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DynamoDBquery~5 mins

Creating GSI in DynamoDB

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Introduction

A Global Secondary Index (GSI) lets you search your DynamoDB table using different keys than the main one. It helps you find data faster in new ways.

You want to look up items by a different attribute than the main key.
You need to run queries that the main table keys don't support.
You want to improve read performance for specific queries.
You want to sort or filter data differently without changing the main table.
You want to add new search options without rebuilding your table.
Syntax
DynamoDB
CreateTable {
  TableName: string,
  KeySchema: [
    { AttributeName: string, KeyType: 'HASH' | 'RANGE' }
  ],
  AttributeDefinitions: [
    { AttributeName: string, AttributeType: 'S' | 'N' | 'B' }
  ],
  GlobalSecondaryIndexes: [
    {
      IndexName: string,
      KeySchema: [
        { AttributeName: string, KeyType: 'HASH' | 'RANGE' }
      ],
      Projection: {
        ProjectionType: 'ALL' | 'KEYS_ONLY' | 'INCLUDE',
        NonKeyAttributes?: [string]
      },
      ProvisionedThroughput: {
        ReadCapacityUnits: number,
        WriteCapacityUnits: number
      }
    }
  ],
  ProvisionedThroughput: {
    ReadCapacityUnits: number,
    WriteCapacityUnits: number
  }
}

The GlobalSecondaryIndexes section defines one or more GSIs.

Each GSI needs its own IndexName, KeySchema, and Projection to specify what data it holds.

Examples
This example creates a GSI named 'GSI1' using 'Category' as the partition key and includes all attributes.
DynamoDB
GlobalSecondaryIndexes: [
  {
    IndexName: 'GSI1',
    KeySchema: [
      { AttributeName: 'Category', KeyType: 'HASH' }
    ],
    Projection: { ProjectionType: 'ALL' },
    ProvisionedThroughput: { ReadCapacityUnits: 5, WriteCapacityUnits: 5 }
  }
]
This example creates a GSI with a partition key 'Status' and sort key 'CreatedDate'. It only includes specific non-key attributes.
DynamoDB
GlobalSecondaryIndexes: [
  {
    IndexName: 'GSI2',
    KeySchema: [
      { AttributeName: 'Status', KeyType: 'HASH' },
      { AttributeName: 'CreatedDate', KeyType: 'RANGE' }
    ],
    Projection: { ProjectionType: 'INCLUDE', NonKeyAttributes: ['Description', 'Priority'] },
    ProvisionedThroughput: { ReadCapacityUnits: 10, WriteCapacityUnits: 5 }
  }
]
Sample Program

This command creates a DynamoDB table named 'Products' with a primary key 'ProductId'. It also creates a GSI called 'CategoryIndex' that lets you query products by their 'Category'.

DynamoDB
aws dynamodb create-table \
  --table-name Products \
  --attribute-definitions \
    AttributeName=ProductId,AttributeType=S \
    AttributeName=Category,AttributeType=S \
  --key-schema AttributeName=ProductId,KeyType=HASH \
  --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 \
  --global-secondary-indexes \
    '[{
      "IndexName": "CategoryIndex",
      "KeySchema": [{"AttributeName":"Category","KeyType":"HASH"}],
      "Projection": {"ProjectionType":"ALL"},
      "ProvisionedThroughput": {"ReadCapacityUnits":5,"WriteCapacityUnits":5}
    }]'
OutputSuccess
Important Notes

GSIs let you query your data in new ways without changing your main table keys.

Remember to define the attributes used in your GSI in AttributeDefinitions.

Provisioned throughput for GSIs is separate from the main table and affects cost.

Summary

GSIs let you search your DynamoDB table using different keys.

They require defining new key schemas and projections.

Use GSIs to add flexible query options without rebuilding your table.

Practice

(1/5)
1. What is the main purpose of creating a Global Secondary Index (GSI) in DynamoDB?
easy
A. To automatically backup the table data
B. To increase the storage capacity of the table
C. To allow querying the table using alternative key attributes
D. To encrypt the table data at rest

Solution

  1. Step 1: Understand what a GSI does

    A GSI lets you query a DynamoDB table using different key attributes than the primary key.

