[pgpool-general: 4005] Re: wd_lifecheck_method

[Yugo Nagata]

Hi,

On Tue, 25 Aug 2015 16:34:45 +1000
James Sewell <james.sewell at lisasoft.com> wrote:

> Hello,
> 
> I was just interested at what most people are using for this setting when
> using Watchdog?
> 
> I assume 'heartbeat' just does a network level heartbeat to the other
> PGPool, but query actually runs a query through the PGPool.

Yes. The 'heartbeat' mode monitors the process of the other pgpool-II,
while the 'query' mode checks if pgpool-II can accept a query. 
However, please note that the pgpool-II makes a connection to the other
pgpool-II. So, if there are many connections that are more large than 
num_init_childlen, the monitoring fails even when the pgpool-II is ok.

In addition, even if monitoring by 'query' fails, we can't tell which
of pgpool-II or PostgreSQL has failure. pgpool-II is monitoring backend
PostgreSQL by healcheck, which is other mechanism from watchdog. So,
watchdog have to monitor the other pgpool only.

These are the reasons why we recomend to use heartbeat mode instead 
of query mode.

> 
> This would suggest that query might be a better implementation?
> 
> Cheers,
> 
> James Sewell,
> PostgreSQL Team Lead / Solutions Architect
> ______________________________________
> 
> 
> Level 2, 50 Queen St, Melbourne VIC 3000
> 
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-- 
Yugo Nagata <nagata at sraoss.co.jp>