Configuration parameter values that you have set are preserved by the upgrade. Only those parameters that are set at “DEFAULT” in the server configuration file are changed to the new version’s default value. Because some parameter default values are now higher, values that you set in the older version may not be high enough for the new version. The following parameters can cause problems during or after upgrade if they are set too low:
cpu grace time
enable housekeeper GC
The parameter enable xact coordination can cause a problem for RPCs when set at default. These issues are explained the next sections.