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

From: Guillaume Lelarge <guillaume(at)lelarge(dot)info>
To: Raghavendra <raghavendra(dot)rao(at)enterprisedb(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Show <parameter> in psql does any calculations?
Date: 2011-12-27 09:56:20
Message-ID: 1324979780.3291.7.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-general
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


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