Global and Local Secondary Indexes

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Global and Local Secondary Indexes are used to optimize query performance in Amazon DynamoDB. A Global Secondary Index (GSI) is an index that has a partition key and an optional sort key different from the base table. It allows you to query the data with a different primary key. A Local Secondary I…

A Comprehensive Guide to Global and Local Secondary Indexes in Amazon DynamoDB

Amazon DynamoDB is a key-value and document database that delivers high performance at any scale. Within this context, understanding the concept of Global and Local Secondary Indexes is critical.

Why it is important:
DynamoDB provides fast access to items in a table by specifying primary key values. However, many applications might need to perform operations on attributes other than the primary key. To support these needs, DynamoDB provides secondary indexes. Understanding the implementation and efficient use of these secondary indexes is crucial for your AWS Solution Architect journey, as well as in maximizing the performance of your DynamoDB database operations.

What it is:
Secondary Indexes in DynamoDB are a way to provide alternate key structures to query against. They come in two forms: Global Secondary Indexes (GSI) and Local Secondary Indexes (LSI). GSIs support any hash and range key combination, while LSIs support only the same hash key but different range keys.

How it works:
- Global Secondary Indexes (GSIs): These are indexes that have a partition key and an optional sort key that can be different from those on the base table - Local Secondary Indexes (LSIs): These are indexes that have the same partition key as the base table but a different sort key.

Exam Tips: Answering Questions on Global and Local Secondary Indexes
In the exam, you may find questions aimed to test your understanding of secondary indexes. Here are some tips: - Understand the performance implications: Secondary indexes use up additional storage and can impact costs - Understand the differences: Remember, GSIs can have different partition and optional sort key from the base table, while LSIs have the same partition key but a different sort key - Read the questions carefully: The AWS exams are known for their tricky wordings. Always read the question and the answer options carefully.

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Question 1

You are designing a DynamoDB table to store information about music artists and their songs. You need to efficiently search for songs by the artist's name and release year. Which design would best suit this scenario?

Create a Global Secondary Index with the Artist Name as partition key and Release Year as sort key. Create a Local Secondary Index with the Artist Name as partition key and Release Year as sort key. Create a Global Secondary Index with the Song ID as partition key and Release Year as sort key. Create a Local Secondary Index with the Song ID as partition key and Release Year as sort key.

Correct Answer: Create a Global Secondary Index with the Artist Name as partition key and Release Year as sort key.

A Global Secondary Index would be the best solution because it allows queries based on a different partition key (Artist Name) from the original table and with a different sort key (Release Year). A Local Secondary Index would not be efficient in this case as it requires the same partition key as the original table.

Question 2

You have a DynamoDB table with information about books and their authors. You want to retrieve the top reviewed books for a selected author. Which design would be best?

Create a Local Secondary Index with Book ID as partition key and Review Score as sort key. Create a Local Secondary Index with Author as partition key and Review Score as sort key. Create a Global Secondary Index with Book ID as partition key and Review Score as sort key. Create a Global Secondary Index with Author as partition key and Review Score as sort key.

Correct Answer: Create a Global Secondary Index with Author as partition key and Review Score as sort key.

A Global Secondary Index would be best because it allows queries based on a different partition key (Author) and with a different sort key (Review Score) from the original table. A Local Secondary Index would not be efficient as it requires the same partition key as the original table.

Question 3

You need to retrieve a list of all customer orders made within the last month sorted by order creation date. Which design would you choose for the best performance?

Create a Local Secondary Index with Order Creation Month as partition key and Order Creation Date as sort key. Create a Global Secondary Index with Customer ID as partition key and Order Creation Date as sort key. Create a Local Secondary Index with Customer ID as partition key and Order Creation Date as sort key. Create a Global Secondary Index with Order Creation Month as partition key and Order Creation Date as sort key.

Correct Answer: Create a Global Secondary Index with Order Creation Month as partition key and Order Creation Date as sort key.

A Global Secondary Index would be the best solution because it allows queries based on a different partition key (Order Creation Month) and with a different sort key (Order Creation Date). This design ensures only relevant data is accessed, minimizing Read/Write capacity units usage.

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