tHDFSInput – Docs for ESB 5.x

Component family

Big Data / Hadoop

Function

tHDFSInput reads a file located
on a given Hadoop distributed file system (HDFS) and puts the data
of interest from this file into a Talend schema. Then it passes the
data to the component that follows.

If you have subscribed to one of the Talend solutions with Big Data, you are
able to use this component in a Talend Map/Reduce Job to generate
Map/Reduce code. For further information, see tHDFSInput in Talend Map/Reduce
Jobs.

Purpose

tHDFSInput extracts the data in a
HDFS file for other components to process it.

Basic settings

Property type

Either Built-in or Repository

Built-in: No property data stored
centrally.

Repository: Select the repository
file in which the properties are stored. The fields that follow are
completed automatically using the data retrieved.

Since version 5.6, both the Built-In mode and the Repository mode are
available in any of the Talend solutions.

Schema and Edit
Schema

A schema is a row description. It defines the number of fields to be processed and passed on
to the next component. The schema is either Built-In or
stored remotely in the Repository.

Since version 5.6, both the Built-In mode and the Repository mode are
available in any of the Talend solutions.

Click Edit schema to make changes to the schema. If the
current schema is of the Repository type, three options are
available:

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.

Version

Distribution

Select the cluster you are using from the drop-down list. The options in the list vary
depending on the component you are using. Among these options, the following ones requires
specific configuration:

Hadoop version

Select the version of the Hadoop distribution you are using. The available options vary
depending on the component you are using. Along with the evolution of Hadoop, please note
the following changes:

 Authentication

Use kerberos authentication

If you are accessing the Hadoop cluster running with Kerberos security, select this check
box, then, enter the Kerberos principal name for the NameNode in the field displayed. This
enables you to use your user name to authenticate against the credentials stored in
Kerberos.

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 Hadoop 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.

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 NameNode is the master node of a Hadoop system.
For example, we assume that you have chosen a machine called masternode as the NameNode of an Apache Hadoop distribution, then the
location is hdfs://masternode:portnumber.

User name

Enter the user authentication name of HDFS.

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 directory in HDFS where the data you need to use is.

If the path you set points to a folder, this component will read
all of the files stored in that folder. Furthermore, if sub-folders
exist in that folder and you need to read files in the sub-folders,
select the Include sub-directories if path is
directory check box in the Advanced settings view.

File type

Type

Select the type of the file to be processed. The type of the file may be:

Row separator

Enter the separator used to identify the end of a row.

This field is not available for a Sequence file.

Field separator

Enter character, string or regular expression to separate fields for the transferred
data.

This field is not available for a Sequence file.

Header

Set values to ignore the header of the transferred data. For
example, enter 0 to ignore no
rows for the data without header and set 1 for the data with header at the first row.

This field is not available for a Sequence file.

Custom encoding

You may encounter encoding issues when you process the stored data. In that situation, select
this check box to display the Encoding list.

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

This option is not available for a Sequence file.

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.

This option is not available for a Sequence file.

Advanced settings

Include sub-directories if path is
directory

Select this check box to read not only the folder you have
specified in the File name field
but also the sub-folders in that folder.

Hadoop properties

Talend Studio uses a default configuration for its engine to perform
operations in a Hadoop distribution. If you need to use a custom configuration in a specific
situation, complete this table with the property or properties to be customized. Then at
runtime, the customized property or properties will override those default ones.

For further information about the properties required by Hadoop and its related systems such
as HDFS and Hive, see the documentation of the Hadoop distribution you
are using or see Apache’s Hadoop documentation on http://hadoop.apache.org/docs and then select the version of the documentation you want. For demonstration purposes, the links to some properties are listed below:

tStatCatcher Statistics

Select this check box to collect log data at the component level.
Note that this check box is not available in the Map/Reduce version
of the component.

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 more information on Dynamic settings and context
variables, see Talend Studio User Guide.

Global Variables

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

This component needs an output link.

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.

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

Log4j

The activity of this component can be logged using the log4j feature. For more information on this feature, see Talend Studio User
Guide.

For more information on the log4j logging levels, see the Apache documentation at http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Level.html.

Limitations

JRE 1.6+ is required.

Component family

MapReduce / Input

Basic settings

Property type

Either Built-in or Repository.

Built-in: no property data stored
centrally.

Repository: reuse properties
stored centrally under the Hadoop
Cluster node of the Repository tree.

The fields that come after are pre-filled in using the fetched
data.

For further information about the Hadoop
Cluster node, see the Getting Started Guide.

Schema and Edit
Schema

A schema is a row description. It defines the number of fields to be processed and passed on
to the next component. The schema is either Built-In or
stored remotely in the Repository.

Click Edit Schema to make changes to the schema. Note that if you make changes, the schema automatically becomes
built-in.

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.

Folder/File

Browse to, or enter the directory in HDFS where the data you need to use is.

If the path you set points to a folder, this component will read
all of the files stored in that folder, for example, /user/talend/in; if sub-folders exist,
the sub-folders are automatically ignored unless you define the path
like
/user/talend/in/*.

If you want to specify more than one files or directories in this
field, separate each path using a coma (,).

If the file to be read is a compressed one, enter the file name
with its extension; then tHDFSInput
automatically decompresses it at runtime. The supported compression
formats and their corresponding extensions are:

Note that you need
to ensure you have properly configured the connection to the Hadoop
distribution to be used in the Hadoop
configuration tab in the Run view.

Die on error

Select this check box to stop the execution of the Job when an error occurs.

Clear the check box to skip any rows on error and complete the process for error-free rows.
When errors are skipped, you can collect the rows on error using a Row
> Reject link.

File type

Type

Select the type of the file to be processed. The type of the file may be:

Row separator

Enter the separator used to identify the end of a row.

This field is not available for a Sequence file.

Field separator

Enter character, string or regular expression to separate fields for the transferred
data.

This field is not available for a Sequence file.

Header

Enter the number of rows to be skipped in the beginning of file.

For example, enter 0 to ignore
no rows for the data without header and set 1 for the data with header at the first row.

This field is not available for a Sequence file.

Custom Encoding

You may encounter encoding issues when you process the stored data. In that situation, select
this check box to display the Encoding list.

Then select the encoding to be used from the list or select
Custom and define it
manually.

This option is not available for a Sequence file.

Advanced settings

Advanced separator (for number)

Select this check box to change the separator used for numbers. By
default, the thousands separator is a coma (,) and the decimal separator is a period (.).

Trim all columns

Select this check box to remove the leading and trailing
whitespaces from all columns. When this check box is cleared, the
Check column to trim table is
displayed, which lets you select particular columns to trim.

Check column to trim

This table is filled automatically with the schema being used. Select the check box(es)
corresponding to the column(s) to be trimmed.

tStatCatcher Statistics

Select this check box to collect log data at the component
level.

Global Variables

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

In a Talend Map/Reduce Job, it is used as a start component and requires
a transformation component as output link. The other components used along with it must be
Map/Reduce components, too. They generate native Map/Reduce code that can be executed
directly in Hadoop.

Once a Map/Reduce Job is opened in the workspace, tHDFSInput as well as the MapReduce
family appears in the Palette of
the Studio.

Note that in this documentation, unless otherwise explicitly stated, a scenario presents
only Standard Jobs, that is to say traditional Talend data
integration Jobs, and non Map/Reduce Jobs.

Hadoop Connection

You need to use the Hadoop Configuration tab in the
Run view to define the connection to a given Hadoop
distribution for the whole Job.

This connection is effective on a per-Job basis.