SignalR Performance

by Patrick Fletcher


This documentation isn't for the latest version of SignalR. Take a look at ASP.NET Core SignalR.

This topic describes how to design for, measure, and improve performance in a SignalR application.

Software versions used in this topic

Previous versions of this topic

For information about earlier versions of SignalR, see SignalR Older Versions.

Questions and comments

Please leave feedback on how you liked this tutorial and what we could improve in the comments at the bottom of the page. If you have questions that are not directly related to the tutorial, you can post them to the ASP.NET SignalR forum or

For a recent presentation on SignalR performance and scaling, see Scaling the Real-time Web with ASP.NET SignalR.

This topic contains the following sections:

Design considerations

This section describes patterns that can be implemented during the design of a SignalR application, to ensure that performance is not being hindered by generating unnecessary network traffic.

Throttling message frequency

Even in an application that sends out messages at a high frequency (such as a realtime gaming application), most applications don't need to send more than a few messages a second. To reduce the amount of traffic that each client generates, a message loop can be implemented that queues and sends out messages no more frequently than a fixed rate (that is, up to a certain number of messages will be sent every second, if there are messages in that time interval to be sent). For a sample application that throttles messages to a certain rate (from both client and server), see High-Frequency Realtime with SignalR.

Reducing message size

You can reduce the size of a SignalR message by reducing the size of your serialized objects. In server code, if you're sending an object that contains properties that don't need to be transmitted, prevent those properties from being serialized by using the JsonIgnore attribute. The names of properties are also stored in the message; the names of properties can be shortened using the JsonProperty attribute. The following code sample demonstrates how to exclude a property from being sent to the client, and how to shorten property names:

.NET server code that demonstrates the JsonIgnore attribute to exclude data from being sent to the client, and the JsonProperty attribute to reduce message size

using Newtonsoft.Json; 
using System; 
public class ShapeModel
    public double Left { get; set; }
    public double Top { get; set; }
    // We don't want the client to get the "LastUpdatedBy" property
    public string LastUpdatedBy { get; set; }

In order to retain readability/ maintainability in the client code, the abbreviated property names can be remapped to human-friendly names after the message is received. The following code sample demonstrates one possible way of remapping shortened names to longer ones, by defining a message contract (mapping), and using the reMap function to apply the contract to the optimized message class:

Client-side JavaScript code that remaps shortened property names to human-readable names

function reMap(smallObject, contract) {
    var largeObject = {};
    for (var smallProperty in contract) {
        largeObject[contract[smallProperty]] = smallObject[smallProperty];
    return largeObject;
var shapeModelContract = {
    l: "left",
    t: "top"
myHub.client.setShape = function (shapeModelSmall) {
    var shapeModel = reMap(shapeModelSmall, shapeModelContract);
    // shapeModelSmall has "l" and "t" properties  but after remapping
    // shapeModel now has "left" and "top" properties

Names can be shortened in messages from the client to the server as well, using the same method.

Reducing the memory footprint (that is, the amount of memory used for the message) of the message object can also improve performance. For example, if the full range of an int is not needed, a short or byte can be used instead.

Since messages are stored in the message bus in server memory, reducing the size of messages can also address server memory issues.

Tuning your SignalR server for performance

The following configuration settings can be used to tune your server for better performance in a SignalR application. For general information on how to improve performance in an ASP.NET application, see Improving ASP.NET Performance.

SignalR configuration settings

  • DefaultMessageBufferSize: By default, SignalR retains 1000 messages in memory per hub per connection. If large messages are being used, this may create memory issues which can be alleviated by reducing this value. This setting can be set in the Application_Start event handler in an ASP.NET application, or in the Configuration method of an OWIN startup class in a self-hosted application. The following sample demonstrates how to reduce this value in order to reduce the memory footprint of your application in order to reduce the amount of server memory used:

    .NET server code in Startup.cs for decreasing default message buffer size

    public class Startup
        public void Configuration(IAppBuilder app)
            // Any connection or hub wire up and configuration should go here
            GlobalHost.Configuration.DefaultMessageBufferSize = 500;

