TTL use cases (sessions, logs, cache) in DynamoDB - Step-by-Step Execution

Concept Flow - TTL use cases (sessions, logs, cache)

Item Created

↓

TTL Attribute Set

↓

Time Passes

↓

DynamoDB Checks TTL

↓

TTL Expired?

No→Item Remains

Yes↓

Item Deleted Automatically

When an item is created, a TTL timestamp is set. DynamoDB checks this timestamp over time and deletes the item automatically when TTL expires.

Execution Sample

DynamoDB

PutItem {"sessionId": "abc123", "userId": "user1", "ttl": 1686000000}

// TTL is a timestamp in the future

// DynamoDB deletes item after TTL expires

This example shows creating a session item with a TTL timestamp. DynamoDB will delete it after the TTL time passes.

Execution Table

Step	Action	TTL Value	Current Time	TTL Expired?	Result
1	Create item with TTL=1686000000	1686000000	1685990000	No	Item stored
2	Time passes	1686000000	1686000001	Yes	Item deleted by DynamoDB
3	Check item existence	-	-	-	Item no longer exists

💡 At step 2, current time exceeds TTL, so DynamoDB deletes the item automatically.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
Item	None	Exists with TTL=1686000000	Deleted	Deleted
Current Time	1685990000	1685990000	1686000001	1686000001
TTL Expired?	No	No	Yes	Yes

Key Moments - 3 Insights

Why doesn't DynamoDB delete the item immediately after creation?

Because TTL is a timestamp in the future. DynamoDB only deletes items after the current time passes the TTL value, as shown in execution_table step 2.

What happens if the TTL attribute is missing or set to a past time?

If TTL is missing, DynamoDB never deletes the item automatically. If TTL is in the past, DynamoDB deletes the item soon after detection, similar to step 2.

Can TTL be used for caching data?

Yes, TTL automatically removes expired cache entries, keeping the table clean without manual deletion, as shown by the automatic deletion in step 2.

Visual Quiz - 3 Questions

Look at the execution_table, what is the TTL Expired? status at Step 1?

A Yes

B Unknown

C No

D Not applicable

💡 Hint

Refer to the 'TTL Expired?' column in execution_table row for Step 1.

At which step does DynamoDB delete the item automatically?

A Step 2

B Step 1

C Step 3

D Never

💡 Hint

Check the 'Result' column in execution_table to see when the item is deleted.

If the TTL value was set to a time in the past at creation, what would happen?

A Item would be deleted immediately

B Item would be deleted after some delay

C Item would never be deleted

D Item would cause an error

💡 Hint

TTL deletion happens after DynamoDB detects expired TTL, which may take some time after current time passes TTL.

Concept Snapshot

TTL (Time To Live) in DynamoDB lets you set an expiration timestamp on items.
DynamoDB automatically deletes items after TTL expires.
Common uses: session expiration, log cleanup, cache eviction.
Set TTL attribute as a Unix epoch timestamp.
DynamoDB checks TTL periodically; deletion is automatic and asynchronous.
No immediate deletion on item creation; deletion happens after TTL passes.

Full Transcript

TTL in DynamoDB is a feature that lets you set an expiration time on items using a timestamp attribute. When you create an item, you add a TTL attribute with a future time. DynamoDB checks this TTL over time and deletes the item automatically when the current time passes the TTL. This is useful for sessions that expire, logs that should be cleaned up, or cache data that should be removed after some time. The execution table shows that at creation, the TTL is not expired, so the item stays. After time passes and TTL expires, DynamoDB deletes the item automatically. Variables like the item existence and TTL expired status change accordingly. Beginners often wonder why deletion is not immediate; it's because TTL is a future timestamp and deletion happens only after that time. If TTL is missing, the item never expires. TTL is a simple way to keep your database clean without manual deletes.