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Q31. What are the factors on which RedShift is priced on ?

Amazon Web Services (AWS)

Ans. Compute Node Hours
Backup
Data Transfer

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Q32. What is the ideal use case for DynamoDB ?

Amazon Web Services (AWS)

Ans. Fast reads
Much more reads than writes

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Q33. What is the limit of read replicas per database ?

Amazon Web Services (AWS)

Ans. 5

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Q34. Difference between multi AZ RDS and Read replicas ?

Amazon Web Services (AWS)

Ans. Multi AZ RDS is for disaster recovery and failover whereas Read replicas are for scaling.

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Q35. What happens to backups if we delete the RDS instance ?

Amazon Web Services (AWS)

Ans. Automated Backups are deleted automatically whereas Snapshots are preserved. Upon terminating RDS instance , AWS gives a warning about that and requests to create a final snapshot before terminating the instance.

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Q36. Difference between Base Class, Derived Class , Abstract Class and Concrete Class ?

Core Java

Ans. Base Class is a relative term used to signify the Parent class in Parent - Child or Base - derived relationship.

Derived Class is a relative term used to signify the Child class in Parent - Child or Base - derived relationship.

Abstract Class is a class that is not allowed to be instantiated and hence can serve only a base class for it's usage.

Concrete Class is the class which is supposed to be instantiated and hence provide definition for all implementing interface methods and extending abstract methods.

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Q37. Can an abstract class be a derived class ?

Core Java

Ans. Yes, an abstract class can extend another class.

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Q38. What is the relationship between Base Class and Abstract Class ?

Core Java

Ans. Abstract Class is a class that's only allowed to be a Base class for it's usage. It can never be instantiated on it's own.

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Q39. How would you securely migrate a database to RDS?

Amazon Web Services (AWS)

^{This question was recently asked at 'Cognizant (C?TS),Overstock'.This question is still unanswered. Can you please provide an answer.}

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Q40. Difference between Region , Availability zone and Edge Locations ?

Amazon Web Services (AWS)

Ans. A Region is a Geographical entity like US-East , US-West etc. Each Region may have multiple availability zones where each zone comprise of 1 or more Data Center located with each other.

Edge Locations are the sites that hosts cached content for faster delivery and for saving network traffic as they feed content from sites that are local or near to consumption.

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Q41. How to avoid cloning, serialization in the singleton class ?

Design

Ans. For Cloning-exception,For deserialization-read.resolve()

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Q42. Explain Hibernate caching mechanism

Hibernate

Ans. Every fresh session having its own cache memory, Caching is a mechanism for storing the loaded objects into cache memory. The advantage of cache mechanism is, whenever again we want to load the same object from the database then instead of hitting the database once again, it loads from the local cache memory only, so that the no. of round trips between an application and a database server got decreased. It means caching mechanism increases the performance of the application.

In hibernate we have two levels of caching

First Level Cache [ or ] Session Cache
Second Level Cache [ or ] Session Factory Cache [ or ] JVM Level Cache

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Q43. Difference between indexing and partioning

Database

Ans. Creating an index creates a separate table. ... Indexes are used to speed the search of data within tables. Partitions provide segregation of the data at the hdfs level, creating sub-directories for each partition. Partitioning allows the number of files read and amount of data searched in a query to be limited

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Q44. Isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?

Core Java

Ans. Both provide the thread safety but the actual difference come when talk about performance. CHM gives best performance when no of writer threads are less in number.

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Q45. Does Java SE has Immutable collections ?

Core Java

Ans. Yes wef from Java 9

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Q46. Have you heard of volatile Table in Teradata ?

Teradata

Ans. If you create table with VOLATILE option, the life of the table will be only for the current session.
It will be automatically dropped by Teradata manager once session expires.

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Q47. What is meant by "unreachable code" ? Can you write a code segment explaining this ?

Core Java

Ans. Unreachable code is a code segment that can never be executed in any case. For example -

int x = 5;
return;
System.out.println(x);

In this code , 2nd line will return the control out of the method and hence 3rd line will never get executed and hence is unreachable code. This will be caught at compile time only.

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Q48. Which jar files need to be included for using Hibernate ?

Hibernate

Ans. hibernate-orm
hibernate-validator
hibernate-ogm
hibernate-search

or you can download hibernate core with all dependencies.

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Q49. Can we declare an Interface with abstract keyword ?

Core Java

Ans. Yes

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Q50. How many VTables are there for each class ?

Core Java

Ans. There is one VTable for each class.

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Q51. How is the virtual method table implemented in Java?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

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Q52. What is virtual table with respect to method overriding in Java ?

Core Java

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Q53. Given an Employee Table with Salary Column, Find 2nd and 5th highest salary in a particular department.

SQL

Ans. Select salary from (select salary from employee where department = order by salary desc limit 5) emp order by salary limit 1 AND Select salary from (select salary from employee where department = order by salary desc limit 2) emp2 order by salary limit 1

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Q54. How to sort objects based on one of the field ?

Core Java

Ans. Using comparable and comparator and sorted collections like TreeSet or TreeMap.

or

use stream api from java 8 onwards which internally refers to comparable and comparator through lambda expressions

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Q55. Can we have multiple inheritance in java using abstract class ?

Core Java

Ans. No

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Q56. Difference between == and === ?

JavaScript

Ans. == compares values === is used in scripting languages for comparing two values as well as there data tpe. like in js,php.

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Q57. Write SQL to get all members and the count of books they have checked out , even the ones that haven't checked out anything.

SQL

^{This question was recently asked at 'Canopy Tax'.This question is still unanswered. Can you please provide an answer.}

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Library Management System has always been the favorite question. This questions is asked irrespective of level.

Q58. Write data models and service end points for Library Management System ?

Architecture

Ans. Following could be the business sub domains or database schemas in such a system

1. Users / Members
2. Sourcing
3. Inventory Management
4. Operations

Following services end points could be there

1. Users - addNewUser ( put ), removeUser ( post )
2. Sourcing - addSupplier ( put ), removeSupplier ( post )
3. Inventory Management - getInventory ( get )
4. Operations - checkIn ( post ), checkout ( post )

There could be following Tables in Database

1. Users / Members - MEMBER, MEMBERSHIP_TYPE
2. Sourcing - SUPPLIER, SUPPLIER_PRODUCT, PRODUCT_REORDER_LEVELS
3. Inventory Management - INVENTORY,PRODUCTS
4. Operations - TRANSACTION

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Q59. Design database schema for Facebook like application.

Database

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Q60. What is immutability and What are it's disadvantages ?

Design

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