April 21, 2022

Top 20 AWS DynamoDB Interview Questions and Answers


        Amazon Amazon Web Services' DynamoDB service is a proprietary NoSQL database service. It uses synchronous replication across many data centres to handle key-value and document data structures for all of its data services. DynamoDB has a high level of durability and availability as a result of this. Users of DynamoDB can additionally take advantage of Auto Scaling. DynamoDB automatically scales the database when it is enabled. DyanamoDb's primary data structures are hashing and B-trees. Data is first distributed using hashing into multiple divisions in the first entry. DynamoDB is compatible with a variety of languages, including Java, JavaScript, Node.js, Go, C#.NET, Perl, PHP, Python, Ruby, and many others.

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Ques. 1): What are the main advantages of DynamoDB?


DynamoDB offers us a number of advantages, including consistency, availability, and partition tolerance. It provides facilities to easily store the graph data, which is not available to SQL.

Below are the major advantages of DynamoDB

Scalable: Virtual unlimited storage, users can store infinity amount of data according to their need

Cost Effective: It seems to be cutting costs, while a big part of data is able to migrate from SQL to NOSQL. Basically it charges for reading, writing, and storing data along with any optional features you choose to enable in DynamoDB

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Data Replication: All data items are stored on SSDs and replication is managed internally across multiple availability zones in a region or can be made available across multiple regions.

DynamoDB is a serverless database that scales horizontally by distributing a single table over several servers.

Easy Administration: Because Amazon DynamoDB is a fully managed service, you won't have to worry about hardware or software provisioning, setup and configuration, software patching, or partitioning data across several instances as you scale.

Secure: Customizable traffic filtering, Regulatory Compliance Automation, Database Threat Detection, and Advanced Notification and Reporting System

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Ques. 2): What does the DynamoDBMapper class entail?


The DynamoDBMapper class provides access to Amazon DynamoDB. It gives you access to a DynamoDB API and lets you access your data across several tables. It also allows you to run queries and scans against tables, as well as perform different create, read, update, and delete (CRUD) activities on objects.

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Ques. 3): What are disadvantages of DynamoDB?


The disadvantages of DynamoDB are as follows-

  • Deployable only on AWS and cannot be installed on individual desktops/servers
  • Queries - Querying data is extremely limited
  • Table Joins- Joins are impossible
  • No Triggers
  • No foreign keys concept to refer to other table items
  • No server side scripts

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Ques. 4): Is DynamoDB a SQL database?


DynamoDB is a NoSQL database that can manage structured and semi-structured data, as well as JSON documents. DynamoDB smoothly scales to handle massive volumes of data and a large number of users.

SQL is the industry standard for data storage and retrieval. Although relational databases include a variety of tools for facilitating the building of database-driven applications, they always employ SQL.

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Ques. 5): What distinguishes Amazon DynamoDB from Amazon Aurora?


Aurora is a relational database service, whereas DynamoDB is a NoSQL database service.

For data manipulation and retrieval, Aurora employs SQL, but DynamoDB uses a unique syntax.

In Aurora, horizontal partitioning is used, whereas in DynamoDB, sharding is used.

DynamoDB implements key-value and document models, while Aurora uses a relational database management system.

DynamoDB does not support server-side scripting, although Aurora does.

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Ques. 6): What are the data types supported by DynamoDB?


DynamoDB supports a large set of data types for table attributes. Each data type falls into one of the three following categories -

  • Scalar - These types represent a single value, and include number, string, binary, Boolean, and null.
  • Document - These types represent a complex structure possessing nested attributes, and include lists and maps.
  • Set - These types represent multiple scalars, and include string sets, number sets, and binary sets.

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Ques. 7): What is the DynamoDB Query functionality and how does it work?


In DynamoDB, you have two choices for accessing data from collections: Query and Scan. Scan searches the whole database for records that match the criteria, whereas Query performs a direct lookup for a specified data set based on key restrictions.

In addition to the main key, DynamoDB uses a global secondary key, a local secondary key, and a partition primary key to improve read/write speed.

As a result, it is faster and more efficient than the DynamoDB Scan function, and it is recommended for most data retrieval applications.

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Ques. 8): How does DynamoDB protect data from being lost?


