Re: Streaming Replication archive_command is really needed?

Am 21.07.2017 um 08:01 schrieb Michael Paquier:
> On Thu, Jul 20, 2017 at 10:07 PM, Leonardo M. Ramé <l(dot)rame(at)griensu(dot)com> wrote:
>> El 20/07/17 a las 16:57, Andreas Kretschmer escribió:
>>> On 20 July 2017 21:46:09 GMT+02:00, "Leonardo M. Ramé"
>>> <l(dot)rame(at)griensu(dot)com> wrote:
>>>> Hi, I wonder if archive_mode=on and archive_command parameters in
>>>> postgresql.conf are really needed for streaming replication between two
>>>>
>>>> servers (master-slave).
>>> No.
>> So, can I just comment those commands and remove the main/archive directory?
> "No" is not completely exact and lacks in details. There are two cases
> where having an archive is helpful:
> 1) The standby has disconnected from its primary for a time long
> enough that WAL segments have been rotated by two completed
> checkpoints. If that happens, when the standby reconnects it would
> fail, and you would need to take a new base backup.

you can prevent that using replication slots, but i'm pretty sure you
(Michael) knows that ;-)
(
http://paquier.xyz/postgresql-2/postgres-9-4-feature-highlight-replication-phydical-slots/
)

> 2) Backup strategies. Keeping a larger history set of WAL segments is
> helpful for incremental backups, which is partially the point actually
> raised upthread about PITR.

Ack, that's right. Using both (streaming and wal-shipping/archiving)
will make it more robust, and you have (with archiving) the posibility
for PITR.
BUT, you can build a streaming replication without archiving, even you
can build a continuous backup using only streaming (Barman, streaming
only mode).

Regards, Andreas

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