[pgpool-general: 3080] Re: Failover - new primary selection process?

Yugo Nagata nagata at sraoss.co.jp
Wed Jul 30 07:57:08 JST 2014


On Tue, 29 Jul 2014 07:49:52 +0900 (JST)
Tatsuo Ishii <ishii at postgresql.org> wrote:

> > Sorry for the delay in getting this to you, Ishii-san. All of my VM's
> > were powered down after the chassis received a weekend upgrade.
> > 
> > The log message I was referring to is (from a failover test performed
> > last week):
> > 
> > 2014-07-23 24:54:56 LOG: pid 70166: pgpool_down: I'm *oldest* so
> > standing for master
> 
> I think "watchdog" subsystem of pgpool-II emits the message and I
> believe "master" does not mean PostgreSQL master or primary node,
> rather pgpool-II master of watchdog.
> 
> Yugo should be familiar with this. Yugo?

Yes, this message is of watchdog and means as exact as Ishii-san said.
When watchdog is used, the oldest pgpool becomes "active pgpool", that
is VIP holder. However, this is called "master pgpool" internally.

> 
> > This is written almost immediately before ifconfig brings up the IP
> > alias address and before the failover_command is executed. That's what
> > led me to my comments, although as I admitted, I had not read the code
> > in this area. If selection is just by sequential node ID, that's a
> > little misleading.
> > 
> > On 7/28/2014 7:05 AM, Tatsuo Ishii wrote:
> >> What are you referring to error message? I do not see anything like
> >> "I'm the oldest, so assuming the master role." message in pgpool-II
> >> code anywhere.
> >>
> >> Best regards,
> >> --
> >> Tatsuo Ishii
> >> SRA OSS, Inc. Japan
> >> English: http://www.sraoss.co.jp/index_en.php
> >> Japanese:http://www.sraoss.co.jp
> >>
> >>> Then, I hate to say it, Ishii-san, but your log message is a bit
> >>> misleading. For instance, I always see a message during a failover
> >>> where the standby claims, "I'm the oldest, so assuming the master
> >>> role." So, maybe it should just "I have the lowest remaining node
> >>> number, so I'm assuming the master role."  That wouldn't imply logic
> >>> based on time, only sequences.
> >>>
> >>> Sent from my iPad
> >>>
> >>>> On Jul 28, 2014, at 3:20 AM, Tatsuo Ishii <ishii at postgresql.org>
> >>>> wrote:
> >>>>
> >>>> No. Pgpool-II has no idea which server has been running longer.
> >>>>
> >>>> Pgpool-II has no built-in logic to choose next
> >>>> to-be-primary-candidate. Which slave node will be promoted next time
> >>>> is completely depending on your failover script. In general most
> >>>> people specifies the candidate slave as the master node, which has the
> >>>> yonguest node number among live slave nodes (%m in failover script).
> >>>> Example: you have node 0 primary, node 1&2 standby.
> >>>>
> >>>> 1) node 0 is down.
> >>>>
> >>>> 2) node 1 is chosen as the next primary because it's the youngest live
> >>>> node (master).
> >>>>
> >>>> 3) node 1 is down.
> >>>>
> >>>> 4) node 2 is chosen as the next primary because it's the youngest live
> >>>> node (master).
> >>>>
> >>>> Best regards,
> >>>> --
> >>>> Tatsuo Ishii
> >>>> SRA OSS, Inc. Japan
> >>>> English: http://www.sraoss.co.jp/index_en.php
> >>>> Japanese:http://www.sraoss.co.jp
> >>>>
> >>>>> Hey jay, thank you for the replay.
> >>>>> Is this is a formal conclusion? Maybe the oldest is the one with the
> >>>>> smaller ID ?
> >>>>>
> >>>>>
> >>>>>
> >>>>>> On Sun, Jul 27, 2014 at 2:50 PM, <jayknowsunix at gmail.com> wrote:
> >>>>>>
> >>>>>> Guy,
> >>>>>>
> >>>>>> I run a master with 2 slaves. During a failover, I always see the
> >>>>>> oldest
> >>>>>> slave promoted to master. So, the selection is based on the server
> >>>>>> which
> >>>>>> has been running longer.
> >>>>>>
> >>>>>> --
> >>>>>> Jay
> >>>>>>
> >>>>>> Sent from my iPad
> >>>>>>
> >>>>>>> On Jul 27, 2014, at 3:48 AM, Guy Meler <melguy at gmail.com> wrote:
> >>>>>>>
> >>>>>>> Hey :)
> >>>>>>> In master/slave mode, what is the algorithm for choosing the next
> >>>>>> available primary backend?
> >>>>>>> I want to make sure that if primary in site A goes down, than the next
> >>>>>> available primary is in the same site.
> >>>>>>> Thank you
> >>>>>>>
> >>>>>>> _______________________________________________
> >>>>>>> pgpool-general mailing list
> >>>>>>> pgpool-general at pgpool.net
> >>>>>>> http://www.pgpool.net/mailman/listinfo/pgpool-general
> > 
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-- 
Yugo Nagata <nagata at sraoss.co.jp>


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