Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)

On Mon, Apr 10, 2023 at 3:41 AM Pavel Luzanov <p(dot)luzanov(at)postgrespro(dot)ru> wrote:
>
> On 05.04.2023 03:41, Melanie Plageman wrote:
> > On Tue, Apr 4, 2023 at 4:35 PM Pavel Luzanov <p(dot)luzanov(at)postgrespro(dot)ru> wrote:
> >
> >> After a little thought... I'm not sure about the term 'bootstrap
> >> process'. I can't find this term in the documentation.
> > There are various mentions of "bootstrap" peppered throughout the docs
> > but no concise summary of what it is. For example, initdb docs mention
> > the "bootstrap backend" [1].
> >
> > Interestingly, 910cab820d0 added "Bootstrap superuser" in November. This
> > doesn't really cover what bootstrapping is itself, but I wonder if that
> > is useful? If so, you could propose a glossary entry for it?
> > (preferably in a new thread)
>
> I'm not sure if this is the reason for adding a new entry in the glossary.
>
> >> Do I understand correctly that this is a postmaster? If so, then the
> >> postmaster process is not shown in pg_stat_activity.
> > No, bootstrap process is for initializing the template database. You
> > will not be able to see pg_stat_activity when it is running.
>
> Oh, it's clear to me now. Thank you for the explanation.
>
> > You can query pg_stat_activity from single user mode, so it is relevant
> > to pg_stat_activity also. I take your point that bootstrap mode isn't
> > relevant for pg_stat_activity, but I am hesitant to add that distinction
> > to the pg_stat_io docs since the reason you won't see it in
> > pg_stat_activity is because it is ephemeral and before a user can access
> > the database and not because stats are not tracked for it.
> >
> > Can you think of a way to convey this?
>
> See my attempt attached.
> I'm not sure about the wording. But I think we can avoid the term
> 'bootstrap process'
> by replacing it with "database cluster initialization", which should be
> clear to everyone.

I like that idea.

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 3f33a1c56c..45e20efbfb 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -991,6 +991,9 @@ postgres 27093 0.0 0.0 30096 2752 ?
Ss 11:34 0:00 postgres: ser
<literal>archiver</literal>,
<literal>startup</literal>, <literal>walreceiver</literal>,
<literal>walsender</literal> and <literal>walwriter</literal>.
+ The special type <literal>standalone backend</literal> is used

I think referring to it as a "special type" is a bit confusing. I think
you can just start the sentence with "standalone backend". You could
even include it in the main list of backend_types since it is possible
to see it in pg_stat_activity when in single user mode.

+ when initializing a database cluster by <xref linkend="app-initdb"/>
+ and when running in the <xref linkend="app-postgres-single-user"/>.
In addition, background workers registered by extensions may have
additional types.
</para></entry>

I like the rest of this.

I copied the committer who most recently touched pg_stat_io (Michael
Paquier) to see if we could get someone interested in committing this
docs update.

- Melanie