Subject: Re: The description for pg_replication_slots.restart_lsn
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-docs@lists.postgresql.org
References: <20200625010016.GA22779@alvherre.pgsql>
From: Fujii Masao <masao.fujii@oss.nttdata.com>
Message-ID: <0414a23a-974c-04d5-ccb0-70ebcc76fcb7@oss.nttdata.com>
Date: Thu, 25 Jun 2020 14:48:18 +0900
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On 2020/06/25 10:00, Alvaro Herrera wrote:
> 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?

I like having separate column for invalidated_at because (at least for me)
it's a bit confusing to report the different meaning values in the same column
depending on the state.

Regards,
  

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION