Change Data Capture (CDC) Processing Overview

Products

• Datacom
• Datacom/DB

Issue/Introduction

How does the Datacom Change Data Capture (CDC) feature work? 

Environment

z/OS

 

Resolution

Change Data Capture (CDC) is used to replicate changes to a Datacom database into another database. A database needs to be defined where the replicated changes are going to be applied--this could be another Datacom database. CDC captures Log Area (LXX) information in a source MUF and writes the log data to a system database (DBID 2009) in the target MUF. In local mode, the Source and Target MUFs are the same. In remote mode, the Source and Target MUFs are different. 

CDC is activated by coding in the Source MUF the startup option CDC YES and CDC_BASE YES,dbid for the databases to be processed by CDC.

The Change Data Capture Listener (CDCL) program is provided by Datacom and runs in the target MUF. It monitors the source MUF LXX for data being logged for selected tables. It then writes the LXX information to the system database DBID 2009 on the Target MUF. 

The Change Data Capture User Listener (CDCU) program needs to be provided and started by the user. It monitors the CDC system DBID 2009 for committed maintenance log records for selected tables. The CDCU program then processes these requests by applying the changes to the replicated database and then deletes the maintenance records from DBID 2009. Sample program CDC3 is provided in source in the CABDSAMP library and can be used as a model to code your own CDCU program. The Program DBCP1PR provided as a load module can be used to test CDC.

The Change Data Capture Monitor (CDCM) program is provided by Datacom and runs in the Source MUF. It connects to the target MUF and periodically checks the CDCL and CDCU programs to see how current they are relative to the LXX. CDCM program options allow you to specify how often the checks occur and how far the CDCL and CDCU programs can slip behind the LXX before a warning message is issued.