Event stream

An event stream is an ordered, continuous flow of timestamped records, such as page views, transactions or consent changes, that a platform ingests and processes as they occur.

Part of the Learn hub and the customer data glossary.

What it means in practice

An event is a record that something happened: a page was viewed, a payment cleared, a consent changed. It carries who (an identifier), what (a name), when (a timestamp) and properties (the details). A stream is the ordered flow of such events. Log-based brokers such as Apache Kafka retain events for a configured period, so consumers can read at their own pace and re-read from an earlier point.

Streams are the nervous system of real-time decisioning and of activation that reacts as things happen, in contrast to batch loads that move data in scheduled chunks. Design points: partition by person so each person's events stay in order; expect at-least-once delivery, so duplicates will occur and consumers must be idempotent; handle late and out-of-order events; and put every event through an event contract at the door.

Consent changes belong in the stream. A withdrawal is an event like any other, and processing it promptly is what makes suppression work in near real time.

Keep out what should not be there. Cardholder data in event payloads may bring pipelines into PCI DSS scope, and free-text fields can carry health information nobody meant to collect.

Example (retail banking): app and branch events flow into the stream as event types and tokenised references, not card numbers. A decisioning service reads them and suppresses a promotion if a fraud alert has just fired on the account.

Related terms

• Event contract: the schema each event must meet.
• Event replay: re-reading retained events.
• Real-time decisioning: reacts to the stream.
• Destination: where events are forwarded.
• First-party data: what most events carry.

Where it matters

• Customer data platform architecture: ingestion and decisioning.
• PCI DSS v4 and marketing data: keeping cardholder context out.