[pgpool-general: 4731] Re: When is it safe to attach node

[Tatsuo Ishii]

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The risk with replication lag is that SELECT might return outdated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