Обсуждение: database size much bigger than tablespaces on filesystem

I have a Postgresql 8.3 instance with tablespaces totalling on about 74G. This is fine.

But if I ask Postgresql how big my database is, I get a (unexpected) large answer: 595 GB.

This seems very strange. Disk I/O tests on the system are in the 'normal' range, but queries are slower than they used
tobe.
 

Is this corruption of the database? Or are there ways to 'fix' this oddity?

Btw:

I check the tablespace size by the os:

/usr/local/pgsql/data/tblspaces/du -c -h
74G total 

All tablespaces are there. I check this by the \db command in pgsql

I check te database size like this:

select pg_size_pretty(pg_database_size('database')) 
595 GB

 Hi,

 On Wed, 14 Sep 2011 04:03:45 -0700, Rob Audenaerde
 <Rob.Audenaerde@Valuecare.nl> wrote:
> Is this corruption of the database? Or are there ways to 'fix' this
> oddity?

 Try VACUUM ANALYSE and repeat the operation.

 Thanks,
 Gabriele

--
  Gabriele Bartolini - 2ndQuadrant Italia
  PostgreSQL Training, Services and Support
  Gabriele.Bartolini@2ndQuadrant.it - www.2ndQuadrant.it

On Wed, 2011-09-14 at 04:03 -0700, Rob Audenaerde wrote:
> I have a Postgresql 8.3 instance with tablespaces totalling on about 74G. This is fine.
>
> But if I ask Postgresql how big my database is, I get a (unexpected) large answer: 595 GB.
>
> This seems very strange. Disk I/O tests on the system are in the 'normal' range, but queries are slower than they
usedto be. 
>
> Is this corruption of the database? Or are there ways to 'fix' this oddity?
>
> Btw:
>
> I check the tablespace size by the os:
>
> /usr/local/pgsql/data/tblspaces/du -c -h
> 74G total
>
> All tablespaces are there. I check this by the \db command in pgsql
>
> I check te database size like this:
>
> select pg_size_pretty(pg_database_size('database'))
> 595 GB

You should also check the space held in $PGDATA/base.


--
Guillaume
  http://blog.guillaume.lelarge.info
  http://www.dalibo.com

>On Wed, 2011-09-14 at 04:03 -0700, Rob Audenaerde wrote:
>> I have a Postgresql 8.3 instance with tablespaces totalling on about 74G. This is fine.
>>
>> But if I ask Postgresql how big my database is, I get a (unexpected) large answer: 595 GB.
>>
>> This seems very strange. Disk I/O tests on the system are in the 'normal' range, but queries are slower than they
usedto be.
 
>>
>> Is this corruption of the database? Or are there ways to 'fix' this oddity?
>>
>> Btw:
>>
>> I check the tablespace size by the os:
>>
>> /usr/local/pgsql/data/tblspaces/du -c -h
>> 74G total
>>
>> All tablespaces are there. I check this by the \db command in pgsql
>>
>> I check te database size like this:
>>
>> select pg_size_pretty(pg_database_size('database'))
>> 595 GB

> You should also check the space held in $PGDATA/base.

I did. It is only 320 MB.

Rob Audenaerde <Rob.Audenaerde@Valuecare.nl> writes:
>>> I check te database size like this:
>>> select pg_size_pretty(pg_database_size('database'))
>>> 595 GB

>> You should also check the space held in $PGDATA/base.

> I did. It is only 320 MB.

Bizarre.  Try breaking the results down table-by-table to see if you can
find where the discrepancy is.

            regards, tom lane

>>>> I check te database size like this:
>>>> select pg_size_pretty(pg_database_size('database'))
>>>> 595 GB

>>> You should also check the space held in $PGDATA/base.

>> I did. It is only 320 MB.

>Bizarre.  Try breaking the results down table-by-table to see if you can
>find where the discrepancy is.

>                       regards, tom lane

It gets stranger. I try this:

select 
  tablename
, pg_relation_size(tablename) 
, pg_size_pretty(pg_relation_size(tablename) ) as relsize
, pg_size_pretty(pg_total_relation_size(tablename) ) as disksize
, pg_total_relation_size(tablename)
from pg_tables where schemaname <> 'information_schema'
order by 2 desc

And all the tables report a 'disksize' larger than the 'relsize', which seems natural. The biggest table (relsize) is
around5 GB. 
 
I wonder where the rest of the size comes from?

-Rob

Rob Audenaerde <Rob.Audenaerde@Valuecare.nl> writes:
> It gets stranger. I try this:

> select
>   tablename
> , pg_relation_size(tablename)
> , pg_size_pretty(pg_relation_size(tablename) ) as relsize
> , pg_size_pretty(pg_total_relation_size(tablename) ) as disksize
> , pg_total_relation_size(tablename)
> from pg_tables where schemaname <> 'information_schema'
> order by 2 desc

> And all the tables report a 'disksize' larger than the 'relsize',
> which seems natural. The biggest table (relsize) is around 5 GB.

pg_relation_size isn't going to count indexes nor toast tables, and
toast in particular could be where a lot of the space is.  I'd suggest
sorting by pg_total_relation_size to see if anything jumps out at you.

Another problem with the above query is that it supposes that there are
no similarly-named tables in different schemas.  If there are, you'll
get multiple reports of the size of the one that is visible in your
search path, and no reports for the others.  If I were doing this,
I'd not rely on pg_tables but look at pg_class directly so I could use
the OID, something like

    select relname, pg_total_relation_size(c.oid)
    from pg_class c where relkind = 'r'
    order by 2 desc

            regards, tom lane