sys.dm_tran_top_version_generators (Transact-SQL)

Cikk
12/19/2023

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

Returns a virtual table for the objects that are producing the most versions in the version store. sys.dm_tran_top_version_generators returns the top 256 aggregated record lengths that are grouped by the database_id and rowset_id. sys.dm_tran_top_version_generators retrieves data by querying the dm_tran_version_store virtual table. sys.dm_tran_top_version_generators is an inefficient view to run because this view queries the version store, and the version store can be very large. We recommend that you use this function to find the largest consumers of the version store.

Note

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

Syntax

  
sys.dm_tran_top_version_generators

Table Returned

Column name	Data type	Description
database_id	int	Database ID. In Azure SQL Database, the values are unique within a single database or an elastic pool, but not within a logical server.
rowset_id	bigint	Rowset ID.
aggregated_record_length_in_bytes	int	Sum of the record lengths for each database_id and rowset_id pair in the version store.
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.

Remarks

Because sys.dm_tran_top_version_generators might have to read many pages as it scans the entire version store, running sys.dm_tran_top_version_generators can interfere with system performance.

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.

SELECT  
    database_id,  
    rowset_id,  
    aggregated_record_length_in_bytes  
  FROM sys.dm_tran_top_version_generators;

Here's the result set.

database_id rowset_id            aggregated_record_length_in_bytes  
----------- -------------------- ---------------------------------  
9           72057594038321152    87  
9           72057594038386688    33

The output shows that all versions are created by database_id``9 and that the versions generate from two tables.

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