How many versions are created in a delta table in a Data lake on Azure

Question

I have a clarification question. As per what I have read, Delta tables create 0--original data, 1--updated data version of a row in a table.

So basically we have just two versions of the data in Delta tables or this is configurable? what happens, when we update same row multiple times, delta table simply keep latest version of updates?

Thanks in advance.

Answer 1

Delta will create a new version for each operation - insert/update/delete, and also for additional operations, like, changing properties of the table, optimize, vacuum, etc., although some operations will not create new files (update table properties), or even delete not used files (vacuum).

Please take into account that data files in Delta aren't mutable, when you update or delete data, Delta identifies which files contain the data for update/delete, and create new files with modified data. That's why it's important to run VACUUM periodically, so you can get rid of the old files (although it will limit your ability to time travel just to the given period of time - one week by default)