Date: Wed, 20 May 2020 08:31:29 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
	Postgres hackers <pgsql-hackers@lists.postgresql.org>,
	Thomas Munro <thomas.munro@gmail.com>
Subject: Re: pg_stat_wal_receiver and flushedUpto/writtenUpto
Message-ID: <20200519233129.GA2355@paquier.xyz>
References: <20200515230539.GC212736@paquier.xyz>
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 <20200516011547.GD212736@paquier.xyz>
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On Tue, May 19, 2020 at 11:38:52PM +0900, Fujii Masao wrote:
> I found that "received_lsn" is still used in high-availability.sgml.
> We should apply the following change in high-availability?
>=20
> -     view's <literal>received_lsn</literal> indicates that WAL is being
> +     view's <literal>flushed_lsn</literal> indicates that WAL is being

Oops, thanks.  Will fix.

> BTW, we have pg_last_wal_receive_lsn() that returns the same lsn as
> pg_stat_wal_receiver.flushed_lsn. Previously both used the term "receive"
> in their names, but currently not. IMO it's better to use the same term in
> those names for the consistency, but it's not good idea to rename
> pg_last_wal_receive_lsn() to something like pg_last_wal_receive_lsn().
> I have no better idea for now. So I'm ok with the current names.

I think you mean renaming pg_last_wal_receive_lsn() to something like
pg_last_wal_flushed_lsn(), no?  This name may become confusing because
we lose the "receive" idea in the function, that we have with the
"receiver" part of pg_stat_wal_receiver.  Maybe something like that,
though that's long:
- pg_last_wal_receive_flushed_lsn()
- pg_last_wal_receive_written_lsn()=20

Anyway, a rename of this function does not strike me as strongly
necessary, as that's less tied with the shared memory structure, and
we document that pg_last_wal_receive_lsn() tracks the current LSN
received and flushed.  I am actually wondering if in the future it may
not be better to remove this function, but it has no maintenance
cost either so I would just let it as-is.
--
Michael

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