Multiply the number of updates times the number of indexes. Then consider that with such a small table, there's going to be contention for the same rows. Updat

Multiply the number of updates times the number of indexes. Then consider that with such a small table, there's going to be contention for the same rows. Updates actually create new rows, so vacuum needs to be able to remove older, no-longer-visible versions of the row. But vacuum can't keep up, because at any given time many versions of the row are potentially visible.