Date: Thu, 7 Apr 2022 21:37:09 -0700
From: Andres Freund <andres@anarazel.de>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: melanieplageman@gmail.com, pryzby@telsasoft.com, thomas.munro@gmail.com,
	david.g.johnston@gmail.com, pgsql-hackers@lists.postgresql.org
Subject: Re: shared-memory based stats collector - v70
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Hi,

On 2022-04-07 20:59:21 -0700, Andres Freund wrote:
> 
>   <para>
>    Cumulative statistics are collected in shared memory. Every
>    <productname>PostgreSQL</productname> process collects statistics locally
>    then updates the shared data at appropriate intervals.  When a server,
>    including a physical replica, shuts down cleanly, a permanent copy of the
>    statistics data is stored in the <filename>pg_stat</filename> subdirectory,
>    so that statistics can be retained across server restarts.  In contrast,
>    when starting from an unclean shutdown (e.g., after an immediate shutdown,
>    a server crash, starting from a base backup, and point-in-time recovery),
>    all statistics counters are reset.
>   </para>
> ...
>    <para>
>     The cumulative statistics system is active during recovery. All scans,
>     reads, blocks, index usage, etc., will be recorded normally on the
>     standby. However, WAL replay will not increment relation and database
>     specific counters. I.e. replay will not increment pg_stat_all_tables
>     columns (like n_tup_ins), nor will reads or writes performed by the
>     startup process be tracked in the pg_statio views, nor will associated
>     pg_stat_database columns be incremented.
>    </para>

I went with these for now. My guess is that there's further improvements in
them, and in surrounding areas...


With that, I'll close this CF entry. It's been a while.

Greetings,

Andres Freund