Q: Ethereum mempool transaction of Uncle and Fork nodes

Question

In the Bitcoin network when a fork happens, the block transactions from the shortest chain are reinserted again into the mempool.

In Ethereum instead we have Uncle blocks and Fork blocks. What happens to the Uncle block transactions, are they reinserted again into the mempool or the transactions remain confirmed and part of the blockchain?

Answer 1

Uncle Blocks are orphaned blocks, that increase the security of the ethereum blockchain. They are used with the GHOST protocol. Whereas Bitcoin uses the longest chain rule, Ethereum chooses the "heaviest" chain. The following image, taken from this paper, shows this rather well.

But it's important to understand, that the transactions in these blocks are not part of the canonical truth. In other words, transactions in uncle blocks need to be mined again into a new block, if they aren't already part of the "right" blockchain.

This also helps to decrease the centralization of the blockchain, since miners who mined an uncle block are still getting rewarded (a smaller amount, than the miner who mined the commonly accepted block though).