Both tables are in the same file GDB. Both are indexed on the join field. Running Join Field GP tool. After 13 hours, only 30% finished. It is only step one of about 10 such steps. ArcMap is only using 113 MB of my 12 GB of RAM and only one processor of 8, but I don't know how to make it go faster without chopping the data back into shapefile chunks. It's far too late for that this time and I will have to admit defeat *again* to my employer. Is ArcGIS Desktop simply not capable of handling operations on 20+million record joined file GDB tables?