Hello valuable Substrate community,

I started two rococo-local relaychain validators and one custom parachain. The target block time of the parachain is 12 seconds, but the actual block time is 24 seconds on average.

I am using a MacBook Air M1.

How can I reduce the block time to 12 seconds?

What is the cause of the slow block production on my local setup?

  • How many validators are you running? Try running one more!
    – Bruno
    Commented Mar 15, 2023 at 21:30
  • I run two validators for the local Rococo relaychain and one collator on my local parachain. Thanks for the tip! I will try this.
    – Chralt
    Commented Mar 16, 2023 at 18:53
  • 1
    Thanks, two collators fixed the problem!
    – Chralt
    Commented Mar 17, 2023 at 10:38
  • 1
    Could you provide the answer to your question so this question is useful for others? Commented Mar 27, 2023 at 9:27

1 Answer 1


To fix the problem of a block time of 24 seconds you need to add an additional parachain collator.

I just started two local rococo relay chain nodes and one parachain collator.

Then after Brunos suggestion I started another parachain collator and now the block time is consistently 12 seconds as expected.

To run two parachain collators you can follow the commands:

# Collator1
./target/release/polkadot-parachain --collator --alice --force-authoring --tmp --port 40335 --ws-port 9946 -- --execution wasm --chain ../polkadot/rococo-local-cfde.json --port 30335

# Collator2
./target/release/polkadot-parachain --collator --bob --force-authoring --tmp --port 40336 --ws-port 9947 -- --execution wasm --chain ../polkadot/rococo-local-cfde.json --port 30336

More on this here.

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