TTL use cases (sessions, logs, cache) in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

TTL impact on session data expiration

You have a DynamoDB table storing user sessions with a TTL attribute set to expire sessions after 30 minutes. Which of the following describes the expected behavior of expired session items?

A Expired session items are archived automatically to another table before deletion.

B Expired session items remain in the table indefinitely until manually deleted.

C Expired session items are deleted eventually but not immediately after TTL time passes.

D Expired session items are immediately deleted from the table as soon as TTL time passes.

💡 Hint

Think about how DynamoDB handles TTL deletions asynchronously.

DynamoDB TTL deletes expired items asynchronously and not immediately after expiration time. This means expired items may remain visible for some time before deletion.

🧠 Conceptual

intermediate

Choosing TTL for log data retention

You want to store application logs in DynamoDB and automatically remove logs older than 7 days. What is the best way to implement this using TTL?

A Set a TTL attribute on each log item with a timestamp 7 days after the log creation time.

B Set TTL attribute to the current time to delete logs immediately.

C Use a global secondary index to filter logs older than 7 days and delete them manually.

D Manually scan and delete logs older than 7 days every hour.

💡 Hint

TTL works by specifying an expiration timestamp on each item.

Setting a TTL attribute with a timestamp 7 days after creation allows DynamoDB to automatically delete logs after 7 days without manual intervention.

📝 Syntax

advanced

Correct TTL attribute format for cache expiration

Which of the following DynamoDB item attributes correctly sets TTL for cache expiration?

{
  "CacheKey": "item123",
  "Data": "some cached data",
  "ExpiresAt": ?
}

A ExpiresAt: 1717262400

B ExpiresAt: "12:00:00"

C ExpiresAt: "2024-06-01T12:00:00Z"

D ExpiresAt: true

💡 Hint

TTL attribute must be a Unix epoch time in seconds.

DynamoDB TTL expects the attribute to be a number representing Unix epoch time in seconds when the item expires.

❓ optimization

advanced

Optimizing TTL usage for high write volume logs

You have a high volume of log entries written to DynamoDB with TTL set to 30 days. What is the best practice to optimize table performance and cost?

A Use a single large table with TTL enabled and no partition key changes.

B Create multiple tables partitioned by month and enable TTL on each to reduce item scans.

C Disable TTL and manually delete old logs using batch operations.

D Set TTL to a very short time like 1 hour to reduce storage costs.

💡 Hint

Think about how partitioning affects performance and TTL cleanup.

Partitioning logs by month into separate tables with TTL reduces the size of each table and improves performance and cost efficiency.

🔧 Debug

expert

Why are expired cache items not deleted as expected?

You set TTL on cache items with an attribute named "expiryTime" as Unix epoch seconds. After several days, expired items still appear in the table. What is the most likely cause?

A TTL attribute value is a string instead of a number.

B DynamoDB TTL deletes items only once per day, so delay is expected.

C TTL attribute value is set to a future timestamp instead of past.

D TTL attribute name in DynamoDB TTL settings does not match "expiryTime" exactly.

💡 Hint

Check the TTL attribute name configured in the table settings.

DynamoDB TTL requires the attribute name configured in the table TTL settings to exactly match the attribute in items. A mismatch means TTL does not work.