  2. Step 2: Compare options to GSI purpose

    Options A, B, and D describe backup, storage, and encryption, which are unrelated to GSI functionality.

  3. Final Answer:

    To allow querying the table using alternative key attributes -> Option C

  4. Quick Check:

    GSI = alternative query keys [OK]
Hint: GSIs let you query by new keys without changing the table [OK]
Common Mistakes:
  • Thinking GSI increases storage size
  • Confusing GSI with backup or encryption features
  • Assuming GSI changes the primary key
2. Which of the following is the correct syntax snippet to define a GSI named OrderDateIndex with OrderDate as the partition key in a DynamoDB table creation JSON?
easy
A. "GlobalSecondaryIndexes": [{"IndexName": "OrderDateIndex", "KeySchema": [{"AttributeName": "OrderDate", "KeyType": "HASH"}], "Projection": {"ProjectionType": "ALL"}}]
B. "GlobalSecondaryIndexes": [{"IndexName": "OrderDateIndex", "KeySchema": [{"AttributeName": "OrderDate", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"}}]
C. "GlobalSecondaryIndexes": [{"IndexName": "OrderDateIndex", "KeySchema": [{"AttributeName": "OrderDate", "KeyType": "PRIMARY"}], "Projection": {"ProjectionType": "ALL"}}]
D. "GlobalSecondaryIndexes": [{"IndexName": "OrderDateIndex", "KeySchema": [{"AttributeName": "OrderDate", "KeyType": "PARTITION"}], "Projection": {"ProjectionType": "ALL"}}]

Solution

  1. Step 1: Identify correct KeyType for partition key in GSI

    The partition key in DynamoDB GSI uses KeyType "HASH".

  2. Step 2: Check options for correct KeyType and syntax

    "GlobalSecondaryIndexes": [{"IndexName": "OrderDateIndex", "KeySchema": [{"AttributeName": "OrderDate", "KeyType": "HASH"}], "Projection": {"ProjectionType": "ALL"}}] uses "HASH" correctly; B uses "RANGE" (wrong for partition key), C uses invalid "PRIMARY", D uses invalid "PARTITION".

  3. Final Answer:

    "GlobalSecondaryIndexes": [{"IndexName": "OrderDateIndex", "KeySchema": [{"AttributeName": "OrderDate", "KeyType": "HASH"}], "Projection": {"ProjectionType": "ALL"}}] -> Option A

  4. Quick Check:

    Partition key = HASH [OK]
Hint: Partition key in GSI always uses KeyType 'HASH' [OK]
Common Mistakes:
  • Using 'RANGE' instead of 'HASH' for partition key
  • Using invalid KeyType values like 'PRIMARY' or 'PARTITION'
  • Forgetting to define ProjectionType
3. Given a DynamoDB table with a GSI named UserEmailIndex where Email is the partition key, what will be the result of this query?
QueryInput = {
  TableName: "Users",
  IndexName: "UserEmailIndex",
  KeyConditionExpression: "Email = :email",
  ExpressionAttributeValues: {":email": "alice@example.com"}
}
medium
A. Returns all items where Email attribute equals 'alice@example.com' using the GSI
B. Returns all items where Email attribute equals 'alice@example.com' using the main table primary key
C. Returns an error because IndexName cannot be used in QueryInput
D. Returns all items regardless of Email attribute

Solution

  1. Step 1: Understand QueryInput with IndexName

    Specifying IndexName in QueryInput tells DynamoDB to query the GSI instead of the main table.

  2. Step 2: Analyze KeyConditionExpression

    The query filters items where Email equals 'alice@example.com' on the GSI partition key.

