When it comes to the performance of raw databases, the biggest performance gaining mechanism could be the use of indexes. Database indexes improve access to your stored data, so you do not have to scan whole tables for accessing your data.
Indexing saves a lot of CPU, memory and I/O usage. Though, it is useful for databases to use indexes, over time the indexes could become fragmented. It makes the SQL server performance lower than usual, delayed transactions, locking, blocking and decreased throughput.