Health Check

pgpool-II 3.6.5 Documentation
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# 5.8. Health Check

Pgpool-II periodically connects to the configured PostgreSQL backends to detect any error on the servers or networks. This error check procedure is called "health check". If an error is detected, Pgpool-II performs failover or degeneration depending on the configurations.

Caution
Health check requires one extra connection to each backend node, so `max_connections` in the `postgresql.conf` needs to be adjusted accordingly.

`health_check_timeout` (`integer`)

  Specifies the timeout in seconds to give up connecting to the backend PostgreSQL if the TCP connect does not succeed within this time.

  This parameter serves to prevent the health check from waiting for a long time when the network cable is unplugged. Default value is 20. Setting it to 0, disables the timeout (waits until TCP/IP timeout).

  This parameter can be changed by reloading the Pgpool-II configurations.

`health_check_period` (`integer`)

  Specifies the interval between the health checks in seconds. Default is 0, which means health check is disabled.

  This parameter can be changed by reloading the Pgpool-II configurations.

`health_check_user` (`string`)

  Specifies the PostgreSQL user name to perform health check. The same user must exist in all the PostgreSQL backends. Otherwise, health check causes an error.

  This parameter can be changed by reloading the Pgpool-II configurations.

`health_check_password` (`string`)

  Specifies the password for the PostgreSQL user name configured in health_check_user to perform health check. The user and password must be same in all the PostgreSQL backends. Otherwise, health check results in an error.

  This parameter can be changed by reloading the Pgpool-II configurations.

`health_check_database` (`string`)

  Specifies the PostgreSQL database name to perform health check. The default is `''`(empty), which tries `"postgres"` database first, then `"template1"` database until it succeeds

  `health_check_database` was introduced in Pgpool-II V3.5.

  This parameter can be changed by reloading the Pgpool-II configurations.

`health_check_max_retries` (`integer`)

  Specifies the maximum number of retries to do before giving up and initiating failover when health check fails.

  > Tip: This setting can be useful in spotty networks, when it is expected that health checks will fail occasionally even when the master node is fine.

  > Tip: It is advised that fail_over_on_backend_error must be disabled, if you want to enable `health_check_max_retries`.

  Default is 0, which means do not retry.

  This parameter can be changed by reloading the Pgpool-II configurations.

`health_check_retry_delay` (`integer`)

  Specifies the amount of time in seconds to sleep between failed health check retries (not used unless health_check_max_retries is > 0). If 0, then retries are immediate without delay.

  This parameter can be changed by reloading the Pgpool-II configurations.

`connect_timeout` (`integer`)

  Specifies the amount of time in milliseconds before giving up connecting to backend using `connect()` system call. Default is 10000 ms (10 second). The flaky network user may want to increase the value. 0 means no timeout.

  > Note: `connect_timeout` value is not only used for a health check, but also for creating ordinary connection pools.

  This parameter can be changed by reloading the Pgpool-II configurations.

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