gpfdist

Serves data files to or writes data files out from Greenplum Database segments.

Synopsis

  1. gpfdist [-d <directory>] [-p <http_port>] [-P <last_http_port>] [-l <log_file>]
  2.    [-t <timeout>] [-S] [-w <time>] [-v | -V] [-s] [-m <max_length>]
  3.    [--ssl <certificate_path> [--sslclean <wait_time>] ]
  4.    [-c <config.yml>]
  6. gpfdist -? | --help 
  8. gpfdist --version

Description

gpfdist is Greenplum Database parallel file distribution program. It is used by readable external tables and gpload to serve external table files to all Greenplum Database segments in parallel. It is used by writable external tables to accept output streams from Greenplum Database segments in parallel and write them out to a file.

Note: gpfdist and gpload are compatible only with the Greenplum Database major version in which they are shipped. For example, a gpfdist utility that is installed with Greenplum Database 4.x cannot be used with Greenplum Database 5.x or 6.x.

In order for gpfdist to be used by an external table, the LOCATION clause of the external table definition must specify the external table data using the gpfdist:// protocol (see the Greenplum Database command CREATE EXTERNAL TABLE).

Note: If the --ssl option is specified to enable SSL security, create the external table with the gpfdists:// protocol.

The benefit of using gpfdist is that you are guaranteed maximum parallelism while reading from or writing to external tables, thereby offering the best performance as well as easier administration of external tables.

For readable external tables, gpfdist parses and serves data files evenly to all the segment instances in the Greenplum Database system when users SELECT from the external table. For writable external tables, gpfdist accepts parallel output streams from the segments when users INSERT into the external table, and writes to an output file.

Note: When gpfdist reads data and encounters a data formatting error, the error message includes a row number indicating the location of the formatting error. gpfdist attempts to capture the row that contains the error. However, gpfdist might not capture the exact row for some formatting errors.

For readable external tables, if load files are compressed using gzip or bzip2 (have a .gz or .bz2 file extension), gpfdist uncompresses the data while loading the data (on the fly). For writable external tables, gpfdist compresses the data using gzip if the target file has a .gz extension.

Note: Compression is not supported for readable and writeable external tables when the gpfdist utility runs on Windows platforms.

When reading or writing data with the gpfdist or gpfdists protocol, Greenplum Database includes X-GP-PROTO in the HTTP request header to indicate that the request is from Greenplum Database. The utility rejects HTTP requests that do not include X-GP-PROTO in the request header.

Most likely, you will want to run gpfdist on your ETL machines rather than the hosts where Greenplum Database is installed. To install gpfdist on another host, simply copy the utility over to that host and add gpfdist to your $PATH.

Note: When using IPv6, always enclose the numeric IP address in brackets.

Options

-d directory

The directory from which gpfdist will serve files for readable external tables or create output files for writable external tables. If not specified, defaults to the current directory.

-l log_file

The fully qualified path and log file name where standard output messages are to be logged.

-p http_port

The HTTP port on which gpfdist will serve files. Defaults to 8080.

-P last_http_port

The last port number in a range of HTTP port numbers (http_port to last_http_port, inclusive) on which gpfdist will attempt to serve files. gpfdist serves the files on the first port number in the range to which it successfully binds.

-t timeout

Sets the time allowed for Greenplum Database to establish a connection to a gpfdist process. Default is 5 seconds. Allowed values are 2 to 7200 seconds (2 hours). May need to be increased on systems with a lot of network traffic.

-m max_length

Sets the maximum allowed data row length in bytes. Default is 32768. Should be used when user data includes very wide rows (or when line too long error message occurs). Should not be used otherwise as it increases resource allocation. Valid range is 32K to 256MB. (The upper limit is 1MB on Windows systems.)

Note: Memory issues might occur if you specify a large maximum row length and run a large number of gpfdist concurrent connections. For example, setting this value to the maximum of 256MB with 96 concurrent gpfdist processes requires approximately 24GB of memory ( (96 + 1) x 246MB).

