On Tue, 2020-03-17 at 16:07 -0500, Justin Pryzby wrote: > > Assume a scale factor >= 1, for example 2, and n live tuples. > > The table has just been vacuumed. > > > > Now we insert m number tuples (which are live). > > > > Then the condition > > > > threshold + scale_factor * live_tuples < newly_inserted_tuples > > > > becomes > > > > 10000000 + 2 * (n + m) < m > > > > which can never be true for non-negative n and m. > > > > So a scale factor >= 1 disables the feature. > > No, this is what we mailed about privately yesterday, and I demonstrated that > autovac can still run with factor=100. I said:
I remember. Can you point out where exactly the flaw in my reasoning is? > > It's a multiplier, not a percent out of 100 (fraction is not a great choice > > of > > words). > > > > &autovacuum_vac_scale, > > 0.2, 0.0, 100.0, > > > > The default is 0.2 (20%), so 100 means after updating/deleting > > 100*reltuples. Yes, exactly. > If 1.0 disabled the feature, it wouldn't make much sense to allow factor up to > 100. True, we could set the upper limit to 2, but it doesn't matter much. Note that this is different from autovacuum_vacuum_scale_factor, because inserted tuples are live, while dead tuples are not. Yours, Laurenz Albe