The document discusses the N+1 query problem in database performance, where loading a set of objects results in additional queries to fetch associated data, overwhelming the limited number of database connections. It describes how N+1 queries can result in hundreds of queries for a typical page. The solution is to use eager loading to include associated data in the initial queries whenever possible, and to cache counts of objects to avoid unnecessary queries. Optimizing databases through these methods is essential for building scalable web applications.

1. Chris Lehneis
Charlotte Tregelles
How to Deal with N + 1 Queries
Database Performance

2. SCALABILITY

3. Scalability Challenge
❖ Database only has a limited amount of
connections.
❖ Bottleneck occurs when requests exceed number
of connections.

4. What are N + 1 Queries?
!
!
❖ N + 1 problem: Loading many objects from
the database, and for each object 1 or
more queries are made.

5. Models

6. Controller and View

7. Queries
❖ N+1 queries = potentially 100s of queries
❖ Average page has 5-6 queries

8. Bullet
❖ Use eager loading to remove N + 1 queries
❖ Remove eager loading when unnecessary
❖ When to use counter cache

9. Artists Table

10. Summary
❖ Optimizing databases performance is essential for
scalable web applications!
!
❖ Use eager loading, its awesome, but only when
beneficial.
!
❖ Cache when counting objects

11. “Wat?”