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.
To call this from Azure SQL Data Warehouse or Parallel Data Warehouse, use the name sys.dm_pdw_nodes_tran_top_version_generators.
|Column name||Data type||Description|
|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 SQL Data Warehouse, Parallel Data Warehouse
The identifier for the node that this distribution is on.
On SQL Server, requires
VIEW SERVER STATE permission.
On SQL Database Premium Tiers, requires the
VIEW DATABASE STATE permission in the database. On SQL Database Standard and Basic Tiers, requires the Server admin or an Azure Active Directory admin account.
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.
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 is 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.