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English
  • PowerExchange for CDC and Mainframe 10.5.6
  • All Products

Table of Contents

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  1. Preface
  2. Change Data Capture Introduction
  3. PowerExchange Listener
  4. PowerExchange Condense
  5. DB2 for i5/OS Change Data Capture
  6. Remote Logging of Data
  7. Introduction to Change Data Extraction
  8. Extracting Change Data
  9. Monitoring CDC Sessions
  10. Managing Change Data Extractions
  11. Tuning CDC Sessions
  12. Appendix A: DTL__CAPXTIMESTAMP Time Stamps

CDC Guide for i5/OS

CDC Guide for i5/OS

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Recovery and Restart Processing for CDC Sessions

Recovery and Restart Processing for CDC Sessions

If you select the
Resume from last checkpoint
 option for the
Recovery Strategy
 attribute in a CDC session that extracts change data, PWXPC and PowerCenter provide recovery and restart processing for that session.
If a session fails, the PowerCenter Integration Service recovers the session state of operation, and PWXPC recovers the restart information.
PWXPC saves restart information for all sources that are in a CDC session. The restart information for CDC sessions, including the restart tokens, originates from PowerExchange on the system from which the change data is extracted. You can include both relational and nonrelational targets in a single CDC session. PWXPC uses one of the following locations to store and retrieve restart information, based on the target type:
  • For relational targets, PWXPC uses recovery state tables in the target databases. PWXPC, in conjunction with the PowerCenter Integration Service, commits both the change data and the restart tokens for that data in the same commit operation. This commit ensures that the applied data and the restart tokens are in-sync.
  • For nonrelational targets, PWXPC uses the recovery state file that is in the shared location on the PowerCenter Integration Service machine. PWXPC, in conjunction with the PowerCenter Integration Service, writes the change data to the target files and then writes the restart tokens to the recovery state file. As a result, duplicate data might be applied to the targets when you restart the failed CDC sessions.
The PowerCenter Integration Service saves the session state of operation and maintains target recovery tables. The PowerCenter Integration Service stores the session state of operation in the shared location that is specified in $PMStorageDir. The PowerCenter Integration Service saves relational target recovery information in the target database.
When you run a CDC session that uses a resume recovery strategy, PWXPC writes the following message to the session log to indicate that recovery is in effect: 
PWXPC_12094 [INFO] [CDCRestart] Advanced GMD recovery in effect. Recovery is automatic.
When you recover or restart a CDC session, PWXPC uses the saved restart information to resume reading the change data from the point of interruption. The PowerCenter Integration Service restores the session state of operation, including the state of each source, target, and transformation. PWXPC, in conjunction with the PowerCenter Integration Service, determines how much of the source data it needs to reprocess. PowerExchange and PWXPC use the restart information to determine the correct point in the change stream from which to restart extracting change data and then applying it to the targets.
If you run a session with resume recovery strategy and the session fails, do not change the mapping, the session, or the state information before you restart the session. PowerCenter and PWXPC cannot guarantee recovery if you make any of these changes.
If any of the targets in the CDC session use the PowerCenter File Writer to write CDC data to flat files, do not use a resume recovery strategy. Restart tokens for all targets in the CDC session, including relational targets, will be compromised if a flat file target is in the same session. Data loss or duplication might occur.
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