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sys.dm_tran_current_snapshot (Transact-SQL)

  • Άρθρο

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW)

Returns a virtual table that displays all active transactions at the time when the current snapshot transaction starts. If the current transaction is not a snapshot transaction, this function returns no rows. sys.dm_tran_current_snapshot is similar to sys.dm_tran_transactions_snapshot, except that sys.dm_tran_current_snapshot returns only the active transactions for the current snapshot transaction.

Note

To call this from Azure Synapse Analytics or Analytics Platform System (PDW), use the name sys.dm_pdw_nodes_tran_current_snapshot. This syntax is not supported by serverless SQL pool in Azure Synapse Analytics.

Syntax

  
sys.dm_tran_current_snapshot

Table Returned

Column name Data type Description
transaction_sequence_num bigint Transaction sequence number of the active transaction.
pdw_node_id int Applies to: Azure Synapse Analytics, Analytics Platform System (PDW)

The identifier for the node that this distribution is on.

Permissions

On SQL Server and SQL Managed Instance, requires VIEW SERVER STATE permission.

On SQL Database Basic, S0, and S1 service objectives, and for databases in elastic pools, the server admin account, the Microsoft Entra admin account, or membership in the ##MS_ServerStateReader## server role is required. On all other SQL Database service objectives, either the VIEW DATABASE STATE permission on the database, or membership in the ##MS_ServerStateReader## server role is required.

Permissions for SQL Server 2022 and later

Requires VIEW SERVER PERFORMANCE STATE permission on the server.

Examples

The following example uses a test scenario in which four concurrent transactions, each identified by a transaction sequence number (XSN), are running in a database that has the ALLOW_SNAPSHOT_ISOLATION and READ_COMMITTED_SNAPSHOT options set to ON. The following transactions are running:

  • XSN-57 is an update operation under serializable isolation.

  • XSN-58 is the same as XSN-57.

  • XSN-59 is a select operation under snapshot isolation.

  • XSN-60 is the same as XSN-59.

The following query is executed within the scope of XSN-59.

SELECT   
    transaction_sequence_num  
  FROM sys.dm_tran_current_snapshot;

Here's the result set.

transaction_sequence_num  
------------------------  
57  
58

The results show that XSN-57 and XSN-58 were active at the time that the snapshot transaction XSN-59 started. This same result persists, even after XSN-57 and XSN-58 commit or roll back, until the snapshot transaction finishes.

The same query is executed within the scope of XSN-60.

Here's the result set.

transaction_sequence_num  
------------------------  
57  
58  
59

The output for XSN-60 includes the same transactions that appear for XSN-59, but also includes XSN-59, which was active when XSN-60 started.

See Also

Dynamic Management Views and Functions (Transact-SQL)
Transaction Related Dynamic Management Views and Functions (Transact-SQL)