> On Mar 19, 2020, at 15:19, Dennis Jacobfeuerborn <dennisml@xxxxxxxxxxxx> wrote: > I'm currently trying to understand how backups work. In the > documentation in section "25.2. File System Level Backup" it says that > filesystem level backups can only be made when the database if offline > yet pg_basebackup seems to do just that but works while the database is > online. Am I misunderstanding something here or does pg_basebackup use > some particular features of Postgres to accomplish this? pg_basebackup does, indeed, take an inconsistent copy of the file system while it is running; what allows it to bring the database back up to consistency is the write-ahead log segments that are created while pg_basebackup is running. That's why it is important to have all of the WAL segments created during the run (which is what --wal-method=stream provides you). -- -- Christophe Pettus xof@xxxxxxxxxxxx
