Sql server - Explain the isolation level does SQL Server support

Explain the isolation level that SQL Server support.

Isolation levels supported by SQL Server:
- Read uncommitted: Lowest level of isolation
- Read committed: Default
- Repeatable read
- Serializable: Highest level of isolation. All transactions are isolated from each other completely.

Describe isolation levels that SQL server supports

SQL Server isolation levels:
READ COMMITTED: Shared locks are held while any data is being read.

READ UNCOMMITTED: Specifies isolation level 0 locking. There are thus no shared locks or exclusive locks. It is the least restrictive of all the isolation levels.

REPEATABLE READ: Locks are applied on all data being used by a query. However, new phantom rows can be inserted into the data set by another user and are included in later reads within the current transaction.

SERIALIZABLE: Issues a range lock on data set, preventing other users to update or insert data into dataset until the transaction is complete.

Explain the isolation level that SQL Server support.

Isolation levels:-
- READ UNCOMMITTED: - Reads data that has been modified but not committed yet.
- READ UNCOMMITTED: - Cannot Read data that has been modified but not committed yet
- REPEATABLE READ: - cannot read data that has been modified but not yet committed by other transactions and that no other transactions can modify data that has been read by the current transaction until the current transaction completes
- SNAPSHOT: - Data read by any statement in a transaction will be a consistent version of the data that existed at the start of the transaction. Here, the transaction can only identify the data modification that was committed before the start of the transaction.
- SERIALIZABLE:- Cannot Read data that has been modified but not committed yet, until the current transaction completes, no other transaction can modify the data and no other transactions will insert new rows whose keys falls in the range of current transaction

Describe isolation levels that SQL server supports

The isolation level describes the degree to which the data being updated is visible to other transactions

Serializable: All transactions occur in a completely isolated fashion. This means all the transactions must execute serially.

Repeatable Read: All data records that are fetched by the Select statement cannot be changed unless a Phantom read occurs in case where clause is mentioned.

Read committed: Data records retrieved by a query are not prevented from modification by some other transaction. in this level, read locks are acquired on selected data but released immediately. Write locks are released at the end of the transaction

Read Uncommitted: Here, One transaction may see uncommitted changes made by some other transaction. Hence, dirty reads are allowed.
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