-s

Enables simplified logging. When this option is specified, only messages with WARN level and higher are written to the gpfdist log file. INFO level messages are not written to the log file. If this option is not specified, all gpfdist messages are written to the log file.

You can specify this option to reduce the information written to the log file.

-S (use O_SYNC)

Opens the file for synchronous I/O with the O_SYNC flag. Any writes to the resulting file descriptor block gpfdist until the data is physically written to the underlying hardware.

-w time

Sets the number of seconds that Greenplum Database delays before closing a target file such as a named pipe. The default value is 0, no delay. The maximum value is 7200 seconds (2 hours).

For a Greenplum Database with multiple segments, there might be a delay between segments when writing data from different segments to the file. You can specify a time to wait before Greenplum Database closes the file to ensure all the data is written to the file.

--ssl certificate_path

Adds SSL encryption to data transferred with gpfdist. After executing gpfdist with the --ssl certificate\_path option, the only way to load data from this file server is with the gpfdist:// protocol. For information on the gpfdist:// protocol, see “Loading and Unloading Data” in the Greenplum Database Administrator Guide.

The location specified in certificate_path must contain the following files:

  • The server certificate file, server.crt
  • The server private key file, server.key
  • The trusted certificate authorities, root.crt

The root directory (/) cannot be specified as certificate_path.

--sslclean wait_time

When the utility is run with the --ssl option, sets the number of seconds that the utility delays before closing an SSL session and cleaning up the SSL resources after it completes writing data to or from a Greenplum Database segment. The default value is 0, no delay. The maximum value is 500 seconds. If the delay is increased, the transfer speed decreases.

In some cases, this error might occur when copying large amounts of data: gpfdist server closed connection. To avoid the error, you can add a delay, for example --sslclean 5.

-c config.yaml

Specifies rules that gpfdist uses to select a transform to apply when loading or extracting data. The gpfdist configuration file is a YAML 1.1 document.

For information about the file format, see Configuration File Format in the Greenplum Database Administrator Guide. For information about configuring data transformation with gpfdist, see Transforming External Data with gpfdist and gpload in the Greenplum Database Administrator Guide.

This option is not available on Windows platforms.

-v (verbose)

Verbose mode shows progress and status messages.

-V (very verbose)

Verbose mode shows all output messages generated by this utility.

-? (help)

Displays the online help.

--version

Displays the version of this utility.

Notes

The server configuration parameter verify_gpfdists_cert controls whether SSL certificate authentication is enabled when Greenplum Database communicates with the gpfdist utility to either read data from or write data to an external data source. You can set the parameter value to false to deactivate authentication when testing the communication between the Greenplum Database external table and the gpfdist utility that is serving the external data. If the value is false, these SSL exceptions are ignored:

  • The self-signed SSL certificate that is used by gpfdist is not trusted by Greenplum Database.
  • The host name contained in the SSL certificate does not match the host name that is running gpfdist.

Warning: Deactivating SSL certificate authentication exposes a security risk by not validating the gpfdists SSL certificate.

If the gpfdist utility hangs with no read or write activity occurring, you can generate a core dump the next time a hang occurs to help debug the issue. Set the environment variable GPFDIST_WATCHDOG_TIMER to the number of seconds of no activity to wait before gpfdist is forced to exit. When the environment variable is set and gpfdist hangs, the utility aborts after the specified number of seconds, creates a core dump, and sends abort information to the log file.

This example sets the environment variable on a Linux system so that gpfdist exits after 300 seconds (5 minutes) of no activity.

  1. export GPFDIST_WATCHDOG_TIMER=300

Examples

To serve files from a specified directory using port 8081 (and start gpfdist in the background):

  1. gpfdist -d /var/load_files -p 8081 &

To start gpfdist in the background and redirect output and errors to a log file:

  1. gpfdist -d /var/load_files -p 8081 -l /home/gpadmin/log &

To stop gpfdist when it is running in the background:

--First find its process id:

  1. ps ax | grep gpfdist

--Then terminate the process, for example:

  1. kill 3456

See Also

gpload, CREATE EXTERNAL TABLE in the Greenplum Database Reference Guide