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.
standby_mode = on
Tharrr's yer problem. You've configured it as a continuous (warm or hot) standby.
standby_mode in the manual:
standby_mode (boolean)
Specifies whether to start the PostgreSQL server as a standby. If this parameter is on, the server will not stop recovery when the end of archived WAL is reached, but will keep trying to continue recovery by fetching new WAL segments using restore_command and/or by connecting to the primary server as specified by the primary_conninfo setting.
Best Answer
It may not be the data size, but rather the number of tables and schemas. Database dumps and restores are known to run into problems in those cases.
For large backups the preferred backup approach is to use pg_basebackup which creates a snapshot of the database files at a specific time. These are restored much faster. Unfortunately this does not necessarily work for certain sorts of things, like restoring across major versions (but see pg_upgrade).
the raw data size is not a problem. But in your case, pg_dump may not be very useful and you may want to look at other ways of making a backup.