Thread: BUG #13830: pg_table_size and pg_indexes_size
The following bug has been logged on the website:
Bug reference: 13830
Logged by: T_T
Email address: 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]$./psql
psql (9.5beta2)
Type "help" for help.
postgres=# create table b(id int);
CREATE TABLE
postgres=# create index b_idx on b(id);
CREATE INDEX
postgres=# select relname , pg_table_size(oid),pg_indexes_size(oid)
postgres-# from pg_class where relname in ('b','b_idx');
relname | pg_table_size | pg_indexes_size
---------+---------------+-----------------
b | 0 | 8192
b_idx | 8192 | 0
(2 rows)
postgres=#
The b_idex is a index , but pg_indexes_size does not show its size . The b
is a table , but pg_table_size does not show its size .I think the
pg_table_size show the b size , but not pg_indexes_size .
On Wed, Dec 23, 2015 at 7:55 AM, <foggyglass@163.com> wrote:
> The following bug has been logged on the website:
>
> Bug reference: 13830
> Logged by: T_T
> Email address: foggyglass@163.com
> PostgreSQL version: 9.5rc1
> Operating system: centos7
> Description:
>
> Hi friend,
> I think there is a error about pg_table_size and
> pg_indexes_size in
> PostgreSQL .
> This is my operation log
>
> [postgres@c7 bin]$./psql
> psql (9.5beta2)
> Type "help" for help.
>
> postgres=3D# create table b(id int);
> CREATE TABLE
> postgres=3D# create index b_idx on b(id);
> CREATE INDEX
> postgres=3D# 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=3D#
>
> 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 .
=E2=80=8BWorking as documented.=E2=80=8B
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=E2=80=8B, and so
=E2=80=8Byou get 8192 as the size of the index table (i.e., relation). Sin=
ce 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
=E2=80=8BDavid J.=E2=80=8B
=E2=80=8B
foggyglass@163.com writes:
> 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)
Seems fine to me. b is empty at this point, so it has size zero.
btree indexes, on the other hand, never have size zero because their
metapage is created immediately. b_idx has no indexes attached to it,
so pg_indexes_size finds nothing to report on and returns zero for
that.
If you insert any actual data, the results change:
regression=# insert into b values(33);
INSERT 0 1
regression=# select relname , pg_table_size(oid),pg_indexes_size(oid) from pg_class where relname in ('b','b_idx');
relname | pg_table_size | pg_indexes_size
---------+---------------+-----------------
b | 8192 | 16384
b_idx | 16384 | 0
(2 rows)
which maybe looks a bit saner.
regards, tom lane
Mr. David ,
thank you for your explanation .
T.T
å¨ 2015/12/24 2:18, David G. Johnston åé:
> 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 .
>
>
> âWorking as documented.â
>
> 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_sizeâ, and so
> â 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
>
> â David J.â
> â
>
Mr. Tom Lane
Thank you for your explanation .:)
å¨ 2015/12/24 2:22, Tom Lane åé:
> foggyglass@163.com writes:
>> 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)
> Seems fine to me. b is empty at this point, so it has size zero.
> btree indexes, on the other hand, never have size zero because their
> metapage is created immediately. b_idx has no indexes attached to it,
> so pg_indexes_size finds nothing to report on and returns zero for
> that.
>
> If you insert any actual data, the results change:
>
> regression=# insert into b values(33);
> INSERT 0 1
> regression=# select relname , pg_table_size(oid),pg_indexes_size(oid) from pg_class where relname in ('b','b_idx');
> relname | pg_table_size | pg_indexes_size
> ---------+---------------+-----------------
> b | 8192 | 16384
> b_idx | 16384 | 0
> (2 rows)
>
> which maybe looks a bit saner.
>
> regards, tom lane
>