[SPARK-31276] Contrived working example that works with multiple URI file storages for Spark cluster mode

• Type: Wish
• Status: Resolved
• Priority: Major
• Resolution: Not A Problem
• Affects Version/s: 2.4.5
• Component/s: Examples
• Assignee: Unassigned
• Reporter: Jim Huang
• Created: 26/Mar/20 19:05
• Updated: 12/Dec/22 18:11
• Resolved: 07/Apr/20 03:13

Description

This Spark SQL Guide --> Data sources --> Generic Load/Save Functions

https://spark.apache.org/docs/latest/sql-data-sources-load-save-functions.html

described a very simple "local file system load of an example file".  

 

I am looking for an example that demonstrates a workflow that exercises different file systems.  For example, 

1. Driver loads an input file from local file system
2. Add a simple column using lit() and stores that DataFrame in cluster mode to HDFS
3. Write that a small limited subset of that DataFrame back to Driver's local file system.  (This is to avoid the anti-pattern of writing large file and out of the scope for this example.  The small limited DataFrame would be some basic statistics, not the actual complete dataset.)

 

The examples I found on the internet only uses simple paths without the explicit URI prefixes.

Without the explicit URI prefixes, the "filepath" inherits how Spark (mode) was called, local stand alone vs YARN client mode.   So a "filepath" will be read/write locally (file system) vs cluster mode HDFS, without these explicit URIs.

There are situations were a Spark program needs to deal with both local file system and YARN client mode (big data) in the same Spark application, like producing a summary table stored on the local file system of the driver at the end.  

If there are any existing alternatives Spark documentation that provides examples that traverse through the different URIs in Spark YARN client mode or a better or smarter Spark pattern or API that is more suited for this, I am happy to accept that as well.  Thanks!