It allows you to monitor and respond to changes within your SQL database effectively. In the context of the DP-300 exam, understanding how this feature works are vital. This article seeks to explain how to implement this feature in Azure SQL.
Change Tracking in Azure SQL
Change tracking is a lightweight solution that provides an efficient change tracking mechanism for applications. It enables applications to query the database for all changes that have occurred to a table since the last query. It makes synchronous tracking of data changes with versioning.
Enabling Change Tracking
To enable change tracking, you must first have either the `db_owner` or `db_ddladmin` fixed database role. The first step is to enable change tracking at the database level, and then at the table level.
To enable change tracking at the database level, you’d use the following SQL command:
ALTER DATABASE DatabaseName
SET CHANGE_TRACKING = ON
(CHANGE_RETENTION = 2 DAYS, AUTO_CLEANUP = ON)
Next, implement change tracking on the specific table:
ALTER TABLE TableName
ENABLE CHANGE_TRACKING
WITH (TRACK_COLUMNS_UPDATED = ON)
Working with Change Tracking
Once change tracking is enabled for a database and table, you can start querying for changes. The `CHANGETABLE` function is primarily used to retrieve changes.
Here’s an example of how you might use the `CHANGETABLE` function to fetch changes:
SELECT * FROM CHANGETABLE(CHANGES TableName, 0) AS CT
The integer passed to `CHANGETABLE` is the “last change version” that your application knows about. In the above example, we pass `0` to fetch all changes that have occurred to the `TableName` table since the beginning of tracking.
Monitoring Change Tracking Overhead
To monitor the overhead of change tracking, you can use Dynamic Management Views (DMVs) in SQL Server. These DMVs are designed to help monitor performance and status of change tracking:
- `sys.dm_tran_commit_table`
- `sys.dm_tran_active_snapshot_database_transactions`
- `sys.dm_change_tracking_databases`
- `sys.dm_change_tracking_tables`
For example, to view the change tracking information for a particular database and table, use a query like this:
SELECT *
FROM sys.dm_change_tracking_tables
WHERE object_id = OBJECT_ID('TableName')
Processing the Tracked Changes
After retrieving the changes via `CHANGETABLE`, you then need to process these changes based on your application needs – whether that involves reflecting these changes in another database, triggering certain alerts, or taking another type of action.
Remember, the `CHANGETABLE` function provides details of rows that have been added, deleted, or altered. For updated records, you’ll see two entries: one for the old version of the row (with a SYS_CHANGE_OPERATION value of ‘U’) and another for the new version of the row.
In summary, establishing a proper change tracking system is vital for maintaining data integrity and consistency in your Azure SQL database. With a proper grasp of how to set up, query, and monitor change tracking – as explained above – you can ensure that your database is always in the optimal state for your application’s needs while preparing for your DP-300 exam.
Practice Test
True or False: Azure SQL Data Sync enables you to implement automatic data change tracking and synchronization across multiple Azure SQL databases.
- True
- False
Answer: True
Explanation: Azure SQL Data Sync supports automatic change tracking and sync by creating an agent that tracks changes and synchronizes data across databases.
Which of the following is a built-in feature that Azure provides to help track data changes?
- a) SQL Server Change Tracking (CT)
- b) Azure SQL Data Sync
- c) Both a and b
- d) None of the above
Answer: c) Both a and b
Explanation: Azure provides both SQL Server Change Tracking (CT) and Azure SQL Data Sync to track data changes.
True or False: Implementing data change tracking will not impact the performance of your application.
- True
- False
Answer: False
Explanation: Implementing data change tracking may impact application performance, as it needs to keep track of changes in real-time and process them.
Which of the following helps in notifying your application about changes to data?
- a) Polling
- b) Change Data Capture
- c) Both a and b
- d) None of the above
Answer: c) Both a and b
Explanation: Polling regularly checks for changes in data while Change Data Capture (CDC) is a SQL Server feature that captures changes to the data.
True or False: SQL Server’s Change Tracking (CT) feature needs to be enabled manually.
