[Pgpool-general] TCP connections are *not* closed when a backend timeout

[Tatsuo Ishii]

> > > - Why pgpool doesn't monitor when a backend comes back ? Must we have an
> > >   external monitoring software which call pcp_recoevr_node ?
> > 
> > This is a design decision when pgpool was born. In my understanding
> > many HA(High Availability) software systems do like this. The reason
> > for this is if we allow this, some flakey hardwares (for example
> > flakey network cables) might cause repeating fail over/fail back
> > actions.
> 
> Ok, I understand :) Anyway, do you have any monitoring preference ? (do
> you have / do you know any scripts to make the monitoring and call
> pgp_recovery ?)

I'm confused. To call pcp_recovery_node, the target backend must be
in down status.

> > Besides recovery, having different master/slave settings on those two
> > pgpool servers might cause deadlock situation. Consider following
> > scenario: pgpool1 sends "LOCK t1" to backend1 first since backend1 is
> > the master for pgpool1 then sends the same SQL to backend2. At the
> > same time pgpool2 sends "LOCK t1" to backend2 first since backend2 is
> > the master for pgpool2 then sends the same SQL to backend1. As a
> > result pgpool1 waits for completion of LOCK command on backend2, while
> > pgpool2 waits for completion of LOCK command on backend1, which is a
> > deadlock.
> > 
> > I recommend you to have same settings for both pgpool1 and pgpool2:
> > 
> >    pgpool1 ==> master: backend1 , slave : backend2
> >    pgpool2 ==> master: backend1 , slave : backend2
> > 
> > Now for the recovery part. The answer is either pgpool1 or ppool2 can
> > perform the recovery. However while pgpool1(2) performs the recovery
> > pgpool2(1) *must not* access backend1 and backend2.
> > 
> 
> Ok, So i need to have the same master on all nodes. I guess if I have
> more than 2 backends, I also need to keep them in the same order ?

Yes.

> Whn I tried the recovering, the 2nd pgpool doesn't detect that the
> backend is came back.

Yeah, it's the limitation of pgpool-II for now.

> Lust I perform pcp_recovery on both pgpools ?

No. Don't do it.

>  or
> Just I need (for exemple) one pcp_recovery  and smth like
> pcp_attach_node on other pgpool ?

Without testing it, I would say doing pcp_attach_node is enough.

> > > - A more general question, my archive logs take lot of place. How much
> > >   archive_log files must we keep ? only the last ? Is there any
> > >   postgresql configuration capacities to set this rotation, or must I
> > >   use smthg like logrotate?
> > 
> > Actually once you finish the recovery, you do not need to keep take
> > archive logs. There are two ways for this. Change archive_mode to
> > off(require PostgreSQL restarting). The other is set ''(null string)
> > to archive_command. This will not require PostgreSQL restarting. Just
> > pg_ctl reload is enough. I'm not sure if this works for all PostgreSQL
> > versions though.
> But what will happend if a server fails again ?

You need to set archive_command again and do pg_ctl reload.
--
Tatsuo Ishii
SRA OSS, Inc. Japan