Re: BUG #13830: pg_table_size and pg_indexes_size

On Wed, Dec 23, 2015 at 7:55 AM, <foggyglass(at)163(dot)com> wrote:

> The following bug has been logged on the website:
>
> Bug reference: 13830
> Logged by: T_T
> Email address: foggyglass(at)163(dot)com
> PostgreSQL version: 9.5rc1
> Operating system: centos7
> Description:
>
> Hi friend,
> I think there is a error about pg_table_size and
> pg_indexes_size in
> PostgreSQL .
> This is my operation log
>
> [postgres(at)c7 bin]$./psql
> psql (9.5beta2)
> Type "help" for help.
>
> postgres=# create table b(id int);
> CREATE TABLE
> postgres=# create index b_idx on b(id);
> CREATE INDEX
> postgres=# select relname , pg_table_size(oid),pg_indexes_size(oid)
> postgres-# from pg_class where relname in ('b','b_idx');
> relname | pg_table_size | pg_indexes_size
> ---------+---------------+-----------------
> b | 0 | 8192
> b_idx | 8192 | 0
> (2 rows)
>
> postgres=#
>
> The b_idex is a index , but pg_indexes_size does not show its size . The b
> is a table , but pg_table_size does not show its size .I think the
> pg_table_size show the b size , but not pg_indexes_size .

​Working as documented.​

Table "b" has no size of its own - however its one index has a size of 8192.

An index is sometimes considered a "table", in this case when using
pg_table_size​, and so

​you get 8192 as the size of the index table (i.e., relation). Since an
index doesn't have an index of its own pg_indexes_size returns 0.

pg_table_size on "b" returns zero since its size is zero and the
calculation excludes indexes. pg_indexes_size on "b" returns the size of
"b_idx" which is 8192.

http://www.postgresql.org/docs/9.5/interactive/functions-admin.html

​David J.​
​