RE: Pg10 : Client Configuration for Parallelism ? - Mailing list pgsql-performance

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
queryis longer.
 

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

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



Am 17.04.19 um 11:51 schrieb laurent.dechambe@orange.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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