Temporary data with TTL in Redis - Step-by-Step Execution

Concept Flow - Temporary data with TTL

Set key with value

↓

Assign TTL (time to live)

↓

Wait for TTL countdown

↓

TTL expires?

No→Key still exists

Yes↓

Key auto-deleted

↓

Key no longer accessible

This flow shows how a key is set with a value and a time limit (TTL). When the TTL ends, the key is automatically removed.

Execution Sample

Redis

SET session123 "user_data"
EXPIRE session123 5
GET session123
(wait 6 seconds)
GET session123

Set a key with a value and TTL 5 seconds, then get it before and after TTL expires.

Execution Table

Step	Command	Action	Key Exists?	Output
1	SET session123 "user_data"	Store key 'session123' with value 'user_data'	Yes	OK
2	EXPIRE session123 5	Set TTL 5 seconds on 'session123'	Yes	1
3	GET session123 (immediately)	Retrieve value of 'session123'	Yes	"user_data"
4	(Wait 6 seconds)	TTL countdown ends, key expires	No	nil
5	GET session123 (after wait)	Try to get expired key	No	nil

💡 After 5 seconds, TTL expires and Redis deletes the key automatically.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	Final
session123	does not exist	"user_data"	"user_data" (TTL 5s)	deleted	does not exist

Key Moments - 2 Insights

Why does GET return nil after waiting even though we set the key before?

Because the TTL expired after 5 seconds (see execution_table step 4), Redis automatically deleted the key.

What does the EXPIRE command return and why?

It returns 1 to confirm TTL was set successfully (see execution_table step 2). If key did not exist, it would return 0.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output of GET session123 immediately after setting TTL?

A "user_data"

B nil

C Error

D 1

💡 Hint

Check execution_table row 3 under Output column.

At which step does the key 'session123' get deleted automatically?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at execution_table step 4 Action and Key Exists? columns.

If we set TTL to 10 seconds instead of 5, what changes in the execution_table?

A EXPIRE returns 0

B GET returns nil immediately

C Key expires at step 4 after 10 seconds instead of 5

D Key never expires

💡 Hint

TTL controls when the key expires, see execution_table step 4.

Concept Snapshot

SET key value - stores data
EXPIRE key seconds - sets TTL
GET key - retrieves data
After TTL ends, key auto-deletes
GET returns nil if key expired

Full Transcript

This visual trace shows how Redis handles temporary data using TTL (time to live). First, a key 'session123' is set with a value 'user_data'. Then, a TTL of 5 seconds is assigned. Immediately after, getting the key returns the stored value. After waiting 6 seconds, the TTL expires and Redis deletes the key automatically. Trying to get the key now returns nil because it no longer exists. This demonstrates how TTL helps manage temporary data that expires automatically.