If you are concerned about the amount of memory SmarterMail is using on your server, one possible way to manage that is by lowering .NET's Garbage Collection (GC) thresholds. A couple of reasons why you would want to control your server's memory imprint include:
- You're running SmarterMail as a standalone application on the server but you feel like SmarterMail's memory is running too high for your liking, or
- You're running multiple .NET applications on the server and you want to limit memory consumption across all applications.
The main advantage to making these changes is that by allowing .NET to be more aggressive with GC you help limit SmarterMail's memory imprint. However, these changes could also have negative affects that need to be considered as well. These include:
- Your CPU might increase due to GC happening more often.
- Your disk I/O reads could increase because some cached files were garbage collected, so they need to be read from disk more often.
- Your SmarterMail server could run slower due to more GC cycles halting the application.
.NET Garbage Collection
Garbage Collection (GC) becomes more aggressive when SmarterMail's physical memory usage reaches 90% of the total memory available. (NOTE: When running other applications on the server, SmarterMail may NOT be consuming 90% on its own -- other applications will also be consuming memory.) Garbage Collection itself compacts collections to prevent paging. While below this 90% threshold, it favors background collections with shorter pauses. On systems with 80GB+ memory, the default threshold ranges from 90% to 97%. Below are some controls and settings that can be configured for .NET and, specifically, garbage collection.
Garbage Collection Threshold
This can be adjusted using DOTNET_GCHighMemPercent as an environment variable with a hexadecimal value. If you wanted GC to become more aggressive at 80% then the hexadecimal value would be 0x50 and if you wanted GC to become more aggressive at 75% then the hexadecimal value would be 0x4B.
Conserve Memory
This setting configures the garbage collector to conserve memory at the expense of more frequent garbage collections and possibly longer pause times. The default value is 0 which implies no change. Values between 1 and 9 are valid and the higher the value the more the garbage collector tries to conserve memory and thus to keep the heap small. If the value is non-zero, the large object heap will be compacted automatically if it has too much fragmentation.
This threshold can be adjusted using DOTNET_GCConserveMemory as an environment variable with a number value between 0 and 9.
Dynamic Adaptation to Application Sizes (DATAS)
Configures the garbage collector to use DATAS. DATAS adapts to application memory requirements, meaning the app heap size should be roughly proportional to the long-lived data size. Enabled by default starting in .NET 9.
This threshold can be adjusted using DOTNET_GCDynamicAdaptationMode as an environment variable with a number value 1 for enabled and 0 for disabled.
Recommendations
If your SmarterMail memory seems to just increase over time, then the following recommendations would be a good starting point. For more information, and to read how to change these environment variables, see the
Runtime configuration options for garbage collection.
DOTNET_GCHighMemPercent set to a value less than 90%. It's hard to give an exact number but start at 80 (hexadecimal value 0x50) then go down if you feel you need more memory available on the server.
DOTNET_GCConserveMemory set to 1. Increasing this value will cause more frequent garbage collection. Start with 1 and increase if you desire different results.
DOTNET_GCDynamicAdaptationMode set to 0 for disabled. Disabling this will help to keep the application heap size consistent.