It is my understanding that the longest blockchain is the one that should be used.

Is "longest" measured by the number of blocks or the number of transactions?


The longest blockchain is measured by the number of blocks, not the number of transactions. This is because the proof-of-work is linked to the creation of blocks, not transactions.

  • Actually it's the sum of the difficulty of all blocks, but that usually doesn't make a difference when comparing different chains. – jnnk Jan 8 '14 at 20:04

The best chain-tip is picked by the total difficulty of its blocks. This usually corresponds to the chain with the most blocks unless the chain-tips differ in difficulty.

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