>I think it's related to the problem of figuring out how many dead tuples you expect to find in the overall heap, which you need to do to have >any hope of this being a comprehensive estimate.
An estimate of number of index scans while vacuuming can be done using estimate of total dead tuples in the relation and maintenance work mem. n_dead_tuples in pg_stat_all_tables can be used as an estimate of dead tuples. Following can be a way to estimate, if nindexes == 0 index_scans =0 else if pages_all_visible index_scans =0 else index_scans = Max((n_dead_tuples * space occupied by single dead tuple)/m_w_m,1) This estimates index_scans = 1 if n_dead_tuples = 0 assuming lazy scan heap is likely to find some dead_tuples. If n_dead_tuples is non zero the above estimate gives a lower bound on number of index scans possible. Thank you, Rahila Syed
