Purging PITR Backups

WAL-G can delete old cluster backups and the WAL Segments tied to them. Muppy drives that purge two ways:

• from the PostgreSQL server, via the postgres crontab
• from Muppy, via a scheduled Task — the recommendation

From the PostgreSQL server

The purge is configured with the backups, in the Full Backups Configuration group of the cluster's Backup / WAL-G tab — see Via the postgres crontab.

Tick Activate WAL-G in CRONTAB and Muppy shows:

1. Four fields:
   • Nb. of Cluster Backups to keep — how many backups and WAL files to retain. Set it to 0 to disable the crontab purge.
   • WAL-G 'delete' Hour, Minute and Day of Week — when the purge runs. See crontab.guru.
2. The crontab file, with the timestamp of Muppy's last reconfiguration. ==When the purge is enabled, the crontab contains a line with a delete retain … command.==

Info

Muppy does not overwrite the postgres crontab. It injects a block with the commands needed for the WAL-G purge, generated from the CRONTAB Template. The same template covers both the backups and the purge.

Applying the configuration

Click Update 'postgres's user CRONTAB with WAL-G section to rewrite the crontab and enable, reconfigure or disable the purge according to Nb. of Cluster Backups to keep.

Muppy will not know what was purged

A purge run by the server's cron leaves Muppy's Cluster Backups list pointing at files that no longer exist. Schedule a refresh — see Refreshing the list.

From Muppy, via a Task

==Use a scheduled Muppy Task to purge WAL-G backup files.== It gives you:

• notifications on success and on failure
• execution logs
• an always-current Cluster Backups list

The Task walg_backup_delete purges the files and refreshes the Cluster Backups list afterwards — which is exactly what the crontab route cannot do.

Setup

Create a Task Run with:

1. the Task walg_backup_delete
2. the Host running the cluster
3. the Database Cluster to purge
4. the number of Cluster Backups (WAL-G) to keep, and their WAL Segments (default: 20)
5. confirm — left unticked, the purge runs as a dry run and deletes nothing. Tick it to actually delete.
6. a Muppy CRON, via Create Cron, for the recurrence

When it finishes, the Task returns JSON (#7 on the screenshot below) containing:

• data — the command's console output (stdout)
• walg_backup_list_result — the Cluster Backups list as refreshed after the purge

Reading a dry run

In dry-run mode (confirm unticked) walg_backup_list_result still lists the files, because nothing was deleted. Read data to see what a real run would remove.