Re: pgbench results arent accurate

If you have not amended any Postgres config parameters, then you'll get
checkpoints approx every 5 min or so. Thus using a Pgbench run time of
5min is going sometimes miss/sometimes hit a checkpoint in progress -
which will hugely impact test results.

I tend to do Pgbench runs of about 2x checkpoint_timeout - (i.e 10 min
for default configurations). Also for increased repeatability, I do a
manually triggered checkpoint immediately before each run.

regards

Mark

On 13/12/18 1:53 AM, Mariel Cherkassky wrote:
> Hey,
> I installed a new postgres 9.6 on both of my machines. I'm trying to
> measure the differences between the performances in each machine but
> it seems that the results arent accurate.
> I did 2 tests :
>
> 1)In the first test the scale was set to 100 :
> pgbench -i -s 100 -U postgres -d bench -h machine_name
> pgbench -U postgres -d bench  -h machine_name -j 2 -c 16 -T 300
> RUN    TPS - machine1 TPS-machine2
> 1 697 555
> 2 732 861
> 3 784 842
>
>
>
>
>
> 2)In this test the scale was set to 10000 :
> pgbench -i -s 10000 -U postgres -d bench -h machine_name
> pgbench -U postgres -d bench --progress=30 -h machine_name -j 2 -c 16
> -T 300
> RUN TPS-MACHINE1 TPS-MACHINE2
> 1 103 60
> 2 63 66
> 3 74 83
> 4 56 61
> 5 75 53
> 6 73 60
> 7 62 53
>
>
> In both cases after the initalization I restarted the database and
> cleared the cashe(echo 1 > /proc/sys/vm/drop_caches) one time. During
> all the runs I didnt shutdown the machine.
>
> Now, I was hopping the the tps will be almost the same in each machine
> for all the runs. In other words, I wanted to see that the tps in
> machine1 during all the tps are almost the same but I see that the
> values arent accurate.
>
> Any idea what might cause the differences in every run ?