Learn about the timestamp ordering protocol as an alternative to locking.
Timestamp Ordering is a concurrency control protocol that provides an alternative to lock-based methods. Unlike locking, which can lead to deadlocks, timestamp ordering is deadlock-free. The core idea is to order transactions based on their start time. Each transaction is assigned a unique, monotonically increasing timestamp by the system when it begins. This timestamp is used to determine the serializability order. The protocol ensures that any conflicting read and write operations are executed in timestamp order. To manage this, the system keeps track of two timestamps for each data item `X`: `W-timestamp(X)`, the timestamp of the last transaction that successfully wrote to `X`, and `R-timestamp(X)`, the timestamp of the last transaction that successfully read `X`. When a transaction `T` with timestamp `TS(T)` tries to perform a read or write operation on `X`, the system checks its timestamp against the timestamps on `X`. For a read operation, if `TS(T)` is older than the `W-timestamp(X)`, it means a newer transaction has already modified the data, so `T`'s read request is rejected, and `T` is aborted. For a write operation, if `TS(T)` is older than either the `R-timestamp(X)` or `W-timestamp(X)`, it means a newer transaction has already read or written the data, so `T`'s write is rejected, and `T` is aborted. This strict ordering prevents conflicts but can lead to more transaction rollbacks compared to locking protocols.