SQL Server uses locks to manage concurrency and ensure data integrity. These locks determine how data is accessed and modified when multiple users or processes interact with the database. Here are the key lock types you need to know:
🔗 Shared Locks
Shared locks are used during read operations. When a process reads data, SQL Server places a shared lock to prevent any other process from modifying that data while it is being read. Multiple shared locks can exist on the same resource, but they block exclusive locks.
🔐 Exclusive Locks
Exclusive locks occur during insert, update, or delete operations. They ensure that no other process can read or write to the data being changed. An exclusive lock is held until the transaction is completed.
🔄 Update Locks
Update locks are used as a bridge between shared and exclusive locks. They are applied when SQL Server is searching for rows to update or delete. Once the target row is identified, the update lock is converted into an exclusive lock.
🧭 Intent Locks
Intent locks are used to indicate a lower-level lock is being placed. For example, if a transaction wants to acquire an exclusive lock on a row, SQL Server will place an intent exclusive lock on the table. This allows SQL Server to coordinate locking at different granularities like rows, pages, and tables.