[pgpool-general: 2629] Re: master - master mode

[Yugo Nagata]

Hi,

I'm not familiar to and carp or VARP and haven't used these. 
However, if delegate_ip is set empty, pgpool doesn't handle 
virtual IP. So, you might use other tools to manage VIP.

On Thu, 13 Mar 2014 14:55:05 +0900
Tomoyuki Sakurai <tomoyukis at reallyenglish.com> wrote:

> hi,
> 
> my understanding is that pgpool thinks it is the master when it has
> promoted itself. however, there is a use-case where both pgpool nodes
> are master and queries are sent to only one.
> 
> back ground:
> 
> opposed to the official doc, i do not use "ifconfig alias" way to do
> failover. the virtual IP address is NOT managed by pgpool. the reason
> is that, when pgpool is not running and the kernel is running fine,
> there is no way for the slave to take over the virtual IP address.
> what slave pgpool can do is, creating an alias IP address. however,
> this does not work because the master kernel still responds to packets
> to the virtual IP address. this can happen in various scenarios (file
> descriptor exhaustion, disk failure, etc).
> 
> to solve this problem, we use carp(4), which is similar to VRRP in
> linux world. with carp(4), the slave can take over the virtual IP
> address. in this case, both pgpool nodes accept queries regardless
> whether it is master or not. IP address failover can be done by either
> pgpool (watchdog failure) or the kernel (carp(4) timeout), which is
> the problem.
> 
> the problem:
> 
> when the slave, takes over the virtual IP while pgpool on the master
> is running but failed to responds to watchdog health check, everything
> works fine. however, when the kernel of the slave takes over the IP
> address because the other kernel is overloaded, the pgpool on the
> master still thinks it is the master. while the failover works fine,
> the next failover will NOT happen because the old master does not care
> of the old slave. to work around, you need to tell the old master that
> it is a slave.
> 
> it would be nice for pgpool to be able to handle master-master mode.
> does anyone use VRRP or carp(4)?
> 
> -- 
> Tomoyuki Sakurai
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-- 
Yugo Nagata <nagata at sraoss.co.jp>