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Re: pg_class (system) table increasing size. - Mailing list pgsql-general

From Melvin Davidson
Subject Re: pg_class (system) table increasing size.
Date
Msg-id CANu8FizHbfSb=WvzaHHBPPrqKK1_OBr=nAPE4QGb2JxGNKr=2A@mail.gmail.com
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In response to Re: pg_class (system) table increasing size.  (dhaval jaiswal <dhavallj@hotmail.com>)
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On Thu, Nov 17, 2016 at 1:33 PM, dhaval jaiswal <dhavallj@hotmail.com> wrote:

select * from pg_stat_sys_tables where relname = 'pg_class';

-[ RECORD 1 ]-------+-----------
relid               | 1259
schemaname          | pg_catalog
relname             | pg_class
seq_scan            | 1838
seq_tup_read        | 3177416
idx_scan            | 1027456557
idx_tup_fetch       | 959682909
n_tup_ins           | 0
n_tup_upd           | 0
n_tup_del           | 0
n_tup_hot_upd       | 0
n_live_tup          | 0
n_dead_tup          | 0
n_mod_since_analyze | 0
last_vacuum         | 
last_autovacuum     | 
last_analyze        | 
last_autoanalyze    | 
vacuum_count        | 0
autovacuum_count    | 0
analyze_count       | 0
autoanalyze_count   | 0


Yes, the size of pg_class table is of 5 GB.  However, the existing row is only 2380 only. It's got fragmented. 

From: Adrian Klaver <adrian.klaver@aklaver.com>
Sent: Thursday, November 17, 2016 8:29 PM
To: dhaval jaiswal; David G. Johnston
Cc: pgsql-general@postgresql.org
Subject: Re: [GENERAL] pg_class (system) table increasing size.
 
On 11/16/2016 07:08 PM, dhaval jaiswal wrote:
>
>>> Because you are creating (specific) objects.
>
> I have gone through the link and  how would i figure out which
> specific object is causing this.  Can you please elaborate more here.
>
>
> We do not have the much temporary table usage.
>
>
> Since the size is bigger (5 GB) to maintain. does it requires
> maintenance as well for thepg_class.

Should have added to my previous post. What does:

select * from pg_stat_sys_tables where relname = 'pg_class';

show?

>
>
> It seems its affecting performance.
>
>



--
Adrian Klaver
adrian.klaver@aklaver.com


>Yes, the size of pg_class table is of 5 GB.  However, the existing row is only 2380 only. It's got fragmented.

I strongly believe you are incorrect about the size of the pg_class table.
The correct way to determine that size is:

SELECT n.nspname as schema,
       c.relname as table,
       a.rolname as owner,
       c.relfilenode as filename,
       c.reltuples::bigint,
       pg_size_pretty(pg_relation_size(n.nspname|| '.' || c.relname)) as size,
       pg_size_pretty(pg_total_relation_size(n.nspname|| '.' || c.relname)) as total_size,
       pg_relation_size(n.nspname|| '.' || c.relname) as size_bytes,
       pg_total_relation_size(n.nspname|| '.' || c.relname) as total_size_bytes,
       CASE WHEN c.reltablespace = 0
            THEN 'pg_default'
            ELSE (SELECT t.spcname
                    FROM pg_tablespace t WHERE (t.oid = c.reltablespace) )                   
        END as tablespace
FROM pg_class c
  JOIN pg_namespace n ON (n.oid = c.relnamespace)
  JOIN pg_authid a ON ( a.oid = c.relowner )
  WHERE relname = 'pg_class' ;
 
  What does that show for reltuples and total_size ?

--
Melvin Davidson
I reserve the right to fantasize.  Whether or not you
wish to share my fantasy is entirely up to you.

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