[pgpool-general: 2999] Re: PGPool and Watchdog

[James Sewell]

Hi,

In the case you describe below, using DISALLOW_TO_FAILOVER what is the
purpose of the Watchdog?

I have noticed pcp commands which alter node state are at least propagated.

Cheers,
James

On Thursday, 26 June 2014, Yugo Nagata <nagata at sraoss.co.jp> wrote:

> Hi,
>
> On Mon, 23 Jun 2014 16:33:35 +1000
> James Sewell <james.sewell at lisasoft.com <javascript:;>> wrote:
>
> > Hello All,
> >
> > I have a load balancer in front of a pair of pgpool nodes (3.3.1), in
> front
> > of a pair of PostgreSQL   nodes (9.3) which are configured as a streaming
> > pair. I am running on RHEL.
> >
> > I am using another HA tool to manage the failover between the Postgres
> > nodes, and the load is spread between the pgpool nodes with inactive
> nodes
> > being taken out of the load balanced pool.
> >
> > Do I need watchdog in this case? I have seen reports that pgpool still
> > synchronises useful information using this connection, but can't find
> what
> > this information is?
> >
> > If I did use watchdog, which settings would I need in this limited case?
>
> When watchdog enabled, backend status is shared between pgpools.
> For example, when backend goes down ** and when a pgpool detects
> this and handles the failover **, the backend status change is sent
> to another pgpool.
>
> However, if you use another HA tools to protecte backends, you might
> want to use DIALLOW_TO_FAILOVER flag in backend_flag.
> http://www.pgpool.net/docs/latest/pgpool-en.html#BACKEND_FLAG
> If you use DIALLOW_TO_FAILOVER, the backend status change wouldn't
> be sent to another pgpool, since pgpool doesn't handle backend failover.
>
> And in your case, delegate_IP should be empty since virtual IP sn't
> necessary.
>
> >
> > Also is there a pcp command which I can use to tell pgpool that a new
> node
> > is master, but not actually promote it (this would have happened
> already)?
> > Does pcp_promote_node do this when no promotion script is provided?
>
> pcp_promote_node works as follow:
>
> (1) This changes pgpool-II's internal status and set the specified
>     node to primary. The internal status is used in online-recovery
>     and loadbalancing etc..
> ** Note that this doesn't control the backend nodes themselves.**
>
> (2) All nodes other than the new primary are detached from pgpool-II.
>
> (3) pgpool-II execute follow_master command for all the detached nodes.
>
>
> As mentioned at (1), pcp_promote_node doesn't actually promote bacend node.
> However, please note that pcp_promote_node detaches all nodes other than
> the
> new primary. You would have to execute pcp_attach_node to attach the nodes
> in
> follow_master command.
>
> When watchdog enabled, backend status changes by pcp_promote_node and
> pcp_attach_node also are sent to another pgpool.
>
> >
> > Thanks for the help.
> >
> > Cheers,
> >
> > James Sewell,
> > Solutions Architect
> > ______________________________________
> >
> >
> >  Level 2, 50 Queen St, Melbourne VIC 3000
> >
> > *P *(+61) 3 8370 8000  *W* www.lisasoft.com  *F *(+61) 3 8370 8099
> >
> > --
> >
> >
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>
>
> --
> Yugo Nagata <nagata at sraoss.co.jp <javascript:;>>
>


-- 

James Sewell,
PostgreSQL Team Lead / Solutions Architect
______________________________________


 Level 2, 50 Queen St, Melbourne VIC 3000

*P *(+61) 3 8370 8000  *W* www.lisasoft.com  *F *(+61) 3 8370 8099

-- 


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