Re: BUG #13493: pl/pgsql doesn't scale with cpus (PG9.3, 9.4)

On the machine used for this set of benchmarks, THP is set to never. =
I've seen this on several machines with slight variations in their =
configuration.=20

I spent days poring over best practice guides from google and others =
when setting these up, and I try to stay up to date with discussion on =
pgsql-performance for kernel and postgresql.conf.=20

- Don't have any spare machines currently, or time, to test on pg9.5. =
Going into hospital soon and then to a conference. Wanted to get this =
published first.
- may not be able to provide perf data just now. Lots of work, little =
time, bad health. Will try if i can though!

Graeme Bell


> On 8 Jul 2015, at 02:16, Andres Freund <andres@anarazel.de> wrote:
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> On July 8, 2015 12:27:39 AM GMT+02:00, grb@skogoglandskap.no wrote:
>> The following bug has been logged on the website:
>>=20
>> Bug reference:      13493
>> Logged by:          Graeme Bell
>> Email address:      grb@skogoglandskap.no
>> PostgreSQL version: 9.3.9
>> Operating system:   Linux
>> Description:       =20
>>=20
>> Hi,
>>=20
>> pl/pgsql doesn't scale properly on postgres 9.3/9.4 with multiple
>> processors
>> beyond 2-3 processors for me, regardless of the machine I use or the
>> benchmark/project.=20
>>=20
>> I discovered this painfully during a project here where we were =
running
>> a
>> small 'forest simulator' in pl/pgsql on different datasets
>> simultaneously.=20
>>=20
>> To highlight the problem, I've provided a benchmark that demonstrates
>> two
>> problems (on my machines).
>>=20
>> 1. The first problem is scaling when you have lots of pl/pgsql code
>> running
>> and doing real work.=20
>>=20
>> 2. The second problem is scaling when you have a table column as an
>> input
>> parameter.=20
>>=20
>> The benchmark results & source code are here:
>>=20
>> https://github.com/gbb/ppppt
>>=20
>> Another set of benchmarks showing the same phenomena on PG9.3 and =
PG9.4
>> can
>> be found here, under 'BENCHMARKS.md'
>>=20
>> https://github.com/gbb/par_psql
>>=20
>> I would be grateful if others could run the benchmark and
>> confirm/disconfirm
>> the result.=20
>>=20
>> If confirmed, the result may be of special interest to e.g. the =
postgis
>> &
>> pgrouting communities.
>>=20
>> This result is from a 16-core machine with 128GB of memory and a lot =
of
>> random I/O capacity (there's no writing involved though other than a
>> bit of
>> WAL, and not much data, so this shouldn't matter).
>=20
> That sounds odd.. Could you provide perf profiles with this running? =
Also have you reproduced on 9.5?
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> Do you have transparent huge pages disabled?
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> ---=20
> Please excuse brevity and formatting - I am writing this on my mobile =
phone.
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>=20
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