Blocking

coordinator and server could block -> we don’t need all reply, majority reply is enough

Quorums

• key idea: 抽屉原理
• adds: state info (e.g., timestamp) per data item
  • coordinator generates logical timestamp

2PC protocol

• How to make it quorum based?
  • read: find the latest timestamp among R servers
  • write: lock W servers and commit successfully
• How is changing the read/write quorum size useful?
• Strength and weakness of quorum(problems solved/not solved)
  • coordinator down is critical
    • this blocking problem has not been completed solved