BUG #17307: Performance deviation between the multiple iterations (NOPM & TPM values).

PG Bug reporting form <noreply@postgresql.org> writes:

NOPM values captured with HammerDB-v4.3 scripts (schema_tpcc.tcl and
test_tpcc.tcl ) for multiple trails.
The expected performance deviation between multiple trials should be less
than 2%

According to who? Even if you'd provided an easily reproducible
example, I doubt we'd accept this as a bug. Adding more sessions
does not have zero cost.

regards, tom lane

As per HammerDB documentation, the same test running for multiple iterations
in the same Hardware gives less deviation (1%-2%)

We noticed the TPC-C performance(NOPM/TPM) deviation is >2% to 21% with
virtual users(1 to 250 for 2 socket system) on running multiple
iterations(5-6 runs).

Checked on different configurations/ system settings as below :

1.Reduced Max connection i.e., lower connections(example max_connections 1700
to 200 in postgres.conf )

2.Reduced warehouses in schema build i.e. pg_count_ware 800 to pg_count_ware
400/200

3.For each run/iteration rebuild schema(delete schema after results
captured in each iteration and delete/drop tpcc, restart postgres and
rebuild schema for next iteration)

4.For each Iteration unmount and mount /data forlder from SSD.

5.Numa settings like taskset/core pinning and SMT-OFF/SMT-ON.

6 Test run on different NUMA nodes like numactl --interleave=all or
numa auto
balancing.

7.With default PostgreSQL.conf and less virtual users(like
1,2,4,8,12,16,20) and small warehouse like 20 and pg_num_vu 4

8.Run HammerDB in client Machine and PostgreSQL in Master Machine.

Here are the questions:

1. What is the right way to test PostgreSQL with HammerDB for multiple
iterations?

2. Is the performance deviation on multiple runs is expected because of raw
Postgres performance?

3. Can "CPU usage, I/O volume, I/O Latency & HDD/SSD latency" be the reason
for deviation?

Thanks

On Fri, 3 Dec 2021 at 00:22, Tom Lane <tgl@sss.pgh.pa.us> wrote: