Date: Wed, 30 Jan 2019 14:27:01 +0100
From: "Jehan-Guillaume (ioguix) de Rorthais" <ioguix@free.fr>
To: Tumasgiu Rossini <rossini.t@gmail.com>
Cc: Mariel Cherkassky <mariel.cherkassky@gmail.com>,
 pgsql-admin@lists.postgresql.org, pgsql-performance@lists.postgresql.org
Subject: Re: pgstattupple vs pg_total_relation_size
Message-ID: <20190130142701.38992d60@firost>
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On Wed, 30 Jan 2019 14:19:52 +0100
Tumasgiu Rossini <rossini.t@gmail.com> wrote:

> According to the doc [1],
> pg_total_relation_size add toasted data *and* indexes to the mix.

*and* FSM *and* VM.

> Any index, unique constraint, or primary key on your table ?
>=20
> [1]
> https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-AD=
MIN-DBSIZE
>=20
> Le mer. 30 janv. 2019 =C3=A0 11:42, Mariel Cherkassky <
> mariel.cherkassky@gmail.com> a =C3=A9crit : =20
>=20
> > Hey,
> > I'm using postgresql 9.6.11. I wanted to ask something about the functi=
ons
> > I mentioned in the title :
> > I created the next table :
> > postgres=3D# \d students;
> >       Table "public. students  "
> >   Column  |  Type   | Modifiers
> > ----------+---------+-----------
> >  id| integer |
> >  name| text    |
> >  age| integer |
> >  data     | jsonb   |
> >
> > I inserted one row. When I query the table`s size with
> > pg_total_relation_size I see that the data occupies 2 pages :
> >
> > postgres=3D# select pg_total_relation_size(' students  ');
> >  pg_total_relation_size
> > ------------------------
> >                   16384
> > (1 row)
> >
> > postgres=3D# select pg_relation_size(' students  ');
> >  pg_relation_size
> > ------------------
> >              8192
> > (1 row)
> >
> > When I used pgstattuple :
> > postgres=3D# select * from pgstattuple('pg_toast.pg_toast_1187222');
> >  table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count=
 |
> > dead_tuple_len | dead_tuple_percent | free_space | free_percent
> >
> > -----------+-------------+-----------+---------------+-----------------=
-+----------------+--------------------+------------+--------------
> >          0 |           0 |         0 |             0 |                0=
 |
> >             0 |                  0 |          0 |            0
> > (1 row)
> >
> > postgres=3D# select * from pgstattuple('students');
> >  table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count=
 |
> > dead_tuple_len | dead_tuple_percent | free_space | free_percent
> >
> > -----------+-------------+-----------+---------------+-----------------=
-+----------------+--------------------+------------+--------------
> >       8192 |           1 |      1221 |          14.9 |                0=
 |
> >             0 |                  0 |       6936 |        84.67
> > (1 row)
> >
> > Which means, the toasted table is empty and you can see that the row I
> > inserted should occupy only one page(8K in my system).
> >
> > Then, why the pg_total_relation_size shows another page ?(16KB in total)
> >
> >
> >
> >
> > =20


--=20
Jehan-Guillaume de Rorthais
Dalibo