Re: pg9.6: no backup history file (*.backup) created on hot standby

On Tue, 2018-10-09 at 11:45 +0900, Michael Paquier wrote:
> (Please do not forget to add the community mailing list in CC.)
>
> On Tue, Oct 09, 2018 at 10:33:56AM +0800, magodo wrote:
> > Since the backup history aims to aid administrator to identify the
> > point from which wal archive should be kept and before which the
> > archive could be cleaned. It is very helpful in kinds of use cases.
> >
> > Why not also create it when do basebackup on standby?
>
> The backup_label file is equally helpful, and backup history files
> are
> not mandatory for backups. One of the reasons behind why we cannot
> have
> those on standbys is that there is no actual way to ensure the
> uniqueness of this file, as two backups could be started in parallel
> with the same start location and the *same* file name. If an archive
> command is not able to handle correctly the duplicates, you could
> bloat
> pg_wal. And that's a real problem.
> --
> Michael

Oh, I almost forget backup_label.. Thank you for point it out!

Yet, I am still not so clear how does the bloat of pg_wal happen? Do
you mean pg_wal will be filled up by many .backup(s)?

Magodo