How to configure polkadot + parachain locally to validate parachain block each 6 sec?

Question

I want to spin up parachain LOCALLY faster. each 6 sec. How to configure polkadot with parachain?

I have seen this and this and this post

So my zombienet contains polkadot(obviusly😊) and two parachains. each of them with one collator node.

I changed relaychain

pub const MILLISECS_PER_BLOCK: u64 = 3000;

and now relay chain produce the block each 3 sec. it is good.

I changed for parachain runtime. the value. from 12000 to 6000

pub const MILLISECS_PER_BLOCK: u64 = 6000;

BUT parachain still produce the block each 12 sec instead of 6 even when relay chain produce block each 3 sec.

I understand that i need to reconfigure relay chain to sign and send transaction to parachain more often. set_validate_data extrinisc in parachain system

Answer 1

If you want to run the relay chain and parachain locally follow https://docs.substrate.io/tutorials/build-a-parachain/prepare-a-local-relay-chain/.

The above tutorial will help you set up a relay chain locally and also will tell you how to connect a local parachain to it, after setting up the chain you can configure it according to your needs.

Answer 2

polkadot/service/chain_spec.rs will override

MILLISECS_PER_BLOCK

So you do not need change MILLISECS_PER_BLOCK directly. You need to change

session_length_in_blocks

#[cfg(feature = "rococo-native")]
pub fn rococo_development_config() -> Result<RococoChainSpec, String> {
    let wasm_binary = rococo::WASM_BINARY.ok_or("Rococo development wasm not available")?;

        Ok(RococoChainSpec::from_genesis(
            "Development",
            "rococo_dev",
            ChainType::Development,
            move || RococoGenesisExt {
                runtime_genesis_config: rococo_development_config_genesis(wasm_binary),
                // Use 1 minute session length.
                session_length_in_blocks: Some(10),
            },
            vec![],
            None,
            Some(DEFAULT_PROTOCOL_ID),
            None,
            None,
            Default::default(),
        ))
    }

Because the value of MILLISECS_PER_BLOCK will be overided byt this code

#[cfg(feature = "rococo-native")]
impl sp_runtime::BuildStorage for RococoGenesisExt {
    fn assimilate_storage(&self, storage: &mut sp_core::storage::Storage) -> Result<(), String> {
        sp_state_machine::BasicExternalities::execute_with_storage(storage, || {
            if let Some(length) = self.session_length_in_blocks.as_ref() {
                rococo_runtime_constants::time::EpochDurationInBlocks::set(&length);
            }
        });
        self.runtime_genesis_config.assimilate_storage(storage)
    }
}