migsafe 0.4.1

Safe migrations for production PostgreSQL databases

🛡️ migsafe

Safe Alembic migrations for production PostgreSQL databases

migsafe (v0.4.1) is a CLI tool and CI linter that analyzes Alembic and Django migrations before they are applied and warns about dangerous, slow, and blocking schema changes.

Project goal — catch migration problems before deployment, not during production downtime.

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📋 Contents

• Why it’s needed
• What migsafe does
• Installation
• Quick start
• Using in CI
• Supported operations
• Examples
• How it works
• Limitations
• Roadmap
• Contributing

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❓ Why it’s needed

Alembic makes migrations convenient, but not safe by default.

Typical problems migsafe catches early:

Problem	Consequences
❌ ADD COLUMN NOT NULL DEFAULT	Rewrites the entire table
❌ CREATE INDEX without CONCURRENTLY	Blocks writes
❌ ALTER COLUMN TYPE	Long exclusive lock
❌ DROP COLUMN	Data loss
❌ Raw op.execute()	Dangerous SQL (UPDATE/DELETE without WHERE, DDL without CONCURRENTLY)
❌ Data migrations without batching	Long-lasting locks (large INSERTs without LIMIT)

💡 This may “work” on a small database.
⚠️ In production — downtime, night deployments, and emergency rollbacks.

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✨ What migsafe does

Capability	Description
🔍 AST analysis	Analyzes Alembic migrations via AST
🧠 Smart detection	Determines real migration behavior, not just its code
🔎 SQL analysis	Analyzes SQL in op.execute() for dangerous patterns (DDL, JOINs, subqueries, CTEs)
⚠️ Risk classification	OK / WARNING / CRITICAL
💥 CI integration	Fails CI if a migration is dangerous
💡 Recommendations	Suggests how to rewrite migrations safely
🔧 Autofix	Automatically fixes some issues with backup creation
📊 Statistics	Collects statistics and metrics across all migrations
⚙️ Configuration	Flexible configuration via JSON/TOML
🎯 Snapshot execution	Runs migrations on production DB snapshots and measures metrics
📜 History analysis	Analyzes migration history via Git to detect problematic patterns
🐍 Django support	Analyzes Django migrations alongside Alembic
🔌 Plugin system	Create custom analysis rules via plugins

✅ Code is not executed.
✅ Database is not touched.
✅ Analysis is completely safe.

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📦 Installation

From PyPI (recommended)

# Basic installation
pip install migsafe

# With optional dependencies for snapshot execution
pip install migsafe[executors]

# With optional dependencies for improved text output
pip install migsafe[formatters]

# All optional dependencies
pip install migsafe[executors,formatters]

From source (for development)

git clone https://github.com/SuccubHunter/migsafe.git
cd migsafe
pip install -e .

# Or with optional dependencies
pip install -e ".[executors,formatters]"

Requirements: Python >= 3.9

Optional dependencies:

• executors — for migsafe execute (requires psycopg2-binary, alembic, sqlalchemy)
• formatters — improved text output (requires rich)

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🚀 Quick start

Basic usage

In a project directory with Alembic:

migsafe analyze

Analyze specific files/directories

# Analyze a directory
migsafe analyze migrations/

# Analyze a specific file
migsafe analyze migrations/versions/001_add_user.py

Save report

# HTML report
migsafe analyze --format html --output report.html

# JSON report
migsafe analyze --format json --output report.json

Available output formats: text (default), json, html, junit, sarif

Automatic fixes

migsafe can automatically fix some issues:

# Show fixes (dry-run)
migsafe analyze --autofix

# Apply fixes (creates backup)
migsafe analyze --autofix --apply

# Apply without confirmation
migsafe analyze --autofix --apply --yes

# Apply without backup (not recommended)
migsafe analyze --autofix --apply --no-backup

Supported fixes:

• ADD COLUMN NOT NULL → safe pattern (nullable → backfill → NOT NULL)
• CREATE INDEX → add CONCURRENTLY
• DROP INDEX → add CONCURRENTLY

Configuration file

You can configure migsafe using a config file:

migsafe.json:

{
  "exclude": ["**/test_*.py", "**/__pycache__/**"],
  "format": "json",
  "severity": "warning",
  "no_color": true,
  "exit_code": true
}

migsafe.toml:

[migsafe]
exclude = ["**/test_*.py", "**/__pycache__/**"]
format = "json"
severity = "warning"
no_color = true
exit_code = true

Usage:

migsafe analyze --config migsafe.json

CLI parameters override configuration file settings.

