[pgpool-general: 4777] Re: Remove Detached Background Node via reload

Tatsuo Ishii ishii at postgresql.org
Fri Jul 8 07:50:07 JST 2016

> Hi all,
> we are working with pgpool in master/master replication mode for
> scaling in and out postgresql instances. While scaling out works via
> updating the pgpool.conf with the new instance as backend, next do
> "pgpool reload" and "pcp_recovery_node", we have problems for scaling
> in.
> Whenever we remove a backend from the pgpool.conf, call
> "pcp_detach_node" and next "pgpool reload", pgpool does not take this
> into account. We have to do a pgpool restart to remove the backend
> from the pgpool.
> Any suggestions how we can scale-in on the fly, like we do it for
> scale out?

It's a current limitation. From the manual:

> New nodes can be added in this parameter by reloading a configuration
> file. However, values cannot be updated so you must restart pgpool-II
> in that case.

Since deleting backend is treated as "update" above, deleting backend
from pgpool.conf does not take effect until pgpool-II restarts.

Maybe removing this limitation is an interesting project toward
pgpool-II 3.6?

Best regards,
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php

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