Troubleshooting Connection Problems

A number of things can prevent a client application from successfully connecting to LightDB-A Database. This topic explains some of the common causes of connection problems and how to correct them.

Problem	Solution
No `pg_hba.conf` entry for host or user	To enable LightDB-A Database to accept remote client connections, you must configure your LightDB-A Database coordinator instance so that connections are allowed from the client hosts and database users that will be connecting to LightDB-A Database. This is done by adding the appropriate entries to the `pg_hba.conf` configuration file (located in the coordinator instance’s data directory). For more detailed information, see Allowing Connections to LightDB-A Database.
LightDB-A Database is not running	If the LightDB-A Database coordinator instance is down, users will not be able to connect. You can verify that the LightDB-A Database system is up by running the `gpstate` utility on the LightDB-A coordinator host.
Network problems Interconnect timeouts	If users connect to the LightDB-A coordinator host from a remote client, network problems can prevent a connection (for example, DNS host name resolution problems, the host system is down, and so on.). To ensure that network problems are not the cause, connect to the LightDB-A coordinator host from the remote client host. For example: `ping hostname` If the system cannot resolve the host names and IP addresses of the hosts involved in LightDB-A Database, queries and connections will fail. For some operations, connections to the LightDB-A Database coordinator use `localhost` and others use the actual host name, so you must be able to resolve both. If you encounter this error, first make sure you can connect to each host in your LightDB-A Database array from the coordinator host over the network. In the `/etc/hosts` file of the coordinator and all segments, make sure you have the correct host names and IP addresses for all hosts involved in the LightDB-A Database array. The `127.0.0.1` IP must resolve to `localhost`.
Too many clients already	By default, LightDB-A Database is configured to allow a maximum of 250 concurrent user connections on the coordinator and 750 on a segment. A connection attempt that causes that limit to be exceeded will be refused. This limit is controlled by the `max_connections` parameter in the `postgresql.conf` configuration file of the LightDB-A Database coordinator. If you change this setting for the coordinator, you must also make appropriate changes at the segments.

Parent topic: Accessing the Database