Question

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A successful transaction contains this operation.

update customer set balance = balance + 100;

The above operation causes the following actions to take place.

a) Write data to database file

b) Read data from database file into database buffer

c) Write data to log buffer d) Write data to the rollback segment

e) Write data to log file

f) Update data in data buffer

Q. Assume a successful transaction is committed. After which point (from the actions above) will the DBMS have to honour the transaction even if a system or media failure occurs shortly afterwards.

Answer 1

f) update data in data buffer

The above given statement or query is to update the data that is already exists. Data buffer is a physical memory place in computer to store the data temporarily. And here it is said that the transaction is commited. That means a new transaction will take place only after a commited transaction will completes successfully. According to the given query, it's duty is to update the data in data buffer. So it completes it's updation in data buffer and after that the DBMS will have to honour the transaction even if a system or media failure occurs shortly afterwards.

Explaination:

A transaction is a unit of work that can be performed on a database. Transactions are units or sequence of work kept in a logical order. If a transaction is propagating one or more changes in the database, it is very important to control these transactions to ensure data intigrity and to handle database errors.

We can ensure the database security only by using the transaction control commands. Those are commit, save point and roll back. commit is a command that saves the entire transaction after that is completed and it will not allow any other transaction till the transaction which is on process is completed. And it will saves the transactions completely and then allows or honours the another transaction even if a system or media failure occurs.

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