Re: pgsql: pgstat: add/extend tests for resetting various kinds of stats.

Andres Freund <andres@anarazel.de> writes:
> pgstat: add/extend tests for resetting various kinds of stats.

crake just failed [1] with what appears to be a race condition in
a test case added by this commit:

diff -U3 /home/andrew/bf/root/HEAD/pgsql/src/test/regress/expected/stats.out
/home/andrew/bf/root/HEAD/pgsql.build/src/test/recovery/tmp_check/results/stats.out
--- /home/andrew/bf/root/HEAD/pgsql/src/test/regress/expected/stats.out    2022-07-18 13:32:25.155847949 -0400
+++ /home/andrew/bf/root/HEAD/pgsql.build/src/test/recovery/tmp_check/results/stats.out    2022-09-15
12:44:10.022975164-0400 
@@ -563,7 +563,7 @@
 SELECT sessions > :db_stat_sessions FROM pg_stat_database WHERE datname = (SELECT current_database());
  ?column?
 ----------
- t
+ f
 (1 row)

 -- Test pg_stat_bgwriter checkpointer-related stats, together with pg_stat_wal

It seems likely to me that the n_sessions increment hasn't made it to
shared memory because some background process happened to have a lock on
the stats entry when we tried.  Don't we need a pg_stat_force_next_flush()
call before trying to inspect the sessions count?

BTW, the header comment for pgstat_report_stat is badly in need of
copy-editing.

            regards, tom lane

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=crake&dt=2022-09-15%2016%3A18%3A30