BEGIN TRANSACTION (Transact-SQL)
Marks the starting point of an explicit, local transaction. BEGIN TRANSACTION increments @@TRANCOUNT by 1.
BEGIN TRANSACTION represents a point at which the data referenced by a connection is logically and physically consistent. If errors are encountered, all data modifications made after the BEGIN TRANSACTION can be rolled back to return the data to this known state of consistency. Each transaction lasts until either it completes without errors and COMMIT TRANSACTION is issued to make the modifications a permanent part of the database, or errors are encountered and all modifications are erased with a ROLLBACK TRANSACTION statement.
BEGIN TRANSACTION starts a local transaction for the connection issuing the statement. Depending on the current transaction isolation level settings, many resources acquired to support the Transact-SQL statements issued by the connection are locked by the transaction until it is completed with either a COMMIT TRANSACTION or ROLLBACK TRANSACTION statement. Transactions left outstanding for long periods of time can prevent other users from accessing these locked resources, and also can prevent log truncation.
Although BEGIN TRANSACTION starts a local transaction, it is not recorded in the transaction log until the application subsequently performs an action that must be recorded in the log, such as executing an INSERT, UPDATE, or DELETE statement. An application can perform actions such as acquiring locks to protect the transaction isolation level of SELECT statements, but nothing is recorded in the log until the application performs a modification action.
Naming multiple transactions in a series of nested transactions with a transaction name has little effect on the transaction. Only the first (outermost) transaction name is registered with the system. A rollback to any other name (other than a valid savepoint name) generates an error. None of the statements executed before the rollback is, in fact, rolled back at the time this error occurs. The statements are rolled back only when the outer transaction is rolled back.
The local transaction started by the BEGIN TRANSACTION statement is escalated to a distributed transaction if the following actions are performed before the statement is committed or rolled back:
An INSERT, DELETE, or UPDATE statement that references a remote table on a linked server is executed. The INSERT, UPDATE, or DELETE statement fails if the OLE DB provider used to access the linked server does not support the ITransactionJoin interface.
A call is made to a remote stored procedure when the REMOTE_PROC_TRANSACTIONS option is set to ON.
The local copy of SQL Server becomes the transaction controller and uses Microsoft Distributed Transaction Coordinator (MS DTC) to manage the distributed transaction.
A transaction can be explicitly executed as a distributed transaction by using BEGIN DISTRIBUTED TRANSACTION. For more information, see BEGIN DISTRIBUTED TRANSACTION (Transact-SQL).
The WITH MARK option causes the transaction name to be placed in the transaction log. When restoring a database to an earlier state, the marked transaction can be used in place of a date and time. For more information, see Using Marked Transactions (Full Recovery Model) and RESTORE (Transact-SQL).
Additionally, transaction log marks are necessary if you need to recover a set of related databases to a logically consistent state. Marks can be placed in the transaction logs of the related databases by a distributed transaction. Recovering the set of related databases to these marks results in a set of databases that are transactionally consistent. Placement of marks in related databases requires special procedures.
The mark is placed in the transaction log only if the database is updated by the marked transaction. Transactions that do not modify data are not marked.
BEGIN TRAN new_name WITH MARK can be nested within an already existing transaction that is not marked. Upon doing so, new_name becomes the mark name for the transaction, despite the name that the transaction may already have been given. In the following example, M2 is the name of the mark.
BEGIN TRAN T1; UPDATE table1 ...; BEGIN TRAN M2 WITH MARK; UPDATE table2 ...; SELECT * from table1; COMMIT TRAN M2; UPDATE table3 ...; COMMIT TRAN T1;
When nesting transactions, trying to mark a transaction that is already marked results in a warning (not error) message:
"BEGIN TRAN T1 WITH MARK ...;"
"UPDATE table1 ...;"
"BEGIN TRAN M2 WITH MARK ...;"
"Server: Msg 3920, Level 16, State 1, Line 3"
"WITH MARK option only applies to the first BEGIN TRAN WITH MARK."
"The option is ignored."
A. Naming a transaction
The following example shows how to name a transaction.
DECLARE @TranName VARCHAR(20); SELECT @TranName = 'MyTransaction'; BEGIN TRANSACTION @TranName; USE AdventureWorks; DELETE FROM AdventureWorks.HumanResources.JobCandidate WHERE JobCandidateID = 13; COMMIT TRANSACTION @TranName; GO
B. Marking a transaction
The following example shows how to mark a transaction. The transaction CandidateDelete is marked.
BEGIN TRANSACTION CandidateDelete WITH MARK N'Deleting a Job Candidate'; GO USE AdventureWorks; GO DELETE FROM AdventureWorks.HumanResources.JobCandidate WHERE JobCandidateID = 13; GO COMMIT TRANSACTION CandidateDelete; GO