Creating GSI in DynamoDB - Visual Walkthrough

Concept Flow - Creating GSI

Define GSI attributes

↓

Specify GSI key schema

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Add GSI to table creation or update

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DynamoDB creates GSI asynchronously

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GSI becomes ACTIVE

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Use GSI in queries

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END

Creating a Global Secondary Index (GSI) involves defining its attributes and key schema, adding it to the table, waiting for it to become active, then using it for queries.

Execution Sample

DynamoDB

CreateTable {
  TableName: 'Books',
  AttributeDefinitions: [
    {AttributeName: 'ISBN', AttributeType: 'S'},
    {AttributeName: 'Author', AttributeType: 'S'}
  ],
  BillingMode: 'PAY_PER_REQUEST',
  KeySchema: [{AttributeName: 'ISBN', KeyType: 'HASH'}],
  GlobalSecondaryIndexes: [{
    IndexName: 'AuthorIndex',
    KeySchema: [{AttributeName: 'Author', KeyType: 'HASH'}],
    Projection: {ProjectionType: 'ALL'}
  }]
}

This creates a table 'Books' with a GSI named 'AuthorIndex' on the 'Author' attribute.

Execution Table

Step	Action	Input	DynamoDB Response	State Change
1	Define table name and primary key	TableName='Books', KeySchema=ISBN as HASH	Table creation request accepted	Table 'Books' creation started
2	Define GSI attributes and key schema	GSI Name='AuthorIndex', KeySchema=Author as HASH	GSI definition accepted	GSI 'AuthorIndex' added to table creation
3	Send CreateTable request with GSI	Full table and GSI definition	Table status: CREATING	Table and GSI creation in progress
4	Wait for table and GSI to become ACTIVE	Polling status	Table status: ACTIVE, GSI status: ACTIVE	Table and GSI ready to use
5	Query using GSI	Query on 'AuthorIndex' with Author='John Doe'	Query results returned	Data retrieved using GSI
6	End	-	-	Process complete

💡 Table and GSI become ACTIVE, ready for queries

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
TableName	undefined	'Books'	'Books'	'Books'
PrimaryKey	undefined	ISBN (HASH)	ISBN (HASH)	ISBN (HASH)
GSI Name	undefined	'AuthorIndex'	'AuthorIndex'	'AuthorIndex'
GSI KeySchema	undefined	Author (HASH)	Author (HASH)	Author (HASH)
Table Status	undefined	CREATING	ACTIVE	ACTIVE
GSI Status	undefined	CREATING	ACTIVE	ACTIVE

Key Moments - 3 Insights

Why does the GSI creation take time after the table is created?

Because DynamoDB creates GSIs asynchronously, the GSI status changes from CREATING to ACTIVE after some time, as shown in execution_table step 4.

Can I query the GSI before it becomes ACTIVE?

No, queries on the GSI only work after its status is ACTIVE, as shown in execution_table step 5.

Do I need to specify all attributes in the GSI's Projection?

No, you can choose ALL, KEYS_ONLY, or INCLUDE specific attributes. In the example, ProjectionType is ALL, meaning all attributes are projected.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the GSI become ready to use?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Check the 'DynamoDB Response' and 'State Change' columns in step 4 for GSI status.

According to variable_tracker, what is the Table Status after Step 3?

A ACTIVE

B CREATING

C DELETING

D UPDATING

💡 Hint

Look at the 'Table Status' row under 'After Step 2' and 'After Step 4' to infer the status at Step 3.

If the ProjectionType was changed from 'ALL' to 'KEYS_ONLY', what would change in the execution?

A The GSI would include only key attributes in queries

B The GSI creation would fail

C The table would not have a primary key

D The GSI would become ACTIVE faster

💡 Hint

ProjectionType controls which attributes are available in the GSI, see execution_sample code.

Concept Snapshot

Creating a GSI in DynamoDB:
- Define GSI name and key schema (HASH and optional RANGE keys)
- Add GSI to table creation or update request
- DynamoDB creates GSI asynchronously (status: CREATING -> ACTIVE)
- Use GSI in queries once ACTIVE
- ProjectionType controls attributes included in GSI

Full Transcript

Creating a Global Secondary Index (GSI) in DynamoDB involves defining the index's attributes and key schema, then adding it to the table creation or update request. DynamoDB processes the creation asynchronously, changing the GSI status from CREATING to ACTIVE. Only after the GSI is ACTIVE can you query it. The ProjectionType setting determines which attributes are available in the GSI. This process is shown step-by-step in the execution table and variable tracker, illustrating the state changes and key actions.