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From: Amit Kapila <amit.kapila16@gmail.com>
Date: Fri, 13 Jan 2023 09:06:55 +0530
Message-ID: <CAA4eK1JO54=3s0KM9iZGSrQmmfzk9PEOKkW8TXjo2OKaKrSGCA@mail.gmail.com>
Subject: Re: Perform streaming logical transactions by background workers and
 parallel apply
To: Peter Smith <smithpb2250@gmail.com>
Cc: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, shveta malik <shveta.malik@gmail.com>, 
	Masahiko Sawada <sawada.mshk@gmail.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, 
	"shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Dilip Kumar <dilipbalaut@gmail.com>
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Archived-At: <https://www.postgresql.org/message-id/CAA4eK1JO54%3D3s0KM9iZGSrQmmfzk9PEOKkW8TXjo2OKaKrSGCA%40mail.gmail.com>
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On Fri, Jan 13, 2023 at 7:56 AM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Here are my review comments for v79-0001.
>
> ======
>
> General
>
> 1.
>
> When Amit suggested [1] changing the name just to "leader_pid" instead
> of "leader_apply_pid" I thought he was only referring to changing the
> view column name, not also the internal member names of the worker
> structure. Maybe it is OK anyway, but please check if that was the
> intention.
>

Yes, that was the intention.

>
> 3.
>
>        <entry role="catalog_table_entry"><para role="column_definition">
> +       <structfield>leader_pid</structfield> <type>integer</type>
> +      </para>
> +      <para>
> +       Process ID of the leader apply worker if this process is a parallel
> +       apply worker; NULL if this process is a leader apply worker or does not
> +       participate in parallel apply, or a synchronization worker
> +      </para></entry>
>
> I felt this change is giving too many details and ended up just
> muddying the water.
>

I see that we give a similar description for other parameters as well.
For example leader_pid in pg_stat_activity, see client_dn,
client_serial in pg_stat_ssl. It is better to be consistent here and
this gives the reader a bit more information when the value is NULL
for the new column.

>
> 4.
>
> @@ -949,6 +949,7 @@ CREATE VIEW pg_stat_subscription AS
>              su.oid AS subid,
>              su.subname,
>              st.pid,
> +            st.leader_pid,
>              st.relid,
>              st.received_lsn,
>              st.last_msg_send_time,
>
> IMO it would be very useful to have an additional "kind" attribute for
> this view. This will save the user from needing to do mental
> gymnastics every time just to recognise what kind of process they are
> looking at.
>

This could be a separate enhancement as the same should be true for
sync workers.

-- 
With Regards,
Amit Kapila.