Worker Role process - Configuration value polling

Question

I have a Worker Role which processes items off a queue. It is basically an infinite loop which pops items off of the queue and asynchronously processes them.

I have two configuration settings (PollingInterval and MessageGetLimit) which I want the worker role to pick up when changed (so with no restart required).

private TimeSpan PollingInterval 
{
    get
    {
        return TimeSpan.FromSeconds(Convert.ToInt32(RoleEnvironment.GetConfigurationSettingValue("PollingIntervalSeconds")));
    }
}

private int MessageGetLimit 
{ 
    get 
    {
        return Convert.ToInt32(RoleEnvironment.GetConfigurationSettingValue("MessageGetLimit"));
    } 
}

public override void Run()
{
    while (true)
    {
        var messages = queue.GetMessages(MessageGetLimit);

        if (messages.Count() > 0)
        {
            ProcessQueueMessages(messages);
        }
        else
        {
            Task.Delay(PollingInterval);
        }
    }
}

Problem:

During peak hours, the while loop could be running a couple of times per second. This means that it would be querying the config items up to 100,000 times per day.

Is this detrimental or inefficient?

Answer 1

Upfront disclaimer, I haven't used RoleEnvironments.

The MDSN documentation for GetConfigurationSettingValue states that the configuration is read from disk. http://msdn.microsoft.com/en-us/library/microsoft.windowsazure.serviceruntime.roleenvironment.getconfigurationsettingvalue.aspx. So it is sure to be slow when called often.

The MSDN documentation also shows that there is an event fired when a setting changes. http://msdn.microsoft.com/en-us/library/microsoft.windowsazure.serviceruntime.roleenvironment.changed.aspx. You can use this event to only reload the settings when they have actually changed.

Here is one (untested, not compiled) approach.

private TimeSpan mPollingInterval;
private int mMessageGetLimit;

public override void Run()
{
    // Refresh the configuration members only when they change.
    RoleEnvironment.Changed += RoleEnvironmentChanged;

    // Initialize them for the first time
    RefreshRoleEnvironmentSettings();

    while (true)
    {
        var messages = queue.GetMessages(mMessageGetLimit);

        if (messages.Count() > 0)
        {
            ProcessQueueMessages(messages);
        }
        else
        {
            Task.Delay(mPollingInterval);
        }
    }
}

private void RoleEnvironmentChanged(object sender, RoleEnvironmentChangedEventArgs e)
{
    RefreshRoleEnvironmentSettings();    
}

private void RefreshRoleEnvironmentSettings()
{
    mPollingInterval = TimeSpan.FromSeconds(Convert.ToInt32(RoleEnvironment.GetConfigurationSettingValue("PollingIntervalSeconds")));
    mMessageGetLimit = Convert.ToInt32(RoleEnvironment.GetConfigurationSettingValue("MessageGetLimit"));
}