Re: [Todo item] Add entry creation timestamp column to pg_stat_replication

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: "myungkyu(dot)lim" <myungkyu(dot)lim(at)samsung(dot)com>
Cc: 'Masahiko Sawada' <sawada(dot)mshk(at)gmail(dot)com>, 'PostgreSQL-development' <pgsql-hackers(at)postgresql(dot)org>, woosung(dot)sohn(at)samsung(dot)com, don(dot)hong(at)samsung(dot)com
Subject: Re: [Todo item] Add entry creation timestamp column to pg_stat_replication
Date: 2018-12-04 03:56:25
Message-ID: 20181204035625.GQ3423@paquier.xyz
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On Fri, Nov 30, 2018 at 05:54:15PM +0900, Michael Paquier wrote:
> Looks pretty to me at quick glance, unfortunately I have not spent much
> time on it, particularly testing it.
>
> + <row>
> + <entry><structfield>reply_time</structfield></entry>
> + <entry><type>timestamp with time zone</type></entry>
> + <entry>Send time of last message received from WAL
> receiver</entry>
> + </row>
> This is a bit confusing as this counts for the last *standby* message
> ('r'), and not the last feedback message ('h').
>
> + /*
> + * timestamp of the latest message, reported by standby server
> + */
> + TimestampTz replyTime;
>
> A small indentation problem, not a big deal.

I have been looking at this patch more in-depth, and you missed one
critical thing: hot standby feedback messages also include the timestamp
the client used when sending the message, so if we want to track the
latest time when a message has been sent we should track it as much as
the timestamp from status update messages.

Fixing that and updating a couple of comments and variables, I am
finishing with the attached. Thoughts?

(The catversion bump is a self-reminder, don't worry about it.)
--
Michael

Attachment Content-Type Size
standby-message-time-v3.patch text/x-diff 8.8 KB

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