Main difference between Timestamp protocol and Thomas write rule in DBMS

In database systems, the issue of maintaining consistency while executing transactional processes concurrently is very important. Two concurrency control methods that can maintain the correct sequential Transaction processing in such an environment are the Timestamp Protocol and the Thomas Write Rule. These techniques are however convenient and efficient in situations where many transactions are complex and competing and there is a need to manage the conflicts arising out of the multiple transactions. The Timestamp Protocol introduces unique timestamps for transactions and the Thomas Write Rule is a modified version of the timestamp ordering protocol that is more efficient for writing. This paper compares and contrasts these two protocols, how they function, and how they help to maintain consistency in database systems.

What is Timestamp Protocol?

The Timestamp Protocol ensures that every transaction being entered for execution will first receive a timestamp. This timestamp can be used to establish a sequence of the transactions to run, achieve serializability, and avoid interference in multi-transaction situations.

How it Works

• Each transaction is given a timestamp (TS) on the time that it takes to get a particular transaction.
• Each data item in the database has two timestamps:
• R-TS(Q): The maximum number of transactions held by any one of the transactions that have successfully read the data item Q.
• W-TS(Q): The largest integer timestamp of any transaction that has made a successful write of the value of the data item Q.
• Such timestamps are used in the execution of transactions to follow a set protocol where older transactions are favored over the newer ones.

Advantages of Timestamp Protocol

• Achieves serializability by prioritizing transactions according to their time stamps.
• Table 2 shows that it performs well in environments where concurrency is evident.
• It reduces deadlocks as it assigns the use of unique timestamps to each transaction.

Disadvantages of Timestamp Protocol

• May result to avoidable rollbacks especially in case of consistent interferences.
• Difficult to apply in complex systems especially when used in similar applications.

What is Thomas Write Rule?

The Thomas Write Rule is basically another form of timestamp ordering which relaxes some of the write operations which do not affect the consistency of the database. This maximizes the price of transactions as compared to several rollbacks and thus improving on the existing systems.

How it Works

• When a transaction Ti issues a write on a data item Q, the system checks the timestamp:
• This means that TS(Ti)<R-TS(Q), implying the data was needed earlier, and the read operation fails, the system given returns an abort to Ti when doing a write operation.
• Per the relational attribute, if TS(Ti) < W-TS(Q) the system refrains from implementing the write since Ti is about to write an outdated value of Q.
• If none of the above conditions are suitable for the circumstance, the system writes and changes W-TS(Q) to TS(Ti).

Advantages of Thomas Write Rule

• It does not undo unnecessary work by ignoring writes that are made on a stale copy of the data.
• Enhances efficiency by reducing the effect of the write operation in concurrent transactions.

Disadvantages of Thomas Write Rule

• May make it more difficult to execute the plans for the transaction management.
• It must be handled with care where timestamp assignment is concerned.

Difference Between Timestamp Protocol and Thomas Write Rule

Conclusion

Timestamp Protocol and Thomas Write Rule are also critical in the maintenance of concurrency in the systems of the Database. Like the Timestamp Protocol, the Thomas Write Rule requires transactions to run in order, while also minimizing the number of rollbacks by allowing some writes to be ignored. Knowledge of these two categories enables one to select the appropriate concurrency control for a certain system.

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Article Tags :

• DBMS
• Difference Between
• GATE CS
• DBMS-Transactions and Concurrency Control