IIS configuration settings

  • Max concurrent requests per application: Increasing the number of concurrent IIS requests will increase server resources available for serving requests. The default value is 5000; to increase this setting, execute the following commands in an elevated command prompt:

    cd %windir%\System32\inetsrv\
    appcmd.exe set config /section:system.webserver/serverRuntime 
  • ApplicationPool QueueLength: This is the maximum number of requests that Http.sys queues for the application pool. When the queue is full, new requests receive a 503 "Service Unavailable" response. The default value is 1000.

    Shortening the queue length for the worker process in the application pool hosting your application will conserve memory resources. For more information, see Managing, Tuning, and Configuring Application Pools.

ASP.NET configuration settings

This section includes configuration settings that can be set in the aspnet.config file. This file is found in one of two locations, depending on platform:

  • %windir%\Microsoft.NET\Framework\v4.0.30319\aspnet.config
  • %windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet.config

ASP.NET settings that may improve SignalR performance include the following:

  • Maximum concurrent requests per CPU: Increasing this setting may alleviate performance bottlenecks. To increase this setting, add the following configuration setting to the aspnet.config file:

    <?xml version="1.0" encoding="UTF-8" ?>
            <applicationPool maxConcurrentRequestsPerCPU="20000" />
  • Request Queue Limit: When the total number of connections exceeds the maxConcurrentRequestsPerCPU setting, ASP.NET will start throttling requests using a queue. To increase the size of the queue, you can increase the requestQueueLimit setting. To do this, add the following configuration setting to the processModel node in config/machine.config (rather than aspnet.config):

    <processModel autoConfig="false" requestQueueLimit="250000" />

Troubleshooting performance issues

This section describes ways to find performance bottlenecks in your application.

Verifying that WebSocket is being used

While SignalR can use a variety of transports for communication between client and server, WebSocket offers a significant performance advantage, and should be used if the client and server support it. To determine if your client and server meet the requirements for WebSocket, see Transports and Fallbacks. To determine what transport is being used in your application, you can use the browser developer tools, and examine the logs to see what transport is being used for the connection. For information on using the browser development tools in Internet Explorer and Chrome, see Transports and Fallbacks.

Using SignalR performance counters

This section describes how to enable and use SignalR performance counters, found in the Microsoft.AspNet.SignalR.Utils package.

Installing signalr.exe

Performance counters can be added to the server using a utility called SignalR.exe. To install this utility, follow these steps:

  1. In Visual Studio, select Tools > NuGet Package Manager > Manage NuGet Packages for Solution

  2. Search for signalr.utils, and select Install.

    Screenshot that shows Microsoft A S P dot NET Signal R Utilities selected.

  3. Accept the license agreement to install the package.

  4. SignalR.exe will be installed to <project folder>/packages/Microsoft.AspNet.SignalR.Utils.<version>/tools.

Installing performance counters with SignalR.exe

To install SignalR performance counters, run SignalR.exe in an elevated command prompt with the following parameter:

SignalR.exe ipc

To remove SignalR performance counters, run SignalR.exe in an elevated command prompt with the following parameter:

SignalR.exe upc

SignalR Performance counters

The utilities package installs the following performance counters. The "Total" counters measure the number of events since the last application pool or server restart.

Connection metrics

The following metrics measure the connection lifetime events that occur. For more information, see Understanding and Handling Connection Lifetime Events.

  • Connections Connected
  • Connections Reconnected
  • Connections Disconnected
  • Connections Current

Message metrics

The following metrics measure the message traffic generated by SignalR.

  • Connection Messages Received Total
  • Connection Messages Sent Total
  • Connection Messages Received/Sec
  • Connection Messages Sent/Sec

Message bus metrics

The following metrics measure traffic through the internal SignalR message bus, the queue in which all incoming and outgoing SignalR messages are placed. A message is Published when it is sent or broadcast. A Subscriber in this context is a subscription on the message bus; this should equal the number of clients plus the server itself. An Allocated Worker is a component that sends data to active connections; a Busy Worker is one that is actively sending a message.

