WCF Service Throttling

Question

Lets assume that I'm dealing with a service that involves sending large amounts of data.

If I implement this with WCF, will WCF throttle the service based on how much memory each request takes to serve? Or will I be getting continuous out of memory exceptions each time I receive a large number of hits to my service?

I'm quite curious as to dealing with this problem outside of WCF, I'm still a bit new to service development...

Answer 1

WCF does have a default payload size limit that will reject messages over a certain number of bytes. This is configurable of course in the binding section of your configuration file. Here is a crude example with a basicHttpBinding showing you many of the attributes available to you:

<bindings>
    <basicHttpBinding>
     <binding name="testBinding" maxReceivedMessageSize="2147483647">
      <readerQuotas
        maxDepth="2147483647"
        maxStringContentLength="2147483647"
        maxArrayLength="2147483647"
        maxBytesPerRead="2147483647"
        maxNameTableCharCount="2147483647" />
     </binding>
    </basicHttpBinding>

The idea is that you can create many different bindings that you can use for different scenarios. This is nice as you can fine tune how your services are consumed and only increase the message size limit for the endpoints that need them.

Answer 2

While using the binding attributes and readerQuotas like Andrew Hare suggests will allow for essentially an unlimited size for most practical uses, keep in mind that the you will run into other issues such as timeouts if you accept a long running command, no matter how that service is constructed (using WCF or not).

No matter what the size of your message is, the WCF service will need to be throttled for performance so that it is not flooded. If you are hosting it in IIS or WAS, you will have additional built-in features to those hosting environments that will make your service much more "highly available". However, you still need to pay attention to concurrency issues. The following WCF config provides an example of setting some throttling values.

   <system.serviceModel>

    ...

     <behaviors>
       <serviceBehaviors>
         <behavior name="GenericServiceBehavior">
           <serviceTimeouts transactionTimeout="00:09:10"/>
           <serviceThrottling
             maxConcurrentCalls="20"
             maxConcurrentSessions="20"
             maxConcurrentInstances="20"
           />
         </behavior>
       </serviceBehaviors>
     </behaviors>
   </system.serviceModel>

Answer 3

If you're using NetTCPBinding or NetNamedPipeBinding you can use the MaxConnections property:

<bindings>
  <netTcpBinding>
    <binding name="myTCPBinding" maxConnections="15"/>
  </netTcpBinding>
</bindings>