You can use PXF to read data that resides on a network file system mounted on your Greenplum Database hosts. PXF supports reading and writing the following file types from a network file system:
File Type | Profile Name | Operations Supported |
---|---|---|
delimited single line text | file:text | read, write |
delimited single line comma-separated values of text | file:csv | read, write |
delimited text with quoted linefeeds | file:text:multi | read |
Avro | file:avro | read, write |
JSON | file:json | read |
ORC | file:orc | read, write |
Parquet | file:parquet | read, write |
PXF does not support user impersonation when you access a network file system. PXF accesses a file as the operating system user that started the PXF process, usually gpadmin
.
Prerequisites
Before you use PXF to access files on a network file system, ensure that:
- You can identify the PXF runtime configuration directory (
$PXF_BASE
). - You have configured PXF, and PXF is running on each Greenplum Database host. See Configuring PXF for additional information.
- All files are accessible by
gpadmin
or by the operating system user that started the PXF process. - The network file system is correctly mounted at the same local mount point on every Greenplum Database host.
- You can identify the mount or share point of the network file system.
- You have created one or more named PXF server configurations as described in Configuring a PXF Network File System Server.
Configuring a PXF Network File System Server
Before you use PXF to access a file on a network file system, you must create a server configuration and then synchronize the PXF configuration to all Greenplum hosts. This procedure will typically be performed by the Greenplum Database administrator.
Use the server template configuration file <PXF_INSTALL_DIR>/templates/pxf-site.xml
when you configure a network file system server for PXF. This template file includes the mandatory property pxf.fs.basePath
that you configure to identify the network file system share path. PXF considers the file path that you specify in a CREATE EXTERNAL TABLE
LOCATION
clause that uses this server to be relative to this share path.
PXF does not support user impersonation when you access a network file system; you must explicitly turn off user impersonation in a network file system server configuration.
-
Log in to the Greenplum Database master host:
$ ssh gpadmin@<gpmaster>
-
Choose a name for the file system server. You will provide the name to Greenplum users that you choose to allow to read from or write to files on the network file system.
Note: The server name
default
is reserved. -
Create the
$PXF_BASE/servers/<server_name>
directory. For example, use the following command to create a file system server configuration namednfssrvcfg
:gpadmin@gpmaster$ mkdir $PXF_BASE/servers/nfssrvcfg
-
Copy the PXF
pxf-site.xml
template file to thenfssrvcfg
server configuration directory. For example:gpadmin@gpmaster$ cp <PXF_INSTALL_DIR>/templates/pxf-site.xml $PXF_BASE/servers/nfssrvcfg/
-
Open the template server configuration file in the editor of your choice, and uncomment and provide property values appropriate for your environment. For example, if the file system share point is the directory named
/mnt/extdata/pxffs
, uncomment and set these server properties:<?xml version="1.0" encoding="UTF-8"?> <configuration> ... <property> <name>pxf.service.user.impersonation</name> <value>false</value> </property> <property> <name>pxf.fs.basePath</name> <value>/mnt/extdata/pxffs</value> </property> ... </configuration>
-
Save your changes and exit the editor.
-
Synchronize the PXF server configuration to the Greenplum Database cluster:
gpadmin@gpmaster$ pxf cluster sync
Creating the External Table
The following syntax creates a Greenplum Database external table that references a file on a network file system. Use the appropriate file:*
profile for the file type that you want to access.
CREATE [READABLE | WRITABLE] EXTERNAL TABLE <table_name> ( <column_name> <data_type> [, ...] | LIKE <other_table> ) LOCATION ('pxf://<file-path>?PROFILE=file:<file-type>[&SERVER=<server_name>][&<custom-option>=<value>[...]]') FORMAT '[TEXT|CSV|CUSTOM]' (<formatting-properties>);
The specific keywords and values used in the Greenplum Database CREATE EXTERNAL TABLE command are described in the table below.
Keyword | Value |
---|---|
<file‑path> | The path to a directory or file on the network file system. PXF considers this file or path as being relative to the pxf.fs.basePath property value specified in <server_name>’s server configuration. <file‑path> must not specify a relative path nor include the dollar sign ($ ) character. |
PROFILE | The PROFILE keyword value must specify a file:<file-type> identified in the table above. |
SERVER=<server_name> | The named server configuration that PXF uses to access the network file system. PXF uses the default server if not specified. |
<custom‑option>=<value> | <custom-option> is profile-specific. |
FORMAT <value> | PXF profiles support the TEXT , CSV , and CUSTOM formats. |
<formatting‑properties> | Formatting properties supported by the profile; for example, the FORMATTER or delimiter . |
Example: Reading From and Writing to a CSV File on a Network File System
This example assumes that you have configured and mounted a network file system with the share point /mnt/extdata/pxffs
on the Greenplum Database master host, the standby master host, and on each segment host.
