[pgpool-general: 1692] Re: pgpool watchdog and num_init_children

Yugo Nagata nagata at sraoss.co.jp
Wed May 8 12:18:26 JST 2013

On Mon, 6 May 2013 15:45:14 +0800
manphis chen <cs.manphis at gmail.com> wrote:

> Dear Sir,
> My question and assumption are listed below:
> system architecture: 2 pgpools (pgpool A and pgpool B) and 2 postgres
> servers; each pgpool connects to both 2 postgres servers; watchdog of each
> pgpool is ON.
> num_init_children = 3 (pgpool A)
> Question: when all 3 children (process) on pgpool A are occupied by some
> clients, can watchdog on pgpool B use "Select 1" to access pgpool A?

No. Unfortunately, when there are clients more than num_init_children, 
monitoring using query "SELECT 1" fails and VIP holder would be switched
over.  Larger num_init_children, wd_life_point and smaller wd_interval
may prevent the problem somewhat. 

The next major version, pgpool-II 3.3, will support a new monitoring method
which uses UDP heartbeat packets instead of queries to resolve the problem.

> I found that the watchdog on pgpool B seems cannot access pgpool A, because
> all the processes are occupied.
> But in config file, watchdog uses different port (default is 9000) to
> listen the other watchdog.
> So I am confused.

watchdog port (wd_port) is used for information exchange between pgpools
and not for accepting monitoring queries.

> Thank you for your answer.
> BRs

Yugo Nagata <nagata at sraoss.co.jp>

More information about the pgpool-general mailing list