I understand the cost doesn't have to match actual execution duration and it doesn't really matter if it does as long as we can get the relative ordering of plans roughly similar. That's why I'm suggesting not calling the cost seconds, even if we are trying to roughly approximate them. But I don't feel that strongly about this. -- Michael Mior mm...@apache.org
Le sam. 4 janv. 2020 à 14:18, Vladimir Sitnikov <sitnikov.vladi...@gmail.com> a écrit : > > Michael>although I would be hesitant to refer to "seconds" > > Do you have better ideas? > If my memory serves me well, PostgreSQL uses seconds as well for cost units. > OracleDB is using "singleblock read" for the cost unit. > > Michael>how long execution will take on any particular system > > The idea for the cost is to be able to compare different plans. > The cost does not have to match the actual execution duration. > > Then there might be tuning knobs like "how much seconds a single io lasts". > > Vladimir
