PERSIST to remove expiry in Redis - Step-by-Step Execution

Concept Flow - PERSIST to remove expiry

Start with a key

↓

Check if key has expiry?

No→Nothing changes

Yes↓

Run PERSIST command

↓

Expiry removed

↓

Key becomes persistent

↓

End

This flow shows how the PERSIST command removes the expiry time from a Redis key, making it permanent.

Execution Sample

Redis

SET session123 user_data
EXPIRE session123 300
TTL session123
PERSIST session123
TTL session123

This code sets a key with expiry, checks its TTL, removes expiry with PERSIST, then checks TTL again.

Execution Table

Step	Command	Key TTL Before	Action	Key TTL After	Result
1	SET session123 user_data	N/A	Create key without expiry	-1	Key created
2	EXPIRE session123 300	-1	Set expiry 300 seconds	300	Expiry set
3	TTL session123	300	Check TTL	300	TTL is 300 seconds
4	PERSIST session123	300	Remove expiry	-1	Expiry removed, key persistent
5	TTL session123	-1	Check TTL	-1	TTL is -1 (no expiry)

💡 After PERSIST, TTL is -1 meaning no expiry remains on the key.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
TTL(session123)	N/A	-1	300	300	-1	-1

Key Moments - 3 Insights

Why does TTL show -1 after SET but before EXPIRE?

Because the key was created without expiry, TTL returns -1 indicating no expiration (see execution_table step 1).

What does PERSIST do to the key's TTL?

PERSIST removes the expiry, changing TTL from a positive number to -1, meaning the key will not expire (see execution_table step 4).

Why check TTL after PERSIST?

To confirm the expiry was removed and the key is now persistent (see execution_table step 5).

Visual Quiz - 3 Questions

Look at the execution_table, what is the TTL of 'session123' right after the EXPIRE command?

A -1

B 0

C 300

D N/A

💡 Hint

Check the 'Key TTL After' column at step 2 in the execution_table.

At which step does the key become persistent with no expiry?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look for when TTL changes to -1 after being positive in the execution_table.

If we skip the PERSIST command, what would TTL show at step 5?

A 300

B -1

C 0

D N/A

💡 Hint

Without PERSIST, expiry remains so TTL stays positive (see step 3 and 5 comparison).

Concept Snapshot

PERSIST key
- Removes expiry from a Redis key
- Makes key persistent (TTL = -1)
- Use after EXPIRE to keep key forever
- TTL command shows -1 if no expiry
- Useful to cancel automatic deletion

Full Transcript

This visual execution shows how the Redis PERSIST command removes the expiry time from a key. First, a key 'session123' is created without expiry (TTL is -1). Then expiry is set to 300 seconds. Checking TTL confirms 300 seconds remain. Running PERSIST removes the expiry, changing TTL back to -1, meaning the key will not expire. Checking TTL again confirms no expiry remains. This helps understand how PERSIST cancels expiry on keys.