CHANGE DATA CAPTURE
& CHANGE TRACKING
DEEP DIVE
W. Kevin Hazzard
LinchpinPeople.com
Group Principal
CHANGE DATA CAPTURE
• Turn it on
EXECUTE sys.sp_cdc_enable_db;
• Which generates for the whole database
analysis
transactions
sources
data
mart
• A capture job
• A cleanup job
• Then include at least one table with
EXECUTE sys.sp_cdc_enable_table …;
• Which creates a capture instance containing
capture
job
• A change table
ETL
• An all-changes function
• A net-changes function (optional)
ETL
changes
warehouse
archive
sector
CAPTURE INSTANCE
• Contains
• The capture table
• cdc.fn_cdc_get_all_changes_<instance name> function
• cdc.fn_cdc_get_net_changes_<instance name> function (optional)
• Maximum two per source table
SYS.SP_CDC_ENABLE_TABLE
• @source_schema
• @index_name
• @source_name
• @captured_column_list
• @supports_net_changes
• @allow_partition_switch
• @role_name
• @capture_instance
• @filegroup_name
DEMONSTRATION
Enabling Change Data Capture (CDC)
Creating a CDC Capture Instance
Querying CDC Tables as Things Change
SQL SERVER AGENT JOBS
• cdc.Capture_capture
• Starts with SQL Agent
• RAISERROR(22801, 10, -1);
• EXEC sys.sp_MScdc_capture_job;
• Just a wrapper for sys.sp_cdc_scan
• cdc.Capture_cleanup
• Runs at 02:00 daily
• EXEC sys.sp_MScdc_cleanup_job;
CDC DATA RETENTION
• Based on LSN Validity Intervals
• Database
• Capture Instance
• The cleanup job deletes CDC data acording to retention policy
SELECT * FROM msdb.dbo.cdc_jobs WHERE job_type = N'cleanup';
• You can start the cleanup job manually
EXEC sys.sp_cdc_start_job @job_type = N'cleanup';
HANDLING SCHEMA CHANGES
• Deleted and new columns are handled well
• Modified columns require specific steps:
• Stop the capture and cleanup jobs
• Change the schema as necessary
• Generate new capture instances for all modified tables
• Process all data in the old and new capture instances
• Manually run the cleanup job
• Delete the old capture instance
• Turn the capture and cleanup jobs back on
CHANGE TRACKING
• Turn it on for one database
ALTER DATABASE <DBNAME> SET
CHANGE_TRACKING = ON;
• Then enable a table
ALTER TABLE <TBLNAME> ENABLE
CHANGE_TRACKING;
transactions
sync
sources
ETL
warehouse
archive
sector
CHANGE TRACKING TABLES & FUNCTIONS
• sys.change_tracking_databases
• sys.change_tracking_tables
• CHANGETABLE(CHANGES)
• CHANGETABLE(VERSION)
• CHANGE_TRACKING_CURRENT_VERSION()
• CHANGE_TRACKING_MIN_VALID_VERSION()
• CHANGE_TRACKING_IS_COLUMN_IN_MASK()
• WITH CHANGE_TRACKING_CONTEXT
DEMONSTRATION
Enabling Change Tracking (CT) for a Database
Enabling CT on a Table
Querying CT Tables and Functions as Things Change
HANDLING SCHEMA CHANGES
• No modifications to the primary key are allowed including related indexes
• Dropping columns is OK but they may still appear in the change data
• When adding columns, changes are tracked but the metadata change is not reported
• Switching partitions will fail on change tracked changes
• Data type changes are not tracked
WHICH ONE IS RIGHT FOR ME?
Change Data Capture
Change Tracking
• Works in Enterprise Edition only
• Works in all versions of SQL Server
• Stores every discrete change
• Returns differences from current
• Storage intensive
• Storage light
• Good for auditing
• Good for device synchronization
• Requires SQL Server agent
• No job agent required
• No special serialization required
• Operates best with snapshot isolation