Django Migrations and Zero-Downtime Strategies

Your approach to minimizing downtime during migrations is an interesting concept that builds on Django's existing migration framework. While Django's migration system doesn't natively support the specific "pending operations" pattern you're describing, there are several ways to implement similar functionality.

Current Django Migration System

Django's migration system is designed as a version control system for your database schema. It uses several commands:

• migrate - applies and unapplies migrations
• makemigrations - creates new migrations based on model changes
• sqlmigrate - displays SQL statements for a migration
• showmigrations - lists migrations and their status

Implementing Your Approach

Your concept of separating migrations into non-destructive and destructive operations is a valid strategy for minimizing downtime. Here are some ways to implement this within Django's framework:

Option 1: Multiple Migration Files

Instead of having pending_ops in the same file, you could split your migrations into two separate files:

1. A file with non-destructive operations that can be applied immediately
2. A file with destructive operations that can be applied later

You would then control when to run the second migration through your deployment process.

Option 2: Custom Migration Operation

You could create a custom migration operation that defers certain actions:

PYTHONCopied
class DeferrableOperation(Operation):
    def __init__(self, operation):
        self.operation = operation
        
    def database_forwards(self, app_label, schema_editor, from_state, to_state):
        if settings.APPLY_DESTRUCTIVE_MIGRATIONS:
            self.operation.database_forwards(app_label, schema_editor, from_state, to_state)
        else:
            # Log that this operation was deferred
            pass

Option 3: Django Admin Integration

Your idea of a Django admin interface to manage pending migrations is feasible. You could:

1. Create a model to track pending migrations
2. Build a custom admin interface to display and apply them
3. Implement a management command that applies these pending migrations

Considerations

When implementing this approach, consider:

1. Database Transactions: Ensure that your migrations are properly wrapped in transactions where appropriate.

2. Testing: As you noted, test environments should probably apply all migrations immediately.

3. Migration Squashing: Django supports squashing migrations to reduce their number. Your approach would need to account for this when tracking pending operations.

4. Deployment Coordination: You'll need a reliable way to track which pending migrations have been applied across all environments.

This approach could be particularly useful for large-scale applications where downtime is costly, though it does add complexity to the migration process. You might want to look at some existing third-party packages that address similar concerns before building a custom solution.