Troubleshooting Connection Problems
A number of things can prevent a client application from successfully connecting to HAWQ. This topic explains some of the common causes of connection problems and how to correct them.
|No pg_hba.conf entry for host or user||To enable HAWQ to accept remote client connections, you must configure your HAWQ master instance so that connections are allowed from the client hosts and database users that will be connecting to HAWQ. This is done by adding the appropriate entries to the pg_hba.conf configuration file (located in the master instance’s data directory). For more detailed information, see Allowing Connections to HAWQ.|
|HAWQ is not running||If the HAWQ master instance is down, users will not be able to connect. You can verify that the HAWQ system is up by running the
|If users connect to the HAWQ master 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 HAWQ master host from the remote client host. For example:
If the system cannot resolve the host names and IP addresses of the hosts involved in HAWQ, queries and connections will fail. For some operations, connections to the HAWQ master use
|Too many clients already||By default, HAWQ is configured to allow a maximum of 200 concurrent user connections on the master and 1280 connections on a segment. A connection attempt that causes that limit to be exceeded will be refused. This limit is controlled by the
|Query failure||Reverse DNS must be configured in your HAWQ cluster network. In cases where reverse DNS has not been configured, failing queries will generate “Failed to reverse DNS lookup for ip <ip-address>” warning messages to the HAWQ master node log file.|