Date: Wed, 24 Jun 2020 21:00:16 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: The description for pg_replication_slots.restart_lsn
Message-ID: <20200625010016.GA22779@alvherre.pgsql>
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On 2020-Jun-17, Fujii Masao wrote:

> The document explains that restart_lsn column in pg_replication_slots view is:
> 
>     The address (LSN) of oldest WAL which still might be required by
>     the consumer of this slot and thus won't be automatically removed
>     during checkpoints.
> 
> But the latter part is not true in v13 thanks to max_slot_wal_keep_size.
> I think that we need to update it as follows. Thought?
> 
>     The address (LSN) of oldest WAL which still might be required by
>     the consumer of this slot and thus won't be automatically removed
>     during checkpoints unless this LSN gets behind more than
>     max_slot_wal_keep_size from the current LSN.

We just added the invalidated_at LSN to replication slots; while working
on the tests for that today, I was thinking that it might be useful to
display that LSN in pg_replication_slots.  What do you think of the idea
of publishing the invalidated_at LSN in pg_replication_slot.restart_lsn
when the slot is invalid?

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services