[pgpool-general: 4736] Re: When is it safe to attach node

[Lucas Luengas]

Hello Avi.

I check standby node is up, with postgresql service running, and configured
as slave server. I check "select * from pg_stat_replication".

Regards.

On Fri, Jun 24, 2016 at 6:33 AM, Tatsuo Ishii <ishii at postgresql.org> wrote:

> Assuming that you are attaching standby node.
>
> > When is it safe to attach a detached node? What do I need to check
> before attaching a node (I have one master one slave setup)?
>
> In summary, the detaching PostgreSQL standby should be running
> normally.
>
> First of all, you need to make sure that the detaching PostgreSQL
> standby node is up and running.
>
> Next you need to make sure that the standby node properly connects to
> the primary PostgreSQL server. You can check it by looking at
> pg_stat_replication view for example.
>
> > *         Do I need to make sure replication lag is 0? If I attach a
> slave when replication lag is not 0 what problems can arise (if any)
>
> If the standby proper connects to the primary, even if replication lag
> is not 0, it is expected that it wil eventually become 0.
>
> The risk with replication lag is that SELECT might return outdated
> data but you could mitigate the problem by using delay_threshold
> parameter.
>
> > *         Before I attach a node do I need to check the state of the
> other node?
>
> No.
>
> > *         What other checks to I need to do before attaching a node?
>
> Best regards,
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese:http://www.sraoss.co.jp
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