Keyspace Notifications

What are keyspace notifications?

Redis can publish a Pub/Sub message whenever certain events happen — a key expires, a SET is issued, a DEL runs, and more. Your application subscribes to these channels to react without polling: for example, invalidate a local cache when a key expires, or trigger a background job when a specific key is written.

Redis exposes two channel types:

• Keyevent channels — one channel per event type; the message payload is the key name. Pattern: __keyevent@<db>__:<event> (example: __keyevent@0__:expired)
• Keyspace channels — one channel per key; the message payload is the event type. Pattern: __keyspace@<db>__:<keyname>

Enabling keyspace notifications

Keyspace notifications are disabled by default because publishing every event adds CPU overhead. Enable them with CONFIG SET at runtime or via redis.conf on startup.

The value is a string of flag characters that select which event classes to publish:

Flag	Events enabled
K	Keyspace events (__keyspace@... channel)
E	Keyevent events (__keyevent@... channel)
x	Expired events (key TTL reached zero)
g	Generic commands: DEL, EXPIRE, RENAME, …
s	Set commands (SADD, SREM, …)
l	List commands (LPUSH, RPOP, …)

For production expiry notifications the common setting is Ex — keyevent channel (E) for expired events only (x):

notify-keyspace-events "Ex"

Or at runtime:

127.0.0.1:6379> CONFIG SET notify-keyspace-events Ex
OK

Subscribing to expiry events

Keyspace notifications use a two-terminal workflow. Open Terminal 1 and subscribe before the key expires:

127.0.0.1:6379> PSUBSCRIBE __keyevent@0__:expired
Reading messages... (press Ctrl-C to quit)

In Terminal 2, set a key with a short TTL to trigger the event:

127.0.0.1:6379> SET demo:token "abc" EX 3
OK

After 3 seconds, Terminal 1 receives the notification:

1) "pmessage"
2) "__keyevent@0__:expired"
3) "__keyevent@0__:expired"
4) "demo:token"

The fourth line is the key name — your subscriber now knows exactly which key expired.

Runnable commands

The commands below enable notifications and set a key with a TTL so you can observe the configuration in action. To see the expired event, open a second redis-cli, run PSUBSCRIBE __keyevent@0__:expired, then in the first terminal run SET demo:token "hello" EX 5 and wait 5 seconds.

CONFIG SET notify-keyspace-events Ex
SET demo:token "hello" EX 5
TTL demo:token

Copy commands ⧉

🟥 Keyspace notifications — react to expirations via Pub/Sub

Keyspace notifications let any subscriber react to key lifecycle events without polling. Subscribe to __keyevent@0__:expired to trigger cache invalidation, job scheduling, or session cleanup when keys expire. Enable only the event classes you need — broad flags like KEA (all events) add measurable overhead on write-heavy workloads.

Which CONFIG flag enables keyevent channels (`__keyevent@...`)?

K E x g

What channel pattern delivers expiry events on database 0?

__expire@0__:keyevent __keyevent@0__:expired __event@0__:expired __keyspace@0__:expire

Are keyspace notifications enabled by default in Redis?

Yes No Only for expiry events Only in Redis 7+

Which PSUBSCRIBE pattern matches all keyevent channels on database 0?

keyevent:0:* __keyevent@0__:* SUBSCRIBE keyevent CONFIG GET notify

Submit

Mark as complete