Migration statistics

The migsafe stats command collects and analyzes migration statistics:

# Show overall statistics
migsafe stats

# Statistics for a specific migration
migsafe stats --migration 001_add_users.py

# Export to JSON
migsafe stats --format json --output stats.json

# Export to CSV
migsafe stats --format csv --output stats.csv

# Filter by severity
migsafe stats --severity critical

# Filter by rule
migsafe stats --rule add_column_not_null_rule

What statistics show:

• Total number of migrations and issues
• Distribution by issue type and severity
• Top issues and rules by frequency
• Automatic recommendations to improve migration practices

Available formats: text (default), json, csv

Demo project

To see the library in action:

python demo/run_demo.py

The demo includes examples of dangerous and safe migrations. See demo/README.md.

New features in version 0.4

Running migrations on snapshots

Execute migrations on production DB snapshots to measure real performance metrics:

⚠️ Required: To use migsafe execute, install optional dependencies: pip install migsafe[executors]

# Create a snapshot and run migration
migsafe execute migration.py --snapshot-url postgresql://user:pass@localhost/db

# Run on an existing snapshot
migsafe execute migration.py --snapshot-url postgresql://user:pass@localhost/db \
    --snapshot-name my_snapshot

# Save results to JSON
migsafe execute migration.py --snapshot-url postgresql://user:pass@localhost/db \
    --format json --output results.json

📄 Detailed guide

Git-based migration history analysis

Track migration changes over time to detect problematic patterns:

# Analyze full migration history
migsafe history

# Analyze a specific migration
migsafe history --migration migrations/001_add_user.py

# Filter by date
migsafe history --since 2025-01-01 --until 2025-12-31

# Filter by author
migsafe history --author "Ivan Ivanov"

📄 Detailed guide

Django migration support

Analyze Django migrations alongside Alembic:

# Auto-detect Django migrations
migsafe analyze

# Analyze migrations of a specific app
migsafe analyze --django-app myapp

# Analyze multiple apps
migsafe analyze --django-app myapp --django-app otherapp

📄 Detailed guide

Plugins

Load custom analysis rules via plugins:

# Use plugins from directory
migsafe analyze --plugins-dir ./plugins

# List loaded plugins
migsafe plugins list

# Plugin info
migsafe plugins info my-plugin

📄 Detailed guide

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📊 Output example

Migration: 2025_12_31_add_email.py

[CRITICAL] add_column_not_null
Table: users
Column: email

Message:
Adding NOT NULL column 'email' to table 'users' rewrites entire table and blocks writes in PostgreSQL

Recommendation:
Use safe pattern:
1) Add column as nullable: op.add_column(..., nullable=True)
2) Backfill data in batches: op.execute('UPDATE ... WHERE ...')
3) Set NOT NULL constraint: op.alter_column(..., nullable=False)

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🔧 Using in CI/CD

Quick start

For CI/CD integration, use migsafe lint, which returns a non-zero exit code if critical issues are found:

migsafe lint --format junit --output report.xml --no-color

Behavior

Level	Exit Code	Behavior
CRITICAL	1	Build fails (migsafe lint or migsafe analyze --exit-code)
WARNING	0	Build passes with warnings
OK	0	Build passes

💡 Note: migsafe lint automatically returns a non-zero exit code on critical issues, making it ideal for CI/CD.

Integration examples

Ready-to-use configs for various CI/CD systems are available in examples/ci/:

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