BatchGetItem in DynamoDB - Step-by-Step Execution

Concept Flow - BatchGetItem

Start BatchGetItem Request

↓

Receive list of keys

↓

Check keys per table

↓

Send batch request to DynamoDB

↓

DynamoDB returns items and unprocessed keys

↓

If unprocessed keys exist?

Yes→Retry unprocessed keys

↓

Repeat until no unprocessed keys

↓

Return all retrieved items

↓

End

BatchGetItem sends multiple keys to DynamoDB, retrieves items in batches, retries unprocessed keys, and returns all found items.

Execution Sample

DynamoDB

BatchGetItem({
  RequestItems: {
    'Table1': { Keys: [{ id: 1 }, { id: 2 }] },
    'Table2': { Keys: [{ id: 3 }] }
  }
})

This request asks DynamoDB to get items with id 1 and 2 from Table1 and id 3 from Table2 in one batch.

Execution Table

Step	Action	Keys Sent	Response	Unprocessed Keys	Notes
1	Send batch request	Table1: [1,2], Table2: [3]	Items for ids 1,2,3 returned	None	All keys processed in first try
2	Return items	N/A	Items for ids 1,2,3	N/A	BatchGetItem completes successfully

💡 All requested keys processed, no unprocessed keys remain

Variable Tracker

Variable	Start	After Step 1	After Step 2
Keys to get	[Table1:1,2; Table2:3]	[None]	[None]
Unprocessed Keys	[All keys]	[None]	[None]
Retrieved Items	[]	[Items for 1,2,3]	[Items for 1,2,3]

Key Moments - 2 Insights

Why do we sometimes get unprocessed keys back from DynamoDB?

DynamoDB limits batch size and throughput. If it can't process all keys at once, it returns unprocessed keys to retry later, as shown in the 'Unprocessed Keys' column in the execution_table.

What happens if there are unprocessed keys after the first request?

The client retries only those unprocessed keys until all are processed, ensuring no data is missed. This retry loop is part of the flow in the concept_flow diagram.

Visual Quiz - 3 Questions

Look at the execution_table, what keys are sent in the first batch request?

A Table1: [1], Table2: [3]

B Table1: [2], Table2: []

C Table1: [1,2], Table2: [3]

D Table1: [], Table2: [3]

💡 Hint

Check the 'Keys Sent' column in Step 1 of the execution_table

At which step does BatchGetItem return the retrieved items?

A Step 1

B Step 2

C Before Step 1

D After Step 3

💡 Hint

Look at the 'Action' and 'Response' columns in the execution_table

If DynamoDB returns unprocessed keys, what should the client do next?

A Retry only the unprocessed keys

B Retry all keys again

C Ignore them and finish

D Stop and report error

💡 Hint

Refer to the concept_flow where unprocessed keys lead to retry

Concept Snapshot

BatchGetItem lets you get multiple items from one or more tables in a single request.
You send a list of keys per table.
DynamoDB returns found items and may return unprocessed keys.
You retry unprocessed keys until all are retrieved.
This reduces multiple calls and improves efficiency.

Full Transcript

BatchGetItem is a DynamoDB operation to fetch multiple items by their keys in one request. You provide keys grouped by table. DynamoDB tries to return all items at once but may return some keys as unprocessed if limits are hit. The client then retries those keys until all are processed. This process reduces network calls and speeds up data retrieval. The execution flow starts with sending keys, receiving items and unprocessed keys, retrying if needed, and finally returning all items. Variables like keys to get, unprocessed keys, and retrieved items change during execution. Understanding retries and unprocessed keys is key to using BatchGetItem effectively.