[pgpool-hackers: 3585] Re: PCP command to interact with Pgpool-II cluster

[Tatsuo Ishii]

Usama,

Thank you for the propsal.

> Hi Hackers,
> 
> When PCP was first added to Pgpool-II it was meant to manage/control
> the single Pgpool-II instance.
> And after the addition of watchdog more often than not multiple
> Pgpool-II nodes are installed the system
> and there is not much work/thoughts have gone into the enhancements of
> the PCP utilities to make
> them work on the Pgpool-II cluster.  So lately I was thinking to
> enhance/add the PCP utilities to make them
> more cluster-mode friendly.
> And for that purpose, I think we would require to add/enhance the
> following PCP commands.
> 
> 1- pcp_reload_config
> ==================
> The utility to make the whole Pgpool-II cluster to reload the
> configuration files at once.
> I think this is required because currently if some installation has
> let say 3 node Pgpool-II cluster
> and we want to change one specific configuration parameter ( for
> example: adding a new backend node)
> we would require to go on and edit Pgpool configuration files on each
> node separately and then
> issue pgpool reload on each node one by one.
> 
> In my opinion, we need multiple enhancement in this area.
> We need some mechanisms to let pgpool-II cluster use the centralized
> configuration
> ( except watchdog config) or at least a mechanism to push the
> configuration settings using some
> new utility like "pcp_load_config" that could take a pgpool.conf file
> and propagate it to all nodes
> using watchdog.

Yeah, we definitely need it.

> The centralized configuration part of the problem is a big task and I
> believe we could take it on after the
> "simplifying watchdog config" feature that Peng is working on.
> Meanwhile, I think we can work on pcp_reload_config utility in
> parallel to make reloading part easier.

+1.

> 2- pcp_restart_pgpool [cluster]
> ==========================
> Sometimes, a simple restart solves more problems than any other remedy
> or debugging.
> So I think we should have a PCP utility to restart a Pgpool-II node or
> all node on Pgpool-II cluster.
> something similar in functionality like "pg_ctl restart" in postgres

+1.

> 3- pcp_watchdog_re-elect
> ======================
> What if we want to change the master/coordinator node of the watchdog cluster.
> There exists no good way for that currently. So I purpose we should
> have a command to make
> watchdog re-do the elections. I already had a discussion on this one
> with Ishii-San sometimes
> back so I will send a separate proposal for that as well

Looking forward to seeing it.

> 4- pcp_stop_pgpool enhancements
> ===================
> pcp_stop_pgpool should be able to stop all the Pgpool-II nodes in
> Pgpool-II cluster.
> And for that, I have also cooked up a POC patch which allows the
> [--all (-a)] option to
> pcp_stop_pgpool utility and when this --all is specified then the
> utility stops all the Pgpool-II
> nodes part of the watchdog cluster.
> So can you please try the patch and also suggest about the command
> line option we should
> use for making the PCP commands interact with cluster rather than the
> single node.
> Because I think --all would not be the best choice since it is used by
> other utilities for a different purpose,
> and we should come up with new standard command-line switch for all
> utilities if they want to operate on
> the cluster rather than on a single node.

+1.

What about:

--cluster, -c	/* affect to whole watchdog cluster */
--local, -l	/* affect only to local watchdog cluster */

We actually need --cluster only but for completeness I feel like we'd
want to have --local as well (it exactly behaves as PCP commands do
today).

> Or another way would be to leave the pcp_stop_pgpool utility untouched
> and add a new utility pcp_stop_cluster ?
> 
> So what are your suggestions and thoughts on this and do you have
> other functions especially related to
> cluster mode of pgpool-II that needed controlling/management using PCP system?

I have tested your patch and it worked as expected. Great!

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp