The gphdfs
LOCATION
clause of the CREATE EXTERNAL TABLE
command for HDFS files differs slightly for Hadoop HA (High Availability) clusters, Hadoop clusters without HA, and MapR clusters.
In a Hadoop HA cluster, the LOCATION
clause references the logical nameservices id (the dfs.nameservices
property in the hdfs-site.xml
configuration file). The hdfs-site.xml
file with the nameservices configuration must be installed on the Greenplum master and on each segment host.
For example, if dfs.nameservices
is set to mycluster
the LOCATION
clause takes this format:
LOCATION ('gphdfs://mycluster/path/filename.txt')
A cluster without HA specifies the hostname and port of the name node in the LOCATION
clause:
LOCATION ('gphdfs://hdfs_host[:port]/path/filename.txt')
If you are using MapR clusters, you specify a specific cluster and the file:
To specify the default cluster, the first entry in the MapR configuration file /opt/mapr/conf/mapr-clusters.conf
, specify the location of your table with this syntax:
LOCATION ('gphdfs:///<file_path>')
The file_path is the path to the file.
To specify another MapR cluster listed in the configuration file, specify the file with this syntax:
LOCATION ('gphdfs:///mapr/<cluster_name>/<file_path>')
The cluster_name is the name of the cluster specified in the configuration file and file_path is the path to the file.
For information about MapR clusters, see the MapR documentation.
Restrictions for HDFS
files are as follows.
You can specify one path for a readable external table with gphdfs
. Wildcard characters are allowed. If you specify a directory, the default is all files in the directory.
You can specify only a directory for writable external tables.
The URI of the LOCATION
clause cannot contain any of these four characters: \
, '
, <
, >
. The CREATE EXTERNAL TABLE
returns a an error if the URI contains any of the characters.
Format restrictions are as follows.
gphdfs_import
formatter is allowed for readable external tables with a custom format.gphdfs_export
formatter is allowed for writable external tables with a custom format.Parent topic: Accessing HDFS Data with gphdfs (Deprecated)
Compression options for Hadoop Writable External Tables use the form of a URI query and begin with a question mark. Specify multiple compression options with an ampersand (&
).
Compression Option | Values | Default Value |
---|---|---|
compress | true or false |
false |
compression_type | BLOCK or RECORD |
RECORD For AVRO format, compression_type must be block if compress is true . |
codec | Codec class name | GzipCodec for text format and DefaultCodec for gphdfs_export format.For AVRO format, the value is either deflate (the default) or snappy . |
codec_level (for AVRO format and deflate codec only) |
integer between 1 and 9 | 6 The level controls the trade-off between speed and compression. Valid values are 1 to 9, where 1 is the fastest and 9 is the most compressed. |
Place compression options in the query portion of the URI.