CDC Guide for Linux, UNIX, and Windows

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Continuous Mode

In continuous mode, the PowerExchange Logger process runs continuously until you manually stop it.

Use continuous mode in the following situations:

You have a database with a high level of change activity that occurs continuously.

You have a database with intermittent activity that occurs at unpredictable intervals.

You want to avoid the overhead of scheduling PowerExchange Logger runs.

You cannot restart the PowerExchange Logger process often enough to keep up with the change volume.

To enable continuous mode, set the COLL_END_LOG parameter to 0.

In continuous mode, each time the Writer subtask completes a logging cycle, the PowerExchange Logger process is temporarily suspended. The next logging cycle is triggered by any of the following events:

The wait interval that is defined in the NO_DATA_WAIT parameter of the pwxccl configuration file elapses.

The CONDENSE command is manually entered at the command line or with the pwxcmd program.

The FILESWITCH command is manually entered at the command line or with the pwxcmd program.

The PowerExchange Logger process continues to run until you enter the SHUTDOWN or SHUTCOND command. To prevent log files from becoming too large, the PowerExchange Logger process periodically performs a file switch. Log files that are very large can prolong restart times for CDC sessions that run in continuous extraction mode or batch extraction mode.

You can use the NO_DATA_WAIT2 parameter in the pwxccl configuration file to prevent the PowerExchange Logger from consuming too much CPU time when PowerExchange is not receiving change data. For example, if you set the NO_DATA_WAIT2 parameter to 30 seconds, the PowerExchange Logger sleeps for 30 seconds, provided that no updates are received, and then performs another processing cycle. However, a large NO_DATA_WAIT2 value can delay processing of a SHUTDOWN command. If you need to reduce the amount of time that the PowerExchange Logger sleeps on a quiet system, you can adjust the FILE_FLUSH_VAL and FILE_SWITCH_VAL parameters.

Also, specify the RSTRADV time interval in the source-specific MSQL or UDB CAPI_CONNECTION statement or the OPTIONS statement of the PowerExchange Express CDC for Oracle configuration file to enable the PowerExchange Logger to advance its restart and sequence tokens even when UOWs do not contain any change data of interest for the data sources.

When you run the PowerExchange Logger in continuous mode, you can use either continuous or batch extraction mode for workflows that extract change data from the PowerExchange Logger log files.

Run the PowerExchange Logger in continuous mode unless you have a reason to use batch mode. On Linux or UNIX, you can run a continuous PowerExchange Logger process in background mode and use the pwxcmd program to send commands to that background PowerExchange Logger process.

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CDC Guide for Linux, UNIX, and Windows

CDC Guide for Linux, UNIX, and Windows

Continuous Mode

Continuous Mode