Re: BUG #13830: pg_table_size and pg_indexes_size

Mr. David ,
     thank you for your explanation .


T.T
在 2015/12/24 2:18, David G. Johnston 写道:
> On Wed, Dec 23, 2015 at 7:55 AM, <foggyglass@163.com
> <mailto:foggyglass@163.com>>wrote:
>
>     The following bug has been logged on the website:
>
>     Bug reference:      13830
>     Logged by:          T_T
>     Email address: foggyglass@163.com <mailto:foggyglass@163.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@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.​
> ​
>