区块链基本概念之：Permissioned vs Permissionless Blockchains

关于区块链的划分，通常包括公链、联盟链和私有链（个人认为私有链就是一个伪命题）。更为严谨的定义，即permissionless（or public）chain和permissioned chain。不过两者的本质还是SMR（state-machine replication 状态机复制） ，这是分布式系统中最重要的一个概念。

Fabric introduces a new architecture for transactions that we call execute-order-validate. It addresses the resiliency, flexibility, scalability, performance and confidentiality challenges faced by the order-execute model by separating the transaction flow into three steps:

• execute a transaction and check its correctness, thereby endorsing it,
• order transactions via a (pluggable) consensus protocol, and
• validate transactions against an application-specific endorsement policy before committing them to the ledger