location for pg_default tablespace

AI Rumman wrote:

I am new at Postgresql. Previously I used to work with Oracle.
I am surprised to see that the location for pg_default tablespace in
my database for a Postgresql cluster is null.
Could anyone please tell me what is the location of default tablespace
in postgresql and how could I find it?

Its the $PGDATA directory. The location of this varies widely by
operating system and postgres distribution. For instance, the postgres
supplied with fedora and redhat linuxes tend to put this in
/var/lib/pgsql/data ... If you build postgres from source on a
unix-like system, using full defaults, its probably /usr/local/pgsql/data

Thanks.
But actually I want to know that why the value in spclocation is null is
pg_tablespace for pg_default.
Moreover, $PGDATA/pg_tblspc has no file.
Could you please tell me why?

On Tue, Jan 12, 2010 at 11:26 AM, John R Pierce <pierce@hogranch.com> wrote:

AI Rumman wrote:

But actually I want to know that why the value in spclocation is null
is pg_tablespace for pg_default.
Moreover, $PGDATA/pg_tblspc has no file.
Could you please tell me why?

PostgreSQL ships with a blank tablespace setting, which it interprets as
meaning you want to put the database table files into the default
tablespace which is stored in $PGDATA/base

When you create a new tablespace using CREATE TABLESPACE:
http://www.postgresql.org/docs/current/static/sql-createtablespace.html

Then you'll find that pg_tblspc contains a symbolic link to the new
directory you've told it to use. At that point, you can then point all
new creation toward that location by setting default_tablespace, or put
individual bits of data onto there with the appropriate options to
CREATE:
http://www.postgresql.org/docs/current/static/manage-ag-tablespaces.html

--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com www.2ndQuadrant.com

I used the followings:

create tablespace mytabspc location '/var/lib/pgsql/data/pg_tblspc';

create database mydb with tablespace=mytabspc;

drop database mydb;

drop tablespace mytabspc;
ERROR: tablspace 'mytabspc' is not empty

Please tell me why?

On Tue, Jan 12, 2010 at 11:50 AM, Greg Smith <greg@2ndquadrant.com> wrote:

AI Rumman wrote:

I used the followings:

create tablespace mytabspc location '/var/lib/pgsql/data/pg_tblspc';

create database mydb with tablespace=mytabspc;

drop database mydb;

drop tablespace mytabspc;
ERROR: tablspace 'mytabspc' is not empty

Please tell me why?

You don't put things in pg_tblspace yourself; that directory is for the
database to manage. Your tablespace should be somewhere completely
outside of /var/lib/pgsql/data altogether.

--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com www.2ndQuadrant.com

On Tue, Jan 12, 2010 at 7:17 AM, Greg Smith <greg@2ndquadrant.com> wrote:

AI Rumman wrote:

I used the followings:
create tablespace mytabspc location '/var/lib/pgsql/data/pg_tblspc';
create database mydb with tablespace=mytabspc;
drop database mydb;
drop tablespace mytabspc;
ERROR: tablspace 'mytabspc' is not empty
Please tell me why?

You don't put things in pg_tblspace yourself; that directory is for the
database to manage. Your tablespace should be somewhere completely outside
of /var/lib/pgsql/data altogether.

Tablespaces in postgres are quite a bit different from Oracle. In Oracle,
you define a tablespace to be a location that uses one or more datafiles,
and everything belongs in a tablespace.

In postgres, a tablespace is not required. It is nothing more than a
directory on some filesystem that you tell postgres about so that you can
store relations in it. If you don't define a tablespace in postgres, all of
your relations are going to be located in /var/lib/pgsql/base.

That's the difference, you don't NEED a tablespace like Oracle, you'll
only use them in postgres when you're trying to store data in postgres on a
different mountpoint.

Hope this helps.

--Scott