Optimistic Lock, Concurrent timestamp

Optimistic concurrency control (OCC) is a concurrency control method applied to transactional systems such as relational database management systems and software transactional memory. OCC assumes that multiple transactions can frequently complete without interfering with each other. While running, transactions use data resources without acquiring locks on those resources. Before committing, each transaction verifies that no other transaction has modified the data it has read. If the check reveals conflicting modifications, the committing transaction rolls back and can be restarted.[1] Optimistic concurrency control was first proposed by H. T. Kung and John T. Robinson.[2]

Setting a time-stamp in a table as a column to store the entry recorded moment; in a transaction, the values are read along with the timestamp, and after operations on these values, at the moment write back newly modified values, the transaction needs to compare the previous timestamp with the current ones recorded at the Current-timestamp cell, if they are the same, then the data is consistent until now; otherwise, the transaction needs to roll back and repeating the previous the process.