and handle new commits during the migration.

This approach allows you to maintain continuity and minimize downtime. A significant challenge in this process is managing large binary files, which can be addressed using Git LFS and BFG Repo Cleaner. Here, we'll explore the strategies and solutions for a smooth migration without disrupting your team's workflow.

Understanding the Migration Process

The provided scripts automate the process of migrating a large SVN repository to Git. The first script is a bash script designed to be run as a cron job on a Linux machine. It periodically synchronizes the local SVN repository with the remote using svnsync sync. Then, it converts the new SVN revisions to Git commits using svn-all-fast-export --resume-from. The script logs the last converted SVN revision to ensure continuity between syncs. Finally, it updates the local Git repository and pushes the changes to the remote repository.

The second script handles the migration of binary files to Git LFS. It initializes Git LFS in the repository, tracks binary files with git lfs track, and commits these changes. The script uses the BFG Repo Cleaner, invoked with java -jar $BFG_JAR --convert-to-git-lfs, to migrate existing binaries to LFS. It then performs garbage collection with git gc --prune=now --aggressive to clean up the repository and forces a push of the updated history to the remote. This script ensures that large binary files are efficiently managed in the Git repository without cluttering the history.

Automating SVN to Git Sync with Cron

Bash Script for Linux Cron Job

#!/bin/bash
# Variables
SVN_REPO_URL="http://your-svn-repo-url"
SVN_LOCAL_DIR="/path/to/local/svn"
GIT_REPO_DIR="/path/to/local/git"
LOG_FILE="/path/to/log/file"

# Sync SVN repo
svnsync sync file://$SVN_LOCAL_DIR

# Convert new revisions to Git
LAST_REV=$(tail -n 1 $LOG_FILE)
svn-all-fast-export --resume-from=$LAST_REV $SVN_LOCAL_DIR --rules rules.txt --add-metadata --identity-map users.txt

# Update Git repo
cd $GIT_REPO_DIR
git pull
git push

# Log last revision
svn info $SVN_LOCAL_DIR | grep "Revision:" | awk '{print $2}' >> $LOG_FILE

Handling Binary Files with Git LFS and BFG Repo Cleaner

Bash Script for Git LFS Migration

#!/bin/bash
# Variables
GIT_REPO_DIR="/path/to/local/git"
BFG_JAR="/path/to/bfg.jar"

# Initialize Git LFS
cd $GIT_REPO_DIR
git lfs install

# Add binary files to Git LFS tracking
git lfs track "*.bin"
git add .gitattributes
git commit -m "Track binary files with LFS"

# Use BFG to migrate binaries to LFS
java -jar $BFG_JAR --convert-to-git-lfs '*.bin' --no-blob-protection

# Cleanup and push changes
git reflog expire --expire=now --all
git gc --prune=now --aggressive
git push origin --force --all
git push origin --force --tags

Smooth Transition Strategies for Large SVN to Git Migrations

When migrating a large SVN repository to Git, it's crucial to plan for a smooth transition to avoid disruptions. One effective strategy is to implement a dual repository system temporarily. In this system, both SVN and Git repositories are kept in sync during the migration period. This allows teams to continue working with minimal interruptions, as changes in SVN are periodically synced to Git.

Another important aspect to consider is the management of large binary files. Using tools like Git LFS and BFG Repo Cleaner helps to keep the Git repository clean and efficient. Planning the migration of these files early in the process ensures that the repository remains manageable and that the history is not cluttered with large binaries, which can slow down operations.

Common Questions About Migrating from SVN to Git

1. What is the most efficient tool for converting SVN to Git?
2. The most efficient tool for converting SVN to Git is svn-all-fast-export, which handles large repositories well and allows for incremental updates.
3. How can I keep my SVN and Git repositories in sync during migration?
4. You can use svnsync to periodically sync your SVN repository with a local copy and then convert the new revisions to Git using svn-all-fast-export with the --resume-from flag.
5. How do I handle large binary files during the migration?
6. Large binary files can be managed using Git LFS and converted from the existing Git history using the BFG Repo Cleaner.
7. What are the benefits of using Git LFS?
8. Git LFS allows you to store large files outside of the main Git repository, which keeps the repository size manageable and improves performance.
9. How do I perform garbage collection in Git after migrating binary files?
10. Perform garbage collection by using git gc --prune=now --aggressive to clean up unnecessary files and optimize the repository.
11. Can I automate the synchronization and conversion process?
12. Yes, you can automate the process using cron jobs to run the synchronization and conversion scripts at regular intervals.
13. How do I ensure the integrity of the migrated data?
14. Ensure integrity by thoroughly testing the converted repository and comparing it with the original SVN repository to check for discrepancies.
15. What should I do if the Git history is rewritten during the migration?
16. If the Git history is rewritten, make sure to force push the updated repository to the remote and inform your team about the changes.
17. How can I minimize downtime during the final migration?
18. Minimize downtime by planning the final migration during off-hours and communicating the schedule to your team in advance.

Implementing a Seamless SVN to Git Migration

The provided scripts automate the process of migrating a large SVN repository to Git. The first script is a bash script designed to be run as a cron job on a Linux machine. It periodically synchronizes the local SVN repository with the remote using svnsync sync. Then, it converts the new SVN revisions to Git commits using svn-all-fast-export --resume-from. The script logs the last converted SVN revision to ensure continuity between syncs. Finally, it updates the local Git repository and pushes the changes to the remote repository.

The second script handles the migration of binary files to Git LFS. It initializes Git LFS in the repository, tracks binary files with git lfs track, and commits these changes. The script uses the BFG Repo Cleaner, invoked with java -jar $BFG_JAR --convert-to-git-lfs, to migrate existing binaries to LFS. It then performs garbage collection with git gc --prune=now --aggressive to clean up the repository and forces a push of the updated history to the remote. This script ensures that large binary files are efficiently managed in the Git repository without cluttering the history.

Final Thoughts on the Migration Process

Migrating a large SVN repository to Git is a complex but achievable task with the right tools and strategies. By automating the sync and conversion process and managing large binaries effectively, you can ensure a smooth transition. Planning and executing this process with minimal disruption to your team's workflow is crucial for success.