ScyllaDB University LIVE, FREE Virtual Training Event | March 21
Register for Free
ScyllaDB Documentation Logo Documentation
  • Server
  • Cloud
  • Tools
    • ScyllaDB Manager
    • ScyllaDB Monitoring Stack
    • ScyllaDB Operator
  • Drivers
    • CQL Drivers
    • DynamoDB Drivers
  • Resources
    • ScyllaDB University
    • Community Forum
    • Tutorials
Download
ScyllaDB Docs ScyllaDB Enterprise Features Change Data Capture (CDC) CDC Overview

Caution

You're viewing documentation for a previous version. Switch to the latest stable version.

CDC Overview¶

CDC is a feature that allows you to not only query the current state of a database’s table, but also query the history of all changes made to the table.

As an example, suppose you made a sequence of changes to some table in the given order:

UPDATE ks.t SET v = 0 WHERE pk = 0 AND ck = 0;
UPDATE ks.t SET v = 1 WHERE pk = 0 AND ck = 0;
UPDATE ks.t SET v = 2 WHERE pk = 0 AND ck = 0;
UPDATE ks.t SET v = 2 WHERE pk = 0 AND ck = 1;
UPDATE ks.t SET v = 1 WHERE pk = 0 AND ck = 1;
UPDATE ks.t SET v = 0 WHERE pk = 0 AND ck = 1;

Normally, querying the table would return

 pk | ck | v
----+----+---
  0 |  0 | 2
  0 |  1 | 0

(2 rows)

but with CDC, you can also learn the history of all changes:

change at 2020-01-29 14:37:32: UPDATE ks.t SET v = 0 WHERE pk = 0 AND ck = 0;
change at 2020-01-29 14:37:33: UPDATE ks.t SET v = 1 WHERE pk = 0 AND ck = 0;
change at 2020-01-29 14:37:35: UPDATE ks.t SET v = 2 WHERE pk = 0 AND ck = 0; <- latest change
change at 2020-01-29 14:37:38: UPDATE ks.t SET v = 2 WHERE pk = 0 AND ck = 1;
change at 2020-01-29 14:37:39: UPDATE ks.t SET v = 1 WHERE pk = 0 AND ck = 1;
change at 2020-01-29 14:37:40: UPDATE ks.t SET v = 0 WHERE pk = 0 AND ck = 1; <- latest change

(not an actual syntax, the above example just presents the general concept).

Use cases for CDC¶

Some examples where CDC may be beneficial:

  • Heterogeneous database replication: applying captured changes to another database or table. The other database may use a different schema (or no schema at all), better suited for some specific workloads. An example is replication to ElasticSearch for efficient text searches.

  • Implementing a notification system.

  • In-flight analytics: looking for patterns in the changes in order to derive useful information, e.g. for fraud detection.

In ScyllaDB CDC is optional and enabled on a per-table basis. The history of changes made to a CDC-enabled table is stored in a separate associated table.

Terminology¶

  • Base Table - this is the original table, where all changes are made.

  • Log Table - this is the table associated to the base table which is created when CDC is enabled. Read about it in the log table document.

Enabling CDC¶

You can enable CDC when creating or altering a table using the cdc option, for example:

CREATE TABLE ks.t (pk int, ck int, v int, PRIMARY KEY (pk, ck, v)) WITH cdc = {'enabled':true};

Note

If you enabled CDC and later decide to disable it, you need to stop all writes to the base table before issuing the ALTER TABLE ... WITH cdc = {'enabled':false}; command.

