N+1 Query Problem¶
The “N+1 query problem” is a term used in the context of database queries, often in the context of Object-Relational Mapping (ORM) systems. This issue arises when a program queries a database for a set of entities (usually rows from a table) and then, for each of those entities, issues an additional query to retrieve related data. This leads to a large number of individual queries being executed, which can result in poor performance and increased database load.
Here’s a breakdown of the issue:
Initial Query (N queries): The program retrieves a set of main entities, let’s say a list of users. This query retrieves ‘N’ records.
Subsequent Queries (+1 queries): For each of the ‘N’ users, the program issues a separate query to fetch additional related data, such as user roles, posts, comments, etc. This results in an additional ‘N’ queries.
As a result, you end up with a total of ‘N+1’ queries, hence the term “N+1 query problem”. This approach can cause significant performance issues, as executing many individual queries can be slower than fetching the required data in a more optimized way.
See also Eloquent Performance: 4 Examples of N+1 Query Problems, The N+1 Query Problem
Related : Loops