SBob <sbob@xxxxxxxxxxxxxxxxxxxxx> writes: > I do see older backend_start values (from around 6 hours ago). However I am confused as to how a connection to one database in a cluster can prevenr vacuum from cleaning up row versions in a table within another database. How is that possible since onle one database has access to this table? Because the snapshot-horizon calculations are done system-wide. We can't just lobotomize them to only consider the current DB, because that would result in wrong row-cleanup decisions for shared catalogs. There are some attempts to refine that when vacuuming a non-shared table, but that can only go so far given the limited amount of state that backends expose about this. Doing better would require expending more effort in transaction start/transaction stop/snapshot creation, which are hot spots so it hasn't seemed like it'd be a good tradeoff. regards, tom lane
