Re: Show <parameter> in psql does any calculations?

On Tue, 2011-12-27 at 15:21 +0530, Raghavendra wrote:
>
>
> On Tue, Dec 27, 2011 at 3:16 PM, Guillaume Lelarge
> <guillaume(at)lelarge(dot)info> wrote:
> On Tue, 2011-12-27 at 14:56 +0530, Raghavendra wrote:
> > Respected,
> >
> > Am in PG 9.1. See below ouputs.
> >
>
> > *By query:*
> > postgres=# SELECT name, setting, unit,context FROM
> pg_settings WHERE
> > category like '%Resource Usage / Memory%' ORDER BY name;
> > name | setting | unit | context
> > ---------------------------+---------+------+------------
> > maintenance_work_mem | 16384 | kB | user
> > max_prepared_transactions | 0 | |
> postmaster
> > max_stack_depth | 2048 | kB |
> superuser
> > shared_buffers | 4096 | 8kB |
> postmaster
> > temp_buffers | 1024 | 8kB | user
> > track_activity_query_size | 1024 | | postmaster
> > work_mem | 2048 | kB | user
> > (7 rows)
> >
>
> > *By session command:*
> > postgres=# show work_mem ;
> > work_mem
> > ----------
> > 2MB
> > (1 row)
> >
> > postgres=# show shared_buffers ;
> > shared_buffers
> > ----------------
> > 32MB
> > (1 row)
> >
> > By the query, its clear that "setting" value is multiplied
> with unit to get
> > the sesssion level command value which is displayed here.
> However, I am
> > trying to get the query of it which is executed at
> session-level with SHOW
> > command. I tried "psql -E" option tooo..
> >
> > -bash-3.2$ psql -E
> > psql.bin (9.1.0)
> > Type "help" for help.
> >
> > postgres=# show work_mem ;
> > work_mem
> > ----------
> > 2MB
> > (1 row)
> >
> > Why the query is not displayed with -E option ?
> > Am I missing something here, please help me in clarifying
> it.
> >
>
>
> -E works only for meta-commands, ie commands which start with
> \
>
> Moreover, SHOW is an actual SQL command. So I'm not sure what
> you're
> trying to find with the -E command line switch.
>
>
>
> Hey, Many thanks for your quick response.
>
>
> I am looking how SHOW command value is converted into MB's or GB's ?
>

AFAIUI, SHOW gives you the value used internaly, so it doesn't look at
pg_settings at all.

--
Guillaume
http://blog.guillaume.lelarge.info
http://www.dalibo.com
PostgreSQL Sessions #3: http://www.postgresql-sessions.org