Redis 6.0 Client‑Side Caching and Tracking Feature Overview

Redis 6.0 introduces several new features, among which the client‑side caching (tracking) mechanism is a major addition. It allows the server to remember which keys a client has read and to push invalidation messages when those keys change.

The core command is:

CLIENT TRACKING ON|OFF [REDIRECT client-id] [PREFIX prefix] [BCAST] [OPTIN] [OPTOUT] [NOLOOP]

Key options:

REDIRECT : forwards invalidation messages to another client (useful for RESP2 clients).

BCAST : enables broadcast mode, sending invalidations for all keys (or matching prefixes) regardless of whether the client has read them.

PREFIX : in broadcast mode, restricts notifications to keys that start with the given prefix.

OPTIN : only keys read after a CLIENT CACHING YES command are tracked.

OPTOUT : disables tracking for keys read after a CLIENT CACHING OFF command.

NOLOOP : prevents the client that performed the modification from receiving its own invalidation.

Typical workflow:

Start a Redis 6.x server (e.g., redis-server ).

Connect with telnet and enable RESP3: hello 3 .

Enable tracking: client tracking on (optionally add bcast , prefix , etc.).

Read a key (e.g., get a ) to register it.

Modify the key from another client; the tracking client receives an invalidate message.

Examples:

client tracking on
+OK
set a 1
+OK
get a
$1
1

When another client runs set a 2 , the tracking client sees:

>2
$10
invalidate
*1
$1
a

Using BCAST with PREFIX a tracks all keys starting with a . Only those keys generate invalidations, while unrelated keys (e.g., feed:... ) do not.

With OPTIN , tracking starts only after CLIENT CACHING YES is issued; without it, read‑only keys are not tracked. Conversely, OPTOUT stops tracking after CLIENT CACHING OFF .

The NOLOOP flag suppresses self‑generated invalidations, useful to avoid redundant notifications.

Finally, REDIRECT can forward invalidations to a client that only understands RESP2, by sending them through a Pub/Sub channel such as __redis__:invalidate .

All of these features are implemented in Redis’s tracking.c source file.