Pub/sub vs streams comparison in Redis - Visual Side-by-Side Comparison

Concept Flow - Pub/sub vs streams comparison

Publish message

↓

Subscribers get message

↓

No message history

↓

Messages lost if offline

↓

Simple, real-time only

↓

Choose based on use case

Shows the flow of messages in Pub/Sub and Streams, highlighting real-time delivery vs durable storage.

Execution Sample

Redis

PUBLISH news "Hello"
SUBSCRIBE news
XADD mystream * message "Hello"
XREAD COUNT 1 STREAMS mystream 0

Publishes a message to a channel and adds a message to a stream, then reads from the stream.

Execution Table

Step	Command	Action	Result
1	PUBLISH news "Hello"	Send message to 'news' channel	Subscribers to 'news' receive 'Hello' immediately
2	SUBSCRIBE news	Subscribe client to 'news' channel	Client will receive future messages published to 'news'
3	XADD mystream * message "Hello"	Add message to 'mystream' stream	Message stored with ID, durable in stream
4	XREAD COUNT 1 STREAMS mystream 0	Read one message from 'mystream' starting at ID 0	Returns the stored message 'Hello'
5	PUBLISH news "World"	Send another message to 'news' channel	Subscribers receive 'World' immediately
6	XREAD COUNT 1 STREAMS mystream 0	Read next message from 'mystream'	No new message, returns empty
7	Client offline during PUBLISH	Message sent to 'news' while client offline	Client misses message, no recovery
8	Client offline during XADD	Message added to stream while client offline	Client can read message later from stream

💡 Execution stops after showing message delivery and storage differences between Pub/Sub and Streams.

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	After Step 8
PubSub Channel 'news'	empty	message 'Hello' sent	message 'Hello' sent	message 'World' sent	message 'World' sent
Stream 'mystream'	empty	message 'Hello' stored	message 'Hello' stored	message 'Hello' stored	message 'Hello' stored

Key Moments - 3 Insights

Why does a subscriber miss messages if offline in Pub/Sub?

Because Pub/Sub delivers messages only to connected clients at publish time (see execution_table step 7). Offline clients do not get stored messages.

How does Streams ensure message durability?

Streams store messages with IDs in a log, so clients can read messages later even if they were offline (see execution_table steps 3, 4, and 8).

Can Pub/Sub messages be replayed after delivery?

No, Pub/Sub messages are transient and not stored, so they cannot be replayed (see execution_table step 7).

Visual Quiz - 3 Questions

Look at the execution_table, what happens at step 4 when reading from the stream?

A The stored message 'Hello' is returned

B No message is returned

C A new message is published to the channel

D The stream is deleted

💡 Hint

Check the 'Result' column in execution_table row for step 4

At which step does the Pub/Sub subscriber miss a message due to being offline?

A Step 2

B Step 7

C Step 3

D Step 8

💡 Hint

Look for the step describing client offline during PUBLISH in execution_table

If you want to replay messages after being offline, which Redis feature should you use?

A Pub/Sub

B Sorted Sets

C Streams

D Hashes

💡 Hint

Refer to key_moments about message durability and replay

Concept Snapshot

Pub/Sub delivers messages instantly to connected clients only.
No message history; offline clients miss messages.
Streams store messages with IDs for durability.
Clients can read and replay messages later.
Choose Pub/Sub for simple real-time needs.
Choose Streams for reliable, replayable messaging.

Full Transcript

This visual execution compares Redis Pub/Sub and Streams. Pub/Sub sends messages immediately to connected subscribers but does not store messages. If a subscriber is offline, it misses messages. Streams store messages with unique IDs, allowing clients to read messages later, even if they were offline. The execution table shows publishing and subscribing steps, message storage in streams, and how clients read messages. Key moments clarify why Pub/Sub messages are transient and Streams provide durability. The quiz tests understanding of message delivery, offline behavior, and replay capabilities. This helps beginners see the practical differences and choose the right Redis feature for their needs.