On Fri, Dec 22, 2017 at 12:46:01AM -0500, Chapman Flack wrote: > I was noticing that terminology in the long backup-from-standby thread > I was reading, but it wasn't clear to me how the terms originated. > What's exclusive about pg_start_backup/copy/pg_stop_backup? And what's > nonexclusive about pg_basebackup (which, AFAICS, is following roughly > the same sequence under the hood)?
You can run an exclusive backup only once at a time in a given PostgreSQL server as it uses the on-disk backup_label file to determine the state the server is in, while non-exclusive backups can be run across many sessions, at the cost that you need to maintain the session alive for the duration of the backup. pg_basebackup uses always non-exclusive backups, so it never creates an on-disk backup_label file on the instance from which the backup is taken but it writes the file by itself. pg_start_backup and pg_stop_backup include a set of optional arguments to control if you want to do a non-exclusive or an exclusive backup, the default being exclusive. Non-exclusive backups can also be run while an exclusive backup is running. > By the way, what does happen in that case? I'm guessing it wakes up, > sees the backup_label file, decides it's doing a PITR, and starts > replaying already-applied WAL from the start-of-backup checkpoint, > rather than from the most recent one? Oops. In short, yes. And it does not find the backup end record as well. -- Michael
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