The S2 sink delivers database change events to an S2 stream.

S2 (“Stream Store”) is a cloud-native storage layer purpose-built for data in motion. Streams are unlimited, durable, and serverless – you pay only for the data you append and read.

This is the reference for the S2 sink. See the quickstart for a step-by-step walkthrough or the how-to guide for an explanation of how to use the S2 sink.

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Configuration

When you create an S2 sink you’ll provide three fields:

  • Basin

    The S2 basin that owns your stream. A basin is similar to an S3 bucket – it namespaces one or more streams.

  • Stream

    The name of the stream inside the basin (e.g. products).

  • Access Token

    An S2 access token with append permissions for the target stream. Generate tokens in the S2 web console under Access Tokens.

The Sequin S2 sink uses the access token provided to make HTTPS requests to the S2 REST API.

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Message format

Sequin sends JSON messages and is encoded as UTF-8 text.

You can customize the payload with transform functions.

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Retry behavior

If S2 rejects a write (for example due to throttling or network errors) Sequin:

  1. Immediately re-queues the message at the front of the delivery queue.
  2. Retries with exponential back-off
  3. Continues indefinitely until the message is acknowledged by S2 or you “Acknowledge” the message from the Messages tab.

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Record size limits

S2 currently supports records up to 1 MiB (the maximum size of a single append request). If a message exceeds this limit S2 returns payload too large and Sequin will keep retrying. The typical fix is to:

  1. Identify the offending column(s).
  2. Create a transform that removes or compresses those fields.
  3. Retry the failed message or “Acknowledge” it as undeliverable.

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Grouping & ordering

The S2 sink preserves the commit-timestamp order of messages that share the same group. By default the group is the primary key of the source row, ensuring changes to a single row arrive in order.

You can override grouping in the sink UI by specifying one or more columns (for example user_id). Messages with different group values may be interleaved, but messages with the same group value are delivered sequentially.

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Debugging

Use the Sequin console to monitor delivery:

  1. Open the sink and switch to the Messages tab.
  2. Filter by Failed to see messages Sequin could not deliver.
  3. Click a message to inspect the last S2 error response and stack trace.

Common issues include:

  • Invalid or expired access token (S2 returns 401 Unauthorized).
  • Basin / stream name typo (S2 returns 404 Not Found).
  • Record size > 1 MiB (413 Payload Too Large).

For live verification you can tail the stream with the S2 CLI:

s2 tail s2://<basin>/<stream>

Successful reads confirm that S2 is receiving and storing events.

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Routing

The S2 sink supports dynamic routing of the basin and stream using routing functions.

Example routing function:

def route(action, record, changes, metadata) do
  %{
    basin: "logs-" <> metadata.table_schema,
    stream: metadata.table_name
  }
end

When not using a routing function, records will be appended to the basin and stream specified in the sink configuration.