Tomas Vondra <tomas.von...@2ndquadrant.com> writes: > I've started reviewing this patch, thinking that maybe I could get it > committed as it's marked as RFC. In general I agree with having this > fuature, but I think we need to rethink the GUC because the current > approach is just confusing. > ... > What I think we should do instead is to use two minimum thresholds. > 1) log_min_duration_sample - enables sampling of commands, using the > existing GUC log_statement_sample_rate > 2) log_min_duration_statement - logs all commands exceeding this > I think this is going to be much easier for users to understand.
I agree with Tomas' idea. > The one difference between those approaches is in how they work with > existing current settings. That is, let's say you have > log_min_duration_statement = 1000 > log_statement_sample_rate = 0.01 > then no queries below 1000ms will be logged, and 1% of longer queries > will be sampled. And with the original config (as proposed in v3 of the > patch), this would still work the same way. > With the new approach (two min thresholds) it'd behave differently, > because we'd log *all* queries longer than 1000ms (not just 1%). And > whether we'd sample any queries (using log_statement_sample_rate) would > depend on how we'd pick the default value for the other threshold. Well, we do not need to have a backwards-compatibility problem here, because we have yet to release a version containing log_statement_sample_rate. I do not think it's too late to decide that v12's semantics for that are broken, and either revert that patch in v12, or back-patch a fix to make it match this idea. regards, tom lane