pg_stat_statements loaded, with patch:

+ pgbench -s 10 -i
+ pgbench -S -c 10 -T 60 --progress=5
pgbench (18devel)
starting vacuum...end.
progress: 5.0 s, 143408.4 tps, lat 0.065 ms stddev 0.052, 0 failed
progress: 10.0 s, 158556.2 tps, lat 0.060 ms stddev 0.035, 0 failed
progress: 15.0 s, 157828.6 tps, lat 0.060 ms stddev 0.036, 0 failed
progress: 20.0 s, 151674.9 tps, lat 0.062 ms stddev 0.045, 0 failed
progress: 25.0 s, 141632.7 tps, lat 0.067 ms stddev 0.040, 0 failed
progress: 30.0 s, 158796.8 tps, lat 0.060 ms stddev 0.036, 0 failed
progress: 35.0 s, 151054.6 tps, lat 0.063 ms stddev 0.046, 0 failed
progress: 40.0 s, 160659.6 tps, lat 0.059 ms stddev 0.035, 0 failed
progress: 45.0 s, 153981.3 tps, lat 0.062 ms stddev 0.037, 0 failed
progress: 50.0 s, 153105.7 tps, lat 0.062 ms stddev 0.049, 0 failed
progress: 55.0 s, 159450.2 tps, lat 0.060 ms stddev 0.035, 0 failed
progress: 60.0 s, 158979.5 tps, lat 0.060 ms stddev 0.035, 0 failed
transaction type: <builtin: select only>
scaling factor: 10
query mode: simple
number of clients: 10
number of threads: 1
maximum number of tries: 1
duration: 60 s
number of transactions actually processed: 9245654
number of failed transactions: 0 (0.000%)
latency average = 0.062 ms
latency stddev = 0.040 ms
initial connection time = 50.616 ms
tps = 154223.966534 (without initial connection time)

pg_stat_statements loaded, without patch:

+ pgbench -s 10 -i
+ pgbench -S -c 10 -T 60 --progress=5
pgbench (18devel)
starting vacuum...end.
progress: 5.0 s, 144630.1 tps, lat 0.065 ms stddev 0.047, 0 failed
progress: 10.0 s, 159638.0 tps, lat 0.060 ms stddev 0.034, 0 failed
progress: 15.0 s, 158279.1 tps, lat 0.060 ms stddev 0.035, 0 failed
progress: 20.0 s, 150433.4 tps, lat 0.063 ms stddev 0.045, 0 failed
progress: 25.0 s, 159630.2 tps, lat 0.060 ms stddev 0.035, 0 failed
progress: 30.0 s, 157365.3 tps, lat 0.061 ms stddev 0.036, 0 failed
progress: 35.0 s, 148446.3 tps, lat 0.063 ms stddev 0.045, 0 failed
progress: 40.0 s, 155013.4 tps, lat 0.061 ms stddev 0.037, 0 failed
progress: 45.0 s, 154570.3 tps, lat 0.061 ms stddev 0.037, 0 failed
progress: 50.0 s, 148595.7 tps, lat 0.063 ms stddev 0.049, 0 failed
progress: 55.0 s, 155748.6 tps, lat 0.061 ms stddev 0.035, 0 failed
progress: 60.0 s, 156308.7 tps, lat 0.061 ms stddev 0.036, 0 failed
transaction type: <builtin: select only>
scaling factor: 10
query mode: simple
number of clients: 10
number of threads: 1
maximum number of tries: 1
duration: 60 s
number of transactions actually processed: 9243315
number of failed transactions: 0 (0.000%)
latency average = 0.061 ms
latency stddev = 0.039 ms
initial connection time = 39.253 ms
tps = 154155.407337 (without initial connection time)

The above numbers do not include temp tables. To test them, I hacked
pgbench to use temp tables:

create schema templ;
alter table pgbench_accounts set schema templ ;
alter table pgbench_branches set schema templ ;
alter table pgbench_history set schema templ ;
alter table pgbench_tellers set schema templ ;

CREATE OR REPLACE FUNCTION public.login()
 RETURNS event_trigger
 LANGUAGE plpgsql
AS $function$ begin
create temp table pgbench_accounts as select * from templ.pgbench_accounts limit 1;
create temp table pgbench_branches as select * from templ.pgbench_branches limit 1;
create temp table pgbench_history as select * from templ.pgbench_history limit 1;
create temp table pgbench_tellers as select * from templ.pgbench_tellers limit 1;
end;
$function$;

create event trigger login on login execute function login();

temp tables, without patch

+ pgbench -S -c 10 -T 60 --progress=5
pgbench (18devel)
starting vacuum...end.
progress: 5.0 s, 179600.8 tps, lat 0.050 ms stddev 0.029, 0 failed
progress: 10.0 s, 181251.3 tps, lat 0.051 ms stddev 0.032, 0 failed
progress: 15.0 s, 184579.8 tps, lat 0.050 ms stddev 0.028, 0 failed
progress: 20.0 s, 185340.0 tps, lat 0.050 ms stddev 0.027, 0 failed
progress: 25.0 s, 170102.2 tps, lat 0.055 ms stddev 0.041, 0 failed
progress: 30.0 s, 184247.0 tps, lat 0.051 ms stddev 0.028, 0 failed
progress: 35.0 s, 187768.6 tps, lat 0.050 ms stddev 0.027, 0 failed
progress: 40.0 s, 185517.6 tps, lat 0.050 ms stddev 0.034, 0 failed
progress: 45.0 s, 186179.5 tps, lat 0.050 ms stddev 0.027, 0 failed
progress: 50.0 s, 188005.0 tps, lat 0.049 ms stddev 0.027, 0 failed
progress: 55.0 s, 184854.4 tps, lat 0.050 ms stddev 0.034, 0 failed
progress: 60.0 s, 190576.0 tps, lat 0.049 ms stddev 0.027, 0 failed
transaction type: <builtin: select only>
scaling factor: 1
query mode: simple
number of clients: 10
number of threads: 1
maximum number of tries: 1
duration: 60 s
number of transactions actually processed: 11040125
number of failed transactions: 0 (0.000%)
latency average = 0.050 ms
latency stddev = 0.030 ms
initial connection time = 139.621 ms
tps = 184430.801954 (without initial connection time)

Contrary to any "normal" workload, this still aggregates the 10 parallel
sessions' temp table statements:

  query_id              calls     query
  2249050047423342439 │ 1181385 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
  6235824319853410599 │ 1166204 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
  1699131257591049879 │ 1147717 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
 -3332048971696272963 │ 1130036 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
 -6043564579131403500 │ 1105202 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
  6195010893428714792 │ 1095123 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
 -6431540675815678490 │ 1077330 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
  5106269170593406241 │ 1065739 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
 -8943016353683653166 │ 1037755 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
 -5518914812029529229 │ 1033634 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1

with patch:

+ pgbench -S -c 10 -T 60 --progress=5
pgbench (18devel)
starting vacuum...end.
progress: 5.0 s, 181903.0 tps, lat 0.050 ms stddev 0.030, 0 failed
progress: 10.0 s, 169692.8 tps, lat 0.054 ms stddev 0.039, 0 failed
progress: 15.0 s, 189353.0 tps, lat 0.049 ms stddev 0.027, 0 failed
progress: 20.0 s, 191183.2 tps, lat 0.049 ms stddev 0.027, 0 failed
progress: 25.0 s, 184952.4 tps, lat 0.051 ms stddev 0.040, 0 failed
progress: 30.0 s, 187466.2 tps, lat 0.050 ms stddev 0.028, 0 failed
progress: 35.0 s, 190897.7 tps, lat 0.049 ms stddev 0.028, 0 failed
progress: 40.0 s, 183873.0 tps, lat 0.051 ms stddev 0.044, 0 failed
progress: 45.0 s, 187722.6 tps, lat 0.050 ms stddev 0.028, 0 failed
progress: 50.0 s, 190621.6 tps, lat 0.049 ms stddev 0.028, 0 failed
progress: 55.0 s, 184417.7 tps, lat 0.051 ms stddev 0.046, 0 failed
progress: 60.0 s, 181640.5 tps, lat 0.051 ms stddev 0.030, 0 failed
transaction type: <builtin: select only>
scaling factor: 1
query mode: simple
number of clients: 10
number of threads: 1
maximum number of tries: 1
duration: 60 s
number of transactions actually processed: 11118630
number of failed transactions: 0 (0.000%)
latency average = 0.050 ms
latency stddev = 0.034 ms
initial connection time = 123.604 ms
tps = 185692.602764 (without initial connection time)

Now there is only one record for all sessions:

 -8778269477398418330 │ 11118630 │ SELECT abalance FROM pgbench_accounts WHERE aid = $1
  8104237783378095602 │       12 │ create temp table pgbench_history as select * from templ.pgbench_history limit $1
  -108440455751470927 │       12 │ create temp table pgbench_branches as select * from templ.pgbench_branches limit $1
 -4266677110910498212 │       12 │ create temp table pgbench_accounts as select * from templ.pgbench_accounts limit $1
  2367030003062126666 │       12 │ create temp table pgbench_tellers as select * from templ.pgbench_tellers limit $1


Christoph