Are we able to use Snappy-data to Update a record in Azure Data lake ? OR is Azure data lake append only?
Azure Data Lake Store, much like HDFS, is an append only store. You can append to a file or replace it altogether. There is no way to update an existing file.
I've achieved MERGE style behaviour in USQL by using a Azure Data Lake table as the middle ground between input and output. Check out my blog post with the code showing how I did it with a series of joins.
https://www.purplefrogsystems.com/paul/2016/12/writing-a-u-sql-merge-statement/
This will give you append behaviour in your output.