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Enabling Long Polling in Amazon SQS Queues

These AWS SDK for Go examples show you how to:

You can download complete versions of these example files from the aws-doc-sdk-examples repository on GitHub.

Scenario

Long polling reduces the number of empty responses by allowing Amazon SQS to wait a specified time for a message to become available in the queue before sending a response. Also, long polling eliminates false empty responses by querying all of the servers instead of a sampling of servers. To enable long polling, you must specify a non-zero wait time for received messages. You can do this by setting the ReceiveMessageWaitTimeSeconds parameter of a queue or by setting the WaitTimeSeconds parameter on a message when it is received.

The code uses these methods of the Amazon SQS client class:

Prerequisites

Enable Long Polling When Creating a Queue

This example creates a queue with long polling enabled. If the queue already exists, no error is returned.

Create a new Go file named CreateLPQueue.go. You must import the relevant Go and AWS SDK for Go packages by adding the following lines.

import (
    "flag"
    "fmt"
    "strconv"

    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/sqs"
)

Get the queue name and wait time from the command line. Ensure that the wait time is between 0 (zero) and 20 seconds.

queue := flag.String("q", "", "The name of the queue")
waitTime := flag.Int("w", 10, "How long, in seconds, to wait for long polling")
flag.Parse()

if *queue == "" {
    fmt.Println("You must supply a queue name (-q QUEUE")
    return
}

if *waitTime < 1 {
    *waitTime = 1
}

if *waitTime > 20 {
    *waitTime = 20
}

Initialize a session that the SDK will use to load credentials from the shared credentials file, ~/.aws/credentials and the default AWS Region from ~/.aws/config.

sess := session.Must(session.NewSessionWithOptions(session.Options{
    SharedConfigState: session.SharedConfigEnable,
}))

Create a service client and call CreateQueue, passing in the time to wait for messages.

svc := sqs.New(sess)

result, err := svc.CreateQueue(&sqs.CreateQueueInput{
    QueueName: queueName,
    Attributes: aws.StringMap(map[string]string{
        "ReceiveMessageWaitTimeSeconds": strconv.Itoa(*waitTime),
    }),
})

See the complete example on GitHub.

Enable Long Polling on an Existing Queue

Create a new Go file named ConfigureLPQueue.go.

You must import the relevant Go and AWS SDK for Go packages by adding the following lines.

import (
    "flag"
    "fmt"
    "strconv"

    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/sqs"
)

Get the queue name and the optional timeout value from the command line. Ensure that the wait time is between 1 and 20 seconds.

queue := flag.String("q", "", "The name of the queue")
waitTime := flag.Int("w", 10, "The wait time, in seconds, for long polling")
flag.Parse()

if *queue == "" {
    fmt.Println("You must supply a queue name (-q QUEUE")
    return
}

if *waitTime < 1 {
    *waitTime = 1
}

if *waitTime > 20 {
    *waitTime = 20
}

Initialize a session that the SDK will use to load credentials from the shared credentials file, ~/.aws/credentials, and a default AWS Region from ~/.aws/config.

sess := session.Must(session.NewSessionWithOptions(session.Options{
    SharedConfigState: session.SharedConfigEnable,
}))

Get the URL of the queue.

svc := sqs.New(sess)

result, err := svc.GetQueueUrl(&sqs.GetQueueUrlInput{
    QueueName: queue,
})

The URL is in the QueueUrl property of the returned object.

queueURL := result.QueueUrl

Update the queue to enable long polling with a call to SetQueueAttributes, passing in the queue URL.

_, err := svc.SetQueueAttributes(&sqs.SetQueueAttributesInput{
    QueueUrl: queueURL,
    Attributes: aws.StringMap(map[string]string{
        "ReceiveMessageWaitTimeSeconds": strconv.Itoa(aws.IntValue(waitTime)),
    }),
})

See the complete example on GitHub.

Enable Long Polling on Message Receipt

Create a new Go file named ReceiveLPMessage.go.

You must import the relevant Go and AWS SDK for Go packages by adding the following lines.

import (
    "flag"
    "fmt"

    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/sqs"
)

Get the queue name and optional visibility and wait time values from the command line. Ensure that the visibility is between 0 (zero) seconds and 12 hours and that the wait time is between 0 and 20 seconds.

queue := flag.String("q", "", "The name of the queue")
waitTime := flag.Int64("w", 10, "How long the queue waits for messages")
flag.Parse()

if *queue == "" {
    fmt.Println("You must supply a queue name (-q QUEUE")
    return
}

if *waitTime < 0 {
    *waitTime = 0
}

if *waitTime > 20 {
    *waitTime = 20
}

Initialize a session that the SDK will use to load credentials from the shared credentials file, ~/.aws/credentials and the default AWS Region from ~/.aws/config.

sess := session.Must(session.NewSessionWithOptions(session.Options{
    SharedConfigState: session.SharedConfigEnable,
}))

Create a service client and call GetQueueUrl to get the URL of the queue.

svc := sqs.New(sess)

result, err := svc.GetQueueUrl(&sqs.GetQueueUrlInput{
    QueueName: queue,
})

Call ReceiveMessage to get the messages, using long polling, from the queue.

result, err := svc.ReceiveMessage(&sqs.ReceiveMessageInput{
    QueueUrl: queueURL,
    AttributeNames: aws.StringSlice([]string{
        "SentTimestamp",
    }),
    MaxNumberOfMessages: aws.Int64(1),
    MessageAttributeNames: aws.StringSlice([]string{
        "All",
    }),
    WaitTimeSeconds: waitTime,
})

Display the IDs of the mesages.

    fmt.Println("Message IDs:")

    for _, msg := range msgs {
        fmt.Println("    " + *msg.MessageId)
    }

See the complete example on GitHub.