"I'm trying to understand the mechanics of parachain block authorization in blockchain networks like Polkadot and similar multi-chain systems. Specifically, I'd like to know:

  1. How many collators are typically selected at a time to authorize a parachain block?
  2. Is there a selection process for these collators?
  3. How many collators can collate at the same block height ?

I'm interested in the selection process for collators and how many of them are typically involved in producing a parachain block. Any insights, references, or resources on this topic would be greatly appreciated."

1 Answer 1


Because BABE does not function effectively for parachains, I presume that you are utilizing AURA.

AURA generates blocks sequentially, with each collator being assigned a slot one after another. If Collator A is absent (offline or otherwise), Collator B will assume A's slot.

A -> B -> C -> D -> A -> ..

# in case of B being offline

A -> C -> D -> A -> ..

If you are interested in block production, I recommend reading the AURA/BABE documentation first.

  • Does this imply that only a single collator, chosen from among all collators, is responsible for creating a block, and subsequently, only one parachain block generated by that collator is transmitted to the relay validators, establishing a direct connection between the relay chain validators and that specific collator?
    – the dev
    Commented Oct 18, 2023 at 6:12
  • Each slot belongs to only one collator.
    – AurevoirXavier
    Commented Oct 18, 2023 at 16:45

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