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

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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