How Can Raw SQL Optimize Slow Rails Queries?

Boosting Rails Performance: Leveraging Raw SQL for Query Optimization

Slow queries can significantly impact the performance of your Rails application. One approach to resolving this is utilizing raw SQL to optimize your database interactions.

Migrating from ActiveRecord to Raw SQL

The example code uses ActiveRecord to join and order data from two tables. We can enhance this by directly employing raw SQL via ActiveRecord::Base.connection.execute. Here's the optimized SQL:

sql = "SELECT * FROM payment_details
         JOIN projects ON payment_details.project_id = projects.id
         UNION
         SELECT * FROM payment_errors
         JOIN projects ON payment_errors.project_id = projects.id
         ORDER BY payment_details.created_at DESC, payment_errors.created_at DESC;"
records_array = ActiveRecord::Base.connection.execute(sql)

The query results are stored in records_array, allowing for easy iteration and access to individual records.

Enhanced Performance, Especially on Heroku

Employing raw SQL often yields substantial performance improvements, particularly on platforms like Heroku where request timeouts are a common concern. This is because raw SQL bypasses the ActiveRecord ORM layer, reducing processing overhead.

Best Practices for Raw SQL Usage

• Use raw SQL judiciously. Over-reliance can compromise code maintainability.
• Always parameterize your queries to mitigate SQL injection vulnerabilities.
• Rigorous testing is crucial to ensure the raw SQL queries produce the correct results.

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