DynamoDB has long-term storage and a two-tier backup strategy to prevent data loss to a minimum. Each participant has three nodes, each of which holds the same data from the partition. In addition, a B tree is used to locate data, and a replication log is used to track changes in each node. DynamoDB takes snapshots of these and keeps them for a month in another AWS database in case data restoration is required.

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Ques. 9): What are DynamoDB's secondary indexes?


A secondary index is a data structure that stores a portion of a table's properties, as well as an alternate key for Query operations. Query can be used to retrieve data from the index in the same way it can be used to retrieve data from a table.

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Ques. 10): What does Data Pipeline do?


Data Pipeline exports and imports data from S3 bucket, file, etc.It also helps in backups, testing, and for similar needs.

There are 2 types Data Pipeline:

DataPipelineDefaultRole - contains all the ations you permit the pipeline to perform.

DataPipelineDefaultResourceRole - contains all the resources you permit the pipeline to perform.

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Ques. 11): List some important methods of Dynamo DB Mapper Class?


  • Save: Saves a particular object to the table.
  • Load: Retrieves an item from the table
  • Delete: It deletes an item from the table
  • Query: Queries a table or an index
  • Scan page: Scans a table or index and returns a matched result page.
  • Parallel scan: Performs a scan of the entire table or index.
  • Batch save: Saves object to one or more tables.

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Ques. 12): Is it safe to use DynamoDBMapper in a thread?


This class is thread-safe and can be shared across many threads. DynamoDBMapper will throw DynamoDBMappingException while using the save, load, and delete methods to indicate that domain classes are wrongly annotated or otherwise incompatible with this class.

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Ques. 13): Are DynamoDB's write operations atomic?


DynamoDB supports atomic counters, which allow you to add or decrement the value of an existing attribute without interfering with other write requests by using the update method. This attribute is incremented by one each time the application is run.

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Ques. 14): Does Amazon DynamoDB support conditional operations?


For an operation to be completed on an item, you have to specify a condition.

You can define a ConditionExpression that can be constructed from the following:


Comparison operators: =, <>, <, >, <=, >=, BETWEEN, and IN

Logical operators: NOT, AND, and OR.

You can also construct a free-form conditional expression that combines multiple conditional clauses which also includes nested clauses.

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Ques. 15): What are the differences between Amazon SimpleDB and Amazon DynamoDB?


Amazon DynamoDB: It is a highly recommended fast and scalable NoSQL Database Service that is designed for internet scale applications, maintains predictable high performance, and is highly cost-effective for workloads of any scale.

Amazon SimpleDB is an excellent fit for lower workloads that require query flexibility, but it has scaling limits.

It indexes all item attributes automatically and allows for query flexibility at the expense of performance and scale.

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Ques. 16): In Amazon DynamoDB, how do you delete a Global Secondary Index?


The console or an API request can be used to delete a Global secondary index.

On the console, choose the table from which you wish to delete the Global Secondary index, then go to the "indexes" tab under "Table items," select the "indexes" tab, and then click the "Deletion" button next to the delete index.

The Update Table API call can also be used to delete a Global Secondary Index.

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Ques. 17): What is use of Scan operation in DynamoDB?


A Scan operation in Amazon DynamoDB reads every item in a table or a secondary index. By default, a Scan operation returns all of the data attributes for every item in the table or index. You can use the ProjectionExpression parameter so that Scan only returns some of the attributes, rather than all of them.

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Ques. 18): What type of query capabilities does DynamoDB provide?


GET/PUT operations in DynamoDB are supported by a user-defined primary key. The primary key is the sole attribute that objects in a database must have. When you construct a table, you specify the primary key, which uniquely identifies each item. DynamoDB also allows for flexible querying by allowing you to use global secondary indexes and local secondary indexes to query on nonprimary key properties.

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Ques. 19): What are DynamoDB streams, and how do you use them?


DynamoDB Streams is a robust service that may be used in conjunction with other AWS services to solve a variety of challenges. When we enable DynamoDB Streams, it records a time-ordered sequence of item-level alterations in a DynamoDB table and saves the data for up to 24 hours.

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Ques. 20): What are projections and how do they work?


The set of properties that are transferred or projected from a table to an index is known as projections.

They're in addition to the index key and main key qualities, which are projected automatically. When creating a local secondary index, you must first define the properties that will be projected into the index. Each index has a minimum of three properties, which are:

  • The value of the table partition key
  • The attribute that will be used as the index sort key.
  • Sort by key value in the table

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