Restrictions on watchdog
| pgpool-II 4.0.0 Documentation | |||
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2.3.1. Watchdog restriction with query mode lifecheck
In query mode, when all the DB nodes are detached from a Pgpool-II due to PostgreSQL server failure or pcp_detach_node issued, watchdog regards that the Pgpool-II service is in the down status and brings the virtual IP assigned to watchdog down. Thus clients of Pgpool-II cannot connect to Pgpool-II using the virtual IP any more. This is neccessary to avoid split-brain, that is, situations where there are multiple active Pgpool-II .
2.3.2. Connecting to Pgpool-II whose watchdog status is down
Don't connect to Pgpool-II in down status using the real IP. Because a Pgpool-II in down status can't receive information from other Pgpool-II watchdogs so it's backend status may be different from other the Pgpool-II .
2.3.3. Pgpool-II whose watchdog status is down requires restart
Pgpool-II in down status can't become active nor the standby Pgpool-II . Recovery from down status requires the restart of Pgpool-II .
2.3.4. Watchdog promotion to active takes few seconds
After the active Pgpool-II stops, it will take a few seconds until the standby Pgpool-II promote to new active, to make sure that the former virtual IP is brought down before a down notification packet is sent to other Pgpool-II .