Re: About the tps explanation of pgbench, please help - Mailing list pgsql-general

On 11/18/2014 05:53 PM, Yanrui Hu wrote:
> Adrian,
> I saw that in two case, one is 54502 transactions and the other is 13966
> but that is caused by capacity decrease.
> And fps is transaction per second, so it's not the transactions but
> transaction per second, so I don't think the total transactions
> different has any problem.
> Please point if my understanding is not correct.

Alright

If:

kph = kilometer per hour = kilometer/hour

100 km/1 hr = 100 km/hr

200 km/1 hr = 200 km/hr

If you cover 100 km in 1 hour you have an average rate of speed of 100
km/hr if you cover 200 km in 1 hour your average rate of speed is 200 km/hr

then

tps = transactions per second = transactions/sec

54502 transactions/600 sec = 90.84 transactions/sec

13966 transactions/600 sec = 23.28 transactions/sec

The numbers are not exactly the same as the below, but that is probably
down to rounding error. They pass the close enough rule though:) Any way
you look at it, if run a two tests over the same time period and one
does less transactions then the other you will have different
transactions rates(tps) You where asking about the why behind the
different tps rates, the answer is above. In other words you cannot
ignore the raw numbers for the transactions.


> My initial plan is to know the impact if I move that db client (also a
> server runs web server with restful api) out side to internet.
>
> On Tue, Nov 18, 2014 at 10:35 PM, Adrian Klaver
> <adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>> wrote:
>
>     On 11/18/2014 12:33 AM, Yanrui Hu wrote:
>
>         I am working on a evaluation to put db client outside the
>         datacenter and
>         to know how the network impact on the business.
>         After several round of testing, I have a question regarding to
>         the two
>         tps result in stress output.
>
>         Test A:
>         Client and DB server exist in same AWS datacenter.
>         transaction type: Custom query
>         scaling factor: 500
>         query mode: simple
>         number of clients: 25
>         number of threads: 25
>         duration: 600 s
>         number of transactions actually processed: 54502
>         tps = 90.814930 (including connections establishing)
>         tps = 204.574432 (excluding connections establishing)
>
>         Test B:
>         Client and DB server exist in different AWS datacenter (west and
>         east).
>         transaction type: Custom query
>         scaling factor: 500
>         query mode: simple
>         number of clients: 25
>         number of threads: 25
>         duration: 600 s
>         number of transactions actually processed: 13966
>         tps = 23.235705 (including connections establishing)
>         tps = 42.915990 (excluding connections establishing)
>
>         Its obviously that both tps become lower if client and server do not
>         exist in same datacetner since the network connection have more
>         latency.
>         But I can not explain why the tps that excluding connections
>         establishing is changed so much.
>         For my understanding, tps excluding connections establishing get
>         rid of
>         the time that create socket cost. That means in above two test
>         cases(only network different), the tps excluding connections
>         establishing should be very close, right?
>
>
>     Not that I can see from the numbers. In the non-network case you
>     processed 54,502 transactions over 600s and in the network case
>     13,966 transactions over 600s. Even if you factor out the connection
>     establishment you have fewer transactions over the same time period
>     for the network case. So there is no way the tps can be equivalent.
>     As others have pointed out this due to the effect of network latency
>     on the processing of the queries.
>
>     You might want to take a look at the Notes section of here:
>
>     http://www.postgresql.org/__docs/9.3/static/pgbench.html
>     <http://www.postgresql.org/docs/9.3/static/pgbench.html>
>
>     In particular the different logging options that are available. They
>     may make it easier to see what is going on.
>
>
>     Because the database is same
>
>         and capability is same only network latency is different.
>
>
>         --
>         Best Regards,
>
>         Yanrui Hu (Ray)
>
>
>
>     --
>     Adrian Klaver
>     adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
>
>
>
>
> --
> Best Regards,
>
> Yanrui Hu (Ray)


--
Adrian Klaver
adrian.klaver@aklaver.com