Redis transaction implements optimistic locking principle

Transaction implementation

1）multi Pass before order watch Command monitor key;
2） perform multi command ;
3） The list of commands ;
4）exec Order to commit a transaction /discard Command rollback ;

watch Implementation principle of

1）redis Maintain a global watch_keys, Also a <key,value> structure ,key yes key+“&&”+ Connect id, It means that the client connection wants to listen to this key,value yes key Version number of , Every time you modify this key, Version number will be incremented .

2） When executed exec When ordered , Will execute every command in the transaction queue , When executing a write command , Will check the current key Does it exist in watch_keys in , If there is , It will check whether the version numbers of the two are equal , If equal, execute this write command , If they are not equal, no information is returned , Then delete watch_keys Corresponding to key;