IBM Streams 4.2.1

Operator HDFS2FileSource

SPL standard and specialized toolkits > com.ibm.streamsx.hdfs 3.1.0 > com.ibm.streamsx.hdfs > HDFS2FileSource

Primitive operator image not displayed. Problem loading file: ../../image/tk$com.ibm.streamsx.hdfs/op$com.ibm.streamsx.hdfs$HDFS2FileSource.svg

The HDFS2FileSource operator reads files from a Hadoop Distributed File System (HDFS).

The operator opens a file on HDFS and sends out its contents in tuple format on its output port.

If the optional input port is not specified, the operator reads the HDFS file that is specified in the file parameter and provides the file contents on the output port. If the optional input port is configured, the operator reads the files that are named by the attribute in the tuples that arrive on its input port and places a punctuation marker between each file.

Behavior in a consistent region

The HDFS2FileSource operator can participate in a consistent region. The operator can be at the start of a consistent region if there is no input port.

The operator supports periodic and operator-driven consistent region policies. If the consistent region policy is set as operator driven, the operator initiates a drain after a file is fully read. If the consistent region policy is set as periodic, the operator respects the period setting and establishes consistent states accordingly. This means that multiple consistent states can be established before a file is fully read.

At checkpoint, the operator saves the current file name and file cursor location. If the operator does not have an input port, upon application failures, the operator resets the file cursor back to the checkpointed location, and starts replaying tuples from the cursor location. If the operator has an input port and is in a consistent region, the operator relies on its upstream operators to properly reply the filenames for it to re-read the files from the beginning.

Exceptions

The HDFS2FileSource operator terminates in the following cases:
  • The operator cannot connect to HDFS.
  • The file cannot be opened.
  • The file does not exist.
  • The file becomes unreadable.
  • A tuple cannot be created from the file contents (such as a problem with the file format).
Examples

Summary

Ports
This operator has 1 input port and 1 output port.
Windowing
This operator does not accept any windowing configurations.
Parameters
This operator supports 10 parameters.

Optional: authKeytab, authPrincipal, blockSize, configPath, credFile, encoding, file, hdfsUri, hdfsUser, initDelay

Metrics
This operator reports 1 metrics.

Properties

Implementation
Java

Input Ports

Ports (0)

The HDFS2FileSource operator has one optional input port. If an input port is specified, the operator expects an input tuple with a single attribute of type rstring. The input tuples contain the file names that the operator opens for reading. The input port is non-mutating.

Properties

Output Ports

Assignments
Java operators do not support output assignments.
Ports (0)

The HDFS2FileSource operator has one output port. The tuples on the output port contain the data that is read from the files. The operator supports two modes of reading. To read a file line-by-line, the expected output schema of the output port is tuple<rstring line> or tuple<ustring line>. To read a file as binary, the expected output schema of the output port is tuple<blob data>. Use the blockSize parameter to control how much data to retrieve on each read. The operator includes a punctuation marker at the conclusion of each file. The output port is mutating.

Properties

Parameters

Optional: authKeytab, authPrincipal, blockSize, configPath, credFile, encoding, file, hdfsUri, hdfsUser, initDelay

authKeytab

This parameter specifies the file that contains the encrypted keys for the user that is specified by the authPrincipal parameter. The operator uses this keytab file to authenticate the user. The keytab file is generated by the administrator. You must specify this parameter to use Kerberos authentication.

Properties
authPrincipal

This parameter specifies the Kerberos principal that you use for authentication. This value is set to the principal that is created for the InfoSphere Streams instance owner. You must specify this parameter if you want to use Kerberos authentication.

Properties
blockSize

This parameter specifies the maximum number of bytes to be read at one time when reading a file into binary mode (ie, into a blob); thus, it is the maximum size of the blobs on the output stream. The parameter is optional, and defaults to 4096.

Properties
configPath

This parameter specifies the absolute path to the directory that contains the core-site.xml file, which is an HDFS configuration file. If this parameter is not specified, the operator searches the default location for the core-site.xml file.

Properties
credFile

This parameter specifies a file that contains login credentials. The credentials are used to connect to GPFS remotely by using the webhdfs://hdfshost:webhdfsport schema. The credentials file must contain information about how to authenticate with IBM InfoSphere BigInsights when using the webhdfs schema. For example, the file must contain the user name and password for an IBM InfoSphere BigInsights user.

Properties
encoding

This parameter specifies the encoding to use when reading files. The default value is UTF-8.

Properties
file

This parameter specifies the name of the file that the operator opens and reads. This parameter must be specified when the optional input port is not configured. If the optional input port is used and the file name is specified, the operator generates an error.

Properties
hdfsUri
This parameter specifies the uniform resource identifier (URI) that you can use to connect to the HDFS file system. The URI has the following format:
  • To access HDFS locally or remotely, use hdfs://hdfshost:hdfsport
  • To access GPFS locally, use gpfs:///.
  • To access GPFS remotely, use webhdfs://hdfshost:webhdfsport

If this parameter is not specified, the operator expects that the HDFS URI is specified as the fs.defaultFS or fs.default.name property in the core-site.xml HDFS configuration file. The operator expects the core-site.xml file to be in $HADOOP_HOME/../hadoop-conf or $HADOOP_HOME/etc/hadoop.

Properties
hdfsUser

This parameter specifies the user ID to use when you connect to the HDFS file system. If this parameter is not specified, the operator uses the instance owner to connect to the HDFS file system.

When you use Kerberos authentication, the operator authenticates with the Hadoop file system as the instance owner by using the values that are specified in the authPrincipal and authKeytab parameters. After successful authentication, the operator uses the user ID that is specified by the hdfsUser parameter to perform all other operations on the file system.

NOTE: When using Kerberos authentication, the InfoSphere Streams instance owner must have super user privileges on HDFS or GPFS to perform operations as the user that is specified by the hdfsUser parameter.

Properties
initDelay

This parameter specifies the time to wait in seconds before the operator reads the first file. The default value is 0.

Properties

Code Templates

HDFS2FileSource
stream<${streamType}> ${streamName} = HDFS2FileSource() {
                param
                file : "${filename}";
                }

HDFS2FileSource with hdfsUser and hdfsUri
stream<${streamType}> ${streamName} = HDFS2FileSource() {
                param
                file: "${filename}";
                hdfsUser: "${hdfsUser}";
                hdfsUri: "${hdfsUri}";
                }

Metrics

nFilesOpened - Counter

The number of files that are opened by the operator for reading data.

Libraries

Java operator class library
Library Path: ../../impl/java/bin, ../../impl/lib/BigData.jar
apache library
Library Path: @HADOOP_HOME@/../hadoop-conf, @HADOOP_HOME@/etc/hadoop, @HADOOP_HOME@/conf, @HADOOP_HOME@/share/hadoop/hdfs/*, @HADOOP_HOME@/share/hadoop/common/*, @HADOOP_HOME@/share/hadoop/common/lib/*, @HADOOP_HOME@/lib/*, @HADOOP_HOME@/client/*, @HADOOP_HOME@/*, @HADOOP_HOME@/../hadoop-hdfs/*