On Thu, 20 Jan 2022 at 17:01, Peter Geoghegan <p...@bowt.ie> wrote: > > Then there's the fact that you > really cannot think about the rate of XID consumption intuitively -- > it has at best a weak, unpredictable relationship with anything that > users can understand, such as data stored or wall clock time.
This confuses me. "Transactions per second" is a headline database metric that lots of users actually focus on quite heavily -- rather too heavily imho. Ok, XID consumption is only a subset of transactions that are not read-only but that's a detail that's pretty easy to explain and users get pretty quickly. There are corner cases like transactions that look read-only but are actually read-write or transactions that consume multiple xids but complex systems are full of corner cases and people don't seem too surprised about these things. What I find confuses people much more is the concept of the oldestxmin. I think most of the autovacuum problems I've seen come from cases where autovacuum is happily kicking off useless vacuums because the oldestxmin hasn't actually advanced enough for them to do any useful work. -- greg
