Because throttling policies apply to all Exchange users, it's unlikely that CPU usage would exceed the CPUStartPercent limit on an Exchange Client Access server, because individual users or applications cannot gain enough CPU utilization to affect server operation. At CPUStartPercent, the delay is 0 (a thread yield) and it increases linearly up to 500 msec at 100% CPU usage. The delay time is linearly proportional to CPU usage. If a batch EWS request to get 100 items is passed, the server will check the CPU usage 100 times (once per item) for a maximum delay of 50 seconds. This delay is capped at 500 milliseconds (msecs) at a theoretical 100% CPU usage per EWS request. ![]() When this threshold is exceeded, inbound connections to EWS are delayed. This allows the process to respond appropriately to quick spikes in CPU utilization. The sampling logic the Client Access server performs for this value is an average over a 10 second rolling window. You cannot change the value of this policy, but knowing about it can help you troubleshoot performance issues. When the average CPU utilization of Exchange processes running on the Client Access server - including, but not limited to, the EWS process - exceeds the value specified by this policy, inbound requests will be delayed to reduce CPU utilization. The CPUStartPercent throttling policy can affect EWS performance when you are running Exchange 2010. The throttling polices in Exchange affect not only EWS, but also all client connections to the Exchange server, including the protocols used by Office Outlook, Outlook Web App, and Exchange ActiveSync. ![]() When you design multi-threaded applications that will access a large number of mailboxes, or when many clients are accessing the same mailbox, consider the limits on concurrency that the default policy applies to Exchange. Because throttling parameter values cannot be discovered programmatically, your client design specifications should include a plan for the application to adapt to different potential throttling limits. Client and service applications that are designed to access different versions of Exchange will need to account for these settings, whether they be default values, custom values set by an Exchange administrator, or, as for Exchange Online, set by default and not discoverable. Different versions of Exchange have different default values for the EWS throttling parameters. If you are an application developer, you need to factor throttling into your application design. It is more important for you to be aware of the considerations for designing an application that functions within throttling limits and reacts appropriately to throttling scenarios. Because setting values vary across versions, and because Exchange administrators can change the default throttling policies for on-premises deployments, this article does not provide the default setting values. Specific throttling setting values are only accurate for a specific version of Exchange. As applicable, this article also identifies differences in throttling policies in different versions of Exchange.ĭefault throttling policy, access to throttling policy, and throttling policy configuration differs between Exchange Online and Exchange on-premises. This article identifies the different throttling policies and service limits for EWS, whether you are targeting Exchange Online or versions of Exchange on-premises starting with Exchange Server 2010. When you design applications that use EWS, it is important to account for throttling policies, to help ensure application reliability and the health of your Exchange server. The result is that a user may be within their throttling limit and still experience slowdowns until the health of the resource is back to operational levels.Įach client access protocol in Exchange, including EWS, has a throttling policy. When high load factors are detected that degrade the performance of these resources, EWS connections are throttled proportionally based on the amount that each caller has contributed to this high load condition. ![]() Exchange constantly monitors the health of critical infrastructure resources, such as mailbox databases. Throttling is a reactive response to overuse of system resources that may affect service reliability and functionality. Throttling in Exchange helps to ensure server reliability and uptime by limiting the amount of server resources that a single user or application can consume. The article provides information about EWS throttling in Exchange Online, Exchange Online as part of Office 365, and on-premises versions of Exchange starting with Exchange 2010. ![]() Provided by: Glen Scales Michael Mainer, Microsoft Corporation Learn about the throttling policies that affect EWS when you are using Exchange.
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