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Post date: Nov 26, 2013 8:43:12 PM
1. No pg_hba.conf entry for hosts or users
2. Greenplum database is not running
3. Too many clients already connected
4. Interconnect/network issues
* In order for Greenplum Database to be able to accept remote client connections, you must configure your Greenplum Database master instance so that connections are allowed from the client hosts and database users that will be connecting to Greenplum Database. This is done by adding the appropriate entries to the pg_hba.conf configuration file (located in the master instance’s data directory).
** If the Greenplum Database master instance is down, users will not be able to connect. You can verify that the Greenplum Database system is up by running the gpstate utility on the Greenplum master host.
*** By default, Greenplum Database is configured to allow a maximum of 250 concurrent user connections on the master 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 Greenplum Database master. If you change this setting for the master, you must also make appropriate changes at the segments.
**** If users are connecting to the Greenplum master host from a remote client, network problems may be preventing a connection (for example, DNS host name resolution problems, the host system is down, etc.). To ensure that network problems are not the cause, try connecting to the Greenplum master 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 Greenplum Database, queries and connections will fail. Keep in mind that for some operations, connections to the Greenplum Database master use localhost while 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 Greenplum Database array from the master host over the network. In the /etc/hosts file of the master and all segments, make sure you have the correct host names and IP addresses for all hosts involved in the Greenplum Database array. The 127.0.0.1 IP should only resolve to localhost.