TTL use cases (sessions, logs, cache) 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 is TTL useful for managing user sessions?

TTL automatically removes expired session data, helping keep the database clean and ensuring users' sessions do not persist longer than intended.

beginner

Why is TTL helpful for log data in DynamoDB?

Logs can grow very large. TTL deletes old logs automatically after a set time, saving storage space and reducing costs.

beginner

Explain how TTL supports cache management in DynamoDB.

TTL removes cached items after they expire, ensuring the cache stays fresh and does not serve outdated data.

beginner

What happens to an item in DynamoDB when its TTL expires?

When an item's TTL expires, DynamoDB automatically deletes the item without user intervention.

What is the main purpose of TTL in DynamoDB?

A Backup data daily

B Automatically delete expired items

C Encrypt data at rest

D Increase read capacity

TTL automatically deletes items after their expiration time to keep the table clean.

Which use case benefits from TTL by removing old session data?

A Data encryption

B Backup management

C User sessions

D Query optimization

TTL helps remove expired user sessions automatically.

How does TTL help with log data in DynamoDB?

A By indexing logs

B By compressing logs

C By encrypting logs

D By deleting old logs automatically

TTL deletes old logs after a set time to save space.

What happens to cached items when their TTL expires?

A They are deleted

B They are moved to a different table

C They are refreshed automatically

D They are archived

TTL deletes cached items after expiration to keep cache fresh.

TTL in DynamoDB requires which of the following to work?

A A timestamp attribute indicating expiration time

B Manual deletion scripts

C Backup schedules

D Encryption keys

TTL uses a timestamp attribute to know when to delete items.

Describe three common use cases for TTL in DynamoDB and explain why TTL is helpful for each.

Think about data that only needs to exist temporarily.

Explain how TTL works in DynamoDB and what happens when an item's TTL expires.

Focus on the automatic deletion process.

Practice

1. What is the main purpose of TTL (Time To Live) in DynamoDB?

easy

A. Automatically delete items after a specified time to save storage

B. Encrypt data for security

C. Backup data to another region

D. Increase read capacity automatically

Solution

1. Step 1: Understand TTL functionality

   TTL marks items with an expiration timestamp to delete them automatically after that time.

2. Step 2: Identify the main benefit

   This automatic deletion helps save storage and keeps data fresh without manual cleanup.

3. Final Answer:

   Automatically delete items after a specified time to save storage -> Option A

4. Quick Check:

   TTL = automatic deletion [OK]

Hint: TTL deletes expired data automatically to save space [OK]

Common Mistakes:

• Confusing TTL with encryption
• Thinking TTL backs up data
• Assuming TTL changes capacity settings

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

easy

A. String representing a date

B. Boolean indicating expiration

C. Binary data

D. Number representing epoch time in seconds

Solution

1. Step 1: Check TTL attribute requirements

   DynamoDB TTL requires a Number attribute that stores the expiration time as epoch time in seconds.

2. Step 2: Eliminate other types

   String, Boolean, or Binary types are not valid for TTL expiration timestamps.

3. Final Answer:

   Number representing epoch time in seconds -> Option D

4. Quick Check:

   TTL attribute = epoch seconds number [OK]

Hint: TTL attribute must be a number with epoch seconds [OK]

Common Mistakes:

• Using string dates instead of numbers
• Setting TTL attribute as Boolean
• Using binary data for TTL

3. Given a DynamoDB table with TTL enabled on attribute expireAt, what happens to an item with expireAt set to a timestamp 10 minutes in the past?

medium

A. The item is automatically deleted by DynamoDB

B. The item remains until manually deleted

C. The item is archived automatically

D. The item is updated with a new timestamp

Solution

1. Step 1: Understand TTL expiration behavior

   Items with TTL timestamps in the past are marked for deletion by DynamoDB automatically.

2. Step 2: Confirm deletion timing

   DynamoDB deletes expired items typically within 48 hours after expiration, often sooner.

3. Final Answer:

   The item is automatically deleted by DynamoDB -> Option A

4. Quick Check:

   Expired TTL item = auto delete [OK]

Hint: Expired TTL items get deleted automatically [OK]

Common Mistakes:

• Thinking expired items stay forever
• Assuming items get archived
• Believing TTL updates timestamps automatically

4. You enabled TTL on attribute sessionExpiry but items are not being deleted after expiration. What is the most likely cause?

medium

A. TTL only works on string attributes

B. The table has no primary key defined

C. The sessionExpiry attribute is missing or not a number

D. DynamoDB does not support TTL

Solution

1. Step 1: Check TTL attribute correctness

   TTL requires the attribute to exist and be a number representing epoch time; missing or wrong type prevents deletion.

2. Step 2: Verify other options

   Tables must have primary keys, but that doesn't affect TTL. TTL does not work on strings. DynamoDB supports TTL.

3. Final Answer:

   The sessionExpiry attribute is missing or not a number -> Option C

4. Quick Check:

   TTL attribute missing or wrong type = no deletion [OK]

Hint: TTL attribute must exist and be a number [OK]

Common Mistakes:

• Assuming TTL works on strings
• Ignoring missing TTL attribute
• Thinking DynamoDB lacks TTL support

5. You want to use TTL to automatically expire cached items after 1 hour. Which approach correctly sets the TTL attribute cacheExpire when inserting an item?

hard

A. Set cacheExpire to current date string plus 1 hour

B. Set cacheExpire to current epoch time plus 3600 seconds

C. Set cacheExpire to Boolean true

D. Do not set cacheExpire attribute

Solution

1. Step 1: Calculate TTL expiration timestamp

   TTL requires a number representing epoch time in seconds, so add 3600 seconds (1 hour) to current epoch time.

2. Step 2: Confirm correct attribute setting

   Setting a string or Boolean won't work; omitting the attribute disables TTL for that item.

3. Final Answer:

   Set cacheExpire to current epoch time plus 3600 seconds -> Option B

4. Quick Check:

   TTL = current time + seconds [OK]

Hint: TTL value = current epoch seconds + expiration seconds [OK]

Common Mistakes:

• Using date strings instead of epoch seconds
• Setting TTL as Boolean
• Not setting TTL attribute at all