Two Geth nodes were mining in the same private net, and one of them gave ⑂ block became a side fork. I don't get what it means.

I'm new in Ethereum. I'd appreciate it if you give me an explanation for newbies.

1 Answer 1


Both mining nodes are competing to create blocks, and mined a block at around the same time. Both blocks are valid, but they are 2 possible realities. They keep mining and one of them finds another block. The longest chain (2 blocks instead of one) becomes the accepted reality, and the shortest chain (1 block only) is a side fork, it is useless.

It is normal that different nodes can come up simultaneously with solutions, especially as the block generation time is low (it is more likely in Ethereum than Bitcoin for example).

  • 2
    Just to add, those orphaned blocks/transactions aren't useless. The hashing power used in solving the PoW for any sidechains can be claimed back by incorporating those orphans as "uncles" in the canonical chain. See What is an uncle/ommer block?. These are an important feature of the GHOST protocol used in Ethereum. Commented Oct 1, 2017 at 12:38

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