In this example, you:
- Create a CSV file on the network file system and add data to the file.
- Configure a network file system server for the share point.
- Create a PXF readable external table that references the directory containing the CSV file, and read the data.
- Create a PXF writable external table that references the directory containing the CSV file, and write some data.
- Read from the original readable external table again.
Create a CSV File
-
Create a directory (relative to the network file system share point) named
/mnt/extdata/pxffs/ex1
:gpadmin@gpmaster$ mkdir -p /mnt/extdata/pxffs/ex1
-
Create a CSV file named
somedata.csv
in the directory:$ echo 'Prague,Jan,101,4875.33 Rome,Mar,87,1557.39 Bangalore,May,317,8936.99 Beijing,Jul,411,11600.67' > /mnt/extdata/pxffs/ex1/somedata.csv
Create the Network File System Server
Create a server configuration named nfssrvcfg
with share point /mnt/extdata/pxffs
as described in Configuring a PXF Network File System Server.
Read Data
Perform the following procedure to create a PXF external table that references the ex1
directory that you created in a previous section, and then read the data in the somedata.csv
file in that directory:
-
Create a PXF external table that references
ex1
and that specifies thefile:text
profile. For example:gpadmin=# CREATE EXTERNAL TABLE pxf_read_nfs(location text, month text, num_orders int, total_sales float8) LOCATION ('pxf://ex1/?PROFILE=file:text&SERVER=nfssrvcfg') FORMAT 'CSV';
Because the
nfssrvcfg
server configurationpxf.fs.basePath
property value is/mnt/exdata/pxffs
, PXF constructs the path/mnt/extdata/pxffs/ex1
to read the file. -
Display all rows of the
pxf_read_nfs
table:gpadmin=# SELECT * FROM pxf_read_nfs ORDER BY num_orders DESC; location | month | num_orders | total_sales -----------+-------+------------+------------- Beijing | Jul | 411 | 11600.67 Bangalore | May | 317 | 8936.99 Prague | Jan | 101 | 4875.33 Rome | Mar | 87 | 1557.39 (4 rows)
Write Data and Read Again
Perform the following procedure to insert some data into the ex1
directory and then read the data again. You must create a new external table for the write operation.
-
Create a writable PXF external table that references
ex1
and that specifies thefile:text
profile. For example:gpadmin=# CREATE WRITABLE EXTERNAL TABLE pxf_write_nfs(location text, month text, num_orders int, total_sales float8) LOCATION ('pxf://ex1/?PROFILE=file:text&SERVER=nfssrvcfg') FORMAT 'CSV' (delimiter=',');
-
Insert some data into the
pxf_write_nfs
table. For example:gpadmin=# INSERT INTO pxf_write_nfs VALUES ( 'Frankfurt', 'Mar', 777, 3956.98 ); INSERT 0 1 gpadmin=# INSERT INTO pxf_write_nfs VALUES ( 'Cleveland', 'Oct', 3812, 96645.37 ); INSERT 0 1
PXF writes one or more files to the
ex1/
directory when you insert into thepxf_write_nfs
table. -
Use the
pxf_read_nfs
readable external table that you created in the previous section to view the new data you inserted into thepxf_write_nfs
table:gpadmin=# SELECT * FROM pxf_read_nfs ORDER BY num_orders DESC; location | month | num_orders | total_sales -----------+-------+------------+------------- Cleveland | Oct | 3812 | 96645.37 Frankfurt | Mar | 777 | 3956.98 Beijing | Jul | 411 | 11600.67 Bangalore | May | 317 | 8936.99 Prague | Jan | 101 | 4875.33 Rome | Mar | 87 | 1557.39 (6 rows)
When you select from the
pxf_read_nfs
table here, PXF reads thesomedata.csv
file and the new files that it added to theex1/
directory in the previous step.
About Specifying a Parquet Schema File Location
If you use the file:parquet
profile to write to an external table that references a Parquet file and you want to provide the Parquet schema, specify the SCHEMA
custom option in the LOCATION
clause when you create the writable external table. Refer to the Creating the External Table discussion in the PXF HDFS Parquet documentation for more information on the options available when you create an external table.
You must set SCHEMA
to the location of the Parquet schema file on the file system of the specified SERVER=<server_name>
. When the <server_name>
configuration includes a pxf.fs.basePath
property setting, PXF considers the schema file that you specify to be relative to the mount point specified.
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