I want to determine the minimum amount of collators that a specific parachain that is registered on the Rococo network must have running in order for them to generate and finalize blocks once they have all finished synchronising with the Rococo relay chain.

In the Cumulus tutorial here, it says: "You should have at least two validators (relay chain nodes) running for every collator (parachain nodes) on your network."

Elsewhere in the Cumulus tutorial here it says that "chain specs conventionally live in a /res folder that is published in your node's codebase for others to use. For example: Polkadot includes these relay chain chain specs under node/service/res".

It further says "You can modify the first section's provided plain relay chain spec to include more validators for testing, or go the more "correct" route used for production of modifying the source for genesis state in chain_spec.rs for your relay chain to add more validators."

It appears that only the raw rococo_v2 relay chain spec for Rococo is published here as file rococo.json, but the directory doesn't include the Rococo plain relay chain spec where more validators could be included for testing, so it does not appear that this gets modified to included more validators for testing.

Also the Rococo Staging Testnet Genesis Config in chain_spec.rs of the 'master' branch in the Polkadot repository includes eight (8) initial authorities (validators) that do not appear to have been changed. Why doesn't the plain relay chain spec or the list of validators for Rococo Staging Testnet Genesis config in that chain_spec.rs file have to change?

When I connect to Rococo using polkadot.js here and go to menu Developer > Chain state > Storage > session > validators() then it returns the "current set of validators" for Rococo, as shown below:

current set of Rococo validators

There are current thirty nine (39) of them, which does not match the amount of Rococo validators listed in the chain_spec.rs.

So my main questions is: If there are currently thirty nine (39) Rococo validators, and we want to add collators to a parachain that we have registered on Rococo. Does this mean we should have at least twenty (20) collators (parachain nodes) running so that we satisfy the requirement mentioned earlier of having at least two validators running for every collator on your network? If you don't have satisfy that minimum amount of collators running that have finished synchronising with the Rococo relay chain, will your parachain still be able to generate and finalise blocks?

1 Answer 1


You only need 1 collator being synchronized to start building blocks. You also don't need n + 1 validators on the relay chain where n is the number of Parachains. That was the case for Parachains V0 code. However, this was also not related in any way with the collators.

  • Substrate documentation still says that you need n+1 validators on the relay chain where n is the number of parachains connected/to be connected. Is the docs needs to be updated? Apr 11, 2023 at 9:49
  • Yeah it should be updated! Can you post a link?
    – bkchr
    Apr 11, 2023 at 18:48

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