Change Data Capture (CDC) logging

Change Data Capture (CDC) logging captures changes to data.

Change Data Capture (CDC) logging captures and tracks data that has changed. CDC logging is configured per table, with limits on the amount of disk space to consume for storing the CDC logs. CDC logs use the same binary format as the commit log.
Important: When all tables having mutations in a completed commitlog segment are flushed, a hard link to that commitlog segment is created in the cdc_raw directory. This action makes the CDC-enabled mutations available.

If the disk space limit is reached, CDC-enabled tables reject writes until space is freed.

cassandra.yaml

The location of the cassandra.yaml file depends on the type of installation:
Package installations /etc/dse/cassandra/cassandra.yaml
Tarball installations installation_location/resources/cassandra/conf/cassandra.yaml

CDC directory location

The location of the CDC directory depends on the type of installation:
Package installations /var/lib/cassandra/cdc_raw
Tarball installations /var/lib/cassandra/cdc_raw

Prerequisites

Before enabling CDC logging, define a plan for moving and consuming the CDC log information. DataStax recommends a physical device for the CDC log that is separate from the data directories.

Procedure

  1. Enable CDC logging and configure CDC directories and space in cassandra.yaml.
    For example, to enable CDC logging with default values:
    cdc_enabled: true
cdc_total_space_in_mb: 4096
cdc_free_space_check_interval_ms: 250
cdc_raw_directory: /var/lib/cassandra/cdc_raw
  2. Optional: To enable CDC logging for a database table, create or alter the table with the table property.
    For example, to enable CDC logging on the cycling table:
    ALTER TABLE cycling WITH cdc=true;