When a PowerCenter CDC session runs in continuous extraction mode or batch extraction mode, the PowerExchange Listener reads the CDCT file to determine the PowerExchange Logger log files from which to extract change data.

The PowerExchange Logger creates the CDCT file in the directory that is specified by the CAPT_PATH statement in the dbmover configuration file that is on the system where the PowerExchange Logger runs. The CDCT file must reside on local disk. If the CAPT_PATH statement is not specified, the CDCT file is in the local directory from which the PowerExchange Logger is invoked.

The CDCT file name has the format CDCT_

dbid

, where

dbid

is the DBID value in the PowerExchange Logger configuration file.

The first time the PowerExchange Logger receives data of interest after startup or a file switch, the PowerExchange Logger opens a log file to which to write data and creates an entry for this log file in the CDCT file. After the PowerExchange Logger finishes writing data to the log file, it marks the file as closed in the CDCT file. The PowerExchange Logger also updates the restart information in the CDCT file during periods when no changes of CDC interest are received.

If a PowerExchange Logger failure occurs and leaves an open log file, the PowerExchange Logger marks the CDCT entry for that log file for deletion. The next time the PowerExchange Logger starts, it deletes that log file entry and creates a new log file. The log files contain records from which the CDCT entry for the log can be rebuilt.

PowerExchange automatically generates a backup of the CDCT file at PowerExchange Logger initialization and normal termination. These backups are located in the same directory as the CDCT file and have file names with the following formats: CDCT_

dbid

_INIT.bkp and CDCT_

dbid

_TERM.bkp.