- True
- False
Answer: True
Explanation: While Azure SQL does support SQL Server’s Change Tracking (CT) feature, it is not enabled automatically and needs to be manually activated.
In which of the following scenarios would using Azure SQL Data Sync be most effective?
- a) A multinational corporation with databases across time zones needing to be in sync.
- b) Tracking and storing e-commerce transactions in real time.
- c) Both A and B
- d) None of the above
Answer: a) A multinational corporation with databases across time zones needing to be in sync.
Explanation: While Azure SQL Data Sync is used to keep databases in sync, storing transactions in real-time would likely require a different solution.
True or False: Change Data Capture (CDC) can only be used with Azure SQL Managed Instance.
- True
- False
Answer: True
Explanation: CDC uses the SQL Server Agent, which is only available with Azure SQL Managed Instance.
Which feature of Azure SQL keeps geographically distributed data synchronized?
- a) Azure SQL Data Sync
- b) Azure SQL Managed Instance
- c) Azure SQL Database
- d) Azure SQL Data Warehouse
Answer: a) Azure SQL Data Sync
Explanation: Azure SQL Data Sync enables bi-directional data synchronization between multiple Azure SQL databases and SQL Server databases.
True or False: Azure SQL Data Sync supports on-premises SQL Server databases as well.
- True
- False
Answer: True
Explanation: Azure SQL Data Sync can sync data across multiple Azure SQL databases and also between Azure SQL databases and on-premises SQL Server databases.
Is it feasible to combine the use of SQL Server Change Tracking (CT) and Change Data Capture (CDC)?
- Yes
- No
Answer: Yes
Explanation: Both CT and CDC can be used in conjunction, as they provide different advantages and fulfill different needs.
Interview Questions
What is data change tracking in Azure SQL Database?
Data change tracking in Azure SQL Database captures the changes made to the database content. It provides detailed information about the kind of changes made – insert, update, or delete operations.
How can you enable change tracking on a table in Azure SQL Database?
We can enable change tracking on a table in Azure SQL Database by using the ALTER TABLE statement with the ENABLE CHANGE_TRACKING option.
Does change tracking in Azure SQL Database record the historical data for the changes made to data in the table?
No, change tracking does not record the historical data for changes. It only keeps track of the fact that rows have been changed.
What is the AUTO_CLEANUP option in Change Tracking?
The AUTO_CLEANUP option indicates whether or not automatic cleanup of change tracking information is turned on or off.
What are the main system tables that are used in tracking changes in Azure SQL Database?
The main system tables used in tracking changes include Change_tracking_databases, Change_tracking_tables, and Change_tracking_columns.
When you enable change tracking on a database or table level, what is the default retention period?
The default retention period is 2 days.
What function can be used to query change data in Azure SQL?
The CHANGETABLE function can be used to query change data in Azure SQL.
How does Azure SQL Database ensure the privacy and security of change tracking data?
Azure SQL Database ensures the privacy and security of the change tracking data by encrypting it at rest, in transit, and by controlling who has access to it.
Can you disable change tracking once enabled in Azure SQL Database?
Yes, we can disable change tracking by using the ALTER TABLE statement with the DISABLE CHANGE_TRACKING option.
What might cause the failure of change tracking auto cleanup in Azure SQL Database?
The failure of change tracking auto cleanup in Azure SQL Database might be caused by a long-running query or transaction.
Is there a performance impact when enabling change tracking in Azure SQL Database?
Yes, there might be a performance overhead due to maintaining the change tracking information, but it is generally minimal.
What SQL Server permissions are needed to enable or disable Change Tracking?
To enable or disable Change Tracking, CONTROL permissions on the database are required.
What is the max retention period for change tracking in Azure SQL Database?
The maximum retention period for change tracking in Azure SQL Database is 14 days.
How often does change tracking auto cleanup occur?
Change tracking auto cleanup occurs every 30 minutes in Azure SQL Database.
How can we query change tracking information in Azure SQL Database?
We can use the system view sys.change_tracking_changes or the CHANGETABLE function to query change tracking information in Azure SQL Database.
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