CDC Guide for Linux, UNIX, and Windows

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How the PowerExchange Logger Determines the Start Point for a Cold Start

When you cold start a PowerExchange Logger for Linux, UNIX, and Windows process, it uses the RESTART_TOKEN and SEQUENCE_TOKEN parameters, if present, in the pwxccl configuration file to determine the point in the change stream at which to start reading changes.

Based on how you set these parameters, the PowerExchange Logger starts from one of the following points in the change stream:

If you enter valid token values in the RESTART_TOKEN and SEQUENCE_TOKEN parameters, the PowerExchange Logger starts from the point in the change stream that the token values specify. Use this method to start the PowerExchange Logger from a specific point.

If you do not define the RESTART_TOKEN and SEQUENCE_TOKEN parameters, the PowerExchange Loggers starts from the current end-of-log (EOL), or current point in time in the change stream.

You can generate restart and sequence tokens for the current EOL by running the DTLUAPPL utility with the RSTTKN GENERATE parameter or by performing a database row test with the SELECT CURRENT_RESTART SQL statement in PowerExchange Navigator.

If you enter only zeroes (a single 0, or an even number of 0s) in the RESTART_TOKEN and SEQUENCE_TOKEN parameters, the PowerExchange Logger processing starts from one of the following start positions, depending on the data source type:

For Db2 sources on Linux, UNIX, or Windows, processing starts from the position at which the DTLUCUDB utility created the Db2 catalog snapshot to initialize the PowerExchange capture catalog table. However, you can change this default restart position with the DTLUCUDB UPDTDRP command.

For Microsoft SQL Server sources, processing starts from the position of the oldest available data in the distribution database.

For PowerExchange Express CDC for Oracle sources, processing starts from the beginning of the most recent Oracle archive log.

For MySQL sources, processing starts from the oldest data available in the binary log. This position is the beginning of the binary log that has the log name that includes the lowest numeric suffix value. You can use the SHOW BINARY LOGS statement to identify this log.

For PostgreSQL sources, processing starts from the oldest data available in the replication store table. If the replication store table is empty, processing starts from the oldest record waiting to be read from the logical replication slot.

For remote Db2 for i (i5/OS) sources, processing starts from the beginning of the oldest receiver in the current chain of receivers.

For remote z/OS data sources, processing starts from the beginning of the PowerExchange Logger for z/OS active log files.

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Table of Contents

CDC Guide for Linux, UNIX, and Windows

CDC Guide for Linux, UNIX, and Windows

How the PowerExchange Logger Determines the Start Point for a Cold Start

How the PowerExchange Logger Determines the Start Point for a Cold Start