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consortium-v2: only check the current block in GetBestParentBlock #555

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Commits on Sep 4, 2024

  1. consortium-v2: only check the current block in GetBestParentBlock

    In commit 94bcf95 ("fix: miner does not mine its inturn block"), we make
    the miner go backward in the chain to find if it can create an inturn block
    which makes the chain has high difficulty instead of just creating the new block
    on the current block. However, after finality is introduced, this scenario can
    happen
    
    Current chain
    10 <- 11 (diff: 3) <- 12 (diff: 3)
    
    And the miner can create block 11 with difficulty 7. However, block 12 has
    enough finality vote to justify block 11 already. So if the miner still tries to
    create block 11 with difficulty 7, that block will be rejected because the old
    chain has higher justified block number (11 vs maximum 10) and this miner does
    not participate to make a new block in this scenario. This is undesirable as
    this miner can be viewed as down even though it is still online.
    
    PR axieinfinity#422 tries to address the above
    issue but it reverts the purpose of commit 94bcf95 when the TODO is not
    resolved.
    
    This commit tries to simplify the logic of GetBestParentBlock to resolve the
    issue. GetBestParentBlock does not go backward and tries to revert more than 1
    block anymore, it only tries to revert 1 block (i.e. the current block) if
    possible. With the above example, the miner only tries to revert block 12 if it
    can create a new block 12 with difficult 7 and does not try to revert block 11.
    It works with the assumption that in case the current block 12 with difficulty 3
    justify block 11, it means there are enough finality votes for block 11 and the
    newly created block 12 with difficulty 7 can justify block 11 too. So justified
    block number in the newly created chain is the same as the old one but the new
    one will have higher difficulty.
    minh-bq committed Sep 4, 2024
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