Answer
TempDB is SQL Server’s global workspace used by all users and internal operations. It is essential because it handles:
- Sorting operations (ORDER BY, GROUP BY)
- Hash joins and aggregations
- Row versioning for snapshot isolation
- Temporary tables and table variables
- Intermediate spill data during execution
- Cursors and internal worktables
If TempDB becomes slow or suffers contention, the entire SQL Server instance slows down. Proper sizing, fast storage, and multiple data files are critical for performance.