TTL behavior and timing in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

When does DynamoDB delete expired items?

In DynamoDB, after an item's TTL timestamp passes, when will DynamoDB delete that item?

A At the end of each day during a scheduled cleanup window.

B Immediately at the exact second the TTL timestamp is reached.

C Only when a read or write operation accesses the expired item.

D Within 48 hours after the TTL timestamp has passed, but timing is not guaranteed.

💡 Hint

Think about how background processes work asynchronously in cloud services.

DynamoDB's TTL feature deletes expired items asynchronously and typically within 48 hours after expiration, but exact timing is not guaranteed.

❓ query_result

intermediate

Effect of TTL on Query Results

You have a DynamoDB table with TTL enabled on attribute expireAt. You run a Query operation immediately after an item's TTL timestamp has passed but before DynamoDB deletes it. What will the Query return?

A The expired item will be returned because it still exists in the table.

B The expired item will not be returned because TTL hides expired items instantly.

C The Query will return an error due to expired items.

D The Query will return only the expired item and no others.

💡 Hint

Consider when DynamoDB physically removes expired items versus when they expire logically.

TTL expiration marks items for deletion, but they remain in the table until DynamoDB deletes them asynchronously. Queries still return these items until deletion.

📝 Syntax

advanced

Correct TTL Attribute Format

Which of the following DynamoDB item attributes is correctly formatted for TTL to work?

DynamoDB

Item example: { "id": "123", "expireAt": ??? }

A "expireAt": "June 1, 2024 12:00:00"

B "expireAt": "2024-06-01T12:00:00Z"

C "expireAt": 1711896000

D "expireAt": true

💡 Hint

TTL expects a specific type of timestamp value.

DynamoDB TTL requires the attribute to be a Unix epoch time in seconds (a number), not a string or boolean.

❓ optimization

advanced

Reducing Delay in TTL Deletion

You want expired items to be deleted as soon as possible after TTL expiration. Which approach can help reduce the delay?

A Increase the TTL timestamp by a few hours to batch deletions.

B Enable DynamoDB Streams and process expired items manually to delete them faster.

C Disable TTL and delete expired items with a scheduled Lambda function only.

D Set the TTL attribute to a string date format for faster processing.

💡 Hint

Think about how you can react to changes in the table immediately.

Enabling DynamoDB Streams lets you detect expired items quickly and delete them manually, reducing delay beyond the default asynchronous TTL process.

🔧 Debug

expert

Why are expired items not deleted after 48 hours?

You enabled TTL on your DynamoDB table with attribute expireAt. Some items have expired more than 48 hours ago but still appear in the table. What is the most likely reason?

A The TTL attribute is missing or has incorrect data type on those items.

B DynamoDB deletes expired items only during monthly maintenance windows.

C The table's read capacity is too low to allow TTL deletions.

D Expired items are never deleted automatically; TTL only marks them.

💡 Hint

Check the attribute format and presence carefully.

If the TTL attribute is missing or not a valid Unix epoch number, DynamoDB cannot identify the item as expired and will not delete it.