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   == What is Change Data Capture?
   
  -Change Data Capture, or CDC, is an older term for a system that monitors and captures the changes in data so that other software can respond to those changes. Data warehouses often had built-in CDC support, since data warehouses need to stay up-to-date as the data changed in the upstream OLTP databases. 
  +Change Data Capture, or CDC, is an older term for a system that monitors and captures the changes in data so that other software can respond to those changes. Data warehouses often had built-in CDC support, since data warehouses need to stay up-to-date as the data changed in the upstream OLTP databases.
   
   Debezium is essentially a modern, distributed open source _change data capture platform_ that will eventually support monitoring a variety of database systems.
   
  
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  == Why are events so large?
  
  Debezium is designed to monitor upstream databases and produce for each row-level change one or more corresponding events that completely describe those changes. But Debezium connectors work _continuously_, and its events have to make sense even as the structure of the tables in the upstream databases change over time. A consumer is also much easier to write if it only has to deal with a single event at a time, rather than having to track state over the entire history of the event stream.
  
  That means each event needs to be completely self-describing: an event's key and value each contain a _payload_ with the actual information and a _schema_ that fully describes the structure of the information. Consuming applications can process each event, use the schema to understand the structure of the information in that event, and then correctly process the event's payload. The consuming application can take advantage of the fact that the schema will remain the same for many events in a row, and only when the schema changes might the consuming application need to do a bit more work preparing for the changed structure.
  
  