RE: Pg10 : Client Configuration for Parallelism ?

I can see whether there is parallelism with pg_top or barely top on the server.

<DBEAVER>
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
38584 postgres 20 0 8863828 8.153g 8.151g R 100.0 3.2 1:23.01 postgres
10 root 20 0 0 0 0 S 0.3 0.0 88:07.26 rcu_sched

<BASIC JDBC>
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
46687 postgres 20 0 8864620 0.978g 0.977g S 38.5 0.4 0:01.16 postgres
46689 postgres 20 0 8864348 996.4m 995.1m R 38.5 0.4 0:01.16 postgres
46690 postgres 20 0 8864348 987.2m 985.8m S 38.5 0.4 0:01.16 postgres
46691 postgres 20 0 8864348 998436 997084 R 38.5 0.4 0:01.16 postgres
46692 postgres 20 0 8864348 982612 981260 S 38.5 0.4 0:01.16 postgres
46693 postgres 20 0 8864348 979.9m 978.6m R 38.5 0.4 0:01.16 postgres
46694 postgres 20 0 8864348 987.9m 986.6m S 38.5 0.4 0:01.16 postgres
46696 postgres 20 0 8864348 996864 995512 S 38.5 0.4 0:01.16 postgres
46688 postgres 20 0 8864348 982.3m 981.0m R 38.2 0.4 0:01.15 postgres
46695 postgres 20 0 8864348 986.9m 985.6m S 38.2 0.4 0:01.15 postgres
21323 postgres 20 0 8862788 8.096g 8.095g S 0.7 3.2 2:24.75 postgres
46682 postgres 20 0 157996 2596 1548 R 0.7 0.0 0:00.05 top

This is not a matter of cache. If I execute the queries in a different order the result will be the same : DBeaver query is longer.

There is something in documentation that says that there won't be parallelism if " The client sends an Execute message with a non-zero fetch count."
I am not sure what this sentence means.

-----Message d'origine-----
De : Andreas Kretschmer [mailto:andreas(at)a-kretschmer(dot)de]
Envoyé : mercredi 17 avril 2019 12:39
À : pgsql-performance(at)lists(dot)postgresql(dot)org
Objet : Re: Pg10 : Client Configuration for Parallelism ?

Am 17.04.19 um 11:51 schrieb laurent(dot)dechambe(at)orange(dot)com:
>
> Here are the logs (with log_error_verbosity = verbose) :
>
> <DBEAVER>
>
> 2019-04-17 11:30:42 CEST;35895;thedbuser;thedb;00000;LOG:  00000:
> execute <unnamed>: SELECT COUNT(1) FROM big_table
>
> 2019-04-17 11:30:42 CEST;35895;thedbuser;thedb;00000;LOCATION:
> exec_execute_message, postgres.c:1959
>
> 2019-04-17 11:31:08 CEST;35895;thedbuser;thedb;00000;LOG:  00000:
> duration: 25950.908 ms
>
> <BASIC JDBC>
>
> 2019-04-17 11:31:20 CEST;37257;thedbuser;thedb;00000;LOG:  00000:
> execute <unnamed>: SELECT COUNT(1) FROM big_table
>
> 2019-04-17 11:31:20 CEST;37257;thedbuser;thedb;00000;LOCATION:
> exec_execute_message, postgres.c:1959
>
> 2019-04-17 11:31:32 CEST;37257;thedbuser;thedb;00000;LOG:  00000:
> duration: 11459.943 ms
>
>
> <PGADMIN4>
>
> 2019-04-17 11:32:56 CEST;37324;thedbuser;thedb;00000;LOG:  00000:
> statement: SELECT COUNT(1) FROM big_table;
>
> 2019-04-17 11:32:56 CEST;37324;thedbuser;thedb;00000;LOCATION: 
> exec_simple_query, postgres.c:940
>
> 2019-04-17 11:33:08 CEST;37324;thedbuser;thedb;00000;LOG:  00000:
> duration: 11334.677 ms
>
>

That's compareable. The first one took more time, cold cache. The 2nd
and 3rd are faster, warm cache.

But: we can't see if the execution is paralell or not. If you want to
know that, install and use auto_explain.

Regards, Andreas

--
2ndQuadrant - The PostgreSQL Support Company.
www.2ndQuadrant.com

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