Editing Relay (section)

== Core Functions ==
The primary purpose of a relay is to collect, validate, and redistribute [[Data repository|repository]] data from across the network. It does this by crawling user repositories hosted on PDSes throughout the network and consuming their real-time update streams. The relay verifies the cryptographic signatures and [[Merkle Search Tree|Merkle Tree]] proofs on all updates to ensure data integrity.

Importantly, relays themselves does not interpret or index the records in repositories, but simply stores and forwards them. As a result, developers can create new social experiences on top of the AT Protocol by defining new record types with a [[lexicon]], and these records will flow through relays without requiring any changes to their code.

Each relay maintains its own replica of the repositories it tracks, allowing it to detect changes even when real-time notifications are interrupted. This replication provides resilience against network issues and ensures complete data coverage. When network interruptions occur, relays can periodically re-crawl repositories and compare them to its local replica to determine what records have been added or deleted.

Through continuous monitoring, relays produce a [[firehose]] - a consolidated stream of all network activity that notifies subscribers whenever records are added or deleted in any tracked repository. This firehose becomes the foundation for building network-wide services. 

As part of its processing, relays perform initial data cleaning by discarding malformed updates, filtering out illegal content, and reducing high-volume spam, which helps downstream services focus on their specific functions rather than basic data validation.