TTL attribute setup 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 do you enable TTL on a DynamoDB table?

You enable TTL by specifying a TTL attribute name in the table settings. This attribute stores the expiration time as a Unix timestamp.

beginner

What type of value should the TTL attribute hold?

The TTL attribute should hold a Unix epoch timestamp in seconds, indicating when the item should expire.

intermediate

Does DynamoDB delete expired items immediately after the TTL timestamp?

No, DynamoDB deletes expired items within 48 hours after the expiration time. The deletion is eventually consistent.

intermediate

Can you use TTL on any attribute in DynamoDB?

No, TTL must be enabled on a single attribute per table, and that attribute must contain the expiration timestamp.

What data type should the TTL attribute in DynamoDB be?

A Unix timestamp in seconds

B Boolean true/false

C String containing a date

D ISO 8601 formatted string

The TTL attribute must be a Unix timestamp in seconds representing the expiration time.

When does DynamoDB remove expired items after the TTL timestamp?

A Within 48 hours after expiration

B Only when manually deleted

C After 7 days

D Immediately at the timestamp

DynamoDB removes expired items within 48 hours after the TTL timestamp, not immediately.

How many TTL attributes can you enable per DynamoDB table?

A Two

B One

C Unlimited

D None

You can enable TTL on only one attribute per DynamoDB table.

What happens if the TTL attribute is missing or empty for an item?

A Item causes an error

B Item expires immediately

C Item is deleted after 24 hours

D Item never expires

If the TTL attribute is missing or empty, the item does not expire.

Which of the following is required to enable TTL on a DynamoDB table?

A Set a read capacity unit

B Create a global secondary index

C Specify the TTL attribute name

D Enable encryption

You must specify the TTL attribute name to enable TTL on a DynamoDB table.

Explain how to set up TTL on a DynamoDB table and what type of data the TTL attribute should contain.

Think about the attribute name and the format of the expiration time.

Describe what happens to items in DynamoDB after their TTL expiration time passes.

Consider the timing and consistency of the deletion process.

Practice

1. What is the main purpose of setting a TTL attribute in a DynamoDB table?

easy

A. To increase the read capacity of the table

B. To encrypt data stored in the table

C. To create backups of the table data

D. To automatically delete expired items based on a timestamp

Solution

1. Step 1: Understand TTL functionality

   TTL (Time To Live) is used to automatically remove items after a certain time.

2. Step 2: Identify the purpose in DynamoDB context

   In DynamoDB, TTL deletes expired items to save storage and cost.

3. Final Answer:

   To automatically delete expired items based on a timestamp -> Option D

4. Quick Check:

   TTL = auto-delete expired items [OK]

Hint: TTL means auto-delete expired data by timestamp [OK]

Common Mistakes:

• Confusing TTL with encryption
• Thinking TTL increases capacity
• Assuming TTL creates backups

2. Which of the following is the correct way to specify the TTL attribute in DynamoDB?

easy

A. Set a numeric attribute with Unix epoch time in seconds

B. Set a list attribute with expiration dates

C. Set a boolean attribute to true when item expires

D. Set a string attribute with date format 'YYYY-MM-DD'

Solution

1. Step 1: Recall TTL attribute data type

   DynamoDB TTL requires a numeric attribute representing Unix epoch time in seconds.

2. Step 2: Evaluate options

   Only Set a numeric attribute with Unix epoch time in seconds correctly uses numeric Unix epoch seconds for TTL.

3. Final Answer:

   Set a numeric attribute with Unix epoch time in seconds -> Option A

4. Quick Check:

   TTL attribute = numeric Unix epoch seconds [OK]

Hint: TTL attribute must be numeric Unix epoch seconds [OK]

Common Mistakes:

• Using string date formats instead of numeric
• Using boolean or list types for TTL
• Not enabling TTL on the table after setting attribute

3. Given a DynamoDB item with attribute expireAt set to 1700000000 (Unix epoch seconds), and TTL enabled on expireAt, what happens when the current time is 1700000001?

medium

A. The item remains until manually deleted

B. The item is automatically deleted by DynamoDB

C. The item is archived automatically

D. The item is updated with a new TTL value

Solution

1. Step 1: Understand TTL expiration behavior

   When current time exceeds the TTL timestamp, DynamoDB marks the item for deletion.

2. Step 2: Apply to given timestamp

   Since current time 1700000001 > expireAt 1700000000, item is deleted automatically.

3. Final Answer:

   The item is automatically deleted by DynamoDB -> Option B

4. Quick Check:

   Current time > TTL timestamp = item deleted [OK]

Hint: Item deletes when current time passes TTL timestamp [OK]

Common Mistakes:

• Thinking item stays until manual deletion
• Assuming item is archived instead of deleted
• Believing TTL updates item automatically

4. You set the TTL attribute to a string value like "2024-12-31" and enabled TTL on that attribute. What issue will you face?

medium

A. TTL will not delete expired items because attribute is not numeric

B. DynamoDB will throw a syntax error on enabling TTL

C. Items will be deleted immediately regardless of date

D. TTL will convert string to numeric automatically

Solution

1. Step 1: Check TTL attribute type requirement

   TTL attribute must be numeric Unix epoch seconds, not string.

2. Step 2: Analyze effect of string value

   DynamoDB ignores TTL deletion if attribute is not numeric, so items won't expire.

3. Final Answer:

   TTL will not delete expired items because attribute is not numeric -> Option A

4. Quick Check:

   Non-numeric TTL attribute = no deletion [OK]

Hint: TTL attribute must be numeric; strings cause no deletion [OK]

Common Mistakes:

• Expecting DynamoDB to error on TTL enable
• Assuming immediate deletion with wrong type
• Believing automatic type conversion happens

5. You want to set up TTL on a DynamoDB table to delete items 7 days after creation. Which approach correctly sets the TTL attribute expireAt when inserting an item?

hard

A. Set expireAt to a boolean true after 7 days

B. Set expireAt to current date string plus 7 days in 'YYYY-MM-DD' format

C. Set expireAt to current Unix epoch seconds plus 604800 (7 days in seconds)

D. Set expireAt to the current Unix epoch seconds without adding days

Solution

1. Step 1: Calculate TTL timestamp for 7 days later

   7 days = 7 * 24 * 60 * 60 = 604800 seconds; add to current Unix epoch seconds.

2. Step 2: Set TTL attribute correctly

   Assign expireAt the numeric value of current time + 604800 seconds for proper TTL.

3. Final Answer:

   Set expireAt to current Unix epoch seconds plus 604800 (7 days in seconds) -> Option C

4. Quick Check:

   TTL timestamp = now + 7 days in seconds [OK]

Hint: Add 604800 seconds to now for 7-day TTL [OK]

Common Mistakes:

• Using date strings instead of numeric timestamps
• Setting TTL to current time without delay
• Using boolean or other types for TTL