Postgres-XC 1.1 Documentation
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# 17.18. Postgres-XC Specific Parameters

> Note: The following description applies only to Postgres-XC

Because Postgres-XC distribute data into multiple Datanodes and multiple Coordinators can accept transactions in parallel, specific Coordinator must know what Coordinators and Datanodes to connect. Coordinator and Datanode also must know where they can request transaction information. The following describes these additional GUC parameters.

`max_pool_size` (`integer`)

  Specify the maximum connection pool of the Coordinator to Datanodes. Because each transaction can be involved by all the Datanodes, this parameter should at least be `max_connections` multiplied by number of Datanodes.

`min_pool_size` (`integer`)

  Minumum number of the connection from the Coordinator to Datanodes.

`max_coordinators` (`integer`)

  Maximum number of Coordinators that can be configured in the cluster.

`max_datanodes` (`integer`)

  Maximum number of Datanodes that can be configured in the cluster.

`pgxc_node_name` (`integer`)

  Specifies the node name. A node uses this parameter to identify itself with `pgxc_node` .nodename

`pooler_port` (`integer`)

  Reports the port number assigned to the connection pooler.

`gtm_host` (`string`)

  Reports the name or IP address of the `GTM`. If you use `GTM-Proxy`, specify the `GTM-Proxy`'s one.

`gtm_port` (`integer`)

  Reports the port number of GTM.

`gtm_backup_barrier` (`string`)

  Specify if GTM backs up the restart point for each barrier. Default value is "OFF". Superuser may set this variable by SET command, or this can be set in the file `postgresql.conf` file.

`enforce_two_phase_commit` (`boolean`)

  Enforce the usage of two-phase commit instead for transactions involving temporary objects or ON COMMIT actions.

`xc_maintenance_mode` (`bool`)

  Specify to enter into maintenance mode. Turning this parameter to on will change behavior of several statements. Each statement behavior may not be compatible in future releases, so users must be extremely careful when they attempt to set this value to `on`.

  Behavior of COMMIT PREPARED and ROLLBACK PREPARED statements are affected by this parameter.

  If this is set to ON, you can do many other maintenance work to update Datanode locally through `EXECUTE DIRECT` or connecting directly to Datanodes. As a DBA, you are totally responsible to any side effects. You must be extremely careful not to bring in any inconsistencies to Postgres-XC database cluster.

  This parameter can only be set by superuser with `SET` command. Otherwise, the setting will be ignored.

  As a session parameter, this parameter is shared among all the connections of the session. It affects originating Coordinator as well as remote nodes involved in session.

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