Oracle Database Interview Questions & Answers Set-19

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1. What is the difference between value type and reference type?
Ans: Value type and reference type may be similar in terms of declaration syntax and usage but their semantics are distinct
Value type are stored on stack while reference type are stored on heap.
Value type store real data while reference type store reference to the data.
Accessing is faster in value type on comparison to reference type.
Value type can contain null value while reference type can't contain null value.
Value types are derived from System.ValueType while Reference type is derived from System.Object.

2. What is the Boxing and Unboxing concept in .net?
Ans: Boxing: Implicit conversion of a value type (integer, character etc.) to a reference type (object) is called boxing. In boxing process a value type(which generally stores on stack) is being allocated on the heap rather than the stack.

Unboxing: explicit conversion of that same reference type (which is created by boxing process) back to a value type is known as unboxing. In unboxing process boxed value type is unboxed from the heap and allocated on the stack.

3. What is the difference between GET and POST methods?
Ans: GET and POST methods are form submission method. Both are used to send the data from client side to server side. These are some differences between GET and POST method -

In GET method caching is possible while it is not possible in POST method.
Only ASCII character data types are allowed in GET method while in POST method there is no restriction, it allows binary data also.
In GET method length of the string is restricted while in POST method length of the string is not restricted.

4. What is Log Shipping?
Ans: Log shipping is the process of automating the backup of a database and transaction log file on a primary database server, and then restoring them onto a standby server.

The primary purpose of log shipping is to increase database availability just like replication.

5. What are the different type of replication in SQL Server?
Ans: There are three type of replication in SQL Server.

1. snapshot replication: snapshot replication distributes data exactly as it appears at a specific moment. Snapshot replication is best method for replicating data that changes infrequently.
2. transactional replication: transactional replication is generally used in server to server environment. It is more appropriate when you want incremental change propagated to subscriber.
3. merge replication: snapshot replication is a process of distributing data from publisher to subscriber. It is generally used in server to client environment. Merge replication is appropriate when multiple subscribers might update the same data at various time.

6. What do you understand by NoSQL databases? Is MongoDB a NoSQL database? explain.
Ans: At the present time, the internet is loaded with big data, big users, big complexity etc. and also becoming more complex day by day. NoSQL is answer of all these problems, It is not a traditional database management system, not even a relational database management system (RDBMS). NoSQL stands for "Not Only SQL". NoSQL is a type of database that can handle and sort all type of unstructured, messy and complicated data. It is just a new way to think about the database.

Yes. MongoDB is a NoSQL database.

7. What are the different types of NoSQL databases? Give some example.
Ans: NoSQL database can be classified as 4 basic types:
  1. Key value store NoSQL database
  2. Document store NoSQL database
  3. Column store NoSQL database
  4. Graph base NoSQL databse
There are many NoSQL databases. MongoDB, Cassandra, CouchBD, Hypertable, Redis, Riak, Neo4j, HBASE, Couchbase, MemcacheDB, Voldemort, RevenDB etc. are the examples of NoSQL databases.

8. What type of DBMS is MongoDB?
Ans: MongoDB is a document oriented DBMS>

9. What is the difference between MongoDB and MySQL?
Ans: Although MongoDB and MySQL both are free and open source databases, there is a lot of difference between them in the term of data representation, relationship, transaction, querying data, schema design and definition, performance speed, normalization and many more. To compare MySQL with MongoDB is like a comparison between Relational and Non-relational databases.

10. Why MongoDB is known as best NoSQL database?
Ans: MongoDb is the best NoSQL database because, it is:
Document Oriented
Rich Query language
High Performance
Highly Available
Easily Scalable

11. What is the difference b/w MongoDB and CouchDB?
Ans: MongoDB and CouchDB both are the great example of open source NoSQL database. both are document oriented databases. Although both stores data but there is a lot of difference between them in terms of implementation of their data models, interfaces, object storage and replication methods etc.

12. What is a Namespace in MongoDB?
Ans: Namespace is a concatenation of the database name and the collection name. Collection, in which MongoDB stores BSON objects.

13. Can journaling features be used to perform safe hot backups?
Ans: Yes.

14. Why does Profiler use in MongoDB?
Ans: MongoDB uses a database profiler to perform characteristics of each operation against the database. You can use a profiler to find queries and write operations

15. If you remove an object attribute, is it deleted from the database?
Ans: Yes, it be. Remove the attribute and then re-save() the object.

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