How to use a PDI transformation to extract data from HDFS and load it into a RDBMS table. The new RDBMS table will contain the count of page views by IP address and month.

Prerequisites

In order to follow along with this how-to guide you will need the following:

• Hadoop
• Pentaho Data Integration
• RDBMS Database (e.g. MySQL)

Sample Files

The sample data file needed for this guide is:

NOTE: If you have already completed the "Using Pentaho MapReduce to Parse Weblog Data" guide the necessary files will already be in the proper location.
This file should be placed into HDFS at /user/pdi/weblogs/aggregate_mr using the following commands.

hadoop fs -mkdir /user/pdi/weblogs
hadoop fs -mkdir /user/pdi/weblogs/aggregate_mr
hadoop fs -put weblogs_aggregate.txt /user/pdi/weblogs/aggregate_mr/part-00000

Step-By-Step Instructions

Setup

Start Hadoop if it is not already running.

Create a Transformation to Extract Data from HDFS

In this task you will create a transformation to extract data from a HDFS file and load into a RDBMS table.

1. Start PDI on your desktop. Once it is running choose 'File' -> 'New' -> 'Transformation' from the menu system or click on the 'New file' icon on the toolbar and choose the 'Transformation' option.
   
   
2. Add a Hadoop File Input Step: You are going to extract data from HDFS, so expand the 'Big Data' section of the Design palette and drag a 'Hadoop File Input' node onto the transformation canvas. Your transformation should look like:
   
   
   
3. Edit the Input Step: Double-click on the 'Hadoop File Input' node to edit its properties. Do the following:
   1. File or directory: Enter hdfs://<NAMENODE>:<PORT>/user/pdi/weblogs/aggregate_mr
   2. Regular Expression: Enter 'part.*'
   3. Click 'Add' to add the file to the list of input files.
      When you are done your window should look like:
      
      
      
4. Configure Input File Content: You need to tell Pentaho how the input file is formatted, so switch to the 'Content' tab and enter the following:
   1. Separator: Clear and press the 'Insert TAB' button.
   2. Uncheck 'Header'
   3. Format: Select 'Unix'
      When you are done your window should look like:
      
      
      
5. Define the Fields: You need to tell Pentaho what fields are in the file, so switch to the 'Fields' tab and enter the following:

   Name	Type	Length
   client_ip	String	20
   year	Integer
   month_num	Integer
   pageviews	Integer

   
   When you are done your window should look like:
   
   Click 'OK' to close the window.
   
   
6. Add a Table Output Step: You want to write the values to a RDBMS, so expand the 'Output' section of the Design palette and drag a 'Table Output' node onto the transformation canvas. Your transformation should look like:
   
   
   
7. Connect the Input and Table Output steps: Hover the mouse over the 'Hadoop File Input' node and a tooltip will appear. Click on the output connector (the green arrow pointing to the right) and drag a connector arrow to the 'Table Output' node. Your canvas should look like this:
   
   
   
8. Edit the Table Output Step: Double-click on the 'Table Output' node to edit its properties. Do the following:
   1. Connection: Select 'RDBMS'
   2. Target Table: Enter 'aggregate_hdfs'
   3. Check 'Truncate table' so you can re-run this transformation.
   4. Click the 'SQL' button to create the table in your target database.
      
      
      
   5. Click the 'Execute' button to run the SQL.
      
      The 'Results of the SQL statements' window will appear telling you if the SQL was successfully executed or give you troubleshooting information if the SQL failed.
   6. Click 'OK' to close the window.
   7. Click 'Close' to close the 'Simple SQL editor' window.
      When you are done your window should look like:
      
      Click 'OK' to close the window.
      
      
9. Save the Transformation: Choose 'File' -> 'Save as...' from the menu system. Save the transformation as 'hdfs_to_rdbms.ktr' into a folder of your choice.
   
   
10. Run the Transformation: Choose 'Action' -> 'Run' from the menu system or click on the green run button on the transformation toolbar. A 'Execute a transformation' window will open. Click on the 'Launch' button. An 'Execution Results' panel will open at the bottom of the PDI window and it will show you the progress of the transformation as it runs. After several seconds the transformation should finish successfully:

If any errors occurred the job step that failed will be highlighted in red and you can use the 'Logging' tab to view error messages.

Check RDBMS for Aggregated Table

1. Explore the Database: Choose 'Tools' -> 'Database' -> 'Explore' from the menu system.
   
   
2. Select the Connection: In the 'Make your selection' window select 'RDBMS' and click 'OK'.
   
   
   
3. Preview the Table: Expand RDBMS -> Tables. Right click on 'aggregate_hdfs' and select 'Preview first 100'
   

Summary

During this guide you learned how to create a PDI transformation to load an RDBMS table with data sourced from a HDFS file.