Re: does postgresql backup require additional space on disk - Mailing list pgsql-general

On 5/13/19 3:27 PM, Julie Nishimura wrote:
> Adrian, thanks for your reply. I previously found this link, which 
> mentioned 8.2, that is why I assumed it will work with 8.3.

No, what the link showed is:

ALTER DATABASE mydatabase SET default_tablespace = mynewtablespace

That is is the same as changing default_tablespace in postgresql.conf.

It is not the same as:

ALTER DATABASE name SET TABLESPACE

> 
> Too bad we don't have dev with the same version. I guess I will create 

You can use the same commands on dev to test, just not ALTER DATABASE 
name SET TABLESPACE as that is not in 8.3.

> new tablespace using new vol, move the smallest db for which I have 

You cannot move a db as a unit, you will need to move the individual 
tables/indexes in the db.

> backup, create new test table and examine new/existing tables if they 
> have moved by selecting tablespace from pg_tables... right?

Assuming you either specify the new tablespace on table CREATE or have 
set default_tablespace to the new tablespace.

> 
> 
> http://www.postgresonline.com/journal/archives/123-Managing-disk-space-using-table-spaces.html
> Managing disk space using table spaces - Postgres OnLine Journal - 
> Postgres OnLine Journal Magazine Jul 2017 - Dec 2017 
> <http://www.postgresonline.com/journal/archives/123-Managing-disk-space-using-table-spaces.html>
> Below are steps to creating one. First create a folder on an available 
> disk in your filesystem using an filesystem server administrative login; 
> Next give full rights to the postgres server account (the one the daemon 
> process runs under) or you can change the owner of the folder to the 
> postgres account (in linux you can use chown postgres and on windows 
> just use the administrative properties ...
> www.postgresonline.com
> 
> 
> 
> ------------------------------------------------------------------------
> *From:* Adrian Klaver <adrian.klaver@aklaver.com>
> *Sent:* Monday, May 13, 2019 2:47 PM
> *To:* Julie Nishimura; pgsql-general@lists.postgresql.org; pgsql-general
> *Subject:* Re: does postgresql backup require additional space on disk
> On 5/13/19 1:26 PM, Julie Nishimura wrote:
>> Adrian, thanks for your reply. Couple of clarifications/questions:
>> 1) we are on 8.3 for this server
> 
> 8.3 does not have ALTER DATABASE name SET TABLESPACE :
> 
> https://www.postgresql.org/docs/8.3/sql-alterdatabase.html
> 
> It does appear until 8.4.
> 
> 
>> 2) I was under impression, that "ALTER DATABASE name SET TABLESPACE 
>> new_tablespace" won't move anything, and just utilize the new_tablespace 
>> for new tables/indexes. If we would want to move existing tables, we 
>> would need to move them one by one by
> 
> No think of ALTER DATABASE name SET TABLESPACE  as a bulk operation of
> ALTER TABLE /mytableschema.mytable/ SET TABLESPACE /mynewtablespace/
> across all existing tables.  This assumes the all existing tables live
> in the  current default tablespace. It is moot in your case as 8.3 is
> not capable of doing this.
> 
>> ALTER TABLE /mytableschema.mytable/ SET TABLESPACE /mynewtablespace/
>> /
>> /
> 
> The above is your option in 8.3.
> 
>> 3) I thought if I want to have any newly created dbs go to the new vol, 
>> I need to alter template.
> 
> It is not required you can spec the tablespace in the CREATE DATABASE
> command:
> 
> https://www.postgresql.org/docs/8.3/sql-createdatabase.html
> 
> Though you can move them to make the tablespace the default. See above link.
> 
> 
>> 4) I was also thinking about changing parameters in config file to point 
>> to the newly volume and reload postgresql.conf
>> 
>> default_tablespace
>> 
>> temp_tablespaces
> 
> You could that. If you do it, moving the template tables would be redundant.
> 
>> 
>> 
>> Am I wrong here?
>> 
>> 
>> Thanks,
>> 
>> Julie
>> 
>> 
> 
> 
> -- 
> Adrian Klaver
> adrian.klaver@aklaver.com


-- 
Adrian Klaver
adrian.klaver@aklaver.com