CDC record sequence numbers

Most Change Data Capture (CDC) records returned to the client contain a sequence number.

The sequence number associated with a CDC record is a BIGINT data type.

The CDC record sequence number is not necessarily the same as the LSN of the HCL OneDB™ logical log that is being captured.

You can compare sequence numbers for CDC records that are returned for the same transaction. Within a transaction, the sequence numbers of CDC records returned increase over time. For most types of records, lower sequence number indicates that the CDC record was returned earlier than a CDC record with a higher sequence number. However, for a CDC_REC_DISCARD record type, the sequence number indicates from where to discard records.

You can compare the sequence numbers of CDC_REC_BEGINTX records or the sequence numbers of CDC_REC_COMMTX records for different transactions. Each committed transaction has one CDC_REC_BEGINTX record and one CDC_REC_COMMTX record. The sequence numbers for the CDC_REC_BEGINTX and CDC_REC_COMMTX records are in monotonic order. A lower sequence number indicates that the associated transaction was begun or committed earlier than a transaction associated with a higher sequence number.