[pgpool-general: 8548] Re: Issues taking a node out of a cluster

[Emond Papegaaij]

On Thu, Jan 19, 2023 at 7:29 AM Tatsuo Ishii <ishii at sraoss.co.jp> wrote:

> >> I suspect there's something wrong in node 0's pgpool.conf. Can you
> >> share pgpool.conf of node 0? Only the "backend_*" part is enough.
> >>
> >
> > The pgpool.conf for node 0 and 2 are different, as this all happens
> during
> > the process of updating the configuration. Node 0 gets the new
> > configuration (with only 2 backends) first. Notice how the configuration
> > for backend:0 matches, but backend:1 on node 0 matches with backend:2 on
> > node 2.
>
> Pgpool-II does not support watchdog cluster in which pgpool.conf are
> different.
>

Ok, but how do I then change the topology of the cluster without downtime?
Removing or adding a node does not require any downtime from the
perspective of Postgresql (as long as the primary stays online, you'll need
a switchover otherwise). Looking at the documentation, pgpool only allows
adding backends without restart, not removing or updating.

Wouldn't it be possible for pgpool to use the backend_application_name as
identifier, or perhaps add a new configuration option to assign a unique
identifier to a backend? It could then use this identifier to share status
information about backends between nodes in the cluster.

Best regards,
Emond
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