TTL behavior and timing in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the TTL attribute name in DynamoDB.

DynamoDB

ttl_spec = {"AttributeName": "[1]", "Enabled": true}

Drag options to blanks, or click blank then click option'

AExpirationTime

BTTL

CTimeToLive

DDeleteAt

Attempts:

3 left

💡 Hint

Common Mistakes

Using attribute names not recognized by DynamoDB for TTL.

Forgetting to enable TTL after setting the attribute name.

The TTL attribute name is usually set to "TTL" in DynamoDB to mark the expiration timestamp.

2fill in blank

medium

Complete the code to enable TTL on a DynamoDB table using AWS CLI.

DynamoDB

aws dynamodb update-time-to-live --table-name MyTable --time-to-live-specification Enabled=[1],AttributeName=TTL

Drag options to blanks, or click blank then click option'

Atrue

Bfalse

Cenabled

Dyes

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values like 'yes' or 'enabled' instead of boolean true.

Setting Enabled to false disables TTL.

To enable TTL, the Enabled flag must be set to true.

3fill in blank

hard

Fix the error in the TTL attribute value type for DynamoDB items.

DynamoDB

item = {"UserId": "123", "TTL": [1]

Drag options to blanks, or click blank then click option'

A"2024-06-01T00:00:00Z"

B"1685606400"

C1685606400

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using ISO date strings instead of epoch seconds.

Using string type for the timestamp instead of number.

The TTL attribute must be a number representing the Unix epoch time in seconds.

4fill in blank

hard

Fill both blanks to explain when expired items are deleted by DynamoDB TTL.

DynamoDB

Expired items are typically deleted within [1] hours, but actual deletion can take up to [2] hours.

Drag options to blanks, or click blank then click option'

A48

B72

C24

D96

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming immediate deletion right after expiration.

Confusing hours with minutes or days.

DynamoDB usually deletes expired items within 24 hours, but it can take up to 72 hours in some cases.

5fill in blank

hard

Fill all three blanks to describe TTL behavior and timing in DynamoDB.

DynamoDB

TTL attribute must be a [1] representing epoch time in seconds. DynamoDB checks for expired items approximately every [2] minutes. Deletion of expired items can take up to [3] hours.

Drag options to blanks, or click blank then click option'

Anumber

Bstring

C5

D48

Attempts:

3 left

💡 Hint

Common Mistakes

Using string type for TTL attribute.

Thinking TTL checks happen instantly or only once a day.

The TTL attribute is a number (epoch seconds). DynamoDB scans for expired items roughly every 5 minutes. Deletion can take up to 48 hours.

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