Maybe Linux-HA which you recommended is the more promising option for open source tool.
The Postgres resource agent appears to monitor the instance by executing 'SELECT now();' which is typically the recommended check. Though, I do not know Linux-HA well enough to know of any limitations or whether it should be recommend
Will J. Dunn
On Tue, Jul 21, 2015 at 5:35 PM, William Dunn <dunnwjr@xxxxxxxxx> wrote:
On Tue, Jul 21, 2015 at 5:12 PM, Joshua D. Drake <jd@xxxxxxxxxxxxxxxxx> wrote:
"When backend node status changes by failover etc., watchdog notifies the information to other pgpool-IIs and synchronizes them. When online recovery occurs, watchdog restricts client connections to other pgpool-IIs for avoiding inconsistency between backends."You're taking that out of context, though. That is coming from the doc http://www.pgpool.net/docs/latest/pgpool-en.html#watchdog, which is describing how Watchdog coordinates fault of pgpool-II backend processes and coordinates the pgpool-II instances with each other. It is for maintaining availability of pgpool-II and monitoring for failure of pgpool-II backends, not Postgres/postmaster.Will J. DunnOn Tue, Jul 21, 2015 at 5:12 PM, Joshua D. Drake <jd@xxxxxxxxxxxxxxxxx> wrote:
On 07/21/2015 01:37 PM, William Dunn wrote:
But it appears that the fail condition for "watchdog" is the failure of
a pgpool-II instance. In the configuration described in the wiki you
would put a pgpool-II instance on each Postgres node, and if one of the
pgpool-II instances fails it executes a script (which can create the
trigger file to promote the standby to master). However, if the fail
condition for watchdog is a failure of the pgpool-II instance what
happens if the DBMS has availability issues but the pgpool-II process on
that server is ok? The fail condition would never be triggered, right?
What I am going off of is:
"When backend node status changes by failover etc., watchdog notifies the information to other pgpool-IIs and synchronizes them. When online recovery occurs, watchdog restricts client connections to other pgpool-IIs for avoiding inconsistency between backends."
A backend node status would change if say the master went down, at that point pgpool can be instructed either automatically or manually to failover (depending on configuration) and allow the slave to failover.
Sincerely,
JD
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