6.1.8. Tuning CDC Extraction

The frequency of extractions by the CDC extraction mechanism can be controlled by using the maxSleepTime parameter, which controls the maximum sleep time between data checks within the CDC tables. By default, the replicator checks for changes every second.

If there are no changes, the sleep time before the next query is increased by the sleepAddition until the value reaches, or is above, the maxSleepTime parameter. When changes are identified, the sleep time is reset back to 1 second. For example:

Increasing maxSleepTime sets the maximum sleep time and can help to reduce the overall redo log content generated, which in turn reduces the amount of disk space required to store and generate the log content.The value can be set during installation with tpm using:

shell> tpm update alpha --property=replicator.extractor.dbms.maxSleepTime=32 ...

The minimum sleep time can be configured to set the minimum sleep time between checks of the CDC table using the minSleepTime. This reduces the size of the redo log, at the expense of lowering the frequency of updates from the CDC into THL. For example, setting a minimum of 16 seconds would change the sample interval shown in the previous table to:

Sleep Data
16s No data
32s No data
  Data found
16s No data
32s No data
32s No data
32s No data

An additional parameter, sleepAddition, defines the increment value added to the minSleepTime parameter at each call until maxSleepTime is reached. For example, a setting of 8s would generate a table as follows:

Sleep Data
16s No data
24s No data
  Data found
16s No data
24s No data
32s No data
32s No data