[pgpool-general: 5317] Re: About failover execution and master node detection

Lazaro Garcia lazaro3487 at gmail.com
Thu Feb 9 18:57:21 JST 2017


Thanks very much for the help.

-----Mensaje original-----
De: Tatsuo Ishii [mailto:ishii at sraoss.co.jp] 
Enviado el: jueves, 9 de febrero de 2017 01:19 a. m.
Para: lazaro3487 at gmail.com
CC: pgpool-general at pgpool.net
Asunto: Re: [pgpool-general: 5302] About failover execution and master node
detection

> Thank you very much for the explanation, I think this question could 
> be added in the FAQs.
> 
> Is there any plan to implement some functionality for selecting the 
> standby with less delay in the replica?

You can do it today within your fail over script by using
pg_last_xlog_receive_location() or some such.

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

> -----Mensaje original-----
> De: Tatsuo Ishii [mailto:ishii at sraoss.co.jp] Enviado el: miércoles, 8 
> de febrero de 2017 12:10 a. m.
> Para: lazaro3487 at gmail.com
> CC: pgpool-general at pgpool.net
> Asunto: Re: [pgpool-general: 5302] About failover execution and master 
> node detection
> 
> %m is the new master node chosen by Pgpool-II. It is the node being 
> assigned the youngest (smallest) node id which is alive.
> 
> For example if you have 3 nodes, namely node 0, 1, 2. Suppose node 1 
> the primary and all of them are healthy (no down node). If node 1 
> fails, failover_command is called with %m = 0.
> 
> If node 0 is down, %m would be 2.
> 
> Best regards,
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese:http://www.sraoss.co.jp
> 
>> Thanks for your answer.
>> 
>> In the failover_command configuration parameter, %m is the new master 
>> selected by pgpool. With 2 standby servers, what node is selected as
> master?
>> 
>> failover_command = ''
>>                                    # Executes this command at failover
>>                                    # Special values:
>>                                    #   %d = node id
>>                                    #   %h = host name
>>                                    #   %p = port number
>>                                    #   %D = database cluster path
>>                                    #   %m = new master node id
>>                                    #   %H = hostname of the new master
> node
>>                                    #   %M = old master node id
>>                                    #   %P = old primary node id
>> 								   #   %r =
>> new master port number
>> 								   #   %R =
>> new master database cluster path
>>                                    #   %% = '%' carácter
>> 
>> Regards.
>> 
>> -----Mensaje original-----
>> De: Tatsuo Ishii [mailto:ishii at sraoss.co.jp] Enviado el: martes, 7 de 
>> febrero de 2017 04:51 a. m.
>> Para: lazaro3487 at gmail.com
>> CC: pgpool-general at pgpool.net
>> Asunto: Re: [pgpool-general: 5302] About failover execution and 
>> master node detection
>> 
>>> I am Reading the pgpool documentation and i have a doubt related to 
>>> failover and selecting a new master node.
>>> 
>>>  
>>> 
>>> I want to create a cluster with more than 2 nodes for instance 3 
>>> nodes. The question is when the backend shuts down, the new primary 
>>> selected by pgpool and sended to the failover command is the closest 
>>> node to previous master, in terms of replication delay?
>> 
>> Probably you are misunderstanding. Pgpool-II does *not* automatically 
>> choose new primary. It's totally up to you how to select the new 
>> primary node in the failover command script. In other word, the logic 
>> to choose the new primary node should be explicitly coded in the 
>> failover
> command script.
>> 
>> Best regards,
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese:http://www.sraoss.co.jp
>> 
> 



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