Internal Architecture and Implementation of Databases

Question: Explain the internal architecture and implementation of databases (e.g. how a relational database engine is structured internally).

Answer outline: Typical components include a query parser/optimizer (parses SQL, chooses an execution plan using statistics/indices), a storage engine (manages on-disk page layout, B-Tree/B+Tree indices, buffer pool/page cache), a transaction manager (concurrency control via locking or MVCC), and a write-ahead log (WAL) for durability and crash recovery. Discuss how indices speed up lookups at the cost of write amplification, and how the buffer pool caches hot pages in memory to avoid disk I/O.