[pgpool-general: 6572] Re: Pgpool query

[Tatsuo Ishii]

>> Ok. So the reason behind the ask was if pgpool is not going to retry the
> promote on other nodes, I was thinking i can just trigger a force promote
> there by failover and follow master will be run by pgpool itself and i dont
> have to do a failover by myself and run pcp_recovery on all the nodes

Probably you misunderstand what Pgpool-II is expected to do. Pgpool-II
does nothing with PostgreSQL promotion. It's completely the script
writer's responsibility to handle the promotion retrying if
neccessary.

> Regarding 5. It's normal. Don't worry.
> 
> When a standby PostgreSQL node is added, existing connections to
> Pgpool-II are kept (thus do not use the new standby for load
> balacing). After the session ends, Pgpool-II child process checks
> whether the failback has happend. If happend, exits itself so that new
> process is spwan to reflect the fact that new standby node has been
> added (thus it can use the new standby for load balancing).
> 
> 
> 
> 
>> Thanks. Per my understanding, So restart happens only when a new standby
> is added is it. Because i see this frequent restarts happening even when
> there is no fallback.

The failbacke event detection could happen long after the failback
happend if a user keeps on connection to Pgpool-II.

> Also could you please share some light on when the failback_command gets
> executed? I have never seen the command being called.

It is called when pcp_attach_node or pcp_recovery_node get
executed. Also it could happen when follow_master_command gets
executed if it executes pcp_recovery_node inside the command.

> 
> Thanks And Regards,
> 
>    Lakshmi Y M
> 
> On Tue, May 21, 2019 at 8:02 PM Lakshmi Raghavendra <lakshmiym108 at gmail.com>
> wrote:
> 
>> Hi,
>>
>>    I had couple of queries as below :
>>
>> On Thu, May 16, 2019 at 2:17 AM Muhammad Usama <m.usama at gmail.com> wrote:
>>
>>>
>>>
>>> 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,
>>>
>>
>> 1. I tried using the  above wd_escalation_command and wd_de_escalation_command.
>> I have a 3 node cluster, Observed that the escalation command will be
>> triggered if there are at least 2 nodes alive in the pgpool cluster.
>> If there is only master pgpool alive with no slave nodes, the command is
>> never initiated. Is this behavior expected ?
>>
>> 2. Wanted to understand the significance of VIP, Is there any issue caused
>> if I dont use the VIP in a 3-node pgpool cluster.
>>
>> Please let me know.
>>
>> Thanks And Regards,
>>
>>    Lakshmi Y M
>>
>> On Thu, May 16, 2019 at 2:17 AM Muhammad Usama <m.usama at gmail.com> wrote:
>>
>>>
>>>
>>> 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
>>>>
>>>