borgmatic/docs/how-to/backup-your-databases.md at c5776447b9cc7ab542fc92b6fcc1856074980926

Dan Helfman 218cbd5289 In database documentation, include command for finding named pipes and special devices.

2020-07-13 10:56:59 -07:00

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title
How to backup your databases

Database dump hooks

If you want to backup a database, it's best practice with most database systems to backup an exported database dump, rather than backing up your database's internal file storage. That's because the internal storage can change while you're reading from it. In contrast, a database dump creates a consistent snapshot that is more suited for backups.

Fortunately, borgmatic includes built-in support for creating database dumps prior to running backups. For example, here is everything you need to dump and backup a couple of local PostgreSQL databases and a MySQL/MariaDB database:

hooks:
    postgresql_databases:
        - name: users
        - name: orders
    mysql_databases:
        - name: posts

As part of each backup, borgmatic streams a database dump for each configured database directly to Borg, so it's included in the backup without consuming additional disk space. (The one exception is PostgreSQL's "directory" dump format, which can't stream and therefore does consume temporary disk space.)

To support this, borgmatic creates temporary named pipes in ~/.borgmatic by default. To customize this path, set the borgmatic_source_directory option in the location section of borgmatic's configuration.

Also note that using a database hook implicitly enables both the read_special and one_file_system configuration settings (even if they're disabled in your configuration) to support this dump and restore streaming. See Limitations below for more on this.

Here's a more involved example that connects to remote databases:

hooks:
    postgresql_databases:
        - name: users
          hostname: database1.example.org
          port: 5433
          username: postgres
          password: trustsome1
          format: tar
          options: "--role=someone"
    mysql_databases:
        - name: posts
          hostname: database2.example.org
          port: 3307
          username: root
          password: trustsome1
          options: "--skip-comments"

If you want to dump all databases on a host, use all for the database name:

hooks:
    postgresql_databases:
        - name: all
    mysql_databases:
        - name: all

Note that you may need to use a username of the postgres superuser for this to work with PostgreSQL.

Configuration backups

An important note about this database configuration: You'll need the configuration to be present in order for borgmatic to restore a database. So to prepare for this situation, it's a good idea to include borgmatic's own configuration files as part of your regular backups. That way, you can always bring back any missing configuration files in order to restore a database.

Supported databases

As of now, borgmatic supports PostgreSQL and MySQL/MariaDB databases directly. But see below about general-purpose preparation and cleanup hooks as a work-around with other database systems. Also, please file a ticket for additional database systems that you'd like supported.

Database restoration

To restore a database dump from an archive, use the borgmatic restore action. But the first step is to figure out which archive to restore from. A good way to do that is to use the list action:

borgmatic list

(No borgmatic list action? Try the old-style --list, or upgrade borgmatic!)

That should yield output looking something like:

host-2019-01-01T04:05:06.070809      Tue, 2019-01-01 04:05:06 [...]
host-2019-01-02T04:06:07.080910      Wed, 2019-01-02 04:06:07 [...]

Assuming that you want to restore all database dumps from the archive with the most up-to-date files and therefore the latest timestamp, run a command like:

borgmatic restore --archive host-2019-01-02T04:06:07.080910

(No borgmatic restore action? Upgrade borgmatic!)

With newer versions of borgmatic, you can simplify this to:

borgmatic restore --archive latest

The --archive value is the name of the archive to restore from. This restores all databases dumps that borgmatic originally backed up to that archive.

This is a destructive action! borgmatic restore replaces live databases by restoring dumps from the selected archive. So be very careful when and where you run it.

Repository selection

If you have a single repository in your borgmatic configuration file(s), no problem: the restore action figures out which repository to use.

But if you have multiple repositories configured, then you'll need to specify the repository path containing the archive to restore. Here's an example:

borgmatic restore --repository repo.borg --archive host-2019-...

Restore particular databases

If you've backed up multiple databases into an archive, and you'd only like to restore one of them, use the --database flag to select one or more databases. For instance:

borgmatic restore --archive host-2019-... --database users

Limitations

There are a few important limitations with borgmatic's current database restoration feature that you should know about:

You must restore as the same Unix user that created the archive containing the database dump. That's because the user's home directory path is encoded into the path of the database dump within the archive.
As mentioned above, borgmatic can only restore a database that's defined in borgmatic's own configuration file. So include your configuration file in backups to avoid getting caught without a way to restore a database.
borgmatic does not currently support backing up or restoring multiple databases that share the exact same name on different hosts.
Because database hooks implicitly enable the read_special configuration setting to support dump and restore streaming, you'll need to ensure that any special files are excluded from backups (named pipes, block devices, and character devices) to prevent hanging. Try a command like find / -type c,b,p to find such files. Common directories to exclude are /dev and /run, but that may not be exhaustive.

Manual restoration

If you prefer to restore a database without the help of borgmatic, first extract an archive containing a database dump, and then manually restore the dump file found within the extracted ~/.borgmatic/ path (e.g. with pg_restore or mysql commands).

Preparation and cleanup hooks

If this database integration is too limited for needs, borgmatic also supports general-purpose preparation and cleanup hooks. These hooks allows you to trigger arbitrary commands or scripts before and after backups. So if necessary, you can use these hooks to create database dumps with any database system.

Troubleshooting

MySQL table lock errors

If you encounter table lock errors during a database dump with MySQL/MariaDB, you may need to use a transaction. You can add any additional flags to the options: in your database configuration. Here's an example:

hooks:
    mysql_databases:
        - name: posts
          options: "--single-transaction --quick"

borgmatic hangs during backup

See Limitations above about read_special. You may need to exclude certain paths with named pipes, block devices, or character devices on which borgmatic is hanging.

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