Re: Extend documentation for pg_stat_replication.backend_xmin

On Thu, Oct 16, 2025 at 12:47 AM Renzo Dani <arons7(at)gmail(dot)com> wrote:
>
> Hi,
> recently I had some issue understanding what was going on with a replica and the reported xmin.
> I have than created a patch to better specify the value expected into the pg_stat_replication.backend_xmin field.

+1

+ This field will be null if a replication slot is used; in that
case, the xmin is available through <link
linkend="view-pg-replication-slots">pg_replication_slots</link>.

I think it would be better to also mention that this field is null
when hot_standby_feedback is disabled.

Also, <literal> tags should be used for "xmin", and a newline should
be added to avoid an overly long line.

Based on the above comments, how about revising it as follows?

+ This field will be null if a replication slot is used (in this case,
+ the standby's <literal>xmin</literal> is shown in
+ <link linkend="view-pg-replication-slots">pg_replication_slots</link>)
+ or if <varname>hot_standby_feedback</varname> is disabled.

Regards,

--
Fujii Masao