On Fri, Oct 16, 2020 at 11:04 PM Bruce Momjian <br...@momjian.us> wrote: > > On Thu, Oct 15, 2020 at 11:41:23AM +0800, Julien Rouhaud wrote: > > On Wed, Oct 14, 2020 at 10:40 PM Bruce Momjian <br...@momjian.us> wrote: > > > There is that, and log_line_prefix, which I can imaging being useful. > > > My point is that if the queryid is visible, there should be a reason it > > > defaults to show empty. > > > > I did some naive benchmarking. Using a custom pgbench script with this > > query: > > > > SELECT * > > FROM pg_class c > > JOIN pg_attribute a ON a.attrelid = c.oid > > ORDER BY 1 DESC > > LIMIT 1; > > > > I can see around 2% overhead (this query is reported with ~ 3ms > > latency average). Adding a few joins, overhead goes down to 1%. > > That number is too high to enable this by default. I suggest we either > improve the performance of this, or clearly document that you have to > enable the hash computation to see the pg_stat_activity and > log_line_prefix fields.
I realize that I didn't update the documentation part to reflect the new GUC. I'll fix that and add more warnings about the requirements to have values displayed in pg_stat_acitivity and log_line_prefix.
