DBMS

21. What is a recovery scheme?

An integral part of a database system is a recovery scheme that can restore the database to the consistent state that existed before the failure.

22. What are the two types of errors?

The two types of errors are:

Ø Logical error

Ø System error

23. What are the storage types?

The storage types are:

Ø Volatile storage

Ø Nonvolatile storage

24. Define blocks?

The database system resides permanently on nonvolatile storage, and is partitioned into fixed- length storage units called blocks.

25. What is meant by Physical blocks?

The input and output operations are done in block units. The blocks residing on the disk are referred to as physical blocks.

26. What is meant by buffer blocks?

The blocks residing temporarily in main memory are referred to as buffer blocks.

27. What is meant by disk buffer?

The area of memory where blocks reside temporarily is called the disk buffer.

28. What is meant by log-based recovery?

The most widely used structures for recording database modifications is the log. The log is a

sequence of log records, recording all the update activities in the database. There are several types of log records.

29. What are uncommitted modifications?

The immediate-modification technique allows database modifications to be output to the database while the transaction is still in the active state. Data modifications written by active

transactions are called uncommitted modifications.

30. Define shadow paging.

An alternative to log-based crash recovery technique is shadow paging. This technique needs

fewer disk accesses than do the log-based methods.