Can you explain the essence of the N+1 problem in the context of working with databases?

The N+1 problem occurs when working with a database to retrieve related data, where one query is executed for the main entity (1), and then a separate query for each related entity (N). This leads to a large number of queries and decreased performance.

For example, if you need to get a list of users and their addresses, and a separate address query is executed for each user, then with 100 users, there will be 1 query for users + 100 queries for addresses.

To avoid the N+1 problem, the following are used:

• Eager loading — loading related data immediately through JOIN.
• Batch queries — loading related data with a single query filtered by a list of identifiers.

In Python, using the SQLAlchemy ORM, an example solution is:

users = session.query(User).options(joinedload(User.addresses)).all()

This allows retrieving users and their addresses with a single query, avoiding N+1.