Connecting to an external file server

Greenplum® Parallel File Server (gpfdist) is a utility used to read and write data from files located on remote servers. It is installed on each segment host of a Greenplum® cluster and ensures parallel data loading by distributing it across segments either evenly or according to the set distribution key. This improves performance when handling large amounts of external data.

gpfdist works with any delimited text files as well as compressed gzip and bzip2 files.

To read or write files on an external server:

1. Install and run gpfdist as part of the Greenplum® Loader or Greenplum® Database package on the remote server hosting your target files.
2. Create an external table in the Greenplum® database to reference these files.

Running gpfdistRunning gpfdist

1. Download and install the Greenplum® Loader package from the VMware website or the Greenplum® Database package from the Yandex Object Storage bucket by following this guide.

2. Run gpfdist:

   gpfdist -d <data_file_directory> -p <connection_port> -l <log_file_path>
   

   Where:

   • <data_file_directory>: Local path to the directory with files for reading/writing data through an external table.
   • <connection_port>: Port the utility will use to operate. The default value is 8080.
   • <log_file_path>: Optional path to the file gpfdist will write its logs to.

   To distribute the network's workload, you can run several gpfdist instances on the same server by specifying different directories and connection ports, e.g.:

   gpfdist -d /var/load_files1 -p 8081 -l /home/gpadmin/log1 & \
   gpfdist -d /var/load_files2 -p 8082 -l /home/gpadmin/log2 &
   

3. Make sure files from the specified directory are available on the set port from Yandex Cloud. To do this, run the following command from a VM in Yandex Cloud:

   wget http://hostname:port/filename
   

Creating an external table using gpfdistCreating an external table using gpfdist

SQL query syntax for creating an external table:

CREATE [WRITABLE] EXTERNAL TABLE <table_name>
       (<column_name> <data_type> [, ...])
       LOCATION('gpfdist://<path_to_file_on_remote_server>' [, ...])
       FORMAT '[TEXT|CSV|CUSTOM]';

Where:

• <table_name>: Name of the external table that will be created in the Greenplum® database.
• <column_name>: Table column name.
• <data_type>: Table column data type.
• <path_to_file_on_remote_server>: Address of the server gpfdist runs on, connection port, and file path. You can specify a particular file or a mask using the asterisk symbol (*).

The WRITABLE option allows writing data to an external object. To read data from an external object, create an external table with the READABLE option.

Examples of creating external tablesExamples of creating external tables

• Creating an external table with data from file.csv on the hostname server:

  CREATE EXTERNAL TABLE tableName (id int)
         LOCATION('gpfdist://hostname:8080/file.csv')
         FORMAT 'CSV' (DELIMITER ',');
  

• Creating an external table consolidating data from all txt files, with | for a separator and space for NULL, on the hostname1 and hostname2 servers:

  CREATE EXTERNAL TABLE tableName (...)
         LOCATION('gpfdist://hostname1:8081/*.txt',
                  'gpfdist://hostname2:8081/*.txt')
         FORMAT 'TEXT' (DELIMITER '|' NULL ' ');
  

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