CDC Parameters¶

The following table contains parameters available inside the cdc option:

Parameter name

Definition

Default

enabled

If true, the log table is created and each base table write will get a corresponding log table write: a delta row. The delta row describes “what has changed”.

false

preimage

If true, each base write will get a corresponding preimage row in the log table. Preimage rows exist to show the affected row’s state prior to the write. The amount of information can be changed: true value of the 'preimage' parameter configures the preimages to contain only the columns that were changed by the write; 'full' value to the 'preimage' configures the preimages to contain the entire row (how it was before the write was made). In the case of collection columns, preimage contains the state of the whole collection before the change (not only the affected cells of the collection). Note that preimages are costly: they require an additional read-before-write.

false

postimage

If true, each base write will get a corresponding postimage row in the log table. Postimage rows exist to show the affected row’s state after to the write. The postimage row always contains all the columns no matter if they were affected by the change or not. Note that postimages, similarly to preimages, are costly: they require an additional read-before-write. However, if you enable both preimage and postimage, only one read will be required for both of them.

false

delta

If 'full', each delta row will contain information about every modified column. If 'keys', only the primary key of the change will be recorded in the delta row. You may want to use the second option if you’re only interested in preimages and want to save some space.

full

ttl

Each log table row has a TTL (time-to-live) set on each of its columns, so that the log doesn’t grow endlessly. This option specifies what the TTL should be in seconds; the default is 86400 seconds (24 hours). You can also set it to 0, which means that the TTL won’t be set, thus log rows won’t be removed. Be careful however: in that case the log will consume more and more disk space. You will probably want to setup a separate cleaning mechanism if you set TTL to 0.

86400

Using CDC with Applications¶

When writing applications, you can now use our language specific libraries to simplify writing applications which will read from ScyllaDB CDC. The following libraries are available:

  • Go

  • Java

  • Rust

More information¶

ScyllaDB University: Change Data Capture (CDC) lesson - Learn how to use CDC. Some of the topics covered are:

  • An overview of Change Data Capture, what exactly is it, what are some common use cases, what does it do, and an overview of how it works

  • How can that data be consumed? Different options for consuming the data changes including normal CQL, a layered approach, and integrators

  • How does CDC work under the hood? Covers an example of what happens in the DB on different operations to allow CDC

  • A summary of CDC: It’s easy to integrate and consume, it uses plain CQL tables, it’s robust, it’s replicated in the same way as normal data, it has a reasonable overhead, it does not overflow if the consumer fails to act and data is TTL’ed. The summary also includes a comparison with Cassandra, DynamoDB, and MongoDB.

Was this page helpful?

