Restore/upgrade content db from backup

Why

Restore / upgrade the content for a site from a database dump.

Assumptions

You have a dump of the content to restore as a .sql file, which was created by mod_backup.

How

Dumps from postgres include both database structure (tables, sequences, constraints, etc.) as well as content. Therefore it’s not possible to simply import the dump directly into an existing Zotonic database populated with content. The target database must be empty before the dump can be imported. There are (at least) 2 ways to do this:

1. Drop contents of the target db and import the dump file;
2. Create a new database, import contents, rename old database to something temporary, rename new database to match site, and finally delete the old database.

Option 2 seems more involved but is safer and quicker: it’s non-destructive. The old db remains intact until after the new one is activated. If anything goes wrong, you can fall back to the original.

It also means less downtime. The site can stay live on the old db while the new db is being created. Downtime is restricted to the rename operations (which are quick and db size independent).

For small databases the downtime difference will be minimal. However the safety is appealing. Hence this cookbook uses the second approach.

Instructions

These assume the following naming conventions:

• Your Zotonic site is named yoursite.
• The postgres dump file to load is named zotonic-dump.sql.
• Zotonic is installed in ~zotonic/zotonic

Replace these assumptions as appropriate in all commands below. Ensure the db dump file is available on target machine (see pre-requisites).

Create a new database in postgres:

zotonic:~$ sudo su -l postgres
postgres:~$ ~zotonic/zotonic/bin/zotonic createdb yoursite_new
CREATE DATABASE
GRANT
You are now connected to database "zotonic_yoursite_new".
CREATE LANGUAGE
postgres:~$

Import the dump file into the newly created db:

postgres:~$ psql -U zotonic -d zotonic_yoursite_new -f /path/to/zotonic-dump.sql
[…lots of SQL statements…]
postgres:~$

Note: the final sql commands shown will likely say ‘no privileges could be revoked for “public”’. You can ignore this.

Stop Zotonic (if running):

postgres:~$ ~zotonic/zotonic/bin/zotonic stop
Stopping zotonic zotonic001@hostname
Stop:'zotonic001@hostname'
postgres:~$

Rename the databases:

postgres:~$ psql
postgres=# ALTER DATABASE zotonic_yoursite RENAME TO zotonic_yoursite_old;
ALTER DATABASE
postgres=# ALTER DATABASE zotonic_yoursite_new RENAME TO zotonic_yoursite;
ALTER DATABASE
postgres=# \q
postgres:~$ exit
zotonic:~$

Restart Zotonic:

zotonic:~$ ~/zotonic/bin/zotonic start

Browse to your site & test it’s now serving updated content.

(Optional) Drop the old database:

zotonic:~$ sudo -u postgres psql
postgres=# DROP DATABASE zotonic_yoursite_old;
DROP DATABASE
postgres=# \q
zotonic:~$