sys.fn_cdc_get_max_lsn (Transact-SQL)

Άρθρο
02/28/2023

Applies to: SQL Server

Returns the maximum log sequence number (LSN) from the start_lsn column in the cdc.lsn_time_mapping system table. You can use this function to return the high endpoint of the change data capture timeline for any capture instance.

Transact-SQL syntax conventions

Syntax

  
sys.fn_cdc_get_max_lsn ()

Return Types

binary(10)

Remarks

This function returns the maximum LSN in the start_lsn column of the cdc.lsn_time_mapping table. As such, it is the last LSN processed by the capture process when changes are propagated to the database change tables. It serves as the high endpoint for the all timelines that are associated with capture instances defined for the database.

The function is typically used to obtain an appropriate high endpoint for a query interval.

Permissions

Requires membership in the public database role.

Examples

A. Returning the maximum LSN value

The following example returns the maximum LSN for all capture instances in the AdventureWorks2022 database.

USE AdventureWorks2022;  
GO  
SELECT sys.fn_cdc_get_max_lsn()AS max_lsn;

B. Setting the high endpoint of a query range

The following example uses the maximum LSN returned by sys.fn_cdc_get_max_lsn to set the high endpoint for a query range for the capture instance HumanResources_Employee.

USE AdventureWorks2022;  
GO  
DECLARE @from_lsn binary(10), @to_lsn binary(10);  
SET @from_lsn = sys.fn_cdc_get_min_lsn(N'HumanResources_Employee');  
SET @to_lsn = sys.fn_cdc_get_max_lsn();  
SELECT * FROM cdc.fn_cdc_get_all_changes_HumanResources_Employee(@from_lsn, @to_lsn, 'all');  
GO

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