Sunday, September 26, 2010

SQL Transaction isolation level

As a quick reminder for the 70-433 TS: Microsoft SQL Server 2008, Database Development certification, here is the list of SQL 2008 transaction isolation levels:

READ UNCOMMITTED
Specifies that statements can read rows that have been modified by other transactions but not yet committed.

READ COMMITTED
Specifies that statements cannot read data that has been modified but not committed by other transactions. This prevents dirty reads.

REPEATABLE READ
Specifies that statements 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
Specifies that data read by any statement in a transaction will be the transactionally consistent version of the data that existed at the start of the transaction. The transaction can only recognize data modifications that were committed before the start of the transaction.

SERIALIZABLE
Specifies the following:
- Statements cannot read data that has been modified but not yet committed by other transactions.
- No other transactions can modify data that has been read by the current transaction until the current transaction completes.
- Other transactions cannot insert new rows with key values that would fall in the range of keys read by any statements in the current transaction until the current transaction completes.

1 commentaires:

Ram said...

Good post on sql transation it was very informative. Distributed transactions are one of the more powerful and important functions within SQL Server, Transactions provide an all-or-nothing proposition stating that work units performed in a database must be completed in their entirety or take no effect whatsoever. i learning and doing pl/sql training

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