Tablespace setup issue

On Thu, 2019-11-21 at 09:48 -0500, Sébastien Bihorel wrote:

Now, I would like to assign a particular disk location for the tablespace used
by this database but I am getting all kinds of errors apparently linked to folder permissions.

Don't create tablespaces.
Stick with the default tablespace.

Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com

On 11/21/19 8:52 AM, Laurenz Albe wrote:

On Thu, 2019-11-21 at 09:48 -0500, Sébastien Bihorel wrote:

Now, I would like to assign a particular disk location for the tablespace used
by this database but I am getting all kinds of errors apparently linked to folder permissions.

Don't create tablespaces.
Stick with the default tablespace.

Why?

--
Angular momentum makes the world go 'round.

On Thu, 2019-11-21 at 08:54 -0600, Ron wrote:

Don't create tablespaces.
Stick with the default tablespace.

Why?

Because you won't need them.

Tablespaces have a limited number of use cases:
- Distribute I/O across several devices (you can do the same
on a lower level using striping).
- Put some tables or indexes faster and some on slower storage.
- Provide a size limit for a table or a database.
- Have your temporary files on a different file system.

In a virtualized environment, you never want tablespaces.

Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com

On 11/21/19 8:59 AM, Laurenz Albe wrote:

On Thu, 2019-11-21 at 08:54 -0600, Ron wrote:

Don't create tablespaces.
Stick with the default tablespace.

Why?

Because you won't need them.

Tablespaces have a limited number of use cases:
- Distribute I/O across several devices (you can do the same
on a lower level using striping).
- Put some tables or indexes faster and some on slower storage.
- Provide a size limit for a table or a database.
- Have your temporary files on a different file system.

In a virtualized environment, you never want tablespaces.

After adding another 350GB to the data/base filesystem, the storage team
said that the virtual LUN on our ESX host is full.  No more expansion of
this database until and unless they create a new LUN (on storage replicated
to a different DC using SRM).

Thus, to enlarge the database on this VM, we either...

1. create a tablespace on a different (modest sized) LUN, or
2. create a completely new 10TB LUN and migrate the whole db (including
backups) to that new LUN.

Honestly, using a new tablespace seems simpler.

--
Angular momentum makes the world go 'round.

On Thu, 2019-11-21 at 09:11 -0600, Ron wrote:

After adding another 350GB to the data/base filesystem, the storage team
said that the virtual LUN on our ESX host is full. No more expansion of
this database until and unless they create a new LUN (on storage replicated
to a different DC using SRM).

Thus, to enlarge the database on this VM, we either...

1. create a tablespace on a different (modest sized) LUN, or
2. create a completely new 10TB LUN and migrate the whole db (including
backups) to that new LUN.

Honestly, using a new tablespace seems simpler.

Ok, that is a valid use case :^)

Change into the directory with the new file system.
Create a subdirectory and "chown" it to "postgres".
Become operating system user "postgres" and verify
that you can write to that directory.

If not, fix the permissions of the directories on the path.

If you can write to the directory, you will be able to create
a tablespace there.

Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com

Sébastien Bihorel wrote:

Hi,

I am new to this list and reaching out because I am having troubles
setting up a local PostgreSQL database on my laptop. Maybe, as a
preamble, I should say that I am pretty much a novice trying to teach
myself and get practical experience about database and SQL queries (I
have some general idea about relational DB structure and operation but
no actual experience creating a DB or writing SQL queries).

Some background about my setup:
- OS: my laptop runs Linux Mint 19.1 (a flavor of ubuntu 18.04); psql
12.1 was installed along with pgadmin 4. There is a single user (ie,
sebastien) on this machine and the group postgres exists.

I have also successfully created a database (sebastien) for the new
superuser sebastien, and a schema (test) within this database.

Now, I would like to assign a particular disk location for the
tablespace used by this database but I am getting all kinds of errors
apparently linked to folder permissions.

The location is /home/sebastien/data/pgdata96_sebastien

This is probably not what going to do what you want. At best it will be
a spaghetti pile of mixed up permissions, working against several sets
of common practice and security restrictions, to get it to work. I
wouldn't be surprised if you ran into SELinux or AppArmor restrictions
too (or another similar system, I think there are a couple more).

has the following properties:

/home/sebastien/data $ ls -l
drwxr-xr-x 2 sebastien postgres 4096 Nov 19 09:14 pgdata96_sebastien

The manual states "The location must be an existing, empty directory
that is owned by the PostgreSQL operating system user." So, I am not
sure what I am doing wrong. Web searches ran on these error messages did
not enlighten me more...

