[Pgpool-hackers] Automatic reattachment of the node in connection pooling mode

[Tatsuo Ishii]

> One of my customers asks me today why pgpool doesn't check, from time to
> time, that the backend is now available in connection pool mode.
> 
> Here is what we did with a pgpool 3.0.1, configured only for connection
> pooling and health checking:
> 
>  * start postgresql (pg_ctl start)
>  * start pgpool (pgpool -f etc/pgpool.conf start)
>  * every connection works fine
>  * stop postgresql (pg_ctl start)
>  * health check detects the unavailability of the backend
>    and changes status of node 0 to 3
>  * no connection, which is good because backend is unavailable
>  * start postgresql (pg_ctl start)
>  * and the node still remains in status 3.
> 
> What I would like to have is a way to check if the backend is now
> available. And reattach it if it is. All intern to pgpool. Any reason
> why not to do so?
> 
> I can have misread the documentation, and I understand why this cannot
> happen in replication mode or master/slave mode. But in connection
> pooling only mode, I don't get it.
> 
> If it seems to be a nice feature to have, I'm interested in working on this.

I'm not sure if it's good feature. Say you have 2 DB servers and one
of their network connections goes shakey. It continues to up and down
every 10 seconds. If pgpool has such a feature, pgpool repeatedly does
failover every 10 seconds, which will break existing client connection
every 10 seconds. I'm sure the user is not happy with this situation.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp