What is cold backup and hot backup in Oracle : Advantage Disadvantage Explained : RDBMS FAQ

 

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What is cold backup and hot backup ?

1. Cold Backup: It is copying the three sets of files (database files, redo logs, and control file) when the instance is shut down. This is a straight file copy, usually from the disk directly to tape. You must shut down the instance to guarantee a consistent copy. If a cold backup is performed, the only option available in the event of data file loss is restoring all the files from the latest backup. All work performed on the database since the last backup is lost. 

2. Hot Backup: Some sites (such as worldwide airline reservations systems) cannot shut down the database while making a backup copy of the files. The cold backup is not an available option.

What is meant by Proactive, Retroactive and Simultaneous Update.

1. Proactive Update: The updates that are applied to database before it becomes effective in real world.

2. Retroactive Update: The updates that are applied to database after it becomes effective in real world.

3. Simultaneous Update: The updates that are applied to database at the same time when it becomes effective in real world.

 What is Storage Manager?

It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.

 What is Buffer Manager?

It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory.

 What is Transaction Manager?

It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.

What is File Manager?

I

t is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.

What is Authorization and Integrity manager?

It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data.

Describe the three levels of data abstraction? Frequently Asked Top DBMS Interview Exam Questions

Describe the three levels of data abstraction?

There are three levels of abstraction: 

1. Physical level: The lowest level of abstraction describes how data are stored.

2. Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.

3. View level: The highest level of abstraction describes only part of entire database.

Define the "integrity rules" in DBMS (Data Base Management System)?

There are two Integrity rules. 

1. Entity Integrity: States that "Primary key cannot have NULL value"

2. Referential Integrity: States that "Foreign Key can be either a NULL value or should be Primary Key value of other relation.

How is the data structure of System R different from the relational structure?

Unlike Relational systems in System R 

1. Domains are not supported

2. Enforcement of candidate key uniqueness is optional

3. Enforcement of entity integrity is optional

4. Referential integrity is not enforced

What is Data Model?

A collection of conceptual tools for describing data, data relationships data semantics and constraints.

 

What is E-R model?

This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.

 

What is Object Oriented model?

This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.

Frequently Asked Tough Database DBMS job interview Questions Answers & Solve Paper

 Q. Explain the meaning of the expression ACID transaction.

ACID means Atomic, Consistency, Isolation, Durability, so when any transaction happen it should be Atomic that is it should either be complete or fully incomplete. There should not be anything like Semi complete. The Database State should remain consistent after the completion of the transaction. If there are more than one Transaction then the transaction should be scheduled in such a fashion that they remain in Isolation of one another. Durability means that Once a transaction commits, its effects will persist even if there are system failures.

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Q. Explain the difference between an explicit and an implicit lock.

Explicit Lock :- Lock is explicitly requested for a record or table.

Implicit Lock :- Lock is implied but is not acquired.

Q. Explain how a database could be recovered via reprocessing. Why is this generally not feasible?

What do you mean by atomicity and aggregation in DBMS ? Best Tutorial for Competitive Technical Exams

 What do you mean by atomicity and aggregation in DBMS ?

1. Atomicity: Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.

2. Aggregation: A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.

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 What is a Phantom Deadlock?

In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.

 What is a checkpoint and When does it occur?

A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.

What are the different phases of transaction?

Different phases are

1.) Analysis phase,

2.) Redo Phase,

3.) Undo phase.

What is indexing and what are the different kinds of indexing? DBMS Tutorials for Exams & Interviews

 What is indexing and what are the different kinds of indexing?

Indexing is a technique for determining how quickly specific data can be found. 

Types: 

1. Binary search style indexing

2. B-Tree indexing

3. Inverted list indexing

4. Memory resident table

5. Table indexing

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What is system catalog or catalog relation? How is better known as?

A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.

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