Proof-of-history (PoH) is a protocol developed by Solana to create a verifiable timeline of transactions in blockchain without requiring constant network consensus. Each transaction is timestamped using a cryptographic clock that utilizes a verifiable delay function (VDF) based on SHA-256 hashing, forming a chain of uniquely linked hashes. This allows for rapid processing and consensus, as nodes can agree on transaction order without direct communication. Solana combines PoH with proof-of-stake (PoS), determining block producers by stake, enhancing both speed and security. Unlike traditional blockchains with a mempool for unconfirmed transactions, Solana's real-time processing eliminates the need for a mempool, further increasing efficiency. While PoH facilitates swift validation and block creation, concerns exist regarding potential centralization of block production among frequently selected validators, which could impact network diversity and security.

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