Re: How does pg_basebackup manage to create a snapshot of the filesystem?

Greetings,

* Dennis Jacobfeuerborn (dennisml(at)conversis(dot)de) 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?

A simple tar-based backup as discussed in 25.2 can only be done with the
database off-line, but if you're wondering what pg_basebackup is doing
under the covers then you should be reading through 25.3, which talks
about the PostgreSQL WAL, how a backup can be taken in an online manner
provided you retain the WAL that was created during the backup, how to
restore a backup taken in that manner, etc.

All that said, I don't recommend rolling your own backup solution for
PG. There's a number of good ones out there, starting with
pg_basebackup if you really just need something simple.

Thanks,

Stephen