XADD for adding entries in Redis

Introduction

XADD lets you add new messages to a Redis stream, which is like a list that keeps data in order.

You want to record events like user actions in order.

You need to log messages from devices or sensors over time.

You want to build a chat app where messages are stored in order.

You want to track changes or updates in a system step-by-step.

Syntax

Redis

XADD stream_name [MAXLEN ~ max_length] * field1 value1 [field2 value2 ...]

The * means Redis will generate a unique ID for the new entry based on the current time.

MAXLEN ~ max_length trims the stream to keep it from growing too big, but it does this approximately.

Examples

Adds a new entry with fields 'temperature' and 'humidity' to 'mystream'. Redis creates the ID.

Redis

XADD mystream * temperature 22 humidity 60

Adds a new entry with fields 'event' and 'user' and trims the stream to about 1000 entries.

Redis

XADD mystream MAXLEN ~ 1000 * event login user alice

Adds a single field 'message' with a text value to the stream.

Redis

XADD mystream * message "Hello, world!"

Sample Program

Adds two order entries to the 'orders' stream and then reads all entries from it.

Redis

XADD orders * product_id 123 quantity 2
XADD orders * product_id 456 quantity 1
XRANGE orders - +

Important Notes

XADD runs in O(1) time, so adding entries is very fast even for large streams.

Each entry uses space proportional to the number of fields and their values.

A common mistake is forgetting the * for the ID, which causes an error.

Use XADD when you want ordered, append-only logs; use SET for single key-value pairs.

Summary

XADD adds new entries to a Redis stream with a unique ID.

You can limit stream size with MAXLEN to save memory.

Entries are stored in order and can have multiple fields.