Clear DefinitionsHRMP (Horizontal Relay‑routed Message Passing)
1 min read
Pronunciation
[H-R-M-P]
Analogy
Like a postal hub that receives mail from one city and routes it to another through a central sorting facility.
Definition
A Polkadot/Substrate mechanism enabling message passing between parachains via the relay chain, routing messages horizontally across the network.
Key Points Intro
HRMP provides secure, asynchronous communication channels between parachains.
Key Points
Channels: Bi‑directional queues between parachains.
Relay routing: Messages pass through relay chain validators.
Fee system: Payers deposit tokens to open channels.
Guaranteed delivery: Retries until inclusion or timeout.
Example
Technical Deep Dive
HRMP uses on‑chain storage of message queues in the relay chain state. Parachain blocks include outgoing HRMP messages in downward messages. Validators route these into the target parachain’s inbound queue.
Security Warning
Unbounded channels can bloat relay chain state; monitor queue lengths and manage channel lifecycles.
Caveat
HRMP is being phased out in favor of XCMP for efficiency and scalability.
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