I tried doing the upgrade from my starting point of 2.8.6.   Errors.  Recopied 2.86 files (database updates did not seem to take,  so all was well.)  Saw that plugins might be problem,  so i deactivated all my plugins,  copied up 2.9 files again.  Same errors.  Back to 2.8.6 now.  Will wait for specific solutions to my database errors: 

wp database error Unknown system variable ‘NAMES’ for query SET NAMES

happened whether I had plugins active or not ( I have about 15 active plugins,  all that were working in 2.8.6