TTL behavior and timing in DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does TTL stand for in DynamoDB?

TTL stands for Time To Live. It is a feature that automatically deletes expired items from a DynamoDB table.

beginner

How does DynamoDB determine when to delete an item using TTL?

DynamoDB checks the timestamp attribute you specify for TTL. When the current time passes this timestamp, the item becomes eligible for deletion.

intermediate

Does DynamoDB delete expired items immediately after the TTL timestamp passes?

No. DynamoDB deletes expired items within 48 hours after the TTL timestamp passes. The deletion is not immediate but happens asynchronously.

intermediate

What happens if you update the TTL attribute of an item before it expires?

If you update the TTL attribute to a new future timestamp, DynamoDB will use the updated timestamp to determine when to delete the item. This can delay or cancel the deletion.

advanced

Can you recover an item after DynamoDB deletes it due to TTL expiration?

No. Once DynamoDB deletes an item due to TTL expiration, it cannot be recovered. You should back up important data before it expires.

What is the main purpose of TTL in DynamoDB?

A Automatically delete expired items

B Encrypt data at rest

C Backup data regularly

D Improve query speed

TTL automatically deletes items after their expiration time to save storage and manage data lifecycle.

When does DynamoDB delete an item after its TTL timestamp has passed?

A Immediately

B After 7 days

C Within 48 hours

D Only when manually triggered

DynamoDB deletes expired items asynchronously within 48 hours after the TTL timestamp.

Which attribute type must the TTL attribute be in DynamoDB?

A String

B List

C Boolean

D Number (Unix epoch time in seconds)

TTL attribute must be a Number representing Unix epoch time in seconds.

If you remove the TTL attribute from an item before expiration, what happens?

A Item is deleted immediately

B Item will not be deleted by TTL

C Item is archived

D Item is locked

Without the TTL attribute, DynamoDB does not consider the item for TTL deletion.

Can TTL be used to trigger custom actions when an item expires?

A Yes, via DynamoDB Streams and Lambda

B No, TTL only deletes items

C Yes, directly within DynamoDB

D No, TTL archives items instead

You can use DynamoDB Streams with Lambda to react to item deletions caused by TTL.

Explain how TTL works in DynamoDB and its timing behavior.

Think about how DynamoDB knows when to delete and when it actually deletes.

Describe what happens if you update or remove the TTL attribute on an item before it expires.

Consider how DynamoDB uses the TTL attribute to decide deletion.

Practice

1. What does TTL (Time To Live) do in DynamoDB?

easy

A. Encrypts data stored in the table.

B. Backs up data periodically.

C. Automatically deletes items after their expiration time.

D. Indexes data for faster queries.

Solution

1. Step 1: Understand TTL purpose

   TTL is designed to remove expired data automatically to save storage and keep data fresh.

2. Step 2: Identify TTL behavior

   It deletes items after their expiration timestamp passes, not encrypting or backing up data.

3. Final Answer:

   Automatically deletes items after their expiration time. -> Option C

4. Quick Check:

   TTL = automatic deletion [OK]

Hint: TTL means automatic deletion after expiry [OK]

Common Mistakes:

• Thinking TTL encrypts data
• Confusing TTL with backup
• Assuming TTL speeds up queries

2. Which attribute type must the TTL attribute have in DynamoDB?

easy

A. String representing a date in ISO format

B. Number representing Unix epoch time in seconds

C. Boolean indicating if item is expired

D. List of timestamps

Solution

1. Step 1: Recall TTL attribute format

   The TTL attribute must be a number storing the expiration time as Unix epoch seconds.

2. Step 2: Eliminate other types

   Strings, booleans, or lists are not valid for TTL expiration timestamps.

3. Final Answer:

   Number representing Unix epoch time in seconds -> Option B

4. Quick Check:

   TTL attribute = Unix epoch seconds [OK]

Hint: TTL attribute stores expiration as Unix epoch seconds [OK]

Common Mistakes:

• Using string dates instead of numbers
• Using boolean instead of timestamp
• Trying to store multiple timestamps

3. If an item has a TTL attribute set to 1650000000 (Unix epoch seconds), when will DynamoDB delete it?

medium

A. Within 48 hours after 1650000000 seconds

B. Exactly at 1650000000 seconds

C. Immediately after setting the TTL attribute

D. Only when manually deleted

Solution

1. Step 1: Understand TTL deletion timing

   DynamoDB deletes expired items approximately after the TTL timestamp, not exactly at that second.

2. Step 2: Recall deletion delay

   Deletion can take up to 48 hours after the expiration time to occur.

3. Final Answer:

   Within 48 hours after 1650000000 seconds -> Option A

4. Quick Check:

   TTL deletion delay = up to 48 hours [OK]

Hint: TTL deletion can be delayed up to 48 hours [OK]

Common Mistakes:

• Expecting deletion exactly at expiration time
• Thinking deletion is immediate
• Assuming manual deletion is required

4. You set TTL on an attribute but notice expired items are not deleted after 3 days. What is a likely cause?

medium

A. TTL attribute is not a number with Unix epoch seconds

B. TTL is enabled but the table is in a different AWS region

C. You forgot to enable encryption on the table

D. The table has no primary key

Solution

1. Step 1: Check TTL attribute format

   If the TTL attribute is not a number with Unix epoch seconds, DynamoDB ignores it for expiration.

2. Step 2: Verify other options

   Region difference, encryption, or primary key absence do not prevent TTL deletion.

3. Final Answer:

   TTL attribute is not a number with Unix epoch seconds -> Option A

4. Quick Check:

   TTL attribute format error blocks deletion [OK]

Hint: TTL attribute must be Unix epoch number [OK]

Common Mistakes:

• Assuming region affects TTL
• Thinking encryption affects TTL
• Ignoring TTL attribute data type

5. You want to ensure items expire exactly after 24 hours using TTL. Which approach is best considering DynamoDB's TTL behavior?

hard

A. Disable TTL and run a scheduled job to delete expired items

B. Set TTL attribute to current time + 86400 seconds and manually delete items after 24 hours

C. Use a string date format for TTL attribute for precise timing

D. Set TTL attribute to current time + 86400 seconds and accept up to 48-hour deletion delay

Solution

1. Step 1: Understand TTL timing limits

   DynamoDB TTL deletes items approximately after expiration, with up to 48 hours delay.

2. Step 2: Choose best practical approach

   Setting TTL attribute to current time + 86400 seconds (24 hours) is correct; manual deletion adds complexity and string format is invalid.

3. Step 3: Consider alternatives

   Disabling TTL and scheduling deletes is possible but less efficient than TTL's automatic deletion.

4. Final Answer:

   Set TTL attribute to current time + 86400 seconds and accept up to 48-hour deletion delay -> Option D

5. Quick Check:

   TTL delay means accept approximate expiry [OK]

Hint: TTL deletion timing is approximate, plan accordingly [OK]

Common Mistakes:

• Expecting exact deletion timing
• Using string instead of number for TTL
• Disabling TTL unnecessarily