Thread: pgbench and scaling

PG 9.5.3
RHEL Linux

To cut the story short and giving as much details as I can remember:

I created 40 database db1 .. db40 in a cluster.
On each database I initialized pgbench tables with a scale of 15.

Then I concurrently ran 5 pgbenches for 15 min. Each pgbench connected to one db. In other words, no two pgbench
sessionswere working on the same db. 

I noticed that as I scale from 5 to 10 to 20 to 40, the TPS starts falling almost linearly :

with 5, TPS was doing 639
with 10 TPS was down to 490
with 20 TPS was down to 280
and so on.

Are we missing something?  Where do I start looking for the root cause.

thanks

I forgot to mention that the db is replicated synchronously.  I think that is the culprit.

On Thu, Nov 17, 2016 at 8:08 PM, Rakesh Kumar
<rakeshkumar464@outlook.com> wrote:
> I noticed that as I scale from 5 to 10 to 20 to 40, the TPS starts falling almost linearly :
>
> with 5, TPS was doing 639
> with 10 TPS was down to 490
> with 20 TPS was down to 280
> and so on.

Are the TPS numbers per pgbench? If so, then you're getting
10x490=4900 TPS system wide, or 20*280=5600 TPS system wide.

If those are total TPS numbers then you should check your disk
utilization and CPU utilization and see where your bottleneck is.

"Are the TPS numbers per pgbench? If so, then you're getting
10x490=4900 TPS system wide, or 20*280=5600 TPS system wide. "

Per pgbench.

Your explanation makes sense. thanks.



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