HadoopWriter

Available in Community Designer

Short Description
Ports
Metadata
HadoopWriter Attributes
Details
Troubleshooting
See also

Short Description

HadoopWriter writes data into Hadoop sequence files.

ComponentData outputInput portsOutput portsTransformationTransf. requiredJavaCTLAuto-propagated metadata
HadoopWriterHadoop sequence file10
no
no
no
no
no

Ports

Port typeNumberRequiredDescriptionMetadata
Input0
yes
For input data recordsAny

Metadata

HadoopWriter does not propagate metadata.

HadoopWriter has no metadata template.

HadoopWriter Attributes

AttributeReqDescriptionPossible values
Basic
Hadoop connection 

Hadoop connection with Hadoop libraries containing the Hadoop sequence file writer 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
yes

A URL to an output 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 output file should be located on the HDFS, use the URL in form of hdfs://ConnID/path/to/file, where ConnID is the ID of a Hadoop connection (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
yes
The name of an input record field carrying a key for each written key-value pair. 
Value field
yes
The name of an input record field carrying a value for each written key-value pair. 
Advanced
Create empty files 

If set to false, prevents the component from creating an empty output file when there are no input records.

true (default) | false

Details

HadoopWriter writes data into 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 write a single file as well as a partitioned file which has to be located on HDFS or a local file system.

The exact version of the file format created by the HadoopWriter 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 different version.

When writing to a local file system, additional .crc files are created if the Hadoop connection with default settings is used. That is because, by default, Hadoop interacts with a local file system using org.apache.hadoop.fs.LocalFileSystem which creates checksum files for each written file. When reading such files, checksum is verified. You can disable checksum creation/verification by adding this key-value pair in the Hadoop Parameters of the Hadoop connection: fs.file.impl=org.apache.hadoop.fs.RawLocalFileSystem

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

Notes and Limitations

Currently, writing compressed data is not supported.

HadoopWriter cannot write lists and maps.

Troubleshooting

If you write data to a sequence file on a local file system, you may encounter the following error message in the error log:

Cannot run program "chmod": CreateProcess error=2, The system cannot find the file specified

or

Cannot run program "cygpath": CreateProcess error=2, The system cannot find the file specified

To solve this problem, disable checksum creation/verification using the fs.file.impl=org.apache.hadoop.fs.RawLocalFileSystem Hadoop parameter in Hadoop connection configuration.

This issue is related to non-POSIX operating systems (MS Windows).

See also

HadoopReader
Hadoop connection
Common Properties of Components
Common Properties of Writers
Chapter 56, Writers