Earlier this year Microsoft released an important hotfix for .NET 4.5:
A .NET Framework 4.5-based application that excessively uses ExecutionContext objects or WCF may result in too many objects being pinned on the Garbage Collector heap. This causes heap fragmentation along with an increase in memory and CPU usage by the Garbage Collector.
This hotfix prevents objects from being pinned in certain cases. As Exchange 2013 is built upon .NET 4.5 this hotfix can will reduce the memory consumption of the store worker processes
After installing the hotfix, you need to:
- Set the following registry key: HKLMSoftwareMicrosoft.NETFrameworkDisableRetStructPinning=1 (REG_DWORD)
Note that you need to restart the server for the change to become effective.
For more background information see this blog post here