Inner stream joins

Strict join between two event streams

Objective

To perform a strict join between two event streams, an inner join is used.

This join operator emits an event only when a successful match occurs between streams. Otherwise, it waits until the join criteria are met, as determined by the configured policy settings.

Uses

Among the previously mentioned examples in the stream join concept page, the application for inner joins can impact the following:

1. Immediate feedback loop It enables businesses to receive immediate feedback on customer behaviour, allowing for rapid adjustments to marketing strategies.

2. Enhanced customer experience By understanding which ads are clicked by which customers, businesses can personalise experiences and improve overall engagement.

Example

This code defines a join operation for two streams (sitevisits and webpage.adclicks), based on a common customerId.

1. expression The join condition is that sitevisits.customerId should match webpage.adclicks.customerId.

2. merge events When the condition is met, the events from both streams are merged.

3. left policy (time to live) The sitevisits stream events are kept for a maximum of 30 minutes before they expire.

4. right policy (delete on join) Once a matching event from webpage.adclicks is joined with sitevisits, the event from webpage.adclicks is deleted.

This strategy merges data while ensuring that events are kept only within a specific timeframe and properly cleaned up once they are joined.

Inner joins are set by ==

streams join:
  expression: "sitevisits.customerId == webpage.adclicks.customerId"
  merge events: true
  left policy:
    time to live: 30 minutes
  right policy:
    delete on join: true