[ClusterLabs] PostgreSQL PAF failover issue

Fri Jun 14 09:55:10 EDT 2019

On Fri, 14 Jun 2019 13:18:09 +0200
Tiemen Ruiten <t.ruiten at rdmedia.com> wrote:

> Thank you, useful advice!
> 
> Logs are attached, they cover the period between when I set
> maintenance-mode=false till after the node fencing.

Switchover started @ 09:51:43

In fact, the action that timed out was the demote action, not the stop
action:

  pgsqld_demote_0:31997 - timed out after 30000ms

As explained, the demote is doing a stop/start because PgSQL doesn't support hot
demotion. So your demote action should be stop timeout+start timeout. I would
recommend 60s there instead of 30s.

After Pacemaker decide what to do next, you had some more timeouts. I supose
PgSQL logs should give some more explanation of what happen during these long
minutes

  pgsqld_notify_0:37945 - timed out after 60000ms
  ...
  pgsqld_stop_0:7783 - timed out after 60000ms

It is 09:54:16. Now pengine become angry and want to make sure pgsql is stopped
on node 03:

  pengine:  warning: unpack_rsc_op_failure:   Processing failed stop of pgsqld:1
    on ph-sql-03: unknown error | rc=1
  ...
  pengine:  warning: pe_fence_node:   Cluster node ph-sql-03 will be fenced:
    pgsqld:1 failed there
  ...
  pengine:  warning: stage6:  Scheduling Node ph-sql-03 for STONITH
  ...
  pengine:   notice: native_stop_constraints: Stop of failed resource pgsqld:1
    is implicit after ph-sql-03 is fenced

From there node 03 is down for 9 minutes, it comes back at 10:02:59.

Meanwhile, @ 09:54:29, node 5 took over the DC role and decided to promote pgsql
on node 4 as expected.

The pre-promote notify actions are triggered, but at 09:55:24, the
transition is canceled because of maintenance mode:

  Transition aborted by cib-bootstrap-options-maintenance-mode doing modify
   maintenance-mode=true

Soon after, both notify actions timed out on both nodes:

  warning: child_timeout_callback:  pgsqld_notify_0 process (PID 38838) timed
  out

Not sure what happen on your side that could explain these timeouts, but
because the cluster was in maintenance mode, there was a human interaction
ingoing anyway.

> On Fri, 14 Jun 2019 at 12:48, Jehan-Guillaume de Rorthais <jgdr at dalibo.com>
> wrote:
> 
> > Hi,
> >
> > On Fri, 14 Jun 2019 12:27:12 +0200
> > Tiemen Ruiten <t.ruiten at rdmedia.com> wrote:  
> > > I setup a new 3-node PostgreSQL cluster with HA managed by PAF. Nodes are
> > > named ph-sql-03, ph-sql-04, ph-sql-05. Archive mode is on and writing
> > > archive files to an NFS share that's mounted on all nodes using  
> > pgBackRest.  
> > >
> > > What I did:
> > > - Create a pacemaker cluster, cib.xml is attached.
> > > - Set maintenance-mode=true in pacemaker  
> >
> > This is not required. Just build your PgSQL replication, shut down the
> > instances, then add the PAF resource to the cluster.
> >
> > But it's not very important here.
> >  
> > > - Bring up ph-sql-03 with pg_ctl start
> > > - Take a pg_basebackup on ph-sql-04 and ph-sql-05
> > > - Create a recovery.conf on ph-sql-04 and ph-sql-05:
> > >
> > > standby_mode = 'on'
> > > primary_conninfo = 'user=replication password=XXXXXXXXXXXXXXXX
> > > application_name=ph-sql-0x host=10.100.130.20 port=5432 sslmode=prefer
> > > sslcompression=0 krbsrvname=postgres target_session_attrs=any'
> > > recovery_target_timeline = 'latest'
> > > restore_command = 'pgbackrest --stanza=pgdb2 archive-get %f "%p"'  
> >
> > Sounds fine.
> >  
> > > - Bring up ph-sql-04 and ph-sql-05 and let recovery finish
> > > - Set maintenance-mode=false in pacemaker
> > > - Cluster is now running with ph-sql-03 as master and ph-sql-04/5 as  
> > slaves  
> > > At this point I tried a manual failover:
> > > - pcs resource move --wait --master pgsql-ha ph-sql-04
> > > Contrary to my expectations, pacemaker attempted to stop psqld on
> > > ph-sql-03.  
> >
> > Indeed. PostgreSQL doesn't support hot-demote. It has to be shut downed and
> > started as a standby.
> >  
> > > This took longer than the configured timeout of 60s (checkpoint
> > > hadn't completed yet) and the node was fenced.  
> >
> > 60s of checkpoint during a maintenance window? That's important indeed. I
> > would
> > command doing a manual checkpoint before triggering the move/switchover.
> >  
> > > Then I ended up with
> > > ph-sql-04 and ph-sql-05 both in slave mode and ph-sql-03 rebooting.
> > >
> > >  Master: pgsql-ha
> > >   Meta Attrs: notify=true
> > >   Resource: pgsqld (class=ocf provider=heartbeat type=pgsqlms)
> > >    Attributes: bindir=/usr/pgsql-11/bin pgdata=/var/lib/pgsql/11/data
> > > recovery_template=/var/lib/pgsql/recovery.conf.pcmk
> > >    Operations: demote interval=0s timeout=30s (pgsqld-demote-interval-0s)
> > >                methods interval=0s timeout=5 (pgsqld-methods-interval-0s)
> > >                monitor interval=15s role=Master timeout=10s
> > > (pgsqld-monitor-interval-15s)
> > >                monitor interval=16s role=Slave timeout=10s
> > > (pgsqld-monitor-interval-16s)
> > >                notify interval=0s timeout=60s (pgsqld-notify-interval-0s)
> > >                promote interval=0s timeout=30s  
> > (pgsqld-promote-interval-0s)  
> > >                reload interval=0s timeout=20 (pgsqld-reload-interval-0s)
> > >                start interval=0s timeout=60s (pgsqld-start-interval-0s)
> > >                stop interval=0s timeout=60s (pgsqld-stop-interval-0s)
> > >
> > > I understand I should at least increase the timeout of the stop operation
> > > for psqld, though I'm not sure how much. Checkpoints can take up to 15
> > > minutes to complete on this cluster. So is 20 minutes reasonable?  
> >
> > 20 minutes is not reasonable for HA. 2 minutes is for manual procedure.
> > Timeout are here so the cluster knows how to react during unexpected
> > failure.
> > Not during maintenance.
> >
> > As I wrote, just add a manual checkpoint in your switchover procedure
> > before
> > the actual move.
> >  
> > > Any other operations I should increase the timeouts for?
> > >
> > > Why didn't pacemaker elect and promote one of the other nodes?  
> >
> > Do you have logs of all nodes during this time period?
> >
> >  
> 

-- 
Jehan-Guillaume de Rorthais
Dalibo