N+1 Query Problem¶
The N+1 query problem is a term used in the context of queries, and most often in the context of databases and 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, the 1 query: the code retrieves a set of entities. This is a list of
Nresults.Subsequent queries, the N queries: For each of the ‘N’ result, the code issues a separate query to fetch additional related data.
As a result, the code ends up performing N+1 queries, hence the name of N+1 query problem. This approach can cause significant performance issues, as executing many individual queries is slower than fetching the required data in batches: either all of them in one call, or by groups of arbitrary size.
N+1 query problem happens with anything that requires a query. It may be a SQL database, but also remote API calls, or even system calls.
See also Here’s How You Can Stop N+1 Queries Forever, Eloquent Performance: 4 Examples of N+1 Query Problems and The N+1 Query Problem.
Related : Loops, Batch, Object Relational Mapping (ORM), Structured Query Language (SQL)
