Re: pgstattupple vs pg_total_relation_size

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(dot)cherkassky(at)gmail(dot)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)
>
>
>
>
>