PREVIOUS
Change Data Capture (CDC)
NEXT
The CDC Log Table
  • Create an issue

On this page

  • CDC Overview
    • Use cases for CDC
    • Terminology
    • Enabling CDC
    • CDC Parameters
    • Using CDC with Applications
    • More information
ScyllaDB Enterprise
  • enterprise
    • 2024.2
    • 2024.1
    • 2023.1
    • 2022.2
  • Getting Started
    • Install ScyllaDB Enterprise
      • ScyllaDB Web Installer for Linux
      • Install ScyllaDB Without root Privileges
      • Install scylla-jmx Package
      • Air-gapped Server Installation
      • ScyllaDB Housekeeping and how to disable it
      • ScyllaDB Developer Mode
      • Launch ScyllaDB on AWS
      • Launch ScyllaDB on GCP
      • Launch ScyllaDB on Azure
    • Configure ScyllaDB
    • ScyllaDB Configuration Reference
    • ScyllaDB Requirements
      • System Requirements
      • OS Support
      • Cloud Instance Recommendations
      • ScyllaDB in a Shared Environment
    • Migrate to ScyllaDB
      • Migration Process from Cassandra to ScyllaDB
      • ScyllaDB and Apache Cassandra Compatibility
      • Migration Tools Overview
    • Integration Solutions
      • Integrate ScyllaDB with Spark
      • Integrate ScyllaDB with KairosDB
      • Integrate ScyllaDB with Presto
      • Integrate ScyllaDB with Elasticsearch
      • Integrate ScyllaDB with Kubernetes
      • Integrate ScyllaDB with the JanusGraph Graph Data System
      • Integrate ScyllaDB with DataDog
      • Integrate ScyllaDB with Kafka
      • Integrate ScyllaDB with IOTA Chronicle
      • Integrate ScyllaDB with Spring
      • Shard-Aware Kafka Connector for ScyllaDB
      • Install ScyllaDB with Ansible
      • Integrate ScyllaDB with Databricks
      • Integrate ScyllaDB with Jaeger Server
      • Integrate ScyllaDB with MindsDB
    • Tutorials
  • ScyllaDB for Administrators
    • Administration Guide
    • Procedures
      • Cluster Management
      • Backup & Restore
      • Change Configuration
      • Maintenance
      • Best Practices
      • Benchmarking ScyllaDB
      • Migrate from Cassandra to ScyllaDB
      • Disable Housekeeping
    • Security
      • ScyllaDB Security Checklist
      • Enable Authentication
      • Enable and Disable Authentication Without Downtime
      • Creating a Custom Superuser
      • Generate a cqlshrc File
      • Reset Authenticator Password
      • Enable Authorization
      • Grant Authorization CQL Reference
      • Certificate-based Authentication
      • Role Based Access Control (RBAC)
      • ScyllaDB Auditing Guide
      • Encryption: Data in Transit Client to Node
      • Encryption: Data in Transit Node to Node
      • Generating a self-signed Certificate Chain Using openssl
      • Configure SaslauthdAuthenticator
      • Encryption at Rest
      • LDAP Authentication
      • LDAP Authorization (Role Management)
      • Software Bill Of Materials (SBOM)
    • Admin Tools
      • Nodetool Reference
      • CQLSh
      • Admin REST API
      • Tracing
      • ScyllaDB SStable
      • ScyllaDB Types
      • SSTableLoader
      • cassandra-stress
      • SSTabledump
      • SSTableMetadata
      • ScyllaDB Logs
      • Seastar Perftune
      • Virtual Tables
      • Reading mutation fragments
      • Maintenance socket
      • Maintenance mode
      • Task manager
    • Version Support Policy
    • ScyllaDB Monitoring Stack
    • ScyllaDB Operator
    • ScyllaDB Manager
    • Upgrade Procedures
      • About Upgrade
      • Upgrade Guides
    • System Configuration
      • System Configuration Guide
      • scylla.yaml
      • ScyllaDB Snitches
    • Benchmarking ScyllaDB
    • ScyllaDB Diagnostic Tools
  • ScyllaDB for Developers
    • Develop with ScyllaDB
    • Tutorials and Example Projects
    • Learn to Use ScyllaDB
    • ScyllaDB Alternator
    • ScyllaDB Drivers
      • ScyllaDB CQL Drivers
      • ScyllaDB DynamoDB Drivers
  • CQL Reference
    • CQLSh: the CQL shell
    • Appendices
    • Compaction
    • Consistency Levels
    • Consistency Level Calculator
    • Data Definition
    • Data Manipulation
      • SELECT
      • INSERT
      • UPDATE
      • DELETE
      • BATCH
    • Data Types
    • Definitions
    • Global Secondary Indexes
    • Expiring Data with Time to Live (TTL)
    • Functions
    • Wasm support for user-defined functions
    • JSON Support
    • Materialized Views
    • Non-Reserved CQL Keywords
    • Reserved CQL Keywords
    • DESCRIBE SCHEMA
    • Service Levels
    • ScyllaDB CQL Extensions
