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.
Internally, a view is just a table with a rule, so this makes sense.
See here: https://postgresql.org/docs/9.5/static/rules-views.html
Views in PostgreSQL are implemented using the rule system. In fact,
there is essentially no difference between:
CREATE VIEW myview AS SELECT * FROM mytab;
compared against the two commands:
CREATE TABLE myview (same column list as mytab);
CREATE RULE "_RETURN" AS ON SELECT TO myview DO INSTEAD
SELECT * FROM mytab;
because this is exactly what the CREATE VIEW
command does internally.
This has some side effects. One of them is that the information about
a view in the PostgreSQL system catalogs is exactly the same as it is
for a table. So for the parser, there is absolutely no difference
between a table and a view. They are the same thing: relations.
Best Answer
For anyone looking for a workaround, limiting
pg_restore
to a specific schema has helped me get around this bug. See https://stackoverflow.com/a/11776053/11819