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.cherkas...@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) > > > > >
