---
display_name: "Change Data Capture"
---

# CDC - Change Data Capture

## Overview

Change Data Capture (CDC) allows you to track and capture all data changes (inserts, updates, deletes) made to your database tables. This is useful for building reactive applications, syncing data between systems, replication, auditing, and more.

**Note:** This feature is currently marked as unstable, meaning the API is subject to change in future versions. The functionality itself is reliable for use.

## Enabling CDC

CDC is enabled per connection using the PRAGMA command:

```sql
PRAGMA unstable_capture_data_changes_conn('<mode>[,<table_name>]');
```

### Parameters

- **mode**: The capture mode (see below)
- **table_name**: Optional custom table name for storing changes (defaults to `turso_cdc`)

### Capture Modes

- **`off`**: Disable CDC for this connection
- **`id`**: Capture only the primary key/rowid of changed rows
- **`before`**: Capture row state before changes (for updates/deletes)
- **`after`**: Capture row state after changes (for inserts/updates)
- **`full`**: Capture both before and after states, plus update details

## Examples

### Basic Usage

Enable CDC with ID mode (captures primary keys only):
```sql
PRAGMA unstable_capture_data_changes_conn('id');
```

### Using Different Modes

Capture the state before changes:
```sql
PRAGMA unstable_capture_data_changes_conn('before');
```

Capture the state after changes:
```sql
PRAGMA unstable_capture_data_changes_conn('after');
```

Capture complete change information:
```sql
PRAGMA unstable_capture_data_changes_conn('full');
```

### Custom CDC Table

Store changes in a custom table instead of the default `turso_cdc`:
```sql
PRAGMA unstable_capture_data_changes_conn('full,my_changes_table');
```

### Disable CDC

Turn off CDC for the current connection:
```sql
PRAGMA unstable_capture_data_changes_conn('off');
```

## CDC Table Structure

The CDC table (default name: `turso_cdc`) contains the following columns:

| Column | Type | Description |
|--------|------|-------------|
| `change_id` | INTEGER | Auto-incrementing unique identifier for each change |
| `change_time` | INTEGER | Timestamp of the change (Unix epoch) |
| `change_type` | INTEGER | Type of change: 1 (INSERT), 0 (UPDATE), -1 (DELETE) |
| `table_name` | TEXT | Name of the table that was changed |
| `id` | varies | Primary key/rowid of the changed row |
| `before` | BLOB | Row data before the change (for modes: before, full) |
| `after` | BLOB | Row data after the change (for modes: after, full) |
| `updates` | BLOB | Details of updated columns (for mode: full) |

## Querying Changes

Once CDC is enabled, you can query the changes table like any other table:

```sql
-- View all captured changes
SELECT * FROM turso_cdc;

-- View only inserts
SELECT * FROM turso_cdc WHERE change_type = 1;

-- View only updates
SELECT * FROM turso_cdc WHERE change_type = 0;

-- View only deletes
SELECT * FROM turso_cdc WHERE change_type = -1;

-- View changes for a specific table
SELECT * FROM turso_cdc WHERE table_name = 'users';

-- View recent changes (last hour)
SELECT * FROM turso_cdc
WHERE change_time > unixepoch() - 3600;
```

## Practical Example

```sql
-- Create a table
CREATE TABLE users (
    id INTEGER PRIMARY KEY,
    name TEXT,
    email TEXT
);

-- Enable full CDC
PRAGMA unstable_capture_data_changes_conn('full');

-- Make some changes
INSERT INTO users VALUES (1, 'Alice', 'alice@example.com');
INSERT INTO users VALUES (2, 'Bob', 'bob@example.com');
UPDATE users SET email = 'alice@newdomain.com' WHERE id = 1;
DELETE FROM users WHERE id = 2;

-- View the captured changes
SELECT change_type, table_name, id
FROM turso_cdc;

-- Results will show:
-- 1 (INSERT) for Alice
-- 1 (INSERT) for Bob
-- 0 (UPDATE) for Alice's email change
-- -1 (DELETE) for Bob
```

## Multiple Connections

Each connection can have its own CDC configuration:

```sql
-- Connection 1: Capture to 'audit_log' table
PRAGMA unstable_capture_data_changes_conn('full,audit_log');

-- Connection 2: Capture to 'sync_queue' table
PRAGMA unstable_capture_data_changes_conn('id,sync_queue');

-- Changes from Connection 1 go to 'audit_log'
-- Changes from Connection 2 go to 'sync_queue'
```

## Transactions

CDC respects transaction boundaries. Changes are only recorded when a transaction commits:

```sql
BEGIN;
INSERT INTO users VALUES (3, 'Charlie', 'charlie@example.com');
UPDATE users SET name = 'Charles' WHERE id = 3;
-- CDC table is not yet updated

COMMIT;
-- Now both the INSERT and UPDATE appear in the CDC table
```

If a transaction rolls back, no CDC entries are created for those changes.

## Schema Changes

CDC also tracks schema changes when using full mode:

```sql
PRAGMA unstable_capture_data_changes_conn('full');

CREATE TABLE products (id INTEGER PRIMARY KEY, name TEXT);
-- Recorded in CDC as change to sqlite_schema

DROP TABLE products;
-- Also recorded as a schema change
```