Understanding PIG MapReduce Output and HIVE

Описание: Learn how to effectively handle PIG mapreduce output, tackle common issues with field delimiters, and leverage HIVE for further data querying.
---
This video is based on the question https://stackoverflow.com/q/72640582/ asked by the user 'Juan Carlos Castro Piedra' ( https://stackoverflow.com/u/19349222/ ) and on the answer https://stackoverflow.com/a/72651370/ provided by the user 'OneCricketeer' ( https://stackoverflow.com/u/2308683/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: PIG mapreduce output and HIVE

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding PIG MapReduce Output and HIVE

Working with data processing frameworks like Apache PIG and HIVE can sometimes lead to unexpected results, particularly when it comes to handling input and output formats. In this guide, we'll explore a common issue regarding PIG mapreduce output where only the first column of a loaded dataset appears instead of the entire row. We will also discuss how to correctly convert and store this data to achieve the desired output format, as well as how to utilize HIVE for querying the resulting dataset.

The Problem: PIG MapReduce Output Limited to First Column

In our scenario, we have a file named test.txt which contains records delimited by tabs. A simple PIG script is used to load this file and process it. However, the output only consists of the first column of data instead of all fields as intended. This raises several questions:

What happened with the other fields?

Why weren't the tab characters replaced with commas?

How can we achieve the correct output format?

How can we query this output using HIVE?

Let’s delve into each question to clarify these issues and understand the resolutions.

1. What Happened with the Other Fields?

The issue arises from how data is loaded and processed within PIG. By default, the LOAD function in PIG uses a tab delimiter, meaning that when the script is run, it's only grabbing the first column of every record. To retrieve the entire line, we can do one of the following actions:

Use Full Line Loading: Modify the load command to read the full line without separating by fields. This can be done by utilizing USING PigStorage('\n').

Simplify the Script: Alternatively, we can remove the FOREACH block entirely and just store the loaded data directly using PigStorage(','). This approach is more straightforward when you merely want to change the delimiters.

2. Why Weren't the Tab Characters Changed?

The reason the tab characters were not replaced by commas is closely related to the first point. Since the data load was limited to a single field (the first column), there were no tab characters remaining in the output to replace. If you attempt to ‘REPLACE’ something that doesn’t exist in your data—like tabs in this case—nothing happens, resulting in incomplete data output.

3. How Can We Achieve the Correct Output Format?

To obtain the desired output format, we can revise the PIG script. Here’s a corrected version that ensures all fields are loaded and formatted properly:

[[See Video to Reveal this Text or Code Snippet]]

With this modification, we can expect to get the following output:

[[See Video to Reveal this Text or Code Snippet]]

4. How Can We Query That Result with HIVE?

Now that we have our data formatted correctly, it’s time to make it queryable through HIVE. You have a couple of options here:

Using HCatalog: You could store the PIG output using HCatalog which seamlessly integrates PIG with HIVE. Here’s how you can do it:

[[See Video to Reveal this Text or Code Snippet]]

This will create a corresponding table in HIVE that can be queried directly.

Defining an External Table: Alternatively, you can define a HIVE external table that points to the file stored in HDFS. This external table can reference the tab-delimited file like so:

[[See Video to Reveal this Text or Code Snippet]]

With this setup, you can execute typical HIVE queries like:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Handling data in frameworks like PIG and HIVE can be tricky, especially when it comes to input/output formats. By understanding how loading, processing, and storing work together, you can efficiently manage your datasets and ensure you retrieve the full scope of your data, ready for analysis. With