[pgpool-general: 4452] Re: Understanding node info and watchdog info

[Muhammad Usama]

On Sun, Aug 2, 2015 at 7:20 PM, Thomas Bach <t.bach at ilexius.de> wrote:
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> Hi there,
>
> I configured pgpool-IIpgpool-II version 3.3.2 (tokakiboshi) and
> Postgres to run on two separate machines in replication mode. I just
> recently configured watchdog. At some point the two databases diverged
> which is ok because I am currently in the testing phase.
>
> Now on host02 I query watchdog and obtain
>
> host02 # pcp_watchdog_info -v 1 host01 9898 root ****
> Hostname     : host01
> Pgpool port  : 5432
> Watchdog port: 9000
> Status       : 2
> host02 # pcp_watchdog_info -v 1 host02 9898 root ****
> Hostname     : host02
> Pgpool port  : 5432
> Watchdog port: 9000
> Status       : 3
>
> So host02 is active. I obtain the exact same results when issuing
> these queries from host01.

pcp_watchdog_info utility displays the information of pgpool-II
watchdog node, So if the pgpool-II watchdog
cluster is configured and working without any problem, executing the
pcp_watchdog_info on any pgpool-II node
should always displays the same results for all pgpool-II nodes in the cluster.
>
> Anyway, when querying pcp_node_info I obtain the following:
>
> host02 # pcp_node_info -v 1 host01 9898 root **** 0
> Hostname: host01
> Port    : 5433
> Status  : 1          <----------------------
> Weight  : 1.000000
> host02 # pcp_node_info -v 1 host01 9898 root **** 1
> Hostname: host02
> Port    : 5433
> Status  : 1
> Weight  : 0.000000
> host02 # pcp_node_info -v 1 host02 9898 root **** 0
> Hostname: host01
> Port    : 5433
> Status  : 3         <----------------------
> Weight  : 0.000000
> host02 # pcp_node_info -v 1 host02 9898 root **** 1
> Hostname: host02
> Port    : 5433
> Status  : 1
> Weight  : 1.000000
>

As pcp_node_info utility displays the status of Backend (PostgreSQL)
nodes connected with the pgpool-II. And when the pgpool-II are
configured to use watchdog, All pgpool-II connected with watchdog
exchanges the node status when ever the any backend node status is
changed. So agin when the pgpool-II watchdog is configured and working
correctly, All pgpool-IIs in the cluster should have the same status
of backend node. But there is some problem with your setup or in
pgpool-II since pgpool-II on Host1 and Host2 are showing different
status for node 0 which should never happen, Analyzing the pgpool-II
logs of both pgpool-II would be helpful in the situation to analyze
why pgpool-II on host02 thinks the status of PostgreSQL node 0 is down
and what error caused this status not to get replicated with pgpool-II
on host01.

> So, as host02 sees it, host01 is down. But for host01 both itself as
> well as host02 are perfectly sane.
>
> 1) Is such a state intended? I.e. is pgpool-II fully operational in
> this mode?

This is not intended and indicates a problem in pgpool-II or the
setup. pgpool-II logs would be helpful to locate the actual problem.
>
> 2) What will happen when I do an insert via host02? Will it replicate
> to host01?
>
> 3) And even more interesting: what will happen when I do an insert via
> host01?
>

Both pgpool-II (on host01, and host02) will behave according to their
local view of the PostgreSQL backend node statuses.

> 4) What ways do I have at hand to resolve this issue?

As described above, analyzing the pgpool-II log will give more details
about the cause of the problem and a way to rectify it.


Thanks
Kind regards
Muhammad Usama

>
> Regards
>
>         Thomas.
>
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