Re: Stale description for pg_basebackup

On 2021/04/21 11:09, Kyotaro Horiguchi wrote:
> At Wed, 21 Apr 2021 10:43:30 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
>> At Tue, 20 Apr 2021 13:32:35 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
>>> Hello.
>>>
>>> It seems to me that there's a stale description in the documentation
>>> of pg_basebackup.

I think you're right.

> Hmm. Some words need to be qualified. Attached.

+ If you are using <literal>-X none</literal>, there is no guarantee on
+ the primary that all WAL files required for the backup are archived at
+ the end of backup.

I don't think that this should be picked up as a limitation of standby backup.
Because users basically want to make pg_basebackup wait for all required
WAL files to be archived on the standby, in the standby backup case.

When <varname>archive_mode</varname> is set
+ to <literal>on</literal> on the

"on" should be "always"?

+ standby, <application>pg_basebackup</application> may wait for a long
+ time for all the required WAL files to be archived. In that case, You
+ may need to call <function>pg_switch_wal()</function> on the primary to
+ complete it sooner.

What about the following description?

-------------------
When you are using -X none, if write activity on the primary is low,
pg_basebackup may need to wait a long time for all WAL files required for
the backup to be archived. It may be useful to run pg_switch_wal
on the primary in order to trigger an immediate WAL file switch and archiving.
-------------------

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION