[pgpool-general: 6557] Re: Pgpool query

[Muhammad Usama]

On Fri, May 10, 2019 at 6:38 PM Lakshmi Raghavendra <lakshmiym108 at gmail.com>
wrote:

> Hi,
> I am trying pgpool for automatic faliover on my postgresql cluster using
> the watchdog feature
> Wanted to know a couple of things
> 1. Are there any hooks when pgpool re-elects next pgpool master ? wanted
> to run some customization during this time
>

Pgpool executes the user provided commands at the time of acquiring and
releasing of virtual IP by master pgpool node. You can
configure wd_escalation_command and wd_de_escalation_command configuration
parameters to provide the custom command or script.
Pgpool which executed wd_escalation_command command when it gets elected as
a master and performs the escalation
and similarly when the it node will resign as a master the
wd_de_escalation_command
command gets executed,

http://www.pgpool.net/docs/latest/en/html/runtime-watchdog-config.html#CONFIG-WATCHDOG-ESCALATION-DE-ESCALATION


> 2. Will the VIP get assigned ony if there are more than 1 node present in
> the pgpool cluster? I had 3 nodes where i had pgpool running. When the 1st
> and 2nd node's pgpool was shut i was expecting the 3rd node to acquire the
> VIP but it didn't happen. And if my understanding was right i was thinking
> of using the VIP in my database connection string (Since it will always be
> with pgpool master who can connect to my postgresql primary). Now if the
> 3rd node is not acquiring the VIP, i could not use it my connection string.
> Correct me if my understanding is wrong
>

master pgpool only acquires the VIP when the quorum exists ( minimum 50% of
nodes are reachable). This is done by Pgpool to guard against the
split-brain syndrome, which could happen
otherwise in case of network partitioning. So if you have 3 Pgpool nodes
configured than the VIP will only get assigned on master node when at-least
2 Pgpool nodes are alive and reachable.
but in case of 2 node configuration, only 1 node is required to ensure the
quorum and in that case even if the single node is alive, it will get the
VIP

Thanks
Best Regards
Muhammad Usama

>
>
> Thanks in advance
>
>    Lakshmi Y M
> _______________________________________________
> pgpool-general mailing list
> pgpool-general at pgpool.net
> http://www.pgpool.net/mailman/listinfo/pgpool-general
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.sraoss.jp/pipermail/pgpool-general/attachments/20190516/80b061ac/attachment.html>