N+1 Query Problem
Also written as N+1 Queries, Eager Loading
Code that fetches a list, then quietly runs one more database query for every item in it — fine with ten rows, crippling with ten thousand.
Think of it like
Walking back to the storeroom once per item on the shopping list, instead of collecting everything in one trip.
Junior or senior?
One of the most common real causes of a slow application.
Senior sounds like
Has found one in production and can describe how they spotted it.
Ask them
“Tell me about a slow page or endpoint you fixed. How did you find what was actually slow?”
Sounds like real experience
Describes measuring first — query logs, a monitoring tool, a profiler — and finding a specific cause, rather than guessing and rewriting.
Probe further if
Jumps straight to adding caching or a bigger server without having measured what was slow.