BatchWriteItem in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this BatchWriteItem operation?

Consider a DynamoDB table named Users with primary key UserId. You run the following BatchWriteItem request to insert two new users:

{
  "RequestItems": {
    "Users": [
      {"PutRequest": {"Item": {"UserId": {"S": "u1"}, "Name": {"S": "Alice"}}}},
      {"PutRequest": {"Item": {"UserId": {"S": "u2"}, "Name": {"S": "Bob"}}}}
    ]
  }
}

What will the response contain if both writes succeed?

A {"UnprocessedItems": {}}

B {"UnprocessedItems": {"Users": [{"PutRequest": {"Item": {"UserId": {"S": "u1"}, "Name": {"S": "Alice"}}}}]}}

C {"Error": "ProvisionedThroughputExceededException"}

D {"ConsumedCapacity": [{"TableName": "Users", "CapacityUnits": 2}]}

💡 Hint

If all writes succeed, DynamoDB returns an empty UnprocessedItems map.

The BatchWriteItem response includes an UnprocessedItems field listing any items not processed due to throttling or errors. If all writes succeed, this field is empty.

🧠 Conceptual

intermediate

Which limitation applies to BatchWriteItem requests?

When using BatchWriteItem in DynamoDB, which of the following is a true limitation?

A You can write unlimited items as long as the total size is under 100 MB.

B You can write up to 25 items or 16 MB of data per request, whichever limit is hit first.

C BatchWriteItem supports conditional writes on items.

D You can only write items to one table per BatchWriteItem request.

💡 Hint

Check the official AWS DynamoDB limits for batch writes.

BatchWriteItem allows up to 25 Put or Delete requests per call, with a maximum total size of 16 MB. It does not support conditional writes and can target multiple tables.

📝 Syntax

advanced

Which BatchWriteItem request syntax is valid?

Identify the valid JSON syntax for a BatchWriteItem request that deletes an item with UserId 'u3' from the Users table.

A

{
  "RequestItems": {
    "Users": {
      "DeleteRequest": {"Key": {"UserId": {"S": "u3"}}}
    }
  }
}

B

{
  "RequestItems": {
    "Users": [
      {"Delete": {"Key": {"UserId": "u3"}}}
    ]
  }
}

C

{
  "RequestItems": {
    "Users": [
      {"DeleteRequest": {"Key": {"UserId": {"S": "u3"}}}}
    ]
  }
}

D

{
  "RequestItems": [
    {"Users": {"DeleteRequest": {"Key": {"UserId": {"S": "u3"}}}}}
  ]
}

💡 Hint

Remember the structure: RequestItems maps table names to lists of write requests.

The correct syntax uses RequestItems as a map from table name to a list of write requests. Each write request is an object with either PutRequest or DeleteRequest keys.

❓ optimization

advanced

How to handle unprocessed items efficiently after BatchWriteItem?

After calling BatchWriteItem, some items are returned in UnprocessedItems. What is the best practice to handle these unprocessed items?

A Retry the unprocessed items with exponential backoff until all are processed.

B Delete the unprocessed items from your application to avoid duplicates.

C Split unprocessed items into single-item requests and send them immediately without delay.

D Ignore unprocessed items as they will be processed automatically by DynamoDB.

💡 Hint

Think about how to avoid throttling and ensure all writes succeed.

DynamoDB returns unprocessed items when throttling occurs. The recommended approach is to retry these items with exponential backoff to reduce load and avoid repeated throttling.

🔧 Debug

expert

Why does this BatchWriteItem request fail with ValidationException?

You run this BatchWriteItem request to put two items into the Products table:

{
  "RequestItems": {
    "Products": [
      {"PutRequest": {"Item": {"ProductId": {"S": "p1"}, "Price": {"N": "20"}}}},
      {"PutRequest": {"Item": {"ProductId": {"S": "p2"}, "Price": 15}}}
    ]
  }
}

Why does this request cause a ValidationException?

A The JSON syntax is invalid due to a missing comma after the second PutRequest.

B The ProductId attribute must be a number, not a string.

C BatchWriteItem does not support multiple PutRequests in one call.

D The second item's Price attribute is missing the DynamoDB data type wrapper.

💡 Hint

Check the attribute value formats for DynamoDB items.

In DynamoDB JSON format, attribute values must specify their data type. The second item's Price attribute is given as a raw number 15 instead of {"N": "15"}, causing a validation error.