By default the Windows System File Cache is configured without any minimum or maximum limit. The cache is responsible for managing when to release memory, and this behaviour can be somewhat controlled through the use of hints for the Cache Manager.
WT-2670 being implemented, we used the FILE_FLAG_RANDOM_ACCESS flag by default, which instructs the Cache Manager to keep mapped views of the file in memory as long as possible (until Memory Manager doesn't signal low memory condition).
This had the effect of filling up the System File Cache without releasing memory, which resulted in some users enabling direct_io in order to workaround the problem.
WT-2670 has been implemented we no longer see the System File Cache being greedy, therefore the warning about setting a maximum limit seems moot.
Can we investigate removing this warning as it does not appear to be required any more?
Or perhaps the warning should only be displayed if WT is configured to pass the FILE_FLAG_RANDOM_ACCESS flag to the Cache Manager, which occurs when the user indicates a random workload with the WT_FS_OPEN_ACCESS_RAND WT configuration flag.