Using Elasticsearch Percolate for User Notifications
The article explains how to use Elasticsearch's percolate feature to implement user notifications by matching new documents against stored user-defined queries. It covers the setup of a percolator index, how to register user interest queries, and how to efficiently find which users should be notified when a new document is indexed.
Background
- **Elasticsearch** is a popular open-source search and analytics engine used to index, search, and analyze large volumes of data quickly. It's often used for log analysis, full-text search, and real-time applications.
- **Percolate** (or Percolator) is a lesser-known Elasticsearch feature that works in reverse: instead of searching documents against a stored query, it stores queries and checks incoming documents against them. This makes it ideal for alerting or notification systems.
- **Why this matters**: Typical notification systems either poll a database or use complex stream-processing pipelines. The Percolate feature offers a simpler, scalable alternative — push a notification rule as a stored query, and Elasticsearch automatically fires when a new document matches. The article walks through using this design pattern for user notifications at scale.