Operations of Transaction

A user can make different types of requests to access and modify the contents of a database. So, we have different types of operations relating to a transaction. They are discussed as follows:

i) Read(X)

A read operation is used to read the value of X from the database and store it in a buffer in the main memory for further actions such as displaying that value. Such an operation is performed when a user wishes just to see any content of the database and not make any changes to it. For example, when a user wants to check his/her account’s balance, a read operation would be performed on user’s account balance from the database.

ii) Write(X)

A write operation is used to write the value to the database from the buffer in the main memory. For a write operation to be performed, first a read operation is performed to bring its value in buffer, and then some changes are made to it, e.g. some set of arithmetic operations are performed on it according to the user’s request, then to store the modified value back in the database, a write operation is performed. For example, when a user requests to withdraw some money from his account, his account balance is fetched from the database using a read operation, then the amount to be deducted from the account is subtracted from this value, and then the obtained value is stored back in the database using a write operation.

iii) Commit

This operation in transactions is used to maintain integrity in the database. Due to some failure of power, hardware, or software, etc., a transaction might get interrupted before all its operations are completed. This may cause ambiguity in the database, i.e. it might get inconsistent before and after the transaction. To ensure that further operations of any other transaction are performed only after work of the current transaction is done, a commit operation is performed to the changes made by a transaction permanently to the database.

iv) Rollback

This operation is performed to bring the database to the last saved state when any transaction is interrupted in between due to any power, hardware, or software failure. In simple words, it can be said that a rollback operation does undo the operations of transactions that were performed before its interruption to achieve a safe state of the database and avoid any kind of ambiguity or inconsistency.

When the data of users is stored in a database, that data needs to be accessed and modified from time to time. This task should be performed with a specified set of rules and in a systematic way to maintain the consistency and integrity of the data present in a database. In DBMS, this task is called a transaction. It is similar to a bank transaction, where the user requests to withdraw some amount of money from his account. Subsequently, several operations take place such as fetching the user’s balance from the database, subtracting the desired amount from it, and updating the user’s account balance. This series of operations can be called a transaction. Transactions are very common in DBMS. In this article, we will discuss what a transaction means, various operations of transactions, transaction states, and properties of transactions in DBMS.