"Andy Shellam" <andy.shellam@mailnetwork.co.uk> writes:
> If pg_start_backup is used correctly, no data pages will be written to disk
> until pg_stop_backup is called, so this shouldn't be an issue
That's incorrect, the database will continue to operate normally. The
only thing pg_start_backup really does is lay down a marker so you can
tell how far back you need to save WAL files in order to do a PITR
restore using your backup.
The fact that the backup tool might get an inconsistent copy of some
files is not an issue, because replay of the WAL files against the
copied database will fix any inconsistencies.
It definitely is a pain in the neck that GNU tar complains about files
changing underneath it --- I've looked for a way to disable that, or at
least reduce it to a warning instead of an error condition, but gtar
doesn't seem to have such a switch. You should try alternative backup
tools such as cpio or rsync.
regards, tom lane