Property Type

Built-In: You create and store the
schema locally for this component only. Related topic: see
Talend Studio

User Guide.

Repository: You have already created
the schema and stored it in the Repository. You can reuse it in various projects and
Job designs. Related topic: see
Talend Studio

User Guide.

Use an existing connection

Select this check box and in the Component List
click the HDFS connection component from which you want to reuse the connection details
already defined.

Note that when a Job contains the parent Job and the child Job, Component List presents only the connection components in the same
Job level.

Distribution

1. Select Import from existing
   version to import an officially supported distribution as base
   and then add other required jar files which the base distribution does not
   provide.

2. Select Import from zip to
   import the configuration zip for the custom distribution to be used. This zip
   file should contain the libraries of the different Hadoop elements and the index
   file of these libraries.

   In
   Talend
   
   Exchange, members of
   Talend
   community have shared some ready-for-use configuration zip files
   which you can download from this Hadoop configuration
   list and directly use them in your connection accordingly. However, because of
   the ongoing evolution of the different Hadoop-related projects, you might not be
   able to find the configuration zip corresponding to your distribution from this
   list; then it is recommended to use the Import from
   existing version option to take an existing distribution as base
   to add the jars required by your distribution.

   Note that custom versions are not officially supported by
   
   Talend
   .
   Talend
   and its community provide you with the opportunity to connect to
   custom versions from the Studio but cannot guarantee that the configuration of
   whichever version you choose will be easy, due to the wide range of different
   Hadoop distributions and versions that are available. As such, you should only
   attempt to set up such a connection if you have sufficient Hadoop experience to
   handle any issues on your own.

   Note:

   In this dialog box, the active check box must be kept
   selected so as to import the jar files pertinent to the connection to be
   created between the custom distribution and this component.

   For a step-by-step example about how to connect to a custom
   distribution and share this connection, see Connecting to a custom Hadoop distribution.

Hadoop version

Use kerberos authentication

This check box is available depending on the Hadoop distribution you are
connecting to.

Select the Use a keytab to authenticate
check box to log into a Kerberos-enabled system using a given keytab file. A keytab
file contains pairs of Kerberos principals and encrypted keys. You need to enter the
principal to be used in the Principal field and
the access path to the keytab file itself in the Keytab field. This keytab file must be stored in the machine in
which your Job actually runs, for example, on a Talend Jobserver.

Note that the user that executes a keytab-enabled Job is not necessarily
the one a principal designates but must have the right to read the keytab file being
used. For example, the user name you are using to execute a Job is user1 and the principal to be used is guest; in this
situation, ensure that user1 has the right to read the keytab
file to be used.

NameNode URI

Type in the URI of the Hadoop NameNode, the master node of a Hadoop system. For
example, we assume that you have chosen a machine called masternode as the NameNode, then the location is hdfs://masternode:portnumber. If you are using WebHDFS, the location should be
webhdfs://masternode:portnumber; if this WebHDFS is secured
with SSL, the scheme should be swebhdfs and you need to use
a tLibraryLoad in the Job to load the library required by
the secured WebHDFS.

User name

The User name field is available when you are not using
Kerberos to authenticate. In the User name field, enter the
login user name for your distribution. If you leave it empty, the user name of the machine
hosting the Studio will be used.

Group

Enter the membership including the authentication user under which the HDFS instances were
started. This field is available depending on the distribution you are using.

File name

Browse to, or enter the path pointing to the data to be used in the file system.

Row separator

The separator used to identify the end of a row.

Ignore empty rows

Select this check box to skip the empty rows.

Encoding

Select the encoding from the list or select Custom and define it manually. This field is compulsory for database
data handling.

Compression

Select the Uncompress the data check box to uncompress
the input data.

Hadoop provides different compression formats that help reduce the space needed for
storing files and speed up data transfer. When reading a compressed file, the Studio needs
to uncompress it before being able to feed it to the input flow.

Hadoop properties

tStatCatcher Statistics

Global Variables

COUNT: the number of rows in a file. This is a Flow
variable and it returns an integer.

ERROR_MESSAGE: the error message generated by the
component when an error occurs. This is an After variable and it returns a string. This
variable functions only if the Die on error check box is
cleared, if the component has this check box.

A Flow variable functions during the execution of a component while an After variable
functions after the execution of the component.

To fill up a field or expression with a variable, press Ctrl +
Space to access the variable list and choose the variable to use from it.

For further information about variables, see
Talend Studio

User Guide.

Usage rule

tHDFSRowCount is a standalone
component; it must be used with a OnSubjobOk
connection to tJava in
order to return the row count.

In this example, tHDFSRowCount_1 is the label of this component in a Job,
so it may vary among different use cases; COUNT is the global variable of tHDFSRowCount, representing the integer flow of the row
count.

For further information about how to label a component or how to
use a global variable in a Job, see the
Talend Studio

User
Guide.

Dynamic settings

Click the [+] button to add a row in the
table and fill the Code field with a context variable
to choose your HDFS connection dynamically from multiple connections planned in your
Job. This feature is useful when you need to access files in different HDFS systems or
different distributions, especially when you are working in an environment where you
cannot change your Job settings, for example, when your Job has to be deployed and
executed independent of
Talend Studio
.

The Dynamic settings table is
available only when the Use an existing
connection check box is selected in the Basic settings view. Once a dynamic parameter is
defined, the Component List box in the
Basic settings view becomes unusable.

For examples on using dynamic parameters, see Scenario: Reading data from databases through context-based dynamic connections and Scenario: Reading data from different MySQL databases using dynamically loaded connection parameters. For more information on Dynamic
settings and context variables, see
Talend Studio User Guide.

Prerequisites

The Hadoop distribution must be properly installed, so as to guarantee the interaction
with
Talend Studio
. The following list presents MapR related information for
example.

• Ensure that you have installed the MapR client in the machine where the Studio is,
  and added the MapR client library to the PATH variable of that machine. According
  to MapR’s documentation, the library or libraries of a MapR client corresponding to
  each OS version can be found under MAPR_INSTALL
  hadoophadoop-VERSIONlib
  ative. For example, the library for
  Windows is lib
  ativeMapRClient.dll in the MapR
  client jar file. For further information, see the following link from MapR: http://www.mapr.com/blog/basic-notes-on-configuring-eclipse-as-a-hadoop-development-environment-for-mapr.

  Without adding the specified library or libraries, you may encounter the following
  error: no MapRClient in java.library.path.

• Set the -Djava.library.path argument, for example, in the Job Run VM arguments area
  of the Run/Debug view in the [Preferences] dialog box in the Window menu. This argument provides to the Studio the path to the
  native library of that MapR client. This allows the subscription-based users to make
  full use of the Data viewer to view locally in the
  Studio the data stored in MapR.

For further information about how to install a Hadoop distribution, see the manuals
corresponding to the Hadoop distribution you are using.

Limitation

JRE 1.6+ is required.