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Thread: pgstattupple vs pg_total_relation_size

pgstattupple vs pg_total_relation_size

From

Mariel Cherkassky

Date:

30 January 2019, 13:41:55

Hey,

I'm using postgresql 9.6.11. I wanted to ask something about the functions I mentioned in the title :

I created the next table :

postgres=# \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=# select pg_total_relation_size(' students ');

pg_total_relation_size

------------------------

16384

(1 row)

postgres=# select pg_relation_size(' students ');

pg_relation_size

------------------

8192

(1 row)

When I used pgstattuple :

postgres=# select * from pgstattuple('pg_toast.pg_toast_1187222');

-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------

0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0

(1 row)

postgres=# select * from pgstattuple('students');

-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------

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)

Re: pgstattupple vs pg_total_relation_size

From

Tumasgiu Rossini

Date:

30 January 2019, 16:19:52

According to the doc [1],

pg_total_relation_size add toasted data *and* indexes to the mix.

Any index, unique constraint, or primary key on your table ?

[1] https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-DBSIZE

Le mer. 30 janv. 2019 à 11:42, Mariel Cherkassky <mariel.cherkassky@gmail.com> a écrit :

Hey,
I'm using postgresql 9.6.11. I wanted to ask something about the functions I mentioned in the title :
I created the next table :
postgres=# \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=# select pg_total_relation_size(' students ');
pg_total_relation_size
------------------------
16384
(1 row)

postgres=# select pg_relation_size(' students ');
pg_relation_size
------------------
8192
(1 row)

When I used pgstattuple :
postgres=# 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=# 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)

Re: pgstattupple vs pg_total_relation_size

From

Tumasgiu Rossini

Date:

30 January 2019, 16:19:52

According to the doc [1],

pg_total_relation_size add toasted data *and* indexes to the mix.

Any index, unique constraint, or primary key on your table ?

[1] https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-DBSIZE

Le mer. 30 janv. 2019 à 11:42, Mariel Cherkassky <mariel.cherkassky@gmail.com> a écrit :

Hey,
I'm using postgresql 9.6.11. I wanted to ask something about the functions I mentioned in the title :
I created the next table :
postgres=# \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=# select pg_total_relation_size(' students ');
pg_total_relation_size
------------------------
16384
(1 row)

postgres=# select pg_relation_size(' students ');
pg_relation_size
------------------
8192
(1 row)

When I used pgstattuple :
postgres=# 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=# 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)

Re: pgstattupple vs pg_total_relation_size

From

"Jehan-Guillaume (ioguix) de Rorthais"

Date:

30 January 2019, 16:27:01

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 ?
>
> [1]
> https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-DBSIZE
>
> Le mer. 30 janv. 2019 à 11:42, Mariel Cherkassky <
> mariel.cherkassky@gmail.com> a écrit :
>
> > Hey,
> > I'm using postgresql 9.6.11. I wanted to ask something about the functions
> > I mentioned in the title :
> > I created the next table :
> > postgres=# \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=# select pg_total_relation_size(' students  ');
> >  pg_total_relation_size
> > ------------------------
> >                   16384
> > (1 row)
> >
> > postgres=# select pg_relation_size(' students  ');
> >  pg_relation_size
> > ------------------
> >              8192
> > (1 row)
> >
> > When I used pgstattuple :
> > postgres=# 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=# 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)
> >
> >
> >
> >
> >



--
Jehan-Guillaume de Rorthais
Dalibo

Re: pgstattupple vs pg_total_relation_size

From

"Jehan-Guillaume (ioguix) de Rorthais"

Date:

30 January 2019, 16:27:01

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 ?
>
> [1]
> https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-DBSIZE
>
> Le mer. 30 janv. 2019 à 11:42, Mariel Cherkassky <
> mariel.cherkassky@gmail.com> a écrit :
>
> > Hey,
> > I'm using postgresql 9.6.11. I wanted to ask something about the functions
> > I mentioned in the title :
> > I created the next table :
> > postgres=# \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=# select pg_total_relation_size(' students  ');
> >  pg_total_relation_size
> > ------------------------
> >                   16384
> > (1 row)
> >
> > postgres=# select pg_relation_size(' students  ');
> >  pg_relation_size
> > ------------------
> >              8192
> > (1 row)
> >
> > When I used pgstattuple :
> > postgres=# 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=# 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)
> >
> >
> >
> >
> >



--
Jehan-Guillaume de Rorthais
Dalibo

Re: pgstattupple vs pg_total_relation_size

From

Mariel Cherkassky

Date:

30 January 2019, 17:32:01

There aren't any constraint or indexes, just a regular table. I didn't see the fsm and vm files in the base dir. Were they created immediately for every table or after some updates/deletes ?

On Wed, Jan 30, 2019, 3:27 PM Jehan-Guillaume (ioguix) de Rorthais <ioguix@free.fr wrote:

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 ?
>
> [1]
> https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-DBSIZE
>
> Le mer. 30 janv. 2019 à 11:42, Mariel Cherkassky <
> mariel.cherkassky@gmail.com> a écrit :
>
> > Hey,
> > I'm using postgresql 9.6.11. I wanted to ask something about the functions
> > I mentioned in the title :
> > I created the next table :
> > postgres=# \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=# select pg_total_relation_size(' students ');
> > pg_total_relation_size
> > ------------------------
> > 16384
> > (1 row)
> >
> > postgres=# select pg_relation_size(' students ');
> > pg_relation_size
> > ------------------
> > 8192
> > (1 row)
> >
> > When I used pgstattuple :
> > postgres=# 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=# 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)
> >
> >
> >
> >
> >

--
Jehan-Guillaume de Rorthais
Dalibo

Re: pgstattupple vs pg_total_relation_size

From

Mariel Cherkassky

Date:

30 January 2019, 17:32:01

There aren't any constraint or indexes, just a regular table. I didn't see the fsm and vm files in the base dir. Were they created immediately for every table or after some updates/deletes ?

On Wed, Jan 30, 2019, 3:27 PM Jehan-Guillaume (ioguix) de Rorthais <ioguix@free.fr wrote:

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 ?
>
> [1]
> https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-DBSIZE
>
> Le mer. 30 janv. 2019 à 11:42, Mariel Cherkassky <
> mariel.cherkassky@gmail.com> a écrit :
>
> > Hey,
> > I'm using postgresql 9.6.11. I wanted to ask something about the functions
> > I mentioned in the title :
> > I created the next table :
> > postgres=# \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=# select pg_total_relation_size(' students ');
> > pg_total_relation_size
> > ------------------------
> > 16384
> > (1 row)
> >
> > postgres=# select pg_relation_size(' students ');
> > pg_relation_size
> > ------------------
> > 8192
> > (1 row)
> >
> > When I used pgstattuple :
> > postgres=# 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=# 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)
> >
> >
> >
> >
> >

--
Jehan-Guillaume de Rorthais
Dalibo

Re: pgstattupple vs pg_total_relation_size

From

Tom Lane

Date:

30 January 2019, 17:46:49

"Jehan-Guillaume (ioguix) de Rorthais" <ioguix@free.fr> writes:
> 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.

Yeah.  In this particular case, the other page presumably belongs to the
toast table's index, which will have a metapage even if the table is
empty.

            regards, tom lane

Re: pgstattupple vs pg_total_relation_size

From

Tom Lane

Date:

30 January 2019, 17:46:49

"Jehan-Guillaume (ioguix) de Rorthais" <ioguix@free.fr> writes:
> 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.

Yeah.  In this particular case, the other page presumably belongs to the
toast table's index, which will have a metapage even if the table is
empty.

            regards, tom lane