Those days, what I see as "premature database optimization" is non-DBAs, without query plans, EXPLAINS and profiling, sprinkling lots of useless single column i

Those days, what I see as "premature database optimization" is non-DBAs, without query plans, EXPLAINS and profiling, sprinkling lots of useless single column indexes that don't cover the actual columns used for joins and wheres, confusing the query planner and making the database MUCH slower and therefore more deadlock-prone instead.