Using HDFS

This section describes how you interact through the Designer Cloud Powered by Trifacta® platform with your HDFS environment.

• HDFS is a scalable file storage system for use across all of the nodes (servers) of a Hadoop cluster. Many interactions with HDFS are similar with desktop interactions with files and folders. However, what looks like a "file" or "folder" in HDFS may be spread across multiple nodes in the cluster. For more information, see https://en.wikipedia.org/wiki/Apache_Hadoop#HDFS.

Uses of HDFS

The Designer Cloud Powered by Trifacta platform can use HDFS for the following reading and writing tasks:

1. Creating Datasets from HDFS Files: You can read in from a data source stored in HDFS. A source may be a single HDFS file or a folder of identically structured files. See Reading from Sources in HDFS below.
2. Reading Datasets: When creating a dataset, you can pull your data from another dataset defined in HDFS. See Creating Datasets below.
3. Writing Job Results: After a job has been executed, you can write the results back to HDFS. See Writing Job Results below.

In the Designer Cloud application, HDFS is accessed through the HDFS browser. See HDFS Browser.

Before You Begin Using HDFS

• Read/Write Access: Your Hadoop administrator must configure read/write permissions to locations in HDFS. Please see the HDFS documentation provided with your Hadoop distribution.

  Avoid using /trifacta/uploads for reading and writing data. This directory is used by the Designer Cloud application.

• Your Hadoop administrator should provide a place or mechanism for raw data to be uploaded to your Hadoop datastore. 

• Your Hadoop administrator should provide a writeable home output directory for you. This directory location is available through your user profile. See User Profile Page.

Secure Access

Depending on the security features you've enabled, the technical methods by which Alteryx users access HDFS may vary. For more information, see Configure Hadoop Authentication.

Storing Data in HDFS

Your Hadoop administrator should provide raw data or locations and access for storing raw data within HDFS. All Alteryx users should have a clear understanding of the folder structure within HDFS where each individual can read from and write their job results. 

• Users should know where shared data is located and where personal data can be saved without interfering with or confusing other users.

Reading from Sources in HDFS

You can create a dataset from one or more files stored in HDFS.

When you select a folder in HDFS to create your dataset, you select all files in the folder to be included. Notes:

• This option selects all files in all sub-folders. If your sub-folders contain separate datasets, you should be more specific in your folder selection.
• All files used in a single dataset must be of the same format and have the same structure. For example, you cannot mix and match CSV and JSON files if you are reading from a single directory. 
• When a folder is selected from HDFS, the following file types are ignored:
  
  • *_SUCCESS and *_FAILED files, which may be present if the folder has been populated by Hadoop.
  • If you have stored files in HDFS that begin with an underscore (_), these files cannot be read during batch transformation and are ignored. Please rename these files through HDFS so that they do not begin with an underscore. 

Creating Datasets

When creating a dataset, you can choose to read data in from a source stored from HDFS or from a local file.

• HDFS sources are not moved or changed.
• Local file sources are uploaded to /trifacta/uploads where they remain and are not changed.

Data may be individual files or all of the files in a folder. For more information, see Reading from Sources in HDFS.

• In the Import Data page, click the HDFS tab. See Import Data Page.

Writing Job Results

When your job results are generated, they can be stored back in HDFS for you at the location defined for your user account.

• The HDFS location is available through the Export Results window for the job in the Jobs page. See Export Results Window.
• Each set of job results must be stored in a separate folder within your HDFS output home directory. 
• For more information on your output home directory, see User Profile Page.

Access to results:

Depending on how the platform is integrated with HDFS, other users may or may not be able to access your job results.

• If user impersonation is enabled, results are written to HDFS through the HDFS account configured for your use. Depending on the permissions of your HDFS account, you may be the only person who can access these results.

• If user impersonation is not enabled, then each Alteryx user writes results to HDFS using a shared account. Depending on the permissions of that account, your results may be visible to all platform users.

Creating a new dataset from results

As part of writing job results, you can choose to create a new dataset, so that you can chain together data wrangling tasks.