Q. I have a very large number of MSIxxxxx.LOG files in my Windows temp folder, why?
A. I recently had a server whose C: drive had filled and on examination I found I had over 30 GB of small MSIxxxxx.LOG files in the Windows temporary folder, C:\Windows\Temp. After investigation I found this was caused by verbose logging enabled for the Windows Installer service. This can be confirmed by looking at registry key HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Installer and looking for a String value named Logging which will have various letters making up a string. Each letter represents a certain type of logging which is documented at https://support.microsoft.com/en-us/kb/223300. Below is an example of the system that was having the problem. Every type of logging was enabled which caused the large number of log files to be generated anytime the Windows Installer service tried to perform an action.
The solution is to simply delete the Logging string value which will immediately stop the log files from being created. As a best practice the logging should only be enabled when trying to debug a specific problem.