HadoopReader

HDFSReader 64x64

Short description

Ports

Metadata

HadoopReader attributes

Details

Examples

See also

Short description

HadoopReader reads Hadoop sequence files.

Data source Input ports Output ports Each to all outputs Different to different outputs Transformation Transf. req. Java CTL Auto-propagated metadata

Hadoop Sequence File

0–1

1

Ports

Port type Number Required Description Metadata

Input

0

For Input port reading. Only the source mode is supported.

Any

Output

0

For read data records.

Any

Metadata

HadoopReader does not propagate metadata.

HadoopReader has no metadata template.

HadoopReader attributes

Attribute Req Description Possible values

Basic

Hadoop connection

Hadoop connections with Hadoop libraries containing the Hadoop sequence file parser implementation. If the Hadoop connection ID is specified in a hdfs:// URL in the File URL attribute, the value of this attribute is ignored.

Hadoop connection ID

File URL

A URL to a file on HDFS or a local file system.

URLs without a protocol (i.e. absolute or relative path) or with the file:// protocol are considered to be located on the local file system.

If the file to be read is located on the HDFS, use the URL in this form: hdfs://ConnID/path/to/file, where ConnID is the ID of a Hadoop connections (the Hadoop connection component attribute will be ignored), and /path/to/myfile is the absolute path on corresponding HDFS to the file named myfile.

Key field

The name of an output edge record field, where a key of each key-value pair will be stored.

Value field

The name of an output edge record field, where a value of each key-value pair will be stored.

Details

HadoopReader reads data from a special Hadoop sequence file (org.apache.hadoop.io.SequenceFile). These files contain key-value pairs and are used in MapReduce jobs as input/output file formats. The component can read a single file as well as a collection of files which have to be located on HDFS or local file system.

If you connect to local sequence files, there is no need to connect to a Hadoop cluster. However, you still need a valid Hadoop connection (with a correct version of libraries).

The exact version of the file format supported by the HadoopReader component depends on Hadoop libraries which you supply in the Hadoop connection referenced from the File URL attribute. In general, sequence files created by one version of Hadoop may not be readable by a different version.

Hadoop sequence files may contain compressed data. HadoopReader automatically detects this and decompresses the data. Remember that supported compression codecs depend on libraries you specify in the Hadoop connection.

For technical details about Hadoop sequence files, see Apache Hadoop Wiki.

Examples

Reading data from local sequence files

Read records from a Hadoop Sequence file products.dat. The file has ProductID as a key and ProductName as a value.

Solution

Create a valid Hadoop connection or use existing one. See Hadoop connections.

Use the Hadoop connection, File URL, Key field and Key value attributes.

Attribute Value

Hadoop connection

MyHadoopConnection

File URL

${DATA_IN}/products.dat

Key field

ProductID

Value field

ProductName