  • Features
    • Lightweight Transactions
    • Global Secondary Indexes
    • Local Secondary Indexes
    • Materialized Views
    • Counters
    • Change Data Capture
      • CDC Overview
      • The CDC Log Table
      • Basic operations in CDC
      • CDC Streams
      • CDC Stream Generations
      • Querying CDC Streams
      • Advanced column types
      • Preimages and postimages
      • Data Consistency in CDC
    • Workload Attributes
    • Workload Prioritization
  • ScyllaDB Architecture
    • Data Distribution with Tablets
    • ScyllaDB Ring Architecture
    • ScyllaDB Fault Tolerance
    • Consistency Level Console Demo
    • ScyllaDB Anti-Entropy
      • ScyllaDB Hinted Handoff
      • ScyllaDB Read Repair
      • ScyllaDB Repair
    • SSTable
      • ScyllaDB SSTable - 2.x
      • ScyllaDB SSTable - 3.x
    • Compaction Strategies
    • Raft Consensus Algorithm in ScyllaDB
    • Zero-token Nodes
  • Troubleshooting ScyllaDB
    • Errors and Support
      • Report a ScyllaDB problem
      • Error Messages
      • Change Log Level
    • ScyllaDB Startup
      • Ownership Problems
      • ScyllaDB will not Start
      • ScyllaDB Python Script broken
    • Upgrade
      • Inaccessible configuration files after ScyllaDB upgrade
    • Cluster and Node
      • Handling Node Failures
      • Failure to Add, Remove, or Replace a Node
      • Failed Decommission Problem
      • Cluster Timeouts
      • Node Joined With No Data
      • NullPointerException
      • Failed Schema Sync
    • Data Modeling
      • ScyllaDB Large Partitions Table
      • ScyllaDB Large Rows and Cells Table
      • Large Partitions Hunting
      • Failure to Update the Schema
    • Data Storage and SSTables
      • Space Utilization Increasing
      • Disk Space is not Reclaimed
      • SSTable Corruption Problem
      • Pointless Compactions
      • Limiting Compaction
    • CQL
      • Time Range Query Fails
      • COPY FROM Fails
      • CQL Connection Table
    • ScyllaDB Monitor and Manager
      • Manager and Monitoring integration
      • Manager lists healthy nodes as down
    • Installation and Removal
      • Removing ScyllaDB on Ubuntu breaks system packages
  • Knowledge Base
    • Upgrading from experimental CDC
    • Compaction
    • Consistency in ScyllaDB
    • Counting all rows in a table is slow
    • CQL Query Does Not Display Entire Result Set
    • When CQLSh query returns partial results with followed by “More”
    • Run ScyllaDB and supporting services as a custom user:group
    • Customizing CPUSET
    • Decoding Stack Traces
    • Snapshots and Disk Utilization
    • DPDK mode
    • Debug your database with Flame Graphs
    • Efficient Tombstone Garbage Collection in ICS
    • How to Change gc_grace_seconds for a Table
    • Gossip in ScyllaDB
    • Increase Permission Cache to Avoid Non-paged Queries
    • How does ScyllaDB LWT Differ from Apache Cassandra ?
    • Map CPUs to ScyllaDB Shards
    • ScyllaDB Memory Usage
    • NTP Configuration for ScyllaDB
    • Updating the Mode in perftune.yaml After a ScyllaDB Upgrade
    • POSIX networking for ScyllaDB
    • ScyllaDB consistency quiz for administrators
    • Recreate RAID devices
    • How to Safely Increase the Replication Factor
    • ScyllaDB and Spark integration
    • Increase ScyllaDB resource limits over systemd
    • ScyllaDB Seed Nodes
    • How to Set up a Swap Space
    • ScyllaDB Snapshots
    • ScyllaDB payload sent duplicated static columns
    • Stopping a local repair
    • System Limits
    • How to flush old tombstones from a table
    • Time to Live (TTL) and Compaction
    • ScyllaDB Nodes are Unresponsive
    • Update a Primary Key
    • Using the perf utility with ScyllaDB
    • Configure ScyllaDB Networking with Multiple NIC/IP Combinations
  • Reference
    • AWS Images
    • Azure Images
    • GCP Images
    • Configuration Parameters
    • Glossary
    • Limits
    • ScyllaDB Enterprise vs. Open Source Matrix
    • API Reference (BETA)
    • Metrics (BETA)
  • ScyllaDB University
  • ScyllaDB FAQ
  • Alternator: DynamoDB API in Scylla
    • Getting Started With ScyllaDB Alternator
    • ScyllaDB Alternator for DynamoDB users
    • Alternator-specific APIs
Docs Tutorials University Contact Us About Us
© 2025, ScyllaDB. All rights reserved. | Terms of Service | Privacy Policy | ScyllaDB, and ScyllaDB Cloud, are registered trademarks of ScyllaDB, Inc.
Last updated on 09 Apr 2025.
Powered by Sphinx 7.4.7 & ScyllaDB Theme 1.8.6