Key database concepts senior backend engineers must master for interviews

Database knowledge is a critical differentiator in senior backend engineering interviews, as it is difficult to bluff through technical follow-up questions. Interviewers assess whether candidates understand indexing deeply — including column order in composite indexes, write costs, and selectivity — rather than just knowing that indexes speed up reads. A common diagnostic question involves distinguishing a single slow query from an N+1 query pattern, since each requires a completely different fix and the latter does not appear in slow query logs. Candidates are also expected to explain ACID properties through concrete anomalies, such as lost updates or non-repeatable reads, and to articulate why stricter isolation levels are not always used in practice. The overall theme is that senior answers focus on reading query execution plans and understanding trade-offs, rather than jumping straight to generic solutions like adding indexes or caching.