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

Use Case(s)

The XPENDING command in Redis is primarily used to monitor a stream and find out information about pending messages. It's commonly used in situations where you would want to track unacknowledged messages, like consumer group settings where multiple consumers are reading data from the same stream.

Code Examples

Here's an example of using the XPENDING command with Redis in Go using the go-redis package. In this example, assume we've already established a connection to a Redis server and have a stream with some pending messages:

package main

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

var ctx = context.Background()

func main() {

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

    // Assume 'mystream' exists and has some pending messages.
    result, err := client.XPending(ctx, "mystream", "").Result()
    
	if err != nil {
		panic(err)
	}

	fmt.Println(result)
}

In the above code, XPENDING with no additional parameters will return general information about the pending entries for the stream.

If you know the specific consumer group and want to get detailed information, you can pass more arguments as shown below:

result, err := client.XPendingExt(ctx, &redis.XPendingExtArgs{
	Stream: "mystream",
	Group: "mygroup",
	Start: "-", 
	End: "+",
	Count: 10,
}).Result()

This will return the list of pending messages up to 10 messages for consumer group 'mygroup'.

Best Practices

• Always handle errors returned by the XPENDING command. Errors can denote issues like the stream not existing or other database access problems.
• Use the XPENDING command judiciously, especially when dealing with large streams and/or numerous consumer groups to avoid heavy memory and CPU usage.

Common Mistakes

• Not considering that XPENDING can return a lot of data if there are many pending messages. This can lead to increased memory utilization. Hence it's advisable to use the count argument to limit the number of responses.
• Using the wrong stream or consumer group name in the command.

FAQs

Q: What happens if I run XPENDING on a stream that doesn't exist?

A: Running XPENDING on a non-existent stream will result in an error. Ensure you have the correct stream name before running the command.

Q: Can I limit the number of pending entries returned by XPENDING?

A: Yes, you can limit the number of pending entries returned using the Count argument in XPENDINGEXT method.