There is nothing between the first and second time you ran this query, so where did this vacuum analyze .. record came?
Because of the pg_stat_statements_reset() function call to reset the first
query, when the query executed second time the above statement is appeared
as the select query is limiting the result to 5.
2. bench=# SELECT pg_stat_statements_reset(0,0,s.queryid) FROM pg_stat_statements AS s bench-# WHERE s.query = 'UPDATE pgbench_branches SET bbalance = bbalance + $1 WHERE bid = $2';
bench=#
I think it would be good if you show the output of pg_stat_statements_reset statement instead of showing empty line.
The pg_stat_statements_reset() function just returns void, because
of this reason, already existing _reset() call also just lists the empty
line, I also followed the same.
I feel it is better to add the return data for all the _reset() function calls
or leave it as empty.
Another minor point is that in the second statement (pg_stat_statements_reset), you seem to have made it a two-line statement whereas first one looks to be a single-line statement, it would be good from the readability point of view if both looks same. I would prefer the second to look similar to the first one.
