# Database Locks

Source: <https://www.linkedin.com/posts/alexxubyte_systemdesign-coding-interviewtips-activity-7211031615462895616-678T?utm_source=share&utm_medium=member_desktop>

Here are the common types of locks used in databases:

1. Shared Lock (S Lock) It allows multiple transactions to read a resource simultaneously but not modify it. Other transactions can also acquire a shared lock on the same resource.
2. Exclusive Lock (X Lock) allows a transaction to read and modify a resource. No other transaction can acquire any lock on the same resource while an exclusive lock is held.
3. Update Lock (U Lock) It prevents a deadlock scenario when a transaction intends to update a resource.
4. Schema Lock It is used to protect the structure of database objects.
5. Bulk Update Lock (BU Lock): This is used during bulk insert operations to improve performance by reducing the number of locks required.
6. Key-Range Lock It is used in indexed data to prevent phantom reads (inserting new rows into a range that a transaction has already read).
7. Row-Level Lock: It locks a specific row in a table, allowing other rows to be accessed concurrently.
8. Page-Level Lock: It locks a specific page (a fixed-size block of data) in the database.
9. Table-Level Lock It locks an entire table. This is simple to implement but can reduce concurrency significantly.

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