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Compaction for the FileBackend involves restoring the DB from the backup, up to the penultimate state, then taking a snapshot of the restored DB, and then appending the last change to the backup. The new backup is then atomically swapped with the old backup. The special treatment for the last change is necessary as usual due to the rewind functionality, otherwise we'd be in an un-rewindable state, which can cause trouble if c-lightning died without committing the last change.
A simple and reliable backup plugin
This version only supports the default SQLite3 database
This plugin will maintain clean database backups to another location. It uses
the db_write hook to make sure to always have a backup that is not missing any
state updates and is not potentially harmful.
Installation
There are some Python dependencies. You can install them using pip3:
pip3 install --user -r requirements.txt
Setup
Before the backup plugin can be used it has to be initialized once. The following
command will create /mnt/external/location/file.sql as backup file and reference it
in backup.lock in the lightning directory that stores the internal state, and
which makes sure no two instances are using the same backup.
./backup-cli init ~/.lightning/bitcoin file:///mnt/external/location/file.bkp
Notes:
- If you are not using the default lightning directory you'll need to
change
~/.lightning/bitcoinin the command line to point to that directory instead. - You should use some non-local SSH or NFS mount as destination, otherwise any failure of the disk may result in both the original as well as the backup being corrupted.
- Currently only the
file:///URL scheme is supported.
IMPORTANT note about hsm_secret
You need to secure ~/.lightning/bitcoin/hsm_secret once! This
file will not change, but without this file, the database backup will be
unusable!
Make sure it has user read only permissions, otherwise lightningd will refuse
to work: chmod 0400 hsm_secret
Running
In order to tell lightningd to use the plugin you either need to tell it
via the startup option --plugin /path/to/backup.py or by placing it (or a
symlink to it) in the lightning plugin directory (~/.lightning/plugins).
On daemon startup the plugin will check the integrity of the existing backup and complain if there is a version mismatch.
Restoring a backup
If things really messed up and you need to reinstall clightning, you can
restore the database backup by using the backup-cli utility:
./backup-cli restore file:///mnt/external/location ~/.lightning/bitcoin/lightningd.sqlite3