> ## Documentation Index
> Fetch the complete documentation index at: https://sequinstream.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Redis String sink

> Stream Postgres changes to Redis Strings with Sequin's Redis String sink.

The **Redis String sink** writes database changes to a Redis instance as key-value pairs using the Redis [String data type](https://redis.io/docs/latest/develop/data-types/strings/).

<Tip>
  This is the reference for the Redis String sink. See the [quickstart](/quickstart/redis-string) for a step-by-step walkthrough or the [how-to guide](/how-to/stream-postgres-to-redis-string) for an explanation of how to use the Redis String sink.
</Tip>

## Configuration parameters

| Parameter   | Type    | Required | Default | Description                                                       |
| ----------- | ------- | -------- | ------- | ----------------------------------------------------------------- |
| `host`      | string  | Yes      | -       | Hostname or IP address of the Redis server                        |
| `port`      | integer | Yes      | -       | Port number of the Redis server (1-65535)                         |
| `username`  | string  | No       | -       | Username for Redis authentication                                 |
| `password`  | string  | No       | -       | Password for Redis authentication                                 |
| `tls`       | boolean | No       | `false` | Enable TLS/SSL for the connection                                 |
| `database`  | integer | No       | `0`     | Redis database number (≥ 0)                                       |
| `expire_ms` | integer | No       | -       | Key expiration time in milliseconds (≥ 0, omit for no expiration) |

## Redis connection

The sink connects to Redis using the following URL format:

```
redis[s]://[username:password@]host:port/database
```

Where:

* `rediss://` is used when `tls` is enabled, otherwise `redis://`
* Authentication credentials are included when provided

## Key format and operations

For each change to the source table, the sink performs the following Redis operations:

| Change action              | Redis operation | Behavior                                              |
| -------------------------- | --------------- | ----------------------------------------------------- |
| `INSERT`, `UPDATE`, `READ` | `SET`           | Sets the key to the JSON representation of the record |
| `DELETE`                   | `DEL`           | Removes the key from Redis                            |

By default, keys are generated using the format:

```
sequin:{table_name}:{primary_key}
```

For composite primary keys, values are joined with a colon.

### Routing

You can use a [routing function](/reference/routing) to customize the key used for each message. For example, you can use the record's `id` field with your own prefix:

```elixir theme={null}
def route(action, record, changes, metadata) do
  %{
    key: "my_app:users:#{record["id"]}"
  }
end
```

## Data format

Records are stored as JSON strings. The specific format depends on the transform applied to the data:

With no transform, the [**entire message payload**](/reference/messages) is stored as a JSON object

This may not be preferred for most caching use cases. We [**recommend using a transform**](/reference/transforms) to modify the structure and content before storage.

If your transform returns a string or binary-coercible value (such as an integer or boolean), the value is stored directly in Redis.

Otherwise, Sequin will JSON encode the value before storing it in Redis.

## Key expiration

When `expire_ms` is specified, each key is set with an expiration time using Redis' `PX` operation during `SET`. This allows for automatic key cleanup.