Fine tuning FileMaker Server cache can greatly improve performance in a large or heavily used solution. So, what is the optimal cache setting? I find that the general rule for setting cache is to set the RAM to the recommend setting that FileMaker Server suggests. I would leave the interval set at the default 1 minute, increasing the interval could leave you at a greater risk of loosing data.
Depending on what your solution is designed to do and how active the solution is, and whether you are writing or reading more data, you may be able to adjust the cache to tweak performance. Think of it this way, if you are writing more data by doing more edits or creating more records, then a smaller cache size may improve performance. Smaller chucks of data are written at a time. If you are reading more data, like running reports, then a larger cache size may improve performance since more data will be accessed from RAM instead of having to keep reading from disk.
In Windows Server 2003 or 2008, I recently confirmed that the memory usage on fmserver.exe is directly related to cache size. Whatever the cache is set to, that will be the minimum memory usage plus whatever extra ram is needed by FMS. The cache memory is reserved, regardless if it’s filled up or it’s empty. It kind of works like a RAM disk.
If you pop up Task Manager and click on the Processes tab and find fmserver.exe, watch the memory usage. Then go to the Admin Console, Configuration, Database Server, Databases and change the Cache size and click save. Watch the memory usage for fmserver.exe and you’ll see it change as you change the cache. There is need to restart FMS. Now you can tweak the cache setting until you find the optimum performance.