[pgpool-hackers: 3997] Re: [pgpool-general: 7543] VIP with one node

[Tatsuo Ishii]

Hi Usama,

Sorry for late reply.

From: Muhammad Usama <m.usama at gmail.com>
Subject: Re: [pgpool-hackers: 3898] Re: [pgpool-general: 7543] VIP with one node
Date: Thu, 22 Jul 2021 14:12:59 +0500
Message-ID: <CAEJvTzXsKE2B0QMd0AjGBmXK6zocWZZcGU7yzzkSnmff0iAfqA at mail.gmail.com>

> On Tue, Jul 20, 2021 at 4:40 AM Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
> 
>> >> Is it possible to configure watchdog to enable the lost node removal
>> >> function only when a node is properly shutdown?
>> >>
>>
>> > Yes if we disable the wd_lost_node_to_remove_timeout (by setting it to 0)
>> > the lost node removal will only happen for properly shutdown nodes.
>>
>> Oh, I thought setting wd_lost_node_to_remove_timeout to 0 will keep
>> the existing behavior.
>>
> 
> As there are two parts of the proposal, First one deals with removing the
> lost node
> from the cluster after wd_lost_node_to_remove_timeout amount of time. While
> the
> second part is about removing the properly shutdown nodes from the cluster.
> 
> Now disabling the wd_lost_node_to_remove_timeout (setting it to 0) will
> keep the
> existing behaviour as far as removing the lost node portion of proposal is
> concerned.
> 
> While not counting the properly shutdown node as part of watchdog cluster
> is not configurable (as per original proposal), So if we want to make this
> part configurable
> as well so that we can switch to 100% current behaviour then we can add
> another
> config parameter for that. like consider_shutdown_nodes_part_of_wd_cluster
> = [on|off]

+1 to add the new parameter.

The reason is, some users may want to avoid split brain problem even
if quorum/VIP is lost.  Suppose there are two admins A for the system
(OS), B for the database. B never wants to have the split brain
possibility. If A shutdowns the system, B may not notice there are not
enough nodes to form consensus anymore because if
consider_shutdown_nodes_part_of_wd_cluster is on because the
quorum/VIP will be kept until no node remains.

In summary I think there are two use-cases for both
consider_shutdown_nodes_part_of_wd_cluster is on and off.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp