I am using release-v1.0.0 of polkadot. I am going through this tutorial and running two relay chain node but got this error,

Error with block built on 0x05dd517785cae6c35027166fa2d96ae4298de4016d4684b00ec034000a339355: Import failed: Unexpected epoch change

I try to delete db from this directory ~/Library/Application Support/<chain name> but still same issue.

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blocks are producing but after 2-3 block it throws this error and also I am not able to create paraId,

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1 Answer 1


The consensus algorithm BABE assumes that at least one block will be produced per epoch, so probably you stopped your nodes and whenever there is a period of inactivity (no blocks being produced) for more than one epoch BABE is broken.

Because you are in development the best solution for that is to clean the database as you have tried. However I think you are trying to delete the wrong folder, if you are running the same commands as the tutorial you are using the following flag:

--base-path /tmp/relay/alice 

Which is specifying that the chain database stored locally at /tmp/relay/alice try to delete this folder and the same for the other Node Bob.

Another option when you are in development mode is to use the flag --dev because each time you start/restart a node, this will create an delete a temporal folder for the DB.

You are not able to create a paraId because of this issue, when fixed if you follow the step-by-step guide: Connect a local parachain it will work.

  • Ben delete chain database stored locally works but I don't understand how to use --dev flag in this command? because just adding --dev after `--rpc-port 9944 ` doesn't work
    – Ganesh11
    Aug 4, 2023 at 9:47
  • 1
    --dev can not got with --chain, if you delete --chain will work, but if you want to use your chain_spec, use --tmp instead of --dev (will create tmp data and delete it after). With --tmp you don't need to use specify the --base-path
    – Alex Bean
    Aug 4, 2023 at 10:53

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