Inefficient query plans cause production slowdowns despite dev performance

Query runs fast in development but crawls in production, or shows inconsistent latencies during peak usage. Query planner selects inefficient execution paths, performs sequential scans instead of using indexes, or makes expensive joins.

Run EXPLAIN ANALYZE on the slow query to examine the execution plan. Look for sequential scans where indexes should be used, high row counts in intermediate steps, and inefficient join methods. Compare the plan between dev and prod environments. Small changes in filters or joins can flip a plan from efficient to expensive.