Redis XACK in Golang (Detailed Guide w/ Code Examples)

Use Case(s)

The XACK command in Redis is used with stream data structures. It's specifically utilized to acknowledge the processing of a message from a stream by a consumer. When consumers read messages, they can ensure that no message gets lost during processing by using XACK. Typically, this is used in a system where reliability is required and message loss cannot be tolerated such as in messaging queues, event-driven architectures, etc.

Code Examples

Consider a scenario where your application is consuming messages from a stream named "mystream" and the consumer group is named "mygroup".

For the purpose of this example, let's assume that you have already connected to your Redis instance and created a new stream and consumer group.

Let's say that you have read a message and its ID is "1577836800000-0", now you want to acknowledge it:

package main

import (
	"fmt"
	"github.com/go-redis/redis/v8"
	"context"
)

func main() {
	rdb := redis.NewClient(&redis.Options{
		Addr:     "localhost:6379",
		Password: "", 
		DB:       0,
	})

	ctx := context.Background()

	err := rdb.XAck(ctx, "mystream", "mygroup", "1577836800000-0").Err()
	if err != nil {
		panic(err)
	}

	fmt.Println("Message Acknowledged Successfully")
}

This script connects to the Redis server running on localhost and acknowledges the processing of the message with ID "1577836800000-0" in "mystream" by "mygroup".

Best Practices

• Always handle errors after the XACK. If an error occurs and it's not handled, your application might behave unexpectedly.
• Make sure to use context with timeout or deadlines in production code. The above example uses context.Background() which never expires and can cause a goroutine leak if the redis server doesn't respond.

Common Mistakes

• Not acknowledging messages once processed can lead to them being delivered again when a consumer crashes and restarts. This could lead to duplicate processing of messages.
• Acknowledging messages before they are processed can lead to message loss if a consumer crashes after acknowledgement but before processing.

FAQs

Q: Can I acknowledge multiple messages at once?

A: Yes, you can pass multiple IDs to the XAck function to acknowledge multiple messages in one command.

err := rdb.XAck(ctx, "mystream", "mygroup", "1577836800000-0", "1577836900000-0").Err()

Q: What happens if I try to acknowledge a message that does not exist or has already been acknowledged?

A: Redis will silently ignore non-existing IDs or IDs for messages that have already been acknowledged. The XACK command returns the count of IDs actually acknowledged.