PostgreSQL – Replacing a Database with pg_restore

pg-restorepostgresql

I am trying to replace an existing database with pg_restore and am running into issues. I apologize if this issue is elementary.

Specifically my Postgres install is set up like this:

database postgres owned by root
database d owned by u
database restore owned by u (more on this later)

I created a dump like pg_dump --format=custom .... I am now trying to replace d with the contents of that dump. Specifically I am running a command like pg_restore -cC --dbname=$DB --exit-on-error --format=custom --username=$USER.

But it seems no matter what combination of $DB and $USER, Postgres is unable to restore. From the error messages (below) Postgres seems to want the user to simultaneously be root and the owner of d. I have read the man pages and tried various combinations to no avail.

What am I doing wrong?

Specifically, if $DB is d, regardless of $USER, I get

ERROR: cannot drop the currently open database

Command was: DROP DATABASE d;

Fair enough. So let's try $DB=postgres and $USER=root:

ERROR: must be owner of database d

Command was: DROP DATABASE d;

Okay, so let's try $DB=postgres and $USER=u:

ERROR: must be member of role "root"

Command was: ALTER DATABASE d OWNER TO root;

Huh? Maybe that has to do with logging into postgres, which is owned by root? Let's try $DB=restore (created specifically for this purpose) and $USER=u:

ERROR: must be member of role "root"

Command was: ALTER DATABASE d OWNER TO root;

Best Answer

Evidently, "root" is not a superuser (which is a bit odd, given the normal implications of the word "root"). The pg_restore command you wish to run must be run as a superuser. Only a superuser can drop someone else's database, and then create a new database owned by someone else.

Although it looks like the restored database is going to be owned by "root", not "u". I guess that is not what you are expecting, but it is what was encoded in the pg_dump output.

Related Solutions

Postgresql – Ensure correct username when using pg_restore

If you want to create the plpgsql extension I believe you have to be Superuser. My recommendation is to make app_user temporarily a superuser and then revert this. Superusers also are treated as owners of everything.

ALTER USER app_user WITH SUPERUSER;

run the restore, then when you are done

ALTER USER app_user WITH NOSUPERUSER;

This should avoid any other permissions issues but still leave you with the permissions you want.

PostgreSQL – pg_restore Error: Schema ‘public’ Already Exists

The error is harmless but to get rid of it, I think you need to break this restore into two commands, as in:

dropdb -U postgres mydb && \
 pg_restore --create --dbname=postgres --username=postgres pg_backup.dump

The --clean option in pg_restore doesn't look like much but actually raises non-trivial problems.

For versions up to 9.1

The combination of --create and --clean in pg_restore options used to be an error in older PG versions (up to 9.1). There is indeed some contradiction between (quoting the 9.1 manpage):

--clean Clean (drop) database objects before recreating them

and

--create Create the database before restoring into it.

Because what's the point of cleaning inside a brand-new database?

Starting from version 9.2

The combination is now accepted and the doc says this (quoting the 9.3 manpage):

--clean Clean (drop) database objects before recreating them. (This might generate some harmless error messages, if any objects were not present in the destination database.)

--create Create the database before restoring into it. If --clean is also specified, drop and recreate the target database before connecting to it.

Now having both together leads to this kind of sequence during your restore:

DROP DATABASE mydb;
...
CREATE DATABASE mydb WITH TEMPLATE = template0... [other options]
...
CREATE SCHEMA public;
...
CREATE TABLE...

There is no DROP for each individual object, only a DROP DATABASE at the beginning. If not using --create this would be the opposite.

Anyway this sequence raises the error of public schema already existing because creating mydb from template0 has imported it already (which is normal, it's the point of a template database).

I'm not sure why this case is not handled automatically by pg_restore. Maybe this would cause undesirable side-effects when an admin decides to customize template0 and/or change the purpose of public, even if we're not supposed to do that.

Best Answer

Related Solutions

Postgresql – Ensure correct username when using pg_restore

PostgreSQL – pg_restore Error: Schema ‘public’ Already Exists

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