How does timestamp-based concurrency control work?

Timestamp-based concurrency control is a method for managing concurrent transactions in a database to ensure consistency and avoid conflicts. It works as follows:

1. **Timestamp Assignment:** Each transaction is assigned a unique timestamp when it begins. This timestamp determines the transaction's order of execution relative to other transactions.

2. **Read and Write Rules:** 

   - **Read Rule:** A transaction can read data if its timestamp is earlier than the timestamp of the last write to that data. This ensures it sees a consistent snapshot of the data.

   - **Write Rule:** A transaction can write data only if its timestamp is earlier than the timestamps of all transactions that have previously read or written that data. If any such transaction has a later timestamp, the write is aborted to prevent inconsistencies.

3. **Conflict Resolution:** If a transaction attempts to perform an operation that would violate the rules (e.g., write data after another transaction has already written to it), it is rolled back and restarted with a new timestamp.

4. **Consistency Assurance:** By using timestamps, the system maintains a consistent view of the data across all transactions, ensuring that the order of operations respects the sequence established by the timestamps.

This method helps avoid issues such as lost updates and uncommitted data reads by strictly adhering to the transaction order based on timestamps, ensuring a consistent and conflict-free execution of concurrent transactions.