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

[Toshihiro Kitagawa]

On Thu, 27 Jan 2011 13:09:57 +0100
Guillaume Lelarge <guillaume at lelarge.info> wrote:

> Hi,
> 
> 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 don't know the reason. However, there was such a demand since before.
And I think that detaching no node is better than reattach a node.
The reason is because latency for reattaching does not occur.

I attach the prototype patch which I made before.
This patch adds following new parameter to pgpool.conf.

# If true, trigger failover when connecting to master node fails or
# reading/writing data toward master node fails. If false, does not
# trigger failover in that case.
# This parameter has effect in raw mode and master/slave mode.
failover_if_master_fails = true

> 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.

Any comments and improvement for attached patch are welcome.

-- 
Toshihiro Kitagawa
SRA OSS, Inc. Japan
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