Pattern Subscriptions

Pattern subscriptions

PSUBSCRIBE works like SUBSCRIBE but accepts a glob pattern instead of a literal channel name. A single PSUBSCRIBE call can therefore match dozens of channels at once without listing each one individually.

The three glob wildcards Redis supports are:

Pattern	Meaning
*	Match any sequence of characters (including none)
?	Match exactly one character
[abc]	Match one character from the set — e.g. [abc] matches a, b, or c

For example, news.* matches news.sports, news.tech, news.finance, and any other channel that begins with news..

PSUBSCRIBE demo

The interaction below uses two terminals. Terminal 1 subscribes with a pattern; Terminal 2 publishes to several channels.

-- Terminal 1 --
127.0.0.1:6379> PSUBSCRIBE news.*
Reading messages... (press Ctrl-C to quit)
1) "psubscribe"
2) "news.*"
3) (integer) 1

-- Terminal 2 --
127.0.0.1:6379> PUBLISH news.sports "score update"
(integer) 1
127.0.0.1:6379> PUBLISH news.tech "new release"
(integer) 1

-- Terminal 1 receives --
1) "pmessage"
2) "news.*"
3) "news.sports"
4) "score update"
1) "pmessage"
2) "news.*"
3) "news.tech"
4) "new release"

Notice the reply format: pmessage delivers four parts — the event type, the matched pattern, the actual channel, and the payload. This is different from a plain message reply, which only has three parts.

PUBLISH news.sports "score update"
PUBLISH news.tech "new release"
PUBLISH weather.today "sunny"

Publish to channels matched by news.* ⧉

PUNSUBSCRIBE

PUNSUBSCRIBE pattern removes a pattern subscription. Calling it with no argument unsubscribes from all active patterns.

127.0.0.1:6379> PUNSUBSCRIBE news.*
1) "punsubscribe"
2) "news.*"
3) (integer) 0

The third element is the count of remaining pattern subscriptions. When it reaches 0 the client exits pattern-subscribe mode and can issue regular commands again.

Keyspace notifications (teaser)

Redis itself uses the Pub/Sub mechanism internally to emit events about keyspace activity. When enabled, Redis publishes to special built-in channels such as:

• __keyevent@0__:expired — fires whenever a key in database 0 expires
• __keyspace@0__:mykey — fires whenever any command touches mykey

You can enable these notifications with:

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

Then subscribe with PSUBSCRIBE __keyevent@0__:* to catch every keyspace event on database 0. This is an advanced pattern useful for cache invalidation and audit logging — a deeper dive belongs in its own lesson.

🟥 Pattern subscriptions match many channels with one subscriber

A single PSUBSCRIBE news.* replaces a dozen individual SUBSCRIBE calls. The trade-off is a small overhead: Redis must match every published message against every active pattern. Keep patterns specific enough that the fan-out stays manageable in high-throughput systems.

Which glob wildcard matches exactly one character in a PSUBSCRIBE pattern?

* ? [?] #

How many parts does a pmessage reply contain?

2 3 4 5

What is the second element in a pmessage reply?

The payload The actual channel the message was published to The pattern that matched The subscriber count

Which command would you use to receive messages from both `alerts.low` and `alerts.high` with a single subscription?

SUBSCRIBE alerts.* PSUBSCRIBE alerts.* SUBSCRIBE alerts.low alerts.high MULTISUBSCRIBE alerts.*

Submit

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