Sorry, I got tunnel vision about the how the threshold was computed, and forgot about the thing it was compared to. There is a "secret" data point in the stats collector called changes_since_analyze. This is not exposed in the pg_stat_user_tables. But I think it should be as I often have wanted to see it.
Sounds like a very good idea to me - any way I could help to make such a thing happen?
It should be fairly easy to implement because the other columns are already there to show you the way, and if you want to try your hand at hacking pgsql it would be a good introduction to doing so.
Look at each instance in the code of n_dead_dup and pg_stat_get_dead_tuples, and those are the places where changes_since_analyze also need to be addressed, in an analogous manner (assuming it is isn't already there.)
git grep 'n_dead_tup'
It looks like we would need to add an SQL function to retrieve the data, then incorporate that function into the view definitions that make up the pg_stat_user_tables etc. views. and of course update the regression test and the documentation.
Other than implementing it, we would need to convince other hackers that this is desirable to have. I'm not sure how hard that would be. I've looked in the archives to see if this idea was already considered but rejected, but I don't see any indication that it was previously considered.