The files and directories that the Postgres server manages MUST be owned
by the OS user "postgres". This directory is still owned by your OS
user sebastien. You will probably also have to play games with the
permissions on /home/sebastien and /home/sebastien/data to get this to
work at all.

Your OS user will not be able to usefully read any files that Postgres
creates directly, so there's not much value in putting them outside of
the default directory tree under /var/lib/postgres.

Postgres is pretty good about managing its own data files; unless you
need to quickly glue on more storage without disturbing an active
production server, or need to put a particular table or database on
expensive-but-faster (or possibly slower-but-much-larger-and-cheaper)
storage, you probably don't need to use tablespaces.

For experimenting with them it would be a lot simpler to create a
directory (or two, or three) under /var/lib/postgres for them, owned by
the postgres OS user.

-kgd

On 11/21/19 6:48 AM, Sébastien Bihorel wrote:

Hi,

I am new to this list and reaching out because I am having troubles
setting up a local PostgreSQL database on my laptop. Maybe, as a
preamble, I should say that I am pretty much a novice trying to teach
myself and get practical experience about database and SQL queries (I
have some general idea about relational DB structure and operation but
no actual experience creating a DB or writing SQL queries).

Some background about my setup:
- OS: my laptop runs Linux Mint 19.1 (a flavor of ubuntu 18.04); psql
12.1 was installed along with pgadmin 4. There is a single user (ie,
sebastien) on this machine and the group postgres exists.
- database: I have successfully created the new superuser sebastien
                                   List of roles
 Role name |                         Attributes
| Member of
-----------+------------------------------------------------------------+-----------
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS
| {}
 sebastien | Superuser, Create DB
 +| {}
           | Password valid until infinity                              |

I have also successfully created a database (sebastien) for the new
superuser sebastien, and a schema (test) within this database.

Now, I would like to assign a particular disk location for the
tablespace used by this database but I am getting all kinds of errors
apparently linked to folder permissions.

The location is /home/sebastien/data/pgdata96_sebastien has the
following properties:

/home/sebastien/data $ ls -l
drwxr-xr-x 2 sebastien postgres 4096 Nov 19 09:14 pgdata96_sebastien

Starting psql as sebastien, I tried the following requests and got the
following errors:

sebastien=# CREATE TABLESPACE sebdata LOCATION
'/home/sebastien/data/pgdata96_sebastien';
ERROR:  could not set permissions on directory
"/home/sebastien/data/pgdata96_sebastien": Permission denied
sebastien=# ALTER DATABASE sebastien set TABLESPACE
'/home/sebastien/data/pgdata96_sebastien';
ERROR:  syntax error at or near "'/home/sebastien/data/pgdata96_sebastien'"
LINE 1: ALTER DATABASE sebastien set TABLESPACE '/home/sebastien/dat...

The manual states "The location must be an existing, empty directory
that is owned by the PostgreSQL operating system user." So, I am not
sure what I am doing wrong. Web searches ran on these error messages did
not enlighten me more...

As it stands now the directory allows you(sebastien) writes on that
directory. That is not the same as the Postgres system user, which I
assume is postgres. You need to verify this and also who is part of
postgres group and adjust the directory permissions to give the postgres
system user full writes. The thing to remember is that the Postgres
users(postgres, sebastien) are not the same as the system users even if
they have the same name.

I would greatly appreciated any pointers to reference material on these
issues or advises on how to approach this.

Thank you in advance for your time.

--
Adrian Klaver
adrian.klaver@aklaver.com

Thank you everyone for your responses. It is great to see so much feedback.

Based upon all the responses, I was able to successfully set my tablespace
doing the following:

- Using /usr/data/pgdata96_sebastien as target tablespace directory
- Permissions were set to: chmod postgres:postgres
/usr/data/pgdata96_sebastien
- Starting psql using: sudo -u postgres psql
- Issuing:
- CREATE TABLESPACE sebdata LOCATION '/usr/data/pgdata96_sebastien';
- ALTER DATABASE sebastien set TABLESPACE sebdata;

One thing that is still a bit surprising to me is that even if I start psql
with the sebastien user, it seems that psql interacts with the file system
as postgres (at least, that's what I infer from the original error messages
I got when using the sebastien user and trying to set the tablespace to a
file owned by sebastien).

Thanks

On Thu, Nov 21, 2019 at 9:48 AM Sébastien Bihorel <pomchip@free.fr> wrote:

psql is the client, not the server. What user you run psql as doesn’t make a difference, it’s what user the server is running as that makes the difference, since it is the server that interacts with the file system. psql simply connects to and interacts with the PostgreSQL server.

---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145