Key Expiration

TTL-&-EXPIRE

Set automatic expiration on keys to manage cache, sessions, and temporary data. TTL shows remaining time, EXPIRE sets it.

You'll Learn

  • TTL and PTTL for checking expiration
  • EXPIRE and PEXPIRE for setting timeout
  • PERSIST to remove expiration
  • How Redimo shows live countdown
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1. What Is TTL?

TTL (Time To Live) returns the remaining seconds before a key expires and is automatically deleted. PTTL returns milliseconds for precision timing. This is fundamental to Redis's role as a cache.

Redis handles expiration efficiently using a combination of passive expiration (checked on access) and active expiration (periodic sampling). You don't need to clean up expired keys - Redis does it automatically.

Syntax

TTL key                    # Remaining seconds (-1 = no expiry, -2 = key doesn't exist)
PTTL key                   # Remaining milliseconds
EXPIRE key seconds         # Set expiration in seconds from now
PEXPIRE key milliseconds   # Set expiration in milliseconds
EXPIREAT key timestamp     # Set expiration at Unix timestamp (seconds)
PEXPIREAT key timestamp    # Set expiration at Unix timestamp (milliseconds)
PERSIST key                # Remove expiration (make key permanent)
GETEX key EX seconds       # Get value and set/update expiration (Redis 6.2+)

TTL Return Values

  • -2 - Key does not exist
  • -1 - Key exists, no expiration
  • 0+ - Seconds remaining

Common Use Cases

  • • Session tokens (1 hour)
  • • Cache entries (5 minutes)
  • • Rate limit windows (1 minute)
  • • Temporary locks (30 seconds)

2. The CLI Way (Hard Mode)

In CLI, you're constantly typing TTL to check remaining time. No visual feedback when a key is about to expire:

Managing Session Expiration

127.0.0.1:6379> SET session:abc123 "{\"userId\":1001}" EX 3600
OK
127.0.0.1:6379> TTL session:abc123
(integer) 3597
127.0.0.1:6379> TTL session:abc123
(integer) 3594
127.0.0.1:6379> TTL session:abc123
(integer) 3590
127.0.0.1:6379> TTL session:xyz999
(integer) -2

Extending and Removing Expiration

127.0.0.1:6379> EXPIRE session:abc123 7200
(integer) 1
127.0.0.1:6379> TTL session:abc123
(integer) 7199
127.0.0.1:6379> PERSIST session:abc123
(integer) 1
127.0.0.1:6379> TTL session:abc123
(integer) -1
127.0.0.1:6379> PTTL cache:homepage
(integer) 298456

The Problem

You have to keep running TTL manually to track expiration. There's no visual warning when a key is about to expire. And when you SET a value without EX/PX, you lose the existing TTL - a common source of bugs.

3. The Redimo Way (Smart Mode)

Redimo shows a live countdown timer for every key with TTL. Watch the seconds tick down in real-time. Color-coded warnings when keys are about to expire.

What Redimo Does for TTL:

  • ●Live Countdown: TTL counts down in real-time right next to the key. No need to run TTL commands repeatedly.
  • ●Color Warnings: Yellow when under 60 seconds, red when under 10 seconds. Never be surprised by expired keys.
  • ●TTL Preservation: When you edit a value, Redimo automatically preserves the existing TTL. No more accidentally removing expiration.
  • ●Quick Actions: Extend TTL, remove expiration, or set new timeout with a few clicks.
  • ●Filter by TTL: Sort keys by remaining time to find those about to expire.

CLI Pain Points

  • • Manual TTL checks constantly
  • • No visual countdown
  • • No warning for expiring keys
  • • SET without EX loses TTL
  • • Easy to forget expiration

Redimo Solutions

  • • Live countdown display
  • • Yellow/red color warnings
  • • TTL preserved on edit
  • • Click to extend or remove
  • • Sort by expiration time

4. Common Patterns

Session Management

# Create session with 1-hour expiration
SET session:abc123 "{\"userId\":1001,\"role\":\"admin\"}" EX 3600

# Extend session on user activity (sliding window)
EXPIRE session:abc123 3600

# Check if session is still valid
TTL session:abc123  # Positive = valid, -2 = expired

# Use GETEX to get and refresh in one command (Redis 6.2+)
GETEX session:abc123 EX 3600

Cache with Expiration

# Cache API response for 5 minutes
SET cache:api:users "{\"users\":[...]}" EX 300

# Cache with millisecond precision
SET cache:realtime:data "..." PX 500  # 500ms

# Set expiration at specific time (end of day)
EXPIREAT cache:daily:stats 1703548800  # Unix timestamp

# Check remaining time in milliseconds
PTTL cache:realtime:data

Distributed Lock with Timeout

# Acquire lock with 30-second timeout (prevents deadlocks)
SET lock:resource:123 "worker-42" NX EX 30

# If SET returns OK, lock acquired
# If SET returns nil, lock held by someone else

# Extend lock while working (if needed)
EXPIRE lock:resource:123 30

# Release lock when done
DEL lock:resource:123

5. TTL Gotchas

Understanding TTL edge cases will save you from production bugs:

SET removes TTL by default

When you use SET without EX/PX, any existing TTL is removed. The key becomes permanent. This is a common bug when updating cached values.

# Key has 5 minute TTL
SET mykey "value1" EX 300

# Later: update without EX - TTL is LOST!
SET mykey "value2"  # Now permanent!

# Fix: Use SETEX or SET with EX
SET mykey "value2" XX EX 300  # XX = only if exists

GETEX preserves value, updates TTL

Redis 6.2+ added GETEX which gets the value while updating the expiration - perfect for session refresh patterns.

# Get and refresh TTL in one atomic operation
GETEX session:abc123 EX 3600

# Get and remove TTL (make permanent)
GETEX session:abc123 PERSIST

# Get and set absolute expiration
GETEX session:abc123 EXAT 1703548800

Expiration is lazy + active

Expired keys aren't immediately deleted. Redis uses passive deletion (on access) and active deletion (periodic sampling). Memory isn't freed instantly.

6. Pro Tips

Seconds vs Milliseconds

EXPIRE/TTL work in seconds.PEXPIRE/PTTL work in milliseconds. For rate limiting and real-time systems, millisecond precision is often necessary.

Useful TTL Commands

# Set TTL only if key has no expiration (Redis 7.0+)
EXPIRE mykey 3600 NX

# Set TTL only if key already has expiration (Redis 7.0+)
EXPIRE mykey 3600 XX

# Set TTL only if new TTL is greater than current (Redis 7.0+)
EXPIRE mykey 7200 GT

# Set TTL only if new TTL is less than current (Redis 7.0+)
EXPIRE mykey 1800 LT

# Get expiration as Unix timestamp (Redis 7.0+)
EXPIRETIME mykey  # Returns absolute timestamp

Redimo Bonus

When you edit a value in Redimo, it automatically calls PTTL before the update and reapplies the remaining TTL after. You'll never accidentally lose expiration again. This works for all data types - strings, hashes, lists, sets, and sorted sets.

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