  • Message Bus Messages Received Total
  • Message Bus Messages Received/Sec
  • Message Bus Messages Published Total
  • Message Bus Messages Published/Sec
  • Message Bus Subscribers Current
  • Message Bus Subscribers Total
  • Message Bus Subscribers/Sec
  • Message Bus Allocated Workers
  • Message Bus Busy Workers
  • Message Bus Topics Current

Error metrics

The following metrics measure errors generated by SignalR message traffic. Hub Resolution errors occur when a hub or hub method cannot be resolved. Hub Invocation errors are exceptions thrown while invoking a hub method. Transport errors are connection errors thrown during an HTTP request or response.

  • Errors: All Total
  • Errors: All/Sec
  • Errors: Hub Resolution Total
  • Errors: Hub Resolution/Sec
  • Errors: Hub Invocation Total
  • Errors: Hub Invocation/Sec
  • Errors: Transport Total
  • Errors: Transport/Sec

Scaleout metrics

The following metrics measure traffic and errors generated by the scaleout provider. A Stream in this context is a scale unit used by the scaleout provider; this is a table if SQL Server is used, a Topic if Service Bus is used, and a Subscription if Redis is used. Each stream ensures ordered read and write operations; a single stream is a potential scale bottleneck, so the number of streams can be increased to help reduce that bottleneck. If multiple streams are used, SignalR will automatically distribute (shard) messages across these streams in a way that ensures messages sent from any given connection are in order.

The MaxQueueLength setting controls the length of the scaleout send queue maintained by SignalR. Setting it to a value greater than 0 will place all messages in a send queue to be sent one at a time to the configured messaging backplane. If the size of the queue goes above the configured length, subsequent calls to send will fail immediately with an InvalidOperationException until the number of messages in the queue is less than the setting again. Queueing is disabled by default because the implemented backplanes generally have their own queuing or flow-control in place. In the case of SQL Server, connection pooling effectively limits the number of sends going on at any one time.

By default, only one stream is used for SQL Server and Redis, five streams are used for Service Bus, and queueing is disabled, but these settings can be changed through configuration on SQL Server and Service Bus:

.NET Server Code for configuring table count and queue length for SQL Server backplane

var connectionString = "(your connection string)";
var config = new SqlScaleoutConfiguration(connectionString) { 
TableCount = 3,
MaxQueueLength = 50 };

.NET Server Code for configuring topic count and queue length for Service Bus backplane

string connectionString = "(your connection string)";
var config = new ServiceBusScaleoutConfiguration(connectionString, "YourAppName") { 
TopicCount = 3,
MaxQueueLength = 50 };

A Buffering stream is one that has entered a faulted state; when the stream is in the faulted state, all messages sent to the backplane will fail immediately until the stream is no longer faulting. The Send Queue Length is the number of messages that have been posted but not yet sent.

  • Scaleout Message Bus Messages Received/Sec
  • Scaleout Streams Total
  • Scaleout Streams Open
  • Scaleout Streams Buffering
  • Scaleout Errors Total
  • Scaleout Errors/Sec
  • Scaleout Send Queue Length

For more information on what these counters are measuring, see SignalR Scaleout with Azure Service Bus.

Using other performance counters

The following performance counters may also be useful in monitoring your application's performance.


  • .NET CLR Memory\# bytes in all Heaps (for w3wp)


  • ASP.NET\Requests Current
  • ASP.NET\Queued
  • ASP.NET\Rejected


  • Processor Information\Processor Time


  • TCPv6/Connections Established
  • TCPv4/Connections Established

Web Service

  • Web Service\Current Connections
  • Web Service\Maximum Connections


  • .NET CLR Locks And Threads\# of current logical Threads
  • .NET CLR Locks And Threads\# of current physical Threads

Other Resources

For more information on ASP.NET performance monitoring and tuning, see the following topics: