9.5: pg_stat_statement and pgbench execution time discrepancies

[Pavel Suderevsky <psuderevsky@xxxxxxxxx>]

Hi,

During performance tests it was mentioned that pgbench common results are being different from what pg_stat_statements provides.

PostgreSQL version 9.5.3, centos 7.2. First run after pg_stat_extension created and first pgbench run.

pgbench -c 30 -T 300 -U postgres -P 10 -r -v

statement latencies in milliseconds:

        0.003431        \set nbranches 1 * :scale

        0.001046        \set ntellers 10 * :scale

        0.000891        \set naccounts 100000 * :scale

        0.001356        \setrandom aid 1 :naccounts

        0.000938        \setrandom bid 1 :nbranches

        0.000879        \setrandom tid 1 :ntellers

        0.000974        \setrandom delta -5000 5000

        0.102258        BEGIN;

        0.228744        UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;

        0.156087        SELECT abalance FROM pgbench_accounts WHERE aid = :aid;

        17.715645       UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;

        6.222220        UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;

        0.294592        INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);

        0.502843        END;

pg_stat_statements 

Example 1

query               | UPDATE pgbench_accounts SET abalance = abalance + ? WHERE aid = ?;

calls               | 118804

total_time          | 5944.19700000145

min_time            | 0.017

max_time            | 146.501

mean_time           | 0.0500336436483624

stddev_time         | 0.860838186600729

rows                | 118804

Example 2

query               | INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (?, ?, ?, ?, CURRENT_TIMESTAMP);

calls               | 118804

total_time          | 16533.2040000006

min_time            | 0.075

max_time            | 1.583

mean_time           | 0.139163698191979

stddev_time         | 0.0342061695940176

rows                | 118804

 

Could anybody explain why results are different? Where is an inaccuracy - in pg_stat_statements or pgbench?

Thanks in advance.