Candidate Blocks: From Transaction Sets to On-Chain Confirmation
A candidate block is a temporary block constructed by a miner to compete for a block reward. It organizes unconfirmed transactions and attempts to meet proof-of-work requirements. After broadcast, it must still be verified by other nodes and evaluated under chain-selection rules, and it may end up on a competing branch that is not adopted.
How Candidate Blocks Are Produced
Miners first select and organize multiple unconfirmed transactions from the mempool to form a candidate block. At this stage, it is only a temporary block awaiting validation and may not become part of the blockchain. Different miners prepare their own candidate blocks simultaneously and compete for the next opportunity to record a block.
From Merkle Root to Block Hash
Transactions in a candidate block are hashed layer by layer to form a Merkle tree, ultimately producing a Merkle root representing all transaction information. Miners place it, along with the previous block hash, nonce, and other data, into the block header, then calculate the block hash that uniquely identifies the candidate block.
Proof of Work and Network Confirmation
Miners continually adjust the nonce and other block data and repeatedly hash them, seeking a result no greater than the protocol target. Once a result is found, the candidate block is broadcast, and nodes check the proof of work and transaction rules. A valid block may still compete with other blocks; Bitcoin nodes select the valid chain based on cumulative work, so not every valid candidate block remains on the final main chain.
Original Tutorial
https://www.binance.com/zh-CN/academy/glossary/candidate-block
Bitcoin Competing Branches and Chain Selection
https://developer.bitcoin.org/devguide/block_chain.html
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