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What are different locks in SQL Server?
At the table level, there are five different types of locks:
- Shared (S)
- Exclusive (X)
- Intent shared (IS)
- Intent exclusive (IX)
- Shared with intent exclusive (SIX)
What is the use of lock in SQL Server?
Locks are held on SQL Server resources, such as rows read or modified during a transaction, to prevent concurrent use of resources by different transactions. For example, if an exclusive (X) lock is held on a row within a table by a transaction, no other transaction can modify that row until the lock is released.
What is row-level locking in SQL Server?
Row-level locking means that only the row that is accessed by an application will be locked. Hence, all other rows that belong to the same page are free and can be used by other applications. The Database Engine can also lock the page on which the row that has to be locked is stored.
How does the number of locks affect SQL Server?
Forty percent of the value set for the locks property in sp_configure. The locks property in Sp_configure contains the total number of locks SQL Server is permitted to issue. This therefore affects the amount of memory used by SQL Server for locking.
How are s and X locks used in SQL Server?
S locks are taken to read from a resource and X locks are taken to write to a resource. S locks are compatible with each other, X locks are not compatible with anything else. U locks are a hybrid that is used in some cases for deadlock prevention. Now, SQL Server can take locks on several levels:Table, Partition, Page and Row.
What does it mean to have shared lock in SQL Server?
Intent shared (IS) – when an intent shared lock (IS) is acquired it indicates to SQL Server that the transaction has the intention to read some lower hierarchy resources by acquiring shared locks (S) individually on those resources lower in the hierarchy
Where does the locking hierarchy start in SQL Server?
SQL Server has introduced the locking hierarchy that is applied when reading or changing of data is performed. The lock hierarchy starts with the database at the highest hierarchy level and down via table and page to the row at the lowest level.