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The segments access gpfdist at runtime. Ensure that the Greenplum segment hosts have network access to gpfdist. gpfdist is a web server: test connectivity by running the following command from each host in the Greenplum array (segments and master):
$ wget http://gpfdist_hostname:port/filename
The CREATE EXTERNAL TABLE definition must have the correct host name, port, and file names for gpfdist. Specify file names and paths relative to the directory from which gpfdist serves files (the directory path specified when gpfdist started). See Creating External Tables - Examples.
If you start gpfdist on your system and IPv6 networking is disabled, gpfdist displays this warning message when testing for an IPv6 port.
[WRN gpfdist.c:2050] Creating the socket failed
If the corresponding IPv4 port is available, gpfdist uses that port and the warning for IPv6 port can be ignored. To see information about the ports that gpfdist tests, use the -V option.
For information about IPv6 and IPv4 networking, see your operating system documentation.
When reading or writing data with the gpfdist or gfdists protocol, the gpfdist utility rejects HTTP requests that do not include X-GP-PROTO in the request header. If X-GP-PROTO is not detected in the header request gpfist returns a 400 error in the status line of the HTTP response header: 400 invalid request (no gp-proto).
Greenplum Database includes X-GP-PROTO in the HTTP request header to indicate that the request is from Greenplum Database.