redis-- Affairs

• grammar
  • MULTI
    • Open affairs, subsequent commands will be added to the same transaction
    • Operations in the transaction will be sent to the server, but it does not happen immediately, but put on a queue corresponding to the transaction, the server returns QUEUED
  • EXEC
    • After performing EXEC, commands in the transaction will be executed
    • Commands in the transaction when an error occurs, the transaction will not be rolled back will not stop, but continue
  • DISCARD
    • Cancel the transaction, the transaction will clear the queue, the client exits state of affairs
• ACID
  • Atomicity
    • not support
    • It does not roll back and continue
  • Isolation
    • stand by
    • Transaction command execution order, and will not be interrupted (the first EXEC first execution) other clients
    • Stand-alone redis read and write operations using a single-threaded process
  • Endurance
    • It does not support, redis data easily lost
  • consistency
    • not support
    • Strong consistency requirement is achieved by optimistic locking (watch)
      

WATCH

• redis achieve optimistic locking
• mechanism
  • Before the transaction open, listening to the data set, EXEC, if found data has been modified, the transaction is automatically canceled (DISCARD)
  • After the transaction EXEC, regardless of success or failure, the listener will be removed

WATCH mykey  # 监视mykey的值
MULTI  # 开启事务
SET mykey 10  
EXEC  # 如果mykey的值在执行exec之前发生过改变, 则该事务会取消(客户端可以在发生碰撞后不断重试)

setnx and pessimistic locking

• setnx key does not exist, will be set up successfully

• Non-transactional pipeline