Re: Patroni vs pgpool II

On Wed, 05 Apr 2023 16:50:15 +0900 (JST)
Tatsuo Ishii <ishii@sraoss.co.jp> wrote:

> > But, I heard PgPool is still affected by Split brain syndrome.  
> 
> Can you elaborate more? If more than 3 pgpool watchdog nodes (the
> number of nodes must be odd) are configured, a split brain can be
> avoided.

Split brain is a hard situation to avoid. I suppose OP is talking about
PostgreSQL split brain situation. I'm not sure how PgPool's watchdog would
avoid that.

To avoid split brain, you need to implement a combinaison of quorum and
(self-)fencing.

Patroni quorum is in the DCS's hands. Patroni's self-fencing can be achieved
with the (hardware) watchdog. You can also implement node fencing through the
"pre_promote" script to fence the old primary node before promoting the new one.

If you need HA with a high level of anti-split-brain security, you'll not be
able to avoid some sort of fencing, no matter what.

Good luck.