Re: shared-memory based stats collector - v70

On Thu, Apr 7, 2022 at 8:59 PM Andres Freund <andres(at)anarazel(dot)de> 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>
>

I like this. My comment regarding using "i.e.," here stands though.

>
> <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 like this too. The second part with three nors is a bit rough. Maybe:

... specific counters. In particular, replay will not increment
pg_stat_database or pg_stat_all_tables columns, and the startup process
will not report reads and writes for the pg_statio views.

It would helpful to give at least one specific example of what is being
recorded normally, especially since we give three of what is not.

David J.