Been debating with my company's app vendor regarding parallelism. They have maintained that Maxdop = 1 has significant performance improvements for the app/db but they have provided absolutely no proof of this.
I have tested various DOP/CT settings and found a 28% overall performance improvement from automated testing, when using Maxdop 4 (8 hyperthreaded cores) and CT 150.
The vendor's DBA recently said: "There is an issue with internal processes of MSSQL that are able to use this value even if DOP is ‘1’, there are SPID’s lower than 51 in a MSSQL server that is using it, ghost cleanups and like this."
I have researched this and, despite fairly scant information, Paul Randall at least says that ghost cleanup is always single-threaded, so apparently the vendor's dba is incorrect?
Any thoughts on the effect of CT when Maxdop =1?