  3. Final Answer:

    Returns all items where Email attribute equals 'alice@example.com' using the GSI -> Option A

  4. Quick Check:

    Query with IndexName uses GSI keys [OK]
Hint: Use IndexName in query to search by GSI keys [OK]
Common Mistakes:
  • Assuming query uses main table keys when IndexName is set
  • Thinking IndexName causes error in QueryInput
  • Ignoring KeyConditionExpression filtering
4. You tried to create a GSI with this snippet but got an error:
"GlobalSecondaryIndexes": [{
  "IndexName": "StatusIndex",
  "KeySchema": [{"AttributeName": "Status", "KeyType": "HASH"}],
  "Projection": {"ProjectionType": "INCLUDE", "NonKeyAttributes": []}
}]

What is the likely cause of the error?
medium
A. IndexName cannot contain the word 'Index'
B. NonKeyAttributes must be a non-empty array when ProjectionType is INCLUDE
C. KeyType must be RANGE for GSIs
D. ProjectionType cannot be INCLUDE for GSIs

Solution

  1. Step 1: Check ProjectionType and NonKeyAttributes

    When ProjectionType is INCLUDE, NonKeyAttributes must be a non-empty array listing attributes to project.

  2. Step 2: Verify given snippet

    NonKeyAttributes is [], which is empty and invalid when ProjectionType is INCLUDE.

  3. Step 3: Eliminate other options

    ProjectionType INCLUDE is valid; KeyType HASH is valid for partition key; IndexName can contain 'Index'.

  4. Final Answer:

    NonKeyAttributes must be a non-empty array when ProjectionType is INCLUDE -> Option B

  5. Quick Check:

    INCLUDE projection requires NonKeyAttributes [OK]
Hint: INCLUDE projection needs NonKeyAttributes array [OK]
Common Mistakes:
  • Using empty or missing NonKeyAttributes with INCLUDE
  • Confusing KeyType HASH and RANGE for partition key
  • Thinking IndexName naming causes errors
5. You have a DynamoDB table with primary key UserID. You want to query users by their City and SignupDate. Which GSI definition allows efficient queries for all users in a city sorted by signup date?
hard
A. "GlobalSecondaryIndexes": [{"IndexName": "CitySignupIndex", "KeySchema": [{"AttributeName": "SignupDate", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"}}]
B. "GlobalSecondaryIndexes": [{"IndexName": "CitySignupIndex", "KeySchema": [{"AttributeName": "SignupDate", "KeyType": "HASH"}, {"AttributeName": "City", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"}}]
C. "GlobalSecondaryIndexes": [{"IndexName": "CitySignupIndex", "KeySchema": [{"AttributeName": "City", "KeyType": "RANGE"}, {"AttributeName": "SignupDate", "KeyType": "HASH"}], "Projection": {"ProjectionType": "ALL"}}]
D. "GlobalSecondaryIndexes": [{"IndexName": "CitySignupIndex", "KeySchema": [{"AttributeName": "City", "KeyType": "HASH"}, {"AttributeName": "SignupDate", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"}}]

Solution

  1. Step 1: Identify partition and sort keys for query pattern

    To query all users in a city sorted by signup date, City should be the partition key (HASH) and SignupDate the sort key (RANGE).

  2. Step 2: Check options for correct KeySchema order

    "GlobalSecondaryIndexes": [{"IndexName": "CitySignupIndex", "KeySchema": [{"AttributeName": "City", "KeyType": "HASH"}, {"AttributeName": "SignupDate", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"}}] correctly sets City as HASH and SignupDate as RANGE. Options B and C swap keys incorrectly. "GlobalSecondaryIndexes": [{"IndexName": "CitySignupIndex", "KeySchema": [{"AttributeName": "SignupDate", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"}}] lacks partition key.

  3. Final Answer:

    "GlobalSecondaryIndexes": [{"IndexName": "CitySignupIndex", "KeySchema": [{"AttributeName": "City", "KeyType": "HASH"}, {"AttributeName": "SignupDate", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"}}] -> Option D

  4. Quick Check:

    Partition key = City, Sort key = SignupDate [OK]
Hint: Partition key first (HASH), sort key second (RANGE) in KeySchema [OK]
Common Mistakes:
  • Swapping HASH and RANGE keys
  • Missing partition key in GSI
  • Using only one key when two are needed for sorting
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