Over the last few weeks I have been spending some time at one particular customer site and besides looking at their Notes and Domino environment as such I've been trying to diagnose some performance issues they have been having with their Notes 8.0.2 installation. Users were experiencing client hangs and general seeing the spinning Vista wheel of death while the client was "busy". After diagnosing and monitoring server and network load I was asked to look at the client installation since server and network load didn't appear to be an issue.
I spent some time looking into the issue and with previous lessons in mind I asked about their virus scanning setup (Trend Micro). Notes data-directory was already omitted from scans which is part of the recommended best practices. After looking further into the matter I saw that the cache.ndk was relocated as part of a startup script to the users %TEMP% directory using the "Cache" notes.ini setting. This was also fine as the data-directory was kept on a network share.
The relocated cache was the cause however. Not the cache.ndk as such but the fact that the cache.ndk was now realtime virus scanned really slowed down the Notes client. The cache.ndk was now realtime scanned as it was moved out of the data-directory. Pushing out a new virus scan definition excluding %TEMP%\cache.ndk really sped up the client.
So there it is - be aware of realtime scanning when it comes to Notes client performance.
Update: We also exluded the Java shared classes file from the scan. This file is placed in %TEMP%\xpdplat by default.