Working with change data capture (CDC) data
One of the most challenging aspects of working within a data lake environment is the processing of updates to existing data, such as with change data capture (CDC) data. We have discussed CDC data previously, but as a reminder, this is data that contains updates to an existing dataset.
A good example of this is data that comes from a relational database system. After the initial load of data is completed to the data lake, a system (such as Amazon DMS) can read the database transaction logs and write all future database updates to Amazon S3. For each row written to Amazon S3, the first column of the CDC file would contain one of the following characters (see the section on Amazon DMS in Chapter 3, The AWS Data Engineer's Toolkit, for an example of a CDC file generated by Amazon DMS):
- I – Insert: This indicates that this row contains data that was a new insert to the table.
- U – Update: This indicates that...
