XACK for acknowledging messages in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command XACK do?

It acknowledges one or more messages in a Redis stream, marking them as processed so they won't be delivered again to the same consumer group.

beginner

Why is acknowledging messages important in Redis streams?

Acknowledging messages confirms they were processed successfully, preventing them from being redelivered and helping manage message flow reliably.

beginner

What parameters does the XACK command require?

It requires the stream name, the consumer group name, and one or more message IDs to acknowledge.

beginner

If you run XACK mystream mygroup 1526985058136-0, what happens?

The message with ID 1526985058136-0 in the stream mystream is marked as acknowledged for the consumer group mygroup.

intermediate

Can XACK acknowledge multiple messages at once?

Yes, you can list multiple message IDs after the stream and group names to acknowledge several messages in one command.

What is the main purpose of the Redis XACK command?

A To add new messages to a stream

B To delete a stream

C To acknowledge processed messages in a stream

D To create a consumer group

XACK marks messages as processed so they won't be delivered again to the same consumer group.

Which of these is NOT a required parameter for XACK?

A Consumer name

B Consumer group name

C Message ID(s)

D Stream name

XACK needs the stream, group, and message IDs, but not the consumer name.

What happens if you acknowledge a message that was never delivered to your consumer group?

A The command returns an error

B The message is acknowledged anyway

C The message is deleted from the stream

D Nothing happens, no acknowledgment is recorded

Only messages pending for the group can be acknowledged; others are ignored.

Can XACK be used to acknowledge messages from multiple streams at once?

A Yes, you can list multiple streams

B No, it works on one stream at a time

C Only if streams belong to the same group

D Only if streams have the same name

XACK acknowledges messages only from one stream per command.

What does XACK return after successful acknowledgment?

A The number of messages acknowledged

B The list of acknowledged message IDs

C The total number of messages in the stream

D A confirmation string 'OK'

XACK returns how many messages were acknowledged successfully.

Explain how the XACK command helps manage message processing in Redis streams.

Think about how you tell Redis you finished handling messages.

Describe the parameters needed for the XACK command and what each represents.

Consider what